Skip to content

fix(mcp): redirect console.log/warn to stderr in --mcp stdio mode #2840

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
diegosouzapw merged 2 commits into from
May 29, 2026
Merged

fix(mcp): redirect console.log/warn to stderr in --mcp stdio mode #2840

Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
76f9b92
fix(mcp): redirect console.log/warn to stderr in --mcp stdio mode
disonjer May 28, 2026
fd778ec
refactor: use Node.js Console class for stderr redirect
disonjer May 28, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 9 additions & 0 deletions bin/omniroute.mjs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,15 @@ const __filename = fileURLToPath(import.meta.url);
const __dirname = dirname(__filename);
const ROOT = join(__dirname, "..");

// MCP stdio transport uses stdout exclusively for JSON-RPC messages.
// Redirect console.log/warn to stderr early (before loadEnvFile and DB init)
// so no startup output corrupts the protocol.
if (process.argv.includes("--mcp")) {
const _stderrWrite = (msg) => process.stderr.write(msg + "\n");
console.log = (...a) => _stderrWrite(a.join(" "));
console.warn = (...a) => _stderrWrite(a.join(" "));
}
Comment on lines +34 to +39

@gemini-code-assist gemini-code-assist Bot May 28, 2026

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

medium

Overriding console.log and console.warn with a simple a.join(" ") breaks standard Node.js console formatting (such as formatting of objects, multiple arguments, and string formatting placeholders like %s or %j).

To preserve full formatting capabilities while redirecting output to stderr, you can use Node's built-in Console class from node:console.

if (process.argv.includes("--mcp")) {
  const { Console } = await import("node:console");
  const mcpConsole = new Console({ stdout: process.stderr, stderr: process.stderr });
  console.log = mcpConsole.log.bind(mcpConsole);
  console.warn = mcpConsole.warn.bind(mcpConsole);
}


function loadEnvFile() {
const envPaths = [];

Expand Down