feat: add support for custom HTTP headers in StreamableHttpClient#655

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Merged
alexhancock merged 2 commits into from
Feb 13, 2026
Merged

feat: add support for custom HTTP headers in StreamableHttpClient #655

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8bc2d4b
feat: add support for custom HTTP headers in StreamableHttpClient
arichyx Feb 13, 2026
442fe17
feat: implement reserved header checks for custom HTTP headers in Str…
arichyx Feb 13, 2026
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10 changes: 10 additions & 0 deletions crates/rmcp/Cargo.toml
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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
"client",
"server",
"transport-streamable-http-client-reqwest",
"transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"
8 changes: 5 additions & 3 deletions crates/rmcp/src/transport/auth.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
let response = match self
.http_client
.get(discovery_url.clone())
.header("MCP-Protocol-Version", "2024-11-05")
.header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
.send()
.await
{
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
let response = match self
.http_client
.get(url.clone())
.header("MCP-Protocol-Version", "2024-11-05")
.header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
.send()
.await
{
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
let response = match self
.http_client
.get(resource_metadata_url.clone())
.header("MCP-Protocol-Version", "2024-11-05")
.header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
.send()
.await
{
Expand Down
7 changes: 6 additions & 1 deletion crates/rmcp/src/transport/common/auth/streamable_http_client.rs
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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
auth::AuthClient,
streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
message: crate::model::ClientJsonRpcMessage,
session_id: Option<std::sync::Arc<str>>,
mut auth_token: Option<String>,
custom_headers: HashMap<HeaderName, HeaderValue>,
) -> Result<
crate::transport::streamable_http_client::StreamableHttpPostResponse,
StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
auth_token = Some(self.get_access_token().await?);
}
self.http_client
.post_message(uri, message, session_id, auth_token)
.post_message(uri, message, session_id, auth_token, custom_headers)
.await
}
}
1 change: 1 addition & 0 deletions crates/rmcp/src/transport/common/http_header.rs
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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";
28 changes: 25 additions & 3 deletions crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
transport::{
common::http_header::{
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
HEADER_SESSION_ID, JSON_MIME_TYPE,
},
streamable_http_client::*,
},
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
message: ClientJsonRpcMessage,
session_id: Option<Arc<str>>,
auth_token: Option<String>,
custom_headers: HashMap<HeaderName, HeaderValue>,
) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
let mut request = self
.post(uri.as_ref())
.header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
if let Some(auth_header) = auth_token {
request = request.bearer_auth(auth_header);
}

// Apply custom headers
let reserved_headers = [
ACCEPT.as_str(),
HEADER_SESSION_ID,
HEADER_MCP_PROTOCOL_VERSION,
HEADER_LAST_EVENT_ID,
];
for (name, value) in custom_headers {

@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?

ACCEPTHEADER_SESSION_ID etc

@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list

MCP-Protocol-Version is another one that comes to mind

@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.

if reserved_headers
.iter()
.any(|&r| name.as_str().eq_ignore_ascii_case(r))
{
return Err(StreamableHttpError::ReservedHeaderConflict(
name.to_string(),
));
}

request = request.header(name, value);
}
if let Some(session_id) = session_id {
request = request.header(HEADER_SESSION_ID, session_id.as_ref());
}
Expand Down
45 changes: 44 additions & 1 deletion crates/rmcp/src/transport/streamable_http_client.rs
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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
AuthRequired(AuthRequiredError),
#[error("Insufficient scope")]
InsufficientScope(InsufficientScopeError),
#[error("Header name '{0}' is reserved and conflicts with default headers")]
ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
message: ClientJsonRpcMessage,
session_id: Option<Arc<str>>,
auth_header: Option<String>,
custom_headers: HashMap<HeaderName, HeaderValue>,
) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
+ Send
+ '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
initialize_request,
None,
self.config.auth_header,
self.config.custom_headers,
)
.await
{
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
initialized_notification.message,
session_id.clone(),
config.auth_header.clone(),
config.custom_headers.clone(),
)
.await
.map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
message,
session_id.clone(),
config.auth_header.clone(),
config.custom_headers.clone(),
)
.await;
let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
pub allow_stateless: bool,
/// The value to send in the authorization header
pub auth_header: Option<String>,
/// Custom HTTP headers to include with every request
pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
self.auth_header = Some(value.into());
self
}

