fix(readable): consume a body whose end has already been emitted

[marko1olo]

Fixes #5614.

consumeStart() is a free function, called as consumeStart(stream[kConsume]) from the queueMicrotask() above it, so this is undefined inside it under 'use strict'. The state.endEmitted branch read this[kConsume] anyway:

TypeError: Cannot read properties of undefined (reading 'Symbol(kConsume)')
    at consumeStart (lib/api/readable.js:490:20)
    at lib/api/readable.js:450:9
    at node:internal/process/task_queues:149:7

The two lines are character-for-character the same as the ones in the on('end') callback immediately below, which is what makes it easy to read past — those work, because the emitter invokes the callback with the stream as its receiver.

The part that makes it worth fixing rather than tidying is that the caller cannot catch it. The throw happens on a microtask rather than in the promise chain, so awaiting the consume inside try/catch still takes the process down. Draining a body and then deciding to read it after all is enough to reach it.

On the early return

Correcting only the receiver moves the crash rather than removing it:

TypeError: Cannot read properties of null (reading 'resume')
    at consumeStart (lib/api/readable.js:497:18)

consumeEnd() sets consume.stream to null, and the consume.stream.resume() a few lines down then dereferences it — reachable only once the branch above stops throwing first. So the return is part of the fix.

Tests

One case added to test/readable.js: an empty body, drained, then consumed. Without the change the test runner reports it as an uncaught exception rather than a failed assertion, which is the same shape as the bug:

Error: A resource generated asynchronous activity after the test ended. This activity created the
error "TypeError: Cannot read properties of undefined (reading 'Symbol(kConsume)')" which triggered
an uncaughtException event, caught by the test runner.

test/readable.js 11/11 and test/client-request.js 48/48 with the change; eslint clean.

Possible drawbacks

The endEmitted path is reached by consuming a body after 'end', and I have only exercised it with an empty body and with a drained 204 over a real request. A body that emitted data first is disturbed and rejects with TypeError: unusable before reaching this code, both before and after — I checked that separately so the change is not masking it.

Node 24 on Windows only; I have not run the other matrix cells locally. I did not run npm run test:typescript, which fails on clean main in Git Bash for an unrelated reason (the script relies on shell glob expansion for types/*.d.ts).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.51%. Comparing base (1089808) to head (c07ef96).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #5617    +/-   ##
========================================
  Coverage   93.50%   93.51%            
========================================
  Files         110      110            
  Lines       38303    38429   +126     
========================================
+ Hits        35816    35935   +119     
- Misses       2487     2494     +7     

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[mcollina]

lgtm