reqwest-eventsource

Provides a simple wrapper for [reqwest] to provide an Event Source implementation with support for multiple content types including Server-Sent Events (SSE) and Amazon EventStream.

You can learn more about Server Sent Events (SSE) at the MDN docs

Features

• Server-Sent Events (SSE) - Standard text/event-stream support
• Amazon EventStream - Binary application/vnd.amazon.eventstream support (feature gated)
• Custom Parsers - Extensible parser system for any content type
• Automatic Retries - Configurable retry logic for failed connections
• Flexible API - Works with any reqwest::RequestBuilder

Quick Start

Basic Usage

use reqwest_eventsource::{EventSource,Event};use futures::StreamExt;letmut es = EventSource::get("http://localhost:8000/events");whileletSome(event) = es.next().await{match event {Ok(Event::Open) => println!("Connection Open!"),Ok(Event::Message(message)) => println!("Message: {:#?}", message),Err(err) => {println!("Error: {}", err);
es.close();}}}

Using with Amazon Bedrock (EventStream)

use reqwest_eventsource::EventSource;use futures::StreamExt;let client = reqwest::Client::new();let request = client
.post("https://bedrock-runtime.us-east-1.amazonaws.com/model/anthropic.claude-sonnet-4-5-v2/invoke-with-response-stream").header("Content-Type","application/json").header("Authorization","AWS4-HMAC-SHA256 ...")// Your AWS auth.json(&serde_json::json!({"anthropic_version":"bedrock-2023-05-31","max_tokens":1000,"messages":[{"role":"user","content":"Hello!"}]}));letmut es = EventSource::new(request)?;whileletSome(event) = es.next().await{match event? {Event::Open => println!("Stream started"),Event::Message(message) => {match message.event.as_str(){"content_block_delta" => println!("Text: {}", message.data),"message_stop" => break,
_ => println!("Event: {}", message.event),}}}}

Custom Parsers

You can extend the library to support any content type by implementing the ContentParser trait:

Implementing a Custom Parser

use reqwest_eventsource::{ContentParser,ParserRegistryBuilder,EventSource};use eventsource_stream::EventasMessageEvent;use futures_util::StreamExt;/// Custom parser for JSON Lines format (application/x-ndjson)pubstructJsonLinesParser;implContentParserforJsonLinesParser{fncan_parse(&self,content_type:&str) -> bool{
content_type.contains("application/x-ndjson") || content_type.contains("application/jsonlines")}fnparse(&self,response: reqwest::Response) -> Result<reqwest_eventsource::parser::ParsedEventStream,Box<dyn std::error::Error + Send + Sync>>{// Parse JSON lines - each line is a separate JSON objectlet stream = response.bytes_stream().scan(String::new(), |buffer, chunk_result| {asyncmove{match chunk_result {Ok(chunk) => {
buffer.push_str(&String::from_utf8_lossy(&chunk));letmut events = Vec::new();whileletSome(newline_pos) = buffer.find('\n'){let line = buffer.drain(..=newline_pos).collect::<String>();let line = line.trim();if !line.is_empty(){ifletOk(json_value) = serde_json::from_str::<serde_json::Value>(line){let event = MessageEvent{id: json_value.get("id").and_then(|v| v.as_str()).unwrap_or("").to_string(),event: json_value.get("event").and_then(|v| v.as_str()).unwrap_or("message").to_string(),retry:None,data: json_value.to_string(),};
events.push(Ok(event));}}}Some(events)}Err(e) => {Some(vec![Err(Box::new(e)asBox<dyn std::error::Error + Send + Sync>)])}}}}).flat_map(futures_util::stream::iter);Ok(Box::pin(stream))}fnname(&self) -> &'staticstr{"JSON Lines Parser"}}

Using a Custom Parser

use reqwest_eventsource::{EventSource,ParserRegistryBuilder};// Create a registry with default parsers + your custom parserlet registry = ParserRegistryBuilder::new().with_default_parsers()// Includes SSE and Amazon EventStream.with_parser(JsonLinesParser)// Add your custom parser.build();// Create EventSource with custom registrylet request = reqwest::Client::new().get("https://api.example.com/stream").header("Accept","application/x-ndjson");letmut es = EventSource::with_parser_registry(request, registry)?;// The library will automatically use JsonLinesParser for ndjson contentwhileletSome(event) = es.next().await{// Handle events...}

Parser Examples

The library includes examples for various parser types:

• Server-Sent Events (text/event-stream) - Built-in
• Amazon EventStream (application/vnd.amazon.eventstream) - Built-in
• JSON Lines (application/x-ndjson) - Custom parser example
• XML Events (application/xml+events) - Custom parser example

See examples/custom_parser.rs for complete implementations.

Feature Flags

Default Features

[dependencies]
reqwest-eventsource = "0.6.0"

Includes: SSE parser + Amazon EventStream parser

Minimal Build (SSE only)

[dependencies]
reqwest-eventsource = { version = "0.6.0", default-features = false }

Includes: SSE parser only (lighter dependencies)

Custom Features

[dependencies]
reqwest-eventsource = { version = "0.6.0", features = ["amazon-eventstream"] }

API Reference

Core Types

• EventSource - Main stream type
• Event - Event enum (Open, Message)
• ContentParser - Trait for implementing custom parsers
• ParserRegistry - Registry holding multiple parsers
• ParserRegistryBuilder - Builder for creating registries

Key Methods

• EventSource::new(RequestBuilder) - Create with default parsers
• EventSource::with_parser_registry(RequestBuilder, ParserRegistry) - Create with custom parsers
• EventSource::get(url) - Simple GET request
• ParserRegistryBuilder::with_default_parsers() - Add built-in parsers
• ParserRegistryBuilder::with_parser(parser) - Add custom parser

License

MIT OR Apache-2.0