http 405 when LangFlow tries to discover tools

[cranberyxl]

From what I can tell by reading the code, Langflow tries to discover the list of tool using a GET request and apollo mcp throws a 405, curl -N http://localhost:5005/mcp -H "Accept:text/event-stream" -v. I'm not sure which side should be using/accepting a different method, but decide to open the question on this side.

Steps to reproduce:

1. Download langflow
2. Start Apollo MCP in stateless mode
3. create an mcp tool
4. get a 405

[esilverm]

Hi! Thanks for reporting this issue. I've attempted to replicate the issue you are describing and I can't seem to trigger a 405 error in stateless mode.

From what I understand, the MCP client should be sending JSON-RPC messages via HTTP POST rather than GET so this is likely an issue with Langflow.

[cranberyxl]

Ok, I'll open an issue over there as well. On LangFlow 1.6.0 and apollo-mcp-server 0.9.0 I still see the issue. Here's my apollo config, I'm not sure if using it with auth is changing the code path from what you're seeing. It does seem to be down to them trying to detect if it's SSE to streamable_http here: https://github.com/langflow-ai/langflow/blob/main/src/lfx/src/lfx/base/mcp/util.py#L1044-L1046

{
  endpoint: '✂️',
  transport: {
    type: 'streamable_http',
    stateful_mode: false,
    auth: {
      servers: ['✂️'],
      audiences: ['✂️'],
      resource: '✂️',
      scopes: ['openid'],
    },
  },
  operations: { source: 'collection', id: 'default' },
  schema: { source: 'local', path: './api.graphql' },
  overrides: { mutation_mode: 'all' },
  introspection: {
    execute: { enabled: true },
    introspect: { enabled: true },
    search: { enabled: true },
  },
  logging: { level: 'debug' },
  health_check: {
    enabled: true,
    path: '/health',
    readiness: { allowed: 50, interval: { sampling: '10s', unready: '30s' } },
  },
}