/// Set custom HTTP headers to include with every request
///
/// # Arguments
///
/// * `custom_headers` - A HashMap of header names to header values
///
/// # Example
///
/// ```rust,no_run
/// use std::collections::HashMap;
/// use http::{HeaderName, HeaderValue};
/// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
///
/// let mut headers = HashMap::new();
/// headers.insert(
/// HeaderName::from_static("x-custom-header"),
/// HeaderValue::from_static("custom-value")
/// );
///
/// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
/// .custom_headers(headers);
/// ```
pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
self.custom_headers = custom_headers;
self
}
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
channel_buffer_capacity: 16,
allow_stateless: true,
auth_header: None,
custom_headers: HashMap::new(),
}
}
}
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feat: add support for custom HTTP headers in StreamableHttpClient#655

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 Merged

alexhancock
merged 2 commits into

from

Feb 13, 2026
 Merged


feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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alexhancock
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Feb 13, 2026
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feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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 Merged

alexhancock
merged 2 commits into

from

Feb 13, 2026
 Merged


feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
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var changed = false;
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if (u.searchParams.has(p)) {
u.searchParams.delete(p);
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feat: add support for custom HTTP headers in StreamableHttpClient#655

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alexhancock
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Feb 13, 2026
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feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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feat: add support for custom HTTP headers in StreamableHttpClient#655

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 Merged

alexhancock
merged 2 commits into

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Feb 13, 2026
 Merged


feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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 Merged

alexhancock
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Feb 13, 2026
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feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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 Merged

alexhancock
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Feb 13, 2026
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feat: add support for custom HTTP headers in StreamableHttpClient
#655
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8bc2d4b

feat: add support for custom HTTP headers in StreamableHttpClient


arichyx Feb 13, 2026
442fe17

feat: implement reserved header checks for custom HTTP headers in Str…


arichyx Feb 13, 2026

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10 changes: 10 additions & 0 deletions
crates/rmcp/Cargo.toml

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Original file line numberDiff line numberDiff line change
Expand Up@@ -230,3 +230,13 @@ path = "tests/test_sampling.rs"
name = "test_close_connection"
required-features = ["server", "client"]
path = "tests/test_close_connection.rs"

[[test]]
name = "test_custom_headers"
required-features = [
 "client",
 "server",
 "transport-streamable-http-client-reqwest",
 "transport-streamable-http-server",
]
path = "tests/test_custom_headers.rs"

8 changes: 5 additions & 3 deletions
crates/rmcp/src/transport/auth.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -16,6 +16,8 @@ use thiserror::Error;
use tokio::sync::{Mutex, RwLock};
use tracing::{debug, error, warn};

use crate::transport::common::http_header::HEADER_MCP_PROTOCOL_VERSION;

const DEFAULT_EXCHANGE_URL: &str = "http://localhost";

/// Stored credentials for OAuth2 authorization
Expand DownExpand Up@@ -1051,7 +1053,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(discovery_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1171,7 +1173,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand DownExpand Up@@ -1224,7 +1226,7 @@ impl AuthorizationManager {
 let response = match self
 .http_client
 .get(resource_metadata_url.clone())
 .header("MCP-Protocol-Version", "2024-11-05")
 .header(HEADER_MCP_PROTOCOL_VERSION, "2024-11-05")
 .send()
 .await
 {
Expand Down

7 changes: 6 additions & 1 deletion
crates/rmcp/src/transport/common/auth/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,3 +1,7 @@
use std::collections::HashMap;

use http::{HeaderName, HeaderValue};

use crate::transport::{
 auth::AuthClient,
 streamable_http_client::{StreamableHttpClient, StreamableHttpError},
Expand DownExpand Up@@ -47,6 +51,7 @@ where
 message: crate::model::ClientJsonRpcMessage,
 session_id: Option<std::sync::Arc<str>>,
 mut auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<
 crate::transport::streamable_http_client::StreamableHttpPostResponse,
 StreamableHttpError<Self::Error>,
Expand All@@ -55,7 +60,7 @@ where
 auth_token = Some(self.get_access_token().await?);
 }
 self.http_client
 .post_message(uri, message, session_id, auth_token)
 .post_message(uri, message, session_id, auth_token, custom_headers)
 .await
 }
}

