Using cy.intercept to spy adds a "Content-Length: 0" request header

[Bourg]

Current behavior

If an API route is spied on using cy.intercept (e.g. cy.intercept('/api') with no stub), an additional Content-Length: 0 header will be sent to the server, despite the original request from the application code not including a Content-Length header at all.

Without cy.intercept, the headers are left unchanged and there is no bug.

When using cy.intercept to stub (e.g. cy.intercept('/api', {})), there is no bug.

Desired behavior

The headers sent to the server should be identical to the headers in the original request regardless of whether cy.intercept is used to spy on the request.

Test code to reproduce

https://github.com/Bourg/cypress-bug-content-length

Testing this requires a server process since the problematic request headers only show up after the request has left the browser. The repo has a minimal express server and instructions on how to boot it.

Cypress Version

10.11.0

Node version

v18.12.0

Operating System

macOS 12.5.1

Debug Logs

% DEBUG=cypress:net-stubbing* npm run cypress:run

> cypress-header-bug-minimal@1.0.0 cypress:run
> cypress run


====================================================================================================

  (Run Starting)

  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ Cypress:        10.11.0                                                                        │
  │ Browser:        Electron 106 (headless)                                                        │
  │ Node Version:   v18.12.0 (/Users/abourgerie/.nvm/versions/node/v18.12.0/bin/node)              │
  │ Specs:          1 found (interceptBug.cy.js)                                                   │
  │ Searched:       cypress/e2e/**/*.cy.{js,jsx,ts,tsx}                                            │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘


────────────────────────────────────────────────────────────────────────────────────────────────────

  Running:  interceptBug.cy.js                                                              (1 of 1)


