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mcp: allow restricting the protocol versions a server supports (#1199)

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Fixes #945
This commit is contained in:
Guglielmo Colombo 2026-08-28 16:06:10 +02:00 • committed by GitHub
commit 21c18c6229
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1 changed files with 397 additions and 35 deletions
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22
mcp/streamable.go
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@ -363,13 +363,21 @@ func (h *StreamableHTTPHandler) ServeHTTP(w http.ResponseWriter, req *http.Reque
}
// [§2.7] of the spec (2025-06-18): validate the MCP-Protocol-Version
// header. If provided, it must be a supported version. If absent, the
// version is unknown (the request may be an initialize for any version).
// header. If provided, it must be a version the server negotiates, which
// [ServerOptions.SupportedProtocolVersions] may have narrowed. If absent,
// the version is unknown (the request may be an initialize for any
// version).
//
// [§2.7]: https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#protocol-version-header
protocolVersion := req.Header.Get(protocolVersionHeader)
if protocolVersion != "" && !slices.Contains(supportedProtocolVersions, protocolVersion) && protocolVersion < protocolVersion20260728 {
http.Error(w, fmt.Sprintf("Bad Request: Unsupported protocol version (supported versions: %s)", strings.Join(supportedProtocolVersions, ",")), http.StatusBadRequest)
var supportedVersions []string
if server := h.getServer(req); server != nil {
supportedVersions = server.protocolVersions
} else {
supportedVersions = supportedProtocolVersions
}
if protocolVersion != "" && !slices.Contains(supportedVersions, protocolVersion) && protocolVersion < protocolVersion20260728 {
http.Error(w, fmt.Sprintf("Bad Request: Unsupported protocol version (supported versions: %s)", strings.Join(supportedVersions, ",")), http.StatusBadRequest)
return
}
req = req.WithContext(context.WithValue(req.Context(), protocolVersionContextKey{}, protocolVersion))
@ -1541,7 +1549,11 @@ func (c *streamableServerConn) servePOST(w http.ResponseWriter, req *http.Reques
// Advertise only the legacy versions this stateful server accepts
// (i.e. exclude 2026-07-28, since that's what the request asked for
// and what we're rejecting).
legacyVersions := slices.DeleteFunc(slices.Clone(supportedProtocolVersions), func(v string) bool {
advertised := supportedProtocolVersions
if c.server != nil {
advertised = c.server.protocolVersions
}
legacyVersions := slices.DeleteFunc(slices.Clone(advertised), func(v string) bool {
return v >= protocolVersion20260728
})
data, _ := json.Marshal(UnsupportedProtocolVersionData{