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mcp: HTTP Header Standardization for x-mcp-header (#915)

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## Description

Implements
[SEP-2243](https://modelcontextprotocol.io/seps/2243-http-standardization)
(HTTP Header Standardization) for x-mcp-param custom header.

Fixes https://github.com/modelcontextprotocol/go-sdk/issues/905

---------

Co-authored-by: Maciej Kisiel <mkisiel@google.com>
This commit is contained in:
Guglielmo Colombo 2026-05-08 12:39:18 +02:00 • committed by GitHub
commit 909372d8d1
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1 changed files with 1512 additions and 15 deletions
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9
mcp/streamable.go
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@ -491,6 +491,7 @@ func (h *StreamableHTTPHandler) ServeHTTP(w http.ResponseWriter, req *http.Reque
http.Error(w, "failed connection", http.StatusInternalServerError)
return
}
transport.connection.toolLookup = server.getServerTool
// Capture the user ID from the token info to enable session hijacking
// prevention on subsequent requests.
var userID string
@ -669,6 +670,8 @@ type streamableServerConn struct {
logger *slog.Logger
toolLookup func(name string) (*serverTool, bool)
incoming chan jsonrpc.Message // messages from the client to the server
mu sync.Mutex // guards all fields below
@ -1202,9 +1205,9 @@ func (c *streamableServerConn) servePOST(w http.ResponseWriter, req *http.Reques
}
}
// Validate MCP standard headers (Mcp-Method, Mcp-Name)
// Validate MCP standard headers (Mcp-Method, Mcp-Name, Mcp-Param-*)
if !isBatch && len(incoming) == 1 {
if err := validateMcpHeaders(req.Header, incoming[0]); err != nil {
if err := validateMcpHeaders(req.Header, incoming[0], c.toolLookup); err != nil {
resp := &jsonrpc.Response{
Error: jsonrpc2.NewError(CodeHeaderMismatch, err.Error()),
}
@ -1829,7 +1832,7 @@ func (c *streamableClientConn) Write(ctx context.Context, msg jsonrpc.Message) e
}
// Keep this after the setMCPHeaders call to ensure that the
// protocol version header is set.
setStandardHeaders(req.Header, msg)
setStandardHeaders(ctx, req.Header, msg)
resp, err := c.client.Do(req)
if err != nil {
// Any error from client.Do means the request didn't reach the server.