SSE endpoints not working in network mode

b3nw · 2025-07-13T20:11:27-05:00

b3nw commented

2025-07-13 20:11:27 -05:00

Issue Description

In network mode, the HTTP endpoint (/mcp) works perfectly but the SSE endpoints (/sse and /message) return 404 errors. This prevents achieving the goal of having both HTTP and SSE transports on a single port.

Current Status

✅ Working: HTTP endpoint at /mcp with proper session management
❌ Not Working: SSE endpoints at /sse and /message

Environment

Version: network-mode-v0.3.0 branch
mcp-go version: v0.30.0
Transport mode: network
Test server: git.local.ben.io:8080

Working HTTP Endpoint Test

# HTTP endpoint works perfectly
curl -X POST http://git.local.ben.io:8080/mcp \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {"protocolVersion": "2024-11-05", "capabilities": {}}}'

# Returns:
# HTTP/1.1 200 OK
# Mcp-Session-Id: mcp-session-32a4e4af-483b-4b0e-a135-cdc5a1a2c420
# {"jsonrpc":"2.0","id":1,"result":{...}}

Failing SSE Endpoint Tests

# SSE connection endpoint fails
curl -X GET http://git.local.ben.io:8080/sse
# Returns: 404 page not found

# SSE message endpoint fails  
curl -X POST http://git.local.ben.io:8080/message?sessionId=test \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/list","params":{},"id":1}'
# Returns: 404 page not found

Current Implementation

case "network":
    streamableServer := server.NewStreamableHTTPServer(mcpServer)
    sseServer := server.NewSSEServer(mcpServer)
    
    mux := http.NewServeMux()
    mux.Handle("/mcp", streamableServer)
    mux.Handle("/sse", sseServer.SSEHandler())
    mux.Handle("/message", sseServer.MessageHandler())
    
    return http.ListenAndServe(fmt.Sprintf(":%d", flag.Port), mux)

Attempted Solutions

1. Direct SSE Server Mounting

mux.Handle("/sse/", sseServer)  // Tried with trailing slash

Result: Still 404 on /sse/sse and /sse/message

2. Custom SSE Endpoint Configuration

sseServer := server.NewSSEServer(mcpServer,
    server.WithSSEEndpoint("/sse"),
    server.WithMessageEndpoint("/message"),
)
mux.Handle("/sse", sseServer.SSEHandler())
mux.Handle("/message", sseServer.MessageHandler())

Result: Still 404 on both endpoints

3. Default SSE Server with Handler Mounting

sseServer := server.NewSSEServer(mcpServer)
mux.Handle("/sse", sseServer.SSEHandler())
mux.Handle("/message", sseServer.MessageHandler())

Result: Still 404 on both endpoints

Server Binding Confirmation

✅ Server process runs successfully
✅ Port 8080 is bound correctly
✅ HTTP requests to /mcp work perfectly
❌ All requests to /sse and /message return 404

Analysis

The issue appears to be related to how the SSE handlers are being mounted or configured. The mcp-go SSE server expects specific routing that may not be compatible with custom mux mounting.

Investigation Areas

SSE Handler Internal Routing: The SSE handlers may expect to handle their own internal routing
Path Conflicts: There may be path normalization issues with the Go ServeMux
Handler Initialization: The SSE handlers may require specific initialization that's not happening
mcp-go Framework Limitations: The framework may not support custom mounting of SSE handlers

Workaround

Currently, users can use the HTTP endpoint (/mcp) which is fully functional with session management. However, this doesn't achieve the goal of having both transports available.

Next Steps

Examine mcp-go SSE server source code more thoroughly
Test SSE server in isolation to understand expected behavior
Consider alternative mounting strategies
Investigate if custom routing wrapper is needed

Files Modified

operation/operation.go (network mode implementation)
TESTING.md (documentation of endpoints)

Priority

Medium - HTTP endpoint works, but full network mode functionality requires both transports

