fix: fall back to SSE when AutoDetect probe gets 405 with JSON-RPC error body - #1849
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ump45nose wants to merge 1 commit into
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fix: fall back to SSE when AutoDetect probe gets 405 with JSON-RPC error body#1849ump45nose wants to merge 1 commit into
ump45nose wants to merge 1 commit into
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…ror body A 405 Method Not Allowed means the peer does not accept POST at the endpoint, so a JSON-RPC body there is framework-generated rather than evidence of Streamable HTTP support. Previously the SDK adopted Streamable HTTP for any parsed JSON-RPC error, breaking connectivity to SSE-only servers (e.g. gitmcp.io). Treat 405 like other non-JSON-RPC failures and fall back to SSE, and add 405 to the initialize fallback filter.
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Summary
fix: fall back to SSE when AutoDetect probe gets 405 with JSON-RPC error body
Verification
dotnet test tests/ModelContextProtocol.Tests --framework net10.0 -c Release --filter 'FullyQualifiedName
HttpClientTransportAutoDetectTests' (10 passed); 'FullyQualifiedNameJuly2026ProtocolFallbackTests|FullyQualifiedName~HttpClientTransportTests' (34 passed)Related to #1848