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Merged
david-luna merged 7 commits into from
Oct 31, 2025
Merged

fix(instrumentation-fetch): Handling null-body-status responses #6037

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4b09457
adding null-body-status response test
m0sa Oct 22, 2025
6ffb168
handling null-body-status response gracefully
m0sa Oct 22, 2025
88f1fbe
adding changelog entry
m0sa Oct 23, 2025
ca8f2ee
md harder
m0sa Oct 23, 2025
32c82fd
using correct assertion
m0sa Oct 23, 2025
20b8698
adding tests for other cases
m0sa Oct 24, 2025
99e4837
removing 101 case
m0sa Oct 24, 2025
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2 changes: 2 additions & 0 deletions experimental/CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,8 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2

### :bug: Bug Fixes

* fix(instrumentation-fetch): Handling null-body-status responses [#6037](https://github.com/open-telemetry/opentelemetry-js/pull/6037) @m0sa

### :books: Documentation

### :house: Internal
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10 changes: 8 additions & 2 deletions experimental/packages/opentelemetry-instrumentation-fetch/src/fetch.ts
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Expand Up @@ -507,8 +507,14 @@ export class FetchInstrumentation extends InstrumentationBase<FetchInstrumentati
const body = resClone.body;
if (body) {
const reader = body.getReader();

const wrappedBody = withCancelPropagation(response.body, reader);
const isNullBodyStatus =
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@david-luna david-luna Oct 29, 2025

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I assume these statuses are the ones with null body according to a spec. But my experience tells me some apis may not follow these specs and return body anyways. I wonder if it's okay to not process the body in this scenario

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@m0sa m0sa Oct 29, 2025 •
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The new Response({ /* non-null-wrapped-body */ }, { status: 204 /* or 101, 205, 304 */ }) constructor always throws:

Image

The only way of processing it further would mean avoid reconstructing it / preserving a code path that was in place prior to #5894

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@david-luna david-luna Oct 29, 2025

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well, backends could be written in different languages and those may let the dev pass a payload. According to https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Status we should not expect payloads for these statuses so I'm fine. If there is interest in reading the body even with these cases we can add it later.

// 101 responses and protocol upgrading is handled internally by the browser
response.status === 204 ||
response.status === 205 ||
response.status === 304;
const wrappedBody = isNullBodyStatus
? null
: withCancelPropagation(response.body, reader);

proxiedResponse = new Response(wrappedBody, {
status: response.status,
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43 changes: 43 additions & 0 deletions experimental/packages/opentelemetry-instrumentation-fetch/test/fetch.test.ts
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Expand Up @@ -369,6 +369,15 @@ describe('fetch', () => {
msw.http.get('/boom', () => {
return new msw.HttpResponse(null, { status: 500 });
}),
msw.http.get('/null-body-204', () => {
return new msw.HttpResponse(null, { status: 204 });
}),
msw.http.get('/null-body-205', () => {
return new msw.HttpResponse(null, { status: 205 });
}),
msw.http.get('/null-body-304', () => {
return new msw.HttpResponse(null, { status: 304 });
}),
],
callback = () => fetch('/api/status.json'),
config = {},
Expand All @@ -391,6 +400,40 @@ describe('fetch', () => {
return { rootSpan, response };
};

describe('null-bodied response', () => {
// https://chromium.googlesource.com/chromium/src/+/ac85ca2a9cb8c76a37f9d7a6c611c24114f1f05d/third_party/WebKit/Source/core/fetch/Response.cpp#106
it('204 (No Content) will correctly end the span', async () => {
await tracedFetch({
callback: () => fetch('/null-body-204'),
});
assert.strictEqual(exportedSpans.length, 1);
assert.strictEqual(
exportedSpans[0].attributes[ATTR_HTTP_STATUS_CODE],
204
);
});
it('205 (Reset Content) will correctly end the span', async () => {
await tracedFetch({
callback: () => fetch('/null-body-205'),
});
assert.strictEqual(exportedSpans.length, 1);
assert.strictEqual(
exportedSpans[0].attributes[ATTR_HTTP_STATUS_CODE],
205
);
});
it('304 (Not Modified) will correctly end the span', async () => {
await tracedFetch({
callback: () => fetch('/null-body-304'),
});
assert.strictEqual(exportedSpans.length, 1);
assert.strictEqual(
exportedSpans[0].attributes[ATTR_HTTP_STATUS_CODE],
304
);
});
});

describe('simple request', () => {
let rootSpan: api.Span | undefined;
let response: Response | undefined;
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