# SSE Endpoints Not Working in Network Mode ## Issue Description In network mode, the HTTP endpoint (`/mcp`) works perfectly but the SSE endpoints (`/sse` and `/message`) return 404 errors. This prevents achieving the goal of having both HTTP and SSE transports on a single port. ## Current Status ✅ **Working**: HTTP endpoint at `/mcp` with proper session management ❌ **Not Working**: SSE endpoints at `/sse` and `/message` ## Environment - **Version**: network-mode-v0.3.0 branch - **mcp-go version**: v0.30.0 - **Transport mode**: `network` - **Test server**: git.local.ben.io:8080 ## Working HTTP Endpoint Test ```bash # HTTP endpoint works perfectly curl -X POST http://git.local.ben.io:8080/mcp \ -H "Content-Type: application/json" \ -d '{"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": {"protocolVersion": "2024-11-05", "capabilities": {}}}' # Returns: # HTTP/1.1 200 OK # Mcp-Session-Id: mcp-session-32a4e4af-483b-4b0e-a135-cdc5a1a2c420 # {"jsonrpc":"2.0","id":1,"result":{...}} ``` ## Failing SSE Endpoint Tests ```bash # SSE connection endpoint fails curl -X GET http://git.local.ben.io:8080/sse # Returns: 404 page not found # SSE message endpoint fails curl -X POST http://git.local.ben.io:8080/message?sessionId=test \ -H "Content-Type: application/json" \ -d '{"jsonrpc":"2.0","method":"tools/list","params":{},"id":1}' # Returns: 404 page not found ``` ## Current Implementation ```go case "network": streamableServer := server.NewStreamableHTTPServer(mcpServer) sseServer := server.NewSSEServer(mcpServer) mux := http.NewServeMux() mux.Handle("/mcp", streamableServer) mux.Handle("/sse", sseServer.SSEHandler()) mux.Handle("/message", sseServer.MessageHandler()) return http.ListenAndServe(fmt.Sprintf(":%d", flag.Port), mux) ``` ## Attempted Solutions ### 1. Direct SSE Server Mounting ```go mux.Handle("/sse/", sseServer) // Tried with trailing slash ``` **Result**: Still 404 on `/sse/sse` and `/sse/message` ### 2. Custom SSE Endpoint Configuration ```go sseServer := server.NewSSEServer(mcpServer, server.WithSSEEndpoint("/sse"), server.WithMessageEndpoint("/message"), ) mux.Handle("/sse", sseServer.SSEHandler()) mux.Handle("/message", sseServer.MessageHandler()) ``` **Result**: Still 404 on both endpoints ### 3. Default SSE Server with Handler Mounting ```go sseServer := server.NewSSEServer(mcpServer) mux.Handle("/sse", sseServer.SSEHandler()) mux.Handle("/message", sseServer.MessageHandler()) ``` **Result**: Still 404 on both endpoints ## Server Binding Confirmation - ✅ Server process runs successfully - ✅ Port 8080 is bound correctly - ✅ HTTP requests to `/mcp` work perfectly - ❌ All requests to `/sse` and `/message` return 404 ## Analysis The issue appears to be related to how the SSE handlers are being mounted or configured. The mcp-go SSE server expects specific routing that may not be compatible with custom mux mounting. ## Investigation Areas 1. **SSE Handler Internal Routing**: The SSE handlers may expect to handle their own internal routing 2. **Path Conflicts**: There may be path normalization issues with the Go ServeMux 3. **Handler Initialization**: The SSE handlers may require specific initialization that's not happening 4. **mcp-go Framework Limitations**: The framework may not support custom mounting of SSE handlers ## Workaround Currently, users can use the HTTP endpoint (`/mcp`) which is fully functional with session management. However, this doesn't achieve the goal of having both transports available. ## Next Steps 1. Examine mcp-go SSE server source code more thoroughly 2. Test SSE server in isolation to understand expected behavior 3. Consider alternative mounting strategies 4. Investigate if custom routing wrapper is needed ## Files Modified - `operation/operation.go` (network mode implementation) - `TESTING.md` (documentation of endpoints) ## Priority **Medium** - HTTP endpoint works, but full network mode functionality requires both transports

b3nw closed this issue

2025-07-13 21:06:04 -05:00

b3nw commented

2025-07-13 21:06:04 -05:00

This issue is now resolved. The network mode has been updated to correctly handle both HTTP and SSE transports on a single port. The operation/operation.go file was modified to properly initialize and route the SSE server endpoints (/sse and /message), which were previously returning 404 errors. Both transport methods are now fully functional in network mode.

This issue is now resolved. The `network` mode has been updated to correctly handle both HTTP and SSE transports on a single port. The `operation/operation.go` file was modified to properly initialize and route the SSE server endpoints (`/sse` and `/message`), which were previously returning 404 errors. Both transport methods are now fully functional in `network` mode.

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Reference: b3nw/gitea-mcp#13