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fix: work around immutable header guard #1390

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fix: work around immutable header guard #1390

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9 changes: 5 additions & 4 deletions package-lock.json
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2 changes: 1 addition & 1 deletion package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@
"dependencies": {
"@aws-crypto/sha256-js": "^5.2.0",
"@cfworker/json-schema": "^4.0.3",
"@hono/node-server": "^1.3.3",
"@hono/node-server": "^1.19.5",
"@hono/node-ws": "^1.2.0",
"@portkey-ai/mustache": "^2.1.3",
"@smithy/signature-v4": "^2.1.1",
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13 changes: 12 additions & 1 deletion src/handlers/services/responseService.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,11 @@ export class ResponseService {
));
}

this.updateHeaders(finalMappedResponse, cache.cacheStatus, retryAttempt);
finalMappedResponse = this.updateHeaders(
finalMappedResponse,
cache.cacheStatus,
retryAttempt
);

return {
response: finalMappedResponse,
Expand Down Expand Up @@ -99,6 +103,13 @@ export class ResponseService {
cacheStatus: string | undefined,
retryAttempt: number
) {
// Clone response and headers to work around `immutable` header guard
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@narengogi narengogi Oct 24, 2025

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expensive operation, have to see if there are better ways to solve this, dont want to. be slowing down the fastest gateway xd

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@mhassan1 mhassan1 Oct 24, 2025

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understood. i attempted to access the header guard to modify it in place, but undici hides it in a private field (link) and deletes the getters and setters (link).

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@mhassan1 mhassan1 Oct 24, 2025

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this should work:

// Clone headers to work around `immutable` header guard
const kHeaders = Object.getOwnPropertySymbols(response).find((symbol) => symbol.toString() === 'Symbol(headers)');
Object.defineProperty(response, kHeaders, {
  value: new Headers(response.headers),
  writable: true,
  enumerable: true,
  configurable: true,
});

do we like that better? the benefit is that we don't need to construct a new response, but it is making some unsafe assumptions about internals.

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@mhassan1 mhassan1 Oct 28, 2025

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another option:

// Capture internal `getHeadersGuard` and `setHeadersGuard`
let getHeadersGuard, setHeadersGuard
const deleteProperty = Reflect.deleteProperty
Reflect.deleteProperty = function (...args) {
  if (args[1] === 'getHeadersGuard') getHeadersGuard = args[0].getHeadersGuard
  if (args[1] === 'setHeadersGuard') setHeadersGuard = args[0].setHeadersGuard
  return deleteProperty.call(this, ...args)
}

// then
setHeadersGuard(response.headers, 'response')

response = new Response(response.body, {
status: response.status,
statusText: response.statusText,
headers: new Headers(response.headers),
});

// Append headers directly
response.headers.append(
RESPONSE_HEADER_KEYS.LAST_USED_OPTION_INDEX,
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20 changes: 12 additions & 8 deletions tests/unit/src/handlers/services/responseService.test.ts
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Expand Up @@ -393,7 +393,7 @@ describe('ResponseService', () => {
});

it('should add required headers', () => {
responseService.updateHeaders(mockResponse, 'HIT', 2);
mockResponse = responseService.updateHeaders(mockResponse, 'HIT', 2);

expect(
mockResponse.headers.get(RESPONSE_HEADER_KEYS.LAST_USED_OPTION_INDEX)
Expand All @@ -411,14 +411,14 @@ describe('ResponseService', () => {
});

it('should remove problematic headers', () => {
responseService.updateHeaders(mockResponse, undefined, 0);
mockResponse = responseService.updateHeaders(mockResponse, undefined, 0);

expect(mockResponse.headers.get('content-length')).toBeNull();
expect(mockResponse.headers.get('transfer-encoding')).toBeNull();
});

it('should remove brotli encoding', () => {
responseService.updateHeaders(mockResponse, undefined, 0);
mockResponse = responseService.updateHeaders(mockResponse, undefined, 0);

expect(mockResponse.headers.get('content-encoding')).toBeNull();
});
Expand All @@ -429,7 +429,7 @@ describe('ResponseService', () => {
headers: { 'content-encoding': 'gzip' },
});

responseService.updateHeaders(response, undefined, 0);
mockResponse = responseService.updateHeaders(response, undefined, 0);

expect(response.headers.get('content-encoding')).toBeNull();
});
Expand All @@ -440,13 +440,13 @@ describe('ResponseService', () => {
headers: { 'content-encoding': 'gzip' },
});

responseService.updateHeaders(response, undefined, 0);
mockResponse = responseService.updateHeaders(response, undefined, 0);

expect(response.headers.get('content-encoding')).toBe('gzip');
});

it('should not add cache status header when undefined', () => {
responseService.updateHeaders(mockResponse, undefined, 0);
mockResponse = responseService.updateHeaders(mockResponse, undefined, 0);

expect(
mockResponse.headers.get(RESPONSE_HEADER_KEYS.CACHE_STATUS)
Expand All @@ -466,7 +466,7 @@ describe('ResponseService', () => {
mockLogsService
);

serviceWithPortkey.updateHeaders(mockResponse, 'MISS', 0);
mockResponse = serviceWithPortkey.updateHeaders(mockResponse, 'MISS', 0);

expect(mockResponse.headers.get(HEADER_KEYS.PROVIDER)).toBeNull();
});
Expand All @@ -484,7 +484,11 @@ describe('ResponseService', () => {
mockLogsService
);

serviceWithEmptyProvider.updateHeaders(mockResponse, 'MISS', 0);
mockResponse = serviceWithEmptyProvider.updateHeaders(
mockResponse,
'MISS',
0
);

expect(mockResponse.headers.get(HEADER_KEYS.PROVIDER)).toBeNull();
});
Expand Down