  cy.intercept should not change headers
  cypress:net-stubbing:server:intercept-response InterceptResponse { req: { url: '/' }, request: undefined } +0ms
  cypress:net-stubbing:server:intercept-response InterceptResponse { req: { url: '/api' }, request: undefined } +36ms
    ✓ receives no content-length header without cy.intercept (152ms)
  cypress:net-stubbing:server:driver-events received driver event { eventName: 'route:added', args: [ 'route:added', { routeId: '1666797462330-14', hasInterceptor: false, routeMatcher: [Object] } ] } +0ms
  cypress:net-stubbing:server:intercept-response InterceptResponse { req: { url: '/' }, request: undefined } +94ms
  cypress:net-stubbing:server:intercept-request intercepting request { requestId: 'interceptedRequest6', req: { url: '/api' } } +0ms
  cypress:net-stubbing:server:util sending event to driver { eventName: 'before:request', data: { eventId: 'event7', subscription: { eventName: 'before:request', await: false, routeId: '1666797462330-14' }, browserRequestId: '76357.67', requestId: 'interceptedRequest6', data: { headers: [Object], url: 'http://localhost:3000/api', method: 'GET', httpVersion: '1.1', body: '' } } } +0ms
  cypress:net-stubbing:server:intercept-response InterceptResponse { req: { url: 'http://localhost:3000/api' }, request: InterceptedRequest { subscriptionsByRoute: [ [Object] ], includeBodyInAfterResponse: false, responseSent: false, onResponse: [Function (anonymous)], id: 'interceptedRequest6', req: IncomingMessage { _readableState: [ReadableState], _events: [Object: null prototype], _eventsCount: 1, _maxListeners: undefined, socket: [Socket], httpVersionMajor: 1, httpVersionMinor: 1, httpVersion: '1.1', complete: true, rawHeaders: [Array], rawTrailers: [], aborted: false, upgrade: false, url: 'http://localhost:3000/api', method: 'GET', statusCode: null, statusMessage: null, client: [Socket], _consuming: false, _dumped: false, proxiedUrl: 'http://localhost:3000/api', next: [Function: next], baseUrl: '', originalUrl: '/api', _parsedUrl: [Url], params: [Object], query: {}, res: [ServerResponse], secret: undefined, cookies: [Object: null prototype] {}, signedCookies: [Object: null prototype] {}, route: [Route], isAUTFrame: false, browserPreRequest: [Object], requestId: 'interceptedRequest6', body: '', [Symbol(kCapture)]: false, [Symbol(kHeaders)]: [Object], [Symbol(kHeadersCount)]: 28, [Symbol(kTrailers)]: null, [Symbol(kTrailersCount)]: 0, [Symbol(RequestTimeout)]: undefined }, res: ServerResponse { _events: [Object: null prototype], _eventsCount: 1, _maxListeners: undefined, outputData: [], outputSize: 0, writable: true, destroyed: false, _last: false, chunkedEncoding: false, shouldKeepAlive: true, maxRequestsOnConnectionReached: false, _defaultKeepAlive: true, useChunkedEncodingByDefault: true, sendDate: true, _removedConnection: false, _removedContLen: false, _removedTE: false, _contentLength: null, _hasBody: true, _trailer: '', finished: false, _headerSent: false, _closed: false, socket: [Socket], _header: null, _keepAliveTimeout: 5000, _onPendingData: [Function: bound updateOutgoingData], req: [IncomingMessage], _sent100: false, _expect_continue: false, locals: [Object: null prototype] {}, flush: [Function: flush], write: [Function: write], end: [Function: end], on: [Function: on], writeHead: [Function: writeHead], [Symbol(kCapture)]: false, [Symbol(kNeedDrain)]: false, [Symbol(corked)]: 0, [Symbol(kOutHeaders)]: null }, continueRequest: [Function: next], onError: [Function: onError], _onResponse: [Function: onResponse], matchingRoutes: [ [Object] ], state: { requests: [Object], routes: [Array], pendingEventHandlers: {}, reset: [Function: reset] }, socket: SocketE2E { ensureProp: [Function: ensureProp], supportsRunEvents: true, experimentalSessionAndOrigin: false, ended: false, localBus: [EventEmitter], onTestFileChange: [Function: bound ], testFilePath: 'cypress/e2e/interceptBug.cy.js', onStudioTestFileChange: [Function: bound onStudioTestFileChange], removeOnStudioTestFileChange: [Function: bound removeOnStudioTestFileChange], _io: [SocketIOServer], _sendResetBrowserTabsForNextTestMessage: [AsyncFunction (anonymous)], _sendResetBrowserStateMessage: [AsyncFunction (anonymous)], _sendFocusBrowserMessage: [AsyncFunction (anonymous)], _isRunnerSocketConnected: [Function (anonymous)] }, lastEvent: 'before:request' } } +24ms
  cypress:net-stubbing:server:util sending event to driver { eventName: 'response:callback', data: { eventId: 'event9', subscription: { eventName: 'response:callback', await: false, routeId: '1666797462330-14' }, browserRequestId: '76357.67', requestId: 'interceptedRequest6', data: { headers: [Object], url: 'http://localhost:3000/api', method: null, httpVersion: '1.1', statusCode: 200, statusMessage: 'OK', body: '{"connection":"keep-alive","host":"localhost:3000","proxy-connection":"keep-alive","sec-ch-ua":"\\"Not;A=Brand\\";v=\\"99\\", \\"Chromium\\";v=\\"106\\"","sec-ch-ua-mobile":"?0","user-agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Cypress/10.11.0 Chrome/106.0.5249.51 Electron/21.0.0 Safari/537.36","sec-ch-ua-platform":"\\"macOS\\"","accept":"*/*","sec-fetch-site":"same-origin","sec-fetch-mode":"cors","sec-fetch-dest":"empty","referer":"http://localhost:3000/","accept-encoding":"gzip","accept-language":"en-US","if-none-match":"W/\\"229-GpjgY70/3CX5a8rUCAoc+HhB6s0\\"","content-length":"0"}' } } } +7ms
  cypress:net-stubbing:server:intercept-request request/response finished, cleaning up { requestId: 'interceptedRequest6' } +14ms
  cypress:net-stubbing:server:util sending event to driver { eventName: 'after:response', data: { eventId: 'event10', subscription: { eventName: 'after:response', await: false, routeId: '1666797462330-14' }, browserRequestId: '76357.67', requestId: 'interceptedRequest6', data: {} } } +6ms
    1) receives no content-length header when cy.intercept is used to spy
  cypress:net-stubbing:server:driver-events received driver event { eventName: 'route:added', args: [ 'route:added', { routeId: '1666797466567-22', hasInterceptor: false, routeMatcher: [Object], staticResponse: [Object] } ] } +4s
  cypress:net-stubbing:server:intercept-response InterceptResponse { req: { url: '/' }, request: undefined } +4s
  cypress:net-stubbing:server:intercept-request intercepting request { requestId: 'interceptedRequest13', req: { url: '/api' } } +4s
  cypress:net-stubbing:server:util sending event to driver { eventName: 'before:request', data: { eventId: 'event14', subscription: { eventName: 'before:request', await: false, routeId: '1666797466567-22' }, browserRequestId: '76357.69', requestId: 'interceptedRequest13', data: { headers: [Object], url: 'http://localhost:3000/api', method: 'GET', httpVersion: '1.1', body: '' } } } +4s
  cypress:net-stubbing:server:intercept-response InterceptResponse { req: { url: 'http://localhost:3000/api' }, request: InterceptedRequest { subscriptionsByRoute: [ [Object] ], includeBodyInAfterResponse: false, responseSent: true, onResponse: [Function (anonymous)], id: 'interceptedRequest13', req: IncomingMessage { _readableState: [ReadableState], _events: [Object: null prototype], _eventsCount: 1, _maxListeners: undefined, socket: [Socket], httpVersionMajor: 1, httpVersionMinor: 1, httpVersion: '1.1', complete: true, rawHeaders: [Array], rawTrailers: [], aborted: false, upgrade: false, url: 'http://localhost:3000/api', method: 'GET', statusCode: null, statusMessage: null, client: [Socket], _consuming: false, _dumped: false, proxiedUrl: 'http://localhost:3000/api', next: [Function: next], baseUrl: '', originalUrl: '/api', _parsedUrl: [Url], params: [Object], query: {}, res: [ServerResponse], secret: undefined, cookies: [Object: null prototype] {}, signedCookies: [Object: null prototype] {}, route: [Route], isAUTFrame: false, browserPreRequest: [Object], requestId: 'interceptedRequest13', body: '', [Symbol(kCapture)]: false, [Symbol(kHeaders)]: [Object], [Symbol(kHeadersCount)]: 28, [Symbol(kTrailers)]: null, [Symbol(kTrailersCount)]: 0, [Symbol(RequestTimeout)]: