mcp: add ModifyRequest to HTTP client transports #546
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Add ModifyRequest func(*http.Request) field to both SSEClientTransport and StreamableClientTransport. This callback is invoked before each outgoing HTTP request, allowing users to add headers, authentication, or other request modifications. This provides a simpler alternative to implementing custom RoundTrippers for common use cases like adding authorization headers or request IDs. Fixes modelcontextprotocol#533
jba
previously approved these changes
Oct 2, 2025
# Conflicts: # mcp/streamable_test.go
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@jba please check again 🙏 , it appeared to have some merge conflicts prior to merging |
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@manuelibar I think we'll discuss this in the proposal meeting tomorrow and likely approve the proposal (unless anyone objects), so we may as well wait to merge until then. |
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Problem
Users need to modify HTTP requests (add headers, authentication, etc.) but currently must implement custom
RoundTripperimplementations which requires cloning requests and is more complex than necessary.Solution
Add
ModifyRequest func(*http.Request)field to bothSSEClientTransportandStreamableClientTransport. This callback is invoked before each outgoing HTTP request, providing a simple way to modify requests without needing customRoundTripperimplementations.Changes
ModifyRequestfield toSSEClientTransport(called before GET and POST requests)ModifyRequestfield toStreamableClientTransport(called before GET, POST, and DELETE requests)Impact
Fixes #533