Debug

Undici (and subsenquently fetch and websocket) exposes a debug statement that can be enabled by setting NODE_DEBUG within the environment.

The flags available are:

undici

This flag enables debug statements for the core undici library.

NODE_DEBUG=undici node script.js

UNDICI 16241: connecting to nodejs.org using https:h1
UNDICI 16241: connecting to nodejs.org using https:h1
UNDICI 16241: connected to nodejs.org using https:h1
UNDICI 16241: sending request to GET https://nodejs.org/
UNDICI 16241: received response to GET https://nodejs.org/ - HTTP 307
UNDICI 16241: connecting to nodejs.org using https:h1
UNDICI 16241: trailers received from GET https://nodejs.org/
UNDICI 16241: connected to nodejs.org using https:h1
UNDICI 16241: sending request to GET https://nodejs.org/en
UNDICI 16241: received response to GET https://nodejs.org/en - HTTP 200
UNDICI 16241: trailers received from GET https://nodejs.org/en

fetch

This flag enables debug statements for the fetch API.

Note: statements are pretty similar to the ones in the undici flag, but scoped to fetch

NODE_DEBUG=fetch node script.js

FETCH 16241: connecting to nodejs.org using https:h1
FETCH 16241: connecting to nodejs.org using https:h1
FETCH 16241: connected to nodejs.org using https:h1
FETCH 16241: sending request to GET https://nodejs.org/
FETCH 16241: received response to GET https://nodejs.org/ - HTTP 307
FETCH 16241: connecting to nodejs.org using https:h1
FETCH 16241: trailers received from GET https://nodejs.org/
FETCH 16241: connected to nodejs.org using https:h1
FETCH 16241: sending request to GET https://nodejs.org/en
FETCH 16241: received response to GET https://nodejs.org/en - HTTP 200
FETCH 16241: trailers received from GET https://nodejs.org/en

websocket

This flag enables debug statements for the Websocket API.

Note: statements can overlap with UNDICI ones if undici or fetch flag has been enabled as well.

NODE_DEBUG=websocket node script.js

WEBSOCKET 18309: connecting to echo.websocket.org using https:h1
WEBSOCKET 18309: connected to echo.websocket.org using https:h1
WEBSOCKET 18309: sending request to GET https://echo.websocket.org/
WEBSOCKET 18309: connection opened <ip_address>