googleapis/mcp-toolbox · error

sse session not available

Error message

sse session not available

What it means

Error "sse session not available" thrown in googleapis/mcp-toolbox.

Source

Thrown at internal/server/mcp.go:561

	// Create span for HTTP transport
	ctx, span := s.instrumentation.Tracer.Start(ctx, "toolbox/server/mcp/http",
		trace.WithSpanKind(trace.SpanKindServer),
	)
	r = r.WithContext(ctx)

	var sessionId, protocolVersion string
	var session *sseSession

	// check if client connects via sse
	// v2024-11-05 supports http with sse
	paramSessionId := r.URL.Query().Get("sessionId")
	if paramSessionId != "" {
		sessionId = paramSessionId
		protocolVersion = v20241105.PROTOCOL_VERSION
		var ok bool
		session, ok = s.sseManager.get(sessionId)
		if !ok {
			err := fmt.Errorf("sse session not available")
			s.logger.DebugContext(ctx, err.Error())
			_ = render.Render(w, r, newErrResponse(err, http.StatusBadRequest))
			return
		}
	}

	// check if client have `Mcp-Session-Id` header
	// `Mcp-Session-Id` is only set for v2025-03-26 in Toolbox
	headerSessionId := r.Header.Get("Mcp-Session-Id")
	if headerSessionId != "" {
		protocolVersion = v20250326.PROTOCOL_VERSION
	}

	// check if client have `MCP-Protocol-Version` header
	// Only supported for v2025-06-18+.
	headerProtocolVersion := r.Header.Get("Mcp-Protocol-Version")
	if headerProtocolVersion != "" {
		protocolVersion = headerProtocolVersion

View on GitHub (pinned to 8cc6e09de2)

When it happens

Trigger: Thrown at internal/server/mcp.go:561 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/e20f70f61eb0e714. Report an issue: GitHub.