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mcp: relax SSE connection response handling in non-strict mode #611

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Merged
merged 2 commits into from
Nov 3, 2025
Merged

mcp: relax SSE connection response handling in non-strict mode #611

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6c06aa3
mcp: relax SSE connection response handling in non-strict mode
zhxie Oct 30, 2025
b733fdd
mcp: fix test
zhxie Nov 3, 2025
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9 changes: 5 additions & 4 deletions mcp/streamable.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1377,13 +1377,14 @@ func (c *streamableClientConn) connectStandaloneSSE() {
resp.Body.Close()
return
}
if resp.StatusCode == http.StatusNotFound && !c.strict {
// modelcontextprotocol/gosdk#393: some servers return NotFound instead
// of MethodNotAllowed for the standalone SSE stream.
if resp.StatusCode >= 400 && resp.StatusCode < 500 && !c.strict {
// modelcontextprotocol/go-sdk#393,#610: some servers return NotFound or
// other status codes instead of MethodNotAllowed for the standalone SSE
// stream.
//
// Treat this like MethodNotAllowed in non-strict mode.
if c.logger != nil {
c.logger.Warn("got 404 instead of 405 for standalone SSE stream")
c.logger.Warn(fmt.Sprintf("got %d instead of 405 for standalone SSE stream", resp.StatusCode))
}
resp.Body.Close()
return
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12 changes: 10 additions & 2 deletions mcp/streamable_client_test.go
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Expand Up @@ -239,7 +239,11 @@ func TestStreamableClientGETHandling(t *testing.T) {
}{
{http.StatusOK, ""},
{http.StatusMethodNotAllowed, ""},
{http.StatusBadRequest, "standalone SSE"},
// The client error status code is not treated as an error in non-strict
// mode.
{http.StatusNotFound, ""},
{http.StatusBadRequest, ""},
{http.StatusInternalServerError, "standalone SSE"},
}

for _, test := range tests {
Expand Down Expand Up @@ -305,7 +309,11 @@ func TestStreamableClientStrictness(t *testing.T) {
{"strict initialized", true, http.StatusOK, http.StatusMethodNotAllowed, true},
{"unstrict initialized", false, http.StatusOK, http.StatusMethodNotAllowed, false},
{"strict GET", true, http.StatusAccepted, http.StatusNotFound, true},
{"unstrict GET", false, http.StatusOK, http.StatusNotFound, false},
// The client error status code is not treated as an error in non-strict
// mode.
{"unstrict GET on StatusNotFound", false, http.StatusOK, http.StatusNotFound, false},
{"unstrict GET on StatusBadRequest", false, http.StatusOK, http.StatusBadRequest, false},
{"GET on InternlServerError", false, http.StatusOK, http.StatusInternalServerError, true},
}
for _, test := range tests {
t.Run(test.label, func(t *testing.T) {
Expand Down