github/github-mcp-server · warning

internal error

Error message

internal error

What it means

While rendering the OAuth callback success page, successTemplate.Execute returned an error and the handler responds with a bare 500 'internal error' as a last resort. The template is static, pre-parsed, and executed with nil data, so in practice Execute fails because the client disconnected mid-write (broken pipe) - at that point the token exchange has already succeeded. Persistent occurrences would indicate corrupted embedded templates.

Source

Thrown at internal/oauth/callback.go:146

	select {
	case res := <-cs.results:
		return res.code, res.err
	case <-ctx.Done():
		return "", ctx.Err()
	}
}

func (cs *callbackServer) close() {
	shutdownCtx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	_ = cs.server.Shutdown(shutdownCtx)
	_ = cs.listener.Close()
}

func renderSuccess(w http.ResponseWriter) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := successTemplate.Execute(w, nil); err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
	}
}

// renderError shows the failure page. html/template auto-escapes msg, so a
// hostile error_description cannot inject markup.
func renderError(w http.ResponseWriter, msg string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := errorTemplate.Execute(w, struct{ ErrorMessage string }{ErrorMessage: msg}); err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
	}
}

View on GitHub (pinned to 0ea1f775a7)

Solutions

1. Treat one-off occurrences as benign - the authorization already completed before rendering
2. If persistent, rebuild the binary to rule out corrupted embedded templates
3. Ensure no middleware writes headers before the callback handler runs

if err := successTemplate.Execute(w, nil); err != nil {
	// headers may already be flushed; the 500 fallback is best-effort - log at warn, not error
	http.Error(w, "internal error", http.StatusInternalServerError)
}

When it happens

Trigger: User closes the browser tab or the connection drops exactly as the success page streams out at the end of the OAuth flow.

Common situations: End users canceling at the final redirect; mobile browsers backgrounding during callback; scanners hitting the callback URL and disconnecting.

Related errors

• App not connected
• authentication required: set GITHUB_PERSONAL_ACCESS_TOKEN, c
• no authorization code in callback
• failed to download logs: %w
• failed to read response body: %w

AI-assisted analysis of github/github-mcp-server@0ea1f775a7 (2026-08-15). Data as JSON: /api/errors/78a2a6432f61facd. Report an issue: GitHub.