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fix: reconnect expired MCP backend sessions transparently, extend server session timeout #2597
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d291ea2
Initial plan
Copilot 4d26ddd
fix: reconnect HTTP backend sessions on expiry, increase server-side …
Copilot 05becc0
fix: address code review - proper RWMutex sync for session fields, lo…
Copilot 1d95d26
fix: polish comments per code review feedback
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
|
@@ -62,6 +62,24 @@ func isHTTPConnectionError(err error) bool { | |
| return false | ||
| } | ||
|
|
||
| // isSessionNotFoundError checks if an error message indicates a backend MCP session has expired | ||
| // or is not found. This is used to detect when automatic reconnection to the backend is needed. | ||
| func isSessionNotFoundError(err error) bool { | ||
| if err == nil { | ||
| return false | ||
| } | ||
| return strings.Contains(strings.ToLower(err.Error()), "session not found") | ||
| } | ||
|
|
||
| // isSessionNotFoundHTTPResponse checks if an HTTP response indicates the backend session was not found. | ||
| // MCP backends return HTTP 404 with a "session not found" body when a session has expired. | ||
| func isSessionNotFoundHTTPResponse(statusCode int, body []byte) bool { | ||
| if statusCode != http.StatusNotFound { | ||
| return false | ||
| } | ||
| return strings.Contains(strings.ToLower(string(body)), "session not found") | ||
| } | ||
|
|
||
| // parseSSEResponse extracts JSON data from SSE-formatted response | ||
| // SSE format: "event: message\ndata: {json}\n\n" | ||
| func parseSSEResponse(body []byte) ([]byte, error) { | ||
|
|
@@ -436,58 +454,47 @@ func (c *Connection) initializeHTTPSession() (string, error) { | |
| return sessionID, nil | ||
| } | ||
|
|
||
| // sendHTTPRequest sends a JSON-RPC request to an HTTP MCP server | ||
| // The ctx parameter is used to extract session ID for the Mcp-Session-Id header | ||
| func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params interface{}) (*Response, error) { | ||
| // Generate unique request ID using atomic counter | ||
| requestID := atomic.AddUint64(&requestIDCounter, 1) | ||
|
|
||
| // For tools/call, ensure arguments field always exists (MCP protocol requirement) | ||
| if method == "tools/call" { | ||
| params = ensureToolCallArguments(params) | ||
| } | ||
|
|
||
| logConn.Printf("Sending HTTP request to %s: method=%s, id=%d", c.httpURL, method, requestID) | ||
|
|
||
| // Execute HTTP request with custom header modification for session ID | ||
| result, err := c.executeHTTPRequest(ctx, method, params, requestID, func(httpReq *http.Request) { | ||
| // Add Mcp-Session-Id header with priority: | ||
| // 1) Context session ID (if explicitly provided for this request) | ||
| // 2) Stored httpSessionID from initialization | ||
| // buildSessionHeaderModifier returns a header modifier function that adds the Mcp-Session-Id header. | ||
| // Priority: context session ID > stored connection session ID. | ||
| // Context session IDs are static for the lifetime of a single request and are captured once at | ||
| // construction time. Connection session IDs can change during a reconnect, so getHTTPSessionID() | ||
| // is called at request time to always pick up the current value. | ||
| func (c *Connection) buildSessionHeaderModifier(ctx context.Context) func(*http.Request) { | ||
| // Capture any context-provided session ID once (it never changes for this request). | ||
| ctxSessionID, _ := ctx.Value(SessionIDContextKey).(string) | ||
| return func(httpReq *http.Request) { | ||
| var sessionID string | ||
| if ctxSessionID, ok := ctx.Value(SessionIDContextKey).(string); ok && ctxSessionID != "" { | ||
| if ctxSessionID != "" { | ||
| sessionID = ctxSessionID | ||
| logConn.Printf("Using session ID from context: %s", sessionID) | ||
| } else if c.httpSessionID != "" { | ||
| sessionID = c.httpSessionID | ||
| } else if id := c.getHTTPSessionID(); id != "" { | ||
| sessionID = id | ||
| logConn.Printf("Using stored session ID from initialization: %s", sessionID) | ||
| } | ||
|
|
||
| if sessionID != "" { | ||
| httpReq.Header.Set("Mcp-Session-Id", sessionID) | ||
| } else { | ||
| logConn.Printf("No session ID available (backend may not require session management)") | ||
| } | ||
| }) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
