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mcp: fix potential nil-pointer dereference on message send #1115

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Merged
yarolegovich merged 2 commits into from
Jul 27, 2026
+12 −7
Merged

mcp: fix potential nil-pointer dereference on message send #1115

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93cf603
fix nil-interface check
yarolegovich Jul 27, 2026
f476e7e
Merge branch 'main' into yarolegovich/nil-check
yarolegovich Jul 27, 2026
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13 changes: 6 additions & 7 deletions mcp/streamable.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2403,13 +2403,12 @@ func (c *streamableClientConn) setMCPHeaders(req *http.Request, msg jsonrpc.Mess
}
}
}
switch {
case protocolVersionFromMessage(msg) != "":
req.Header.Set(protocolVersionHeader, protocolVersionFromMessage(msg))
case c.initializedResult != nil:
if pv := protocolVersionFromMessage(msg); pv != "" {
req.Header.Set(protocolVersionHeader, pv)
} else if pv := protocolVersionFromContext(req.Context()); pv != "" {
req.Header.Set(protocolVersionHeader, pv)
} else if c.initializedResult != nil {
req.Header.Set(protocolVersionHeader, c.initializedResult.ProtocolVersion)
case protocolVersionFromContext(req.Context()) != "":
req.Header.Set(protocolVersionHeader, protocolVersionFromContext(req.Context()))
}
if c.sessionID != "" {
req.Header.Set(sessionIDHeader, c.sessionID)
Expand All @@ -2424,7 +2423,7 @@ func (c *streamableClientConn) setMCPHeaders(req *http.Request, msg jsonrpc.Mess
// nil msg.
func protocolVersionFromMessage(msg jsonrpc.Message) string {
req, ok := msg.(*jsonrpc.Request)
if !ok {
if !ok || req == nil {
return ""
}
meta := extractRequestMeta(req.Params)
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6 changes: 6 additions & 0 deletions mcp/streamable_client_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1386,6 +1386,12 @@ func TestStreamableClientConnSetMCPHeaders_ProtocolVersion(t *testing.T) {
msg jsonrpc.Message
want string
}{
{
name: "nil checked",
initializedResult: nil,
msg: (*jsonrpc.Request)(nil),
want: "",
},
{
name: "message meta wins when initializedResult unset",
initializedResult: nil,
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