MCP_PROXY_FULL_ADDRESS is respected for /sse request but not /message

[geisbruch]

MCP_PROXY_FULL_ADDRESS is respected for /sse request but not /message

Summary

The MCP_PROXY_FULL_ADDRESS environment variable is not consistently applied across all API endpoints. While the /sse endpoint correctly uses the full proxy address including the base path, the /message endpoint ignores the base path and makes requests directly to the root domain.

Environment

• Inspector Proxy Address: https://mcp-test-new-server-development-puvbs.ey-poc.nullapps.io/inspector/mcp_proxy
• MCP_PROXY_FULL_ADDRESS configured with full path including /inspector/mcp_proxy

Expected Behavior

Both /sse and /message endpoints should respect the full proxy address specified in MCP_PROXY_FULL_ADDRESS, including any base path.

Actual Behavior

• ✅ /sse endpoint (working correctly): Makes requests to https://mcp-test-new-server-development-puvbs.ey-poc.nullapps.io/inspector/mcp_proxy/sse
• ❌ /message endpoint (incorrect behavior): Makes requests to https://mcp-test-new-server-development-puvbs.ey-poc.nullapps.io/message (base path is stripped)

Steps to Reproduce

1. Set MCP_PROXY_FULL_ADDRESS to a URL with a base path (e.g., https://example.com/inspector/mcp_proxy)
2. Start the MCP inspector
3. Observe network requests:
   • /sse requests correctly include the base path
   • /message requests strip the base path and go directly to the root domain

Impact

This inconsistency breaks functionality when the MCP proxy is hosted with a base path, as /message requests fail to reach the correct endpoint.

Suggested Fix

Ensure that both /sse and /message endpoints use the complete URL from MCP_PROXY_FULL_ADDRESS when constructing their request URLs.

[richardkmichael]

@geisbruch Can you confirm if this is working in your setup?