|
|
||
| logConn.Printf("Received HTTP response: status=%d, body_len=%d", result.StatusCode, len(result.ResponseBody)) | ||
|
|
||
| // Parse JSON-RPC response | ||
| // The response might be in SSE format (event: message\ndata: {...}) | ||
| // parseHTTPResult converts a raw httpRequestResult into a JSON-RPC Response, handling non-OK | ||
| // HTTP status codes by synthesising a JSON-RPC error when the server did not provide one. | ||
| func parseHTTPResult(result *httpRequestResult) (*Response, error) { | ||
| // Parse JSON-RPC response. | ||
| // The response might be in SSE format (event: message\ndata: {...}). | ||
| rpcResponse, err := parseJSONRPCResponseWithSSE(result.ResponseBody, result.StatusCode, "JSON-RPC response") | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
|
||
| // Check for HTTP errors after parsing | ||
| // Check for HTTP errors after parsing. | ||
| // If we have a non-OK status but successfully parsed a JSON-RPC response, | ||
| // pass it through (it may already contain an error field) | ||
| // pass it through (it may already contain an error field). | ||
| if result.StatusCode != http.StatusOK { | ||
|
Comment on lines
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495
|
||
| logConn.Printf("HTTP error status=%d with valid JSON-RPC response, passing through", result.StatusCode) | ||
| // If the response doesn't already have an error, construct one | ||
| // If the response doesn't already have an error, construct one. | ||
| if rpcResponse.Error == nil { | ||
| rpcResponse.Error = &ResponseError{ | ||
| Code: -32603, // Internal error | ||
|
|
@@ -499,3 +506,44 @@ func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params | |
|
|
||
| return rpcResponse, nil | ||
| } | ||
|
|
||
| // sendHTTPRequest sends a JSON-RPC request to an HTTP MCP server. | ||
| // The ctx parameter is used to extract session ID for the Mcp-Session-Id header. | ||
| // If the backend returns a "session not found" (HTTP 404) response, it attempts a one-time | ||
| // session reconnect and retries the request transparently. | ||
| func (c *Connection) sendHTTPRequest(ctx context.Context, method string, params interface{}) (*Response, error) { | ||
| // For tools/call, ensure arguments field always exists (MCP protocol requirement) | ||
| if method == "tools/call" { | ||
| params = ensureToolCallArguments(params) | ||
| } | ||
|
|
||
| headerModifier := c.buildSessionHeaderModifier(ctx) | ||
|
|
||
| requestID := atomic.AddUint64(&requestIDCounter, 1) | ||
| logConn.Printf("Sending HTTP request to %s: method=%s, id=%d", c.httpURL, method, requestID) | ||
|
|
||
| result, err := c.executeHTTPRequest(ctx, method, params, requestID, headerModifier) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
|
||
| logConn.Printf("Received HTTP response: status=%d, body_len=%d", result.StatusCode, len(result.ResponseBody)) | ||
|
|
||
| // If the backend reported that the session has expired, reconnect and retry once. | ||
| if isSessionNotFoundHTTPResponse(result.StatusCode, result.ResponseBody) { | ||
| logConn.Printf("Session not found from %s (serverID=%s), attempting reconnect", c.httpURL, c.serverID) | ||
| if reconnErr := c.reconnectPlainJSON(); reconnErr == nil { | ||
| requestID = atomic.AddUint64(&requestIDCounter, 1) | ||
| logConn.Printf("Retrying HTTP request after reconnect: method=%s, id=%d", method, requestID) | ||
| result, err = c.executeHTTPRequest(ctx, method, params, requestID, headerModifier) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| logConn.Printf("Retry HTTP response: status=%d, body_len=%d", result.StatusCode, len(result.ResponseBody)) | ||
| } else { | ||
| logConn.Printf("Session reconnect failed (%v), returning original session-not-found error", reconnErr) | ||
| } | ||
| } | ||
|
|
||
| return parseHTTPResult(result) | ||
| } | ||
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reconnectPlainJSONcallsinitializeHTTPSession(), which usescontext.Background()internally. That means a reconnect ignores caller cancellation/deadlines and can hang until the HTTP client timeout, even if the original request context is canceled. Consider plumbing a context intoinitializeHTTPSession(or adding a context-aware variant) and using a bounded timeout (similar toreconnectSDKTransport) so reconnect attempts are cancelable and predictable.