Enable debug information for `fetch()` via `NODE_DEBUG=http`

[dimw]

What is the problem this feature will solve?

The HTTP debug information for node-fetch can be turned on by setting the the environment variable NODE_DEBUG=http:

// node-fetch.test.js
const fetch = require('node-fetch');

fetch('https://github.com')
  .then(({statusText}) => console.log(statusText));

$ NODE_DEBUG=http node node-fetch.test.js
HTTP 22032: call onSocket 0 0
HTTP 22032: createConnection github.com:443::::::::::::::::::::: [Object: null prototype] {
  protocol: 'https:',
  slashes: true,
[redacted]
HTTP 22032: AGENT incoming response!
OK
HTTP 22032: AGENT socket.destroySoon()
HTTP 22032: CLIENT socket onClose
HTTP 22032: removeSocket github.com:443::::::::::::::::::::: writable: false
HTTP 22032: HTTP socket close

Unfortunately, there is no HTTP debug information is shown when the native fetch() implementation is used:

// fetch.test.js
fetch('https://github.com')
  .then(({statusText}) => console.log(statusText));

$ NODE_DEBUG=http node fetch.test.js
OK

Seeing the HTTP request object can be considered as useful for debugging.

What is the feature you are proposing to solve the problem?

• Either display the HTTP debug statement for the native fetch() when NODE_DEBUG=http is active or
• introduce a new flag to display HTTP debug output.

What alternatives have you considered?

The native fetch() is presenting more information when NODE_DEBUG=net,stream is used. This information is, however, not suitable for HTTP debugging.

[climba03003]

Would diagnostics_channel be sufficient?

You can inspect in any stage according to the document. https://github.com/nodejs/undici/blob/main/docs/api/DiagnosticsChannel.md

Related https://github.com/nodejs/undici/issues/1001

[glenjamin]

When attempting to figure out what's broken in a node-based CLI tool or similar scenarios where the code isn't owned by the person seeing the error, being able to add NODE_DEBUG=http was extremely useful for seeing what's going on.

It would be great if newer versions of Node could preserve this debug interface.

[github-actions[bot]]

There has been no activity on this feature request for 5 months and it is unlikely to be implemented. It will be closed 6 months after the last non-automated comment.

For more information on how the project manages feature requests, please consult the feature request management document.

[targos]

@nodejs/undici wdyt?

[mcollina]

I think this would be a good feature to add to undici. As said by @climba03003, I would recommended building it on top of the diagnostics channel support that we have in Undici. As with most feature requests, this lacks a volunteer to send a PR.

I'm going to move it to undici.

[dakdevs]

Any advice here on how to tell what request params are involved in the error:

[APP] TypeError: fetch failed
[APP]     at Object.fetch (node:internal/deps/undici/undici:11372:11)
[APP]     at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
[APP]   cause: _ConnectTimeoutError: Connect Timeout Error
[APP]       at onConnectTimeout (node:internal/deps/undici/undici:6616:28)
[APP]       at node:internal/deps/undici/undici:6574:50
[APP]       at Immediate._onImmediate (node:internal/deps/undici/undici:6605:13)
[APP]       at process.processImmediate (node:internal/timers:478:21)
[APP]       at process.callbackTrampoline (node:internal/async_hooks:130:17) {
[APP]     code: 'UND_ERR_CONNECT_TIMEOUT'
[APP]   }
[APP] }