Handle JsonRpcError in initialize #563

Closed
#569
Closed
Handle JsonRpcError in initialize#563
#569

Description

@wzxxing
wzxxing
opened on Nov 26, 2025

Describe the bug
A clear and concise description of what the bug is.

When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.

rust-sdk/crates/rmcp/src/service/client.rs

Lines 128 to 129 in 94428d5

// Server SHOULD NOT send any other messages before handshake. We ignore them anyway
_ => tracing::warn!(?message,"Received unexpected message"),

The Specification suggested that

Implementations SHOULD be prepared to handle these error cases:

https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling

To Reproduce
Steps to reproduce the behavior:

  1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.

rust-sdk/crates/rmcp/src/service/client.rs

Lines 229 to 235 in 94428d5

let(response, response_id) = expect_response(
&mut transport,
"initialize response",
&service,
peer.clone(),
)
.await?;

Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.

Expected behavior

My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.

Logs
If applicable, add logs to help explain your problem.

Additional context
Add any other context about the problem here.

Metadata

Metadata

Assignees

No one assigned

    Labels

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    Type

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      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      Handle JsonRpcError in initialize #563
      Closed
      #569
      Closed
      Handle JsonRpcError in initialize#563
      #569
      Description
      @wzxxing
      wzxxing
      opened on Nov 26, 2025
      Describe the bug
      
A clear and concise description of what the bug is.
      When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
      rust-sdk/crates/rmcp/src/service/client.rs
      
Lines 128 to 129
in
94428d5
      // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
       _ => tracing::warn!(?message,"Received unexpected message"),
      The Specification suggested that
      Implementations SHOULD be prepared to handle these error cases:
      https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
      To Reproduce
      
Steps to reproduce the behavior:
      1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
      2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

      expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
      rust-sdk/crates/rmcp/src/service/client.rs
      
Lines 229 to 235
in
94428d5
      let(response, response_id) = expect_response(
      &mut transport,
      "initialize response",
      &service,
       peer.clone(),
      )
      .await?;
      Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
      Expected behavior
      My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
      Logs
      
If applicable, add logs to help explain your problem.
      Additional context
      
Add any other context about the problem here.
      Metadata
      Metadata
      Assignees
      No one assigned
        Labels
        No labels
        No labels
        Type
        No type
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          Handle JsonRpcError in initialize #563
          Closed
          #569
          Closed
          Handle JsonRpcError in initialize#563
          #569
          Description
          @wzxxing
          wzxxing
          opened on Nov 26, 2025
          Describe the bug
          
A clear and concise description of what the bug is.
          When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
          rust-sdk/crates/rmcp/src/service/client.rs
          
Lines 128 to 129
in
94428d5
          // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
           _ => tracing::warn!(?message,"Received unexpected message"),
          The Specification suggested that
          Implementations SHOULD be prepared to handle these error cases:
          https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
          To Reproduce
          
Steps to reproduce the behavior:
          1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
          2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

          expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
          rust-sdk/crates/rmcp/src/service/client.rs
          
Lines 229 to 235
in
94428d5
          let(response, response_id) = expect_response(
          &mut transport,
          "initialize response",
          &service,
           peer.clone(),
          )
          .await?;
          Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
          Expected behavior
          My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
          Logs
          
If applicable, add logs to help explain your problem.
          Additional context
          
Add any other context about the problem here.
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            No labels
            No labels
            Type
            No type
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Handle JsonRpcError in initialize #563
              Closed
              #569
              Closed
              Handle JsonRpcError in initialize#563
              #569
              Description
              @wzxxing
              wzxxing
              opened on Nov 26, 2025
              Describe the bug
              
A clear and concise description of what the bug is.
              When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
              rust-sdk/crates/rmcp/src/service/client.rs
              
Lines 128 to 129
in
94428d5
              // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
               _ => tracing::warn!(?message,"Received unexpected message"),
              The Specification suggested that
              Implementations SHOULD be prepared to handle these error cases:
              https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
              To Reproduce
              
Steps to reproduce the behavior:
              1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
              2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

              expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
              rust-sdk/crates/rmcp/src/service/client.rs
              
Lines 229 to 235
in
94428d5
              let(response, response_id) = expect_response(
              &mut transport,
              "initialize response",
              &service,
               peer.clone(),
              )
              .await?;
              Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
              Expected behavior
              My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
              Logs
              
If applicable, add logs to help explain your problem.
              Additional context
              
Add any other context about the problem here.
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                No labels
                No labels
                Type
                No type
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  Handle JsonRpcError in initialize #563
                  Closed
                  #569
                  Closed
                  Handle JsonRpcError in initialize#563
                  #569
                  Description
                  @wzxxing
                  wzxxing
                  opened on Nov 26, 2025
                  Describe the bug
                  
A clear and concise description of what the bug is.
                  When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
                  rust-sdk/crates/rmcp/src/service/client.rs
                  
Lines 128 to 129
in
94428d5
                  // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
                   _ => tracing::warn!(?message,"Received unexpected message"),
                  The Specification suggested that
                  Implementations SHOULD be prepared to handle these error cases:
                  https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
                  To Reproduce
                  