1 change: 1 addition & 0 deletions
crates/rmcp/src/transport/common/http_header.rs

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Original file line numberDiff line numberDiff line change
@@ -1,4 +1,5 @@
pub const HEADER_SESSION_ID: &str = "Mcp-Session-Id";
pub const HEADER_LAST_EVENT_ID: &str = "Last-Event-Id";
pub const HEADER_MCP_PROTOCOL_VERSION: &str = "MCP-Protocol-Version";
pub const EVENT_STREAM_MIME_TYPE: &str = "text/event-stream";
pub const JSON_MIME_TYPE: &str = "application/json";

28 changes: 25 additions & 3 deletions
crates/rmcp/src/transport/common/reqwest/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,15 +1,16 @@
use std::{borrow::Cow, sync::Arc};
use std::{borrow::Cow, collections::HashMap, sync::Arc};

use futures::{StreamExt, stream::BoxStream};
use http::header::WWW_AUTHENTICATE;
use http::{HeaderName, HeaderValue, header::WWW_AUTHENTICATE};
use reqwest::header::ACCEPT;
use sse_stream::{Sse, SseStream};

use crate::{
 model::{ClientJsonRpcMessage, ServerJsonRpcMessage},
 transport::{
 common::http_header::{
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_SESSION_ID, JSON_MIME_TYPE,
 EVENT_STREAM_MIME_TYPE, HEADER_LAST_EVENT_ID, HEADER_MCP_PROTOCOL_VERSION,
 HEADER_SESSION_ID, JSON_MIME_TYPE,
 },
 streamable_http_client::*,
 },
Expand DownExpand Up@@ -94,13 +95,34 @@ impl StreamableHttpClient for reqwest::Client {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_token: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>> {
 let mut request = self
 .post(uri.as_ref())
 .header(ACCEPT, [EVENT_STREAM_MIME_TYPE, JSON_MIME_TYPE].join(", "));
 if let Some(auth_header) = auth_token {
 request = request.bearer_auth(auth_header);
 }

 // Apply custom headers
 let reserved_headers = [
 ACCEPT.as_str(),
 HEADER_SESSION_ID,
 HEADER_MCP_PROTOCOL_VERSION,
 HEADER_LAST_EVENT_ID,
 ];
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
 if reserved_headers
 .iter()
 .any(|&r| name.as_str().eq_ignore_ascii_case(r))
 {
 return Err(StreamableHttpError::ReservedHeaderConflict(
 name.to_string(),
 ));
 }

 request = request.header(name, value);
 }
 if let Some(session_id) = session_id {
 request = request.header(HEADER_SESSION_ID, session_id.as_ref());
 }
Expand Down

45 changes: 44 additions & 1 deletion
crates/rmcp/src/transport/streamable_http_client.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,7 @@
use std::{borrow::Cow, sync::Arc, time::Duration};
use std::{borrow::Cow, collections::HashMap, sync::Arc, time::Duration};

use futures::{Stream, StreamExt, future::BoxFuture, stream::BoxStream};
use http::{HeaderName, HeaderValue};
pub use sse_stream::Error as SseError;
use sse_stream::Sse;
use thiserror::Error;
Expand DownExpand Up@@ -76,6 +77,8 @@ pub enum StreamableHttpError<E: std::error::Error + Send + Sync + 'static> {
 AuthRequired(AuthRequiredError),
 #[error("Insufficient scope")]
 InsufficientScope(InsufficientScopeError),
 #[error("Header name '{0}' is reserved and conflicts with default headers")]
 ReservedHeaderConflict(String),
}

#[derive(Debug, Clone, Error)]
Expand DownExpand Up@@ -173,6 +176,7 @@ pub trait StreamableHttpClient: Clone + Send + 'static {
 message: ClientJsonRpcMessage,
 session_id: Option<Arc<str>>,
 auth_header: Option<String>,
 custom_headers: HashMap<HeaderName, HeaderValue>,
 ) -> impl Future<Output = Result<StreamableHttpPostResponse, StreamableHttpError<Self::Error>>>
 + Send
 + '_;
Expand DownExpand Up@@ -324,6 +328,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialize_request,
 None,
 self.config.auth_header,
 self.config.custom_headers,
 )
 .await
 {
Expand DownExpand Up@@ -372,6 +377,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 initialized_notification.message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await
 .map_err(WorkerQuitReason::fatal_context(
Expand DownExpand Up@@ -477,6 +483,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
 message,
 session_id.clone(),
 config.auth_header.clone(),
 config.custom_headers.clone(),
 )
 .await;
 let send_result = match response {
Expand DownExpand Up@@ -609,8 +616,10 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// StreamableHttpClientTransportConfig
/// };
/// use std::sync::Arc;
/// use std::collections::HashMap;
/// use futures::stream::BoxStream;
/// use rmcp::model::ClientJsonRpcMessage;
/// use http::{HeaderName, HeaderValue};
/// use sse_stream::{Sse, Error as SseError};
///
/// #[derive(Clone)]
Expand All@@ -634,6 +643,7 @@ impl<C: StreamableHttpClient> Worker for StreamableHttpClientWorker<C> {
/// _message: ClientJsonRpcMessage,
/// _session_id: Option<Arc<str>>,
/// _auth_header: Option<String>,
/// _custom_headers: HashMap<HeaderName, HeaderValue>,
/// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
/// todo!()
/// }
Expand DownExpand Up@@ -690,8 +700,10 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// StreamableHttpClientTransportConfig
 /// };
 /// use std::sync::Arc;
 /// use std::collections::HashMap;
 /// use futures::stream::BoxStream;
 /// use rmcp::model::ClientJsonRpcMessage;
 /// use http::{HeaderName, HeaderValue};
 /// use sse_stream::{Sse, Error as SseError};
 ///
 /// // Define your custom client
Expand All@@ -716,6 +728,7 @@ impl<C: StreamableHttpClient> StreamableHttpClientTransport<C> {
 /// _message: ClientJsonRpcMessage,
 /// _session_id: Option<Arc<str>>,
 /// _auth_header: Option<String>,
 /// _custom_headers: HashMap<HeaderName, HeaderValue>,
 /// ) -> Result<rmcp::transport::streamable_http_client::StreamableHttpPostResponse, rmcp::transport::streamable_http_client::StreamableHttpError<Self::Error>> {
 /// todo!()
 /// }
Expand DownExpand Up@@ -759,6 +772,8 @@ pub struct StreamableHttpClientTransportConfig {
 pub allow_stateless: bool,
 /// The value to send in the authorization header
 pub auth_header: Option<String>,
 /// Custom HTTP headers to include with every request
 pub custom_headers: HashMap<HeaderName, HeaderValue>,
}

impl StreamableHttpClientTransportConfig {
Expand All@@ -779,6 +794,33 @@ impl StreamableHttpClientTransportConfig {
 self.auth_header = Some(value.into());
 self
 }

 /// Set custom HTTP headers to include with every request
 ///
 /// # Arguments
 ///
 /// * `custom_headers` - A HashMap of header names to header values
 ///
 /// # Example
 ///
 /// ```rust,no_run
 /// use std::collections::HashMap;
 /// use http::{HeaderName, HeaderValue};
 /// use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;
 ///
 /// let mut headers = HashMap::new();
 /// headers.insert(
 /// HeaderName::from_static("x-custom-header"),
 /// HeaderValue::from_static("custom-value")
 /// );
 ///
 /// let config = StreamableHttpClientTransportConfig::with_uri("http://localhost:8000")
 /// .custom_headers(headers);
 /// ```
 pub fn custom_headers(mut self, custom_headers: HashMap<HeaderName, HeaderValue>) -> Self {
 self.custom_headers = custom_headers;
 self
 }
}

impl Default for StreamableHttpClientTransportConfig {
Expand All@@ -789,6 +831,7 @@ impl Default for StreamableHttpClientTransportConfig {
 channel_buffer_capacity: 16,
 allow_stateless: true,
 auth_header: None,
 custom_headers: HashMap::new(),
 }
 }
}
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