fix(ext/fetch): do not truncate field value in EventSource

[0f-0b]

Depends on #22493. Closes #22367.

[crowlKats]

could you add a test?

[0f-0b]

EventSource reestablishes the connection if the response stream ends, but the test fails if I add a call to eventSource.close() to prevent this behavior.

running 1 test from ./cli/tests/unit/event_source_test.ts
eventSourceColonInMessage ...
Uncaught error from ./cli/tests/unit/event_source_test.ts FAILED
eventSourceColonInMessage ... cancelled (0ms)

 ERRORS 

./cli/tests/unit/event_source_test.ts (uncaught error)
error: (in promise) AbortError: The signal has been aborted
  eventSource.close();
              ^
    at AbortSignal.[[[signalAbort]]] (ext:deno_web/03_abort_signal.js:135:14)
    at AbortController.abort (ext:deno_web/03_abort_signal.js:280:30)
    at EventSource.close (ext:deno_fetch/27_eventsource.js:186:28)
    at eventSourceColonInMessage (file://.../deno/cli/tests/unit/event_source_test.ts:28:15)
This error was not caught from a test and caused the test runner to fail on the referenced module.
It most likely originated from a dangling promise, event/timeout handler or top-level code.

 FAILURES 

./cli/tests/unit/event_source_test.ts (uncaught error)

FAILED | 0 passed | 2 failed (36ms)

error: Test failed

I'll try to fix this in another PR.

[aapoalas]

Looks good to me! Let's merge this after the linked robustness PR.

Thank you for the contributions <3

[cowboyd]

Is there a way to consume this fix from Deno 1.41.3 in order to work around this issue until there is an official release?

[cowboyd]

Is there a way to consume this fix from Deno 1.41.3 in order to work around this issue until there is an official release?

I found this polyfill for Node which works well with just:

import EventSource from "npm:eventsource";

[0f-0b]

@bartlomieju, please take a look at #22493 first. Testing this fix requires there being no unhandled rejections or resource leaks.

[crowlKats]

LGTM