Steps to reproduce the behavior:
                  1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
                  2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

                  expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
                  rust-sdk/crates/rmcp/src/service/client.rs
                  
Lines 229 to 235
in
94428d5
                  let(response, response_id) = expect_response(
                  &mut transport,
                  "initialize response",
                  &service,
                   peer.clone(),
                  )
                  .await?;
                  Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
                  Expected behavior
                  My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
                  Logs
                  
If applicable, add logs to help explain your problem.
                  Additional context
                  
Add any other context about the problem here.
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    No labels
                    No labels
                    Type
                    No type
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      Handle JsonRpcError in initialize #563
                      Closed
                      #569
                      Closed
                      Handle JsonRpcError in initialize#563
                      #569
                      Description
                      @wzxxing
                      wzxxing
                      opened on Nov 26, 2025
                      Describe the bug
                      
A clear and concise description of what the bug is.
                      When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
                      rust-sdk/crates/rmcp/src/service/client.rs
                      
Lines 128 to 129
in
94428d5
                      // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
                       _ => tracing::warn!(?message,"Received unexpected message"),
                      The Specification suggested that
                      Implementations SHOULD be prepared to handle these error cases:
                      https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
                      To Reproduce
                      
Steps to reproduce the behavior:
                      1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
                      2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

                      expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
                      rust-sdk/crates/rmcp/src/service/client.rs
                      
Lines 229 to 235
in
94428d5
                      let(response, response_id) = expect_response(
                      &mut transport,
                      "initialize response",
                      &service,
                       peer.clone(),
                      )
                      .await?;
                      Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
                      Expected behavior
                      My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
                      Logs
                      
If applicable, add logs to help explain your problem.
                      Additional context
                      
Add any other context about the problem here.
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        No labels
                        No labels
                        Type
                        No type
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          Handle JsonRpcError in initialize #563
                          Closed
                          #569
                          Closed
                          Handle JsonRpcError in initialize#563
                          #569
                          Description
                          @wzxxing
                          wzxxing
                          opened on Nov 26, 2025
                          Describe the bug
                          
A clear and concise description of what the bug is.
                          When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
                          rust-sdk/crates/rmcp/src/service/client.rs
                          
Lines 128 to 129
in
94428d5
                          // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
                           _ => tracing::warn!(?message,"Received unexpected message"),
                          The Specification suggested that
                          Implementations SHOULD be prepared to handle these error cases:
                          https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
                          To Reproduce
                          
Steps to reproduce the behavior:
                          1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
                          2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

                          expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
                          rust-sdk/crates/rmcp/src/service/client.rs
                          
Lines 229 to 235
in
94428d5
                          let(response, response_id) = expect_response(
                          &mut transport,
                          "initialize response",
                          &service,
                           peer.clone(),
                          )
                          .await?;
                          Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
                          Expected behavior
                          My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
                          Logs
                          
If applicable, add logs to help explain your problem.
                          Additional context
                          
Add any other context about the problem here.
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            No labels
                            No labels
                            Type
                            No type
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

                              Skip to content
                              Handle JsonRpcError in initialize #563
                              Closed
                              #569
                              Closed
                              Handle JsonRpcError in initialize#563
                              #569
                              Description
                              @wzxxing
                              wzxxing
                              opened on Nov 26, 2025
                              Describe the bug
                              
A clear and concise description of what the bug is.
                              When the MCP protocol initialization failed, the server can return a JSON RPC Error object, which is currently ignored by the rust SDK.
                              rust-sdk/crates/rmcp/src/service/client.rs
                              
Lines 128 to 129
in
94428d5
                              // Server SHOULD NOT send any other messages before handshake. We ignore them anyway
                               _ => tracing::warn!(?message,"Received unexpected message"),
                              The Specification suggested that
                              Implementations SHOULD be prepared to handle these error cases:
                              https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle#error-handling
                              To Reproduce
                              
Steps to reproduce the behavior:
                              1. I found this when using the Kiro CLI which uses the rust-sdk. Plugging a MCP server that initialize failure. The error can only be found through tracing
                              2025-11-26T11:05:21.291608Z WARN rmcp::service::client: 129: Received unexpected message Error(JsonRpcError { jsonrpc: JsonRpcVersion2_0, id: Number(0), error: ErrorData { code: ErrorCode(-32001), message: "Your AWS session token has expired. Please refresh your credentials and try again. If you're using temporary credentials, you may need to re-authenticate to obtain new credentials.", data: None } })

                              expect_response ignores the mcp jsonrpc error, hence there was never a response received by the client.
                              rust-sdk/crates/rmcp/src/service/client.rs
                              
Lines 229 to 235
in
94428d5
                              let(response, response_id) = expect_response(
                              &mut transport,
                              "initialize response",
                              &service,
                               peer.clone(),
                              )
                              .await?;
                              Because my test-mcp server quits after the initialization error, I got a very generic "connection closed" message.
                              Expected behavior
                              My test server response to initialization with a synthesized JSON RPC error, I expect the JSON RPC error should be used as the ClientInitializeError.
                              Logs
                              
If applicable, add logs to help explain your problem.
                              Additional context
                              
Add any other context about the problem here.
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