feat: add legacy SSE transport support for MCP servers#18801
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Gmatrix2022 wants to merge 1 commit into
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feat: add legacy SSE transport support for MCP servers#18801Gmatrix2022 wants to merge 1 commit into
Gmatrix2022 wants to merge 1 commit into
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Add 'transport: sse' config option for HTTP MCP servers that use
the legacy Server-Sent Events transport (GET /sse + POST /messages/)
instead of StreamableHTTP (POST-only).
Some MCP servers (e.g. Windows-MCP, older community servers) only
support the old SSE protocol. This patch adds an sse_client path
alongside the existing streamablehttp_client, selected via:
mcp_servers:
my_server:
url: http://host:8899/sse
transport: sse
Changes:
- Import mcp.client.sse.sse_client with availability flag
- Add _is_sse() config check method
- Add _run_sse() transport method using SSE client
- Route to SSE path in run() when transport: sse is set
Collaborator
Collaborator
This was referenced May 3, 2026
Contributor
|
This looks implemented on current Evidence:
Thanks for the contribution and the Windows-MCP validation notes. The prior maintainer comments calling out related competing SSE PRs were accurate; the capability has since been incorporated on main. |
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Summary
Adds
transport: sseconfig option for HTTP MCP servers that use the legacy Server-Sent Events transport (GET /sse+POST /messages/) instead of StreamableHTTP.Problem
Some MCP servers (e.g. Windows-MCP, older community servers) only implement the old SSE protocol. Hermes currently only uses
streamablehttp_clientfor HTTP transport, causing405 Method Not Allowederrors when connecting to these servers.Solution
When
transport: sseis set in the MCP server config, Hermes usesmcp.client.sse.sse_clientinstead ofmcp.client.streamable_http.streamablehttp_client.Config
Changes
mcp.client.sse.sse_clientwith_MCP_SSE_AVAILABLEavailability flag_is_sse()config check method_run_sse()transport method using SSE clientrun()whentransport: sseis setTesting
Verified against Windows-MCP v3.2.4 (SSE transport on port 8899). Connection succeeds with
transport: sse, fails with405 Method Not Allowedwithout it.