Request headers types

[JaoodxD]

This relates to

Resolves #2748

Rationale

In PR #2708, request headers were enhanced with iterable support, although the corresponding types and documentation mentions were inadvertently omitted. Current PR will fix it.

Changes

• add iterable to headers types in types/dispatcher.d.ts
• add type tests to iterable headers in test/types/dispatcher.test-d.ts
• add mention of iterables to documentation in docs/api/Dispatcher.md

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[mcollina]

lgtm

[JaoodxD]

lgtm

Fastest approve in the wild west, thanks.

[thgh]

Hi, I encountered the same issue when upgrading from a docker image from node:20.12-alpine to node:20.13-alpine.

There was no error, the app just quits after a couple seconds. I could find the error like this:

process.on('uncaughtException', (err) => {
  console.error('There was an uncaught error', err)
  process.exit(1)
})

The resulting error looked like this:

There was an uncaught error TypeError: request.headers.split is not a function
    at setHeadersOnRequest (/app/node_modules/@sentry/node/cjs/integrations/undici/index.js:247:39)
    at _onRequestCreate (/app/node_modules/@sentry/node/cjs/integrations/undici/index.js:157:9)
    at Channel.publish (node:diagnostics_channel:143:9)
    at new Request (node:internal/deps/undici/undici:6295:27)
    at [dispatch] (node:internal/deps/undici/undici:9077:25)
    at Intercept (node:internal/deps/undici/undici:8812:20)
    at [Intercepted Dispatch] (node:internal/deps/undici/undici:5673:16)
    at Client.dispatch (node:internal/deps/undici/undici:5689:44)

Solution is to upgrade @sentry/node, not sure if updating undici helps.

Just putting this here for future reference. Thanks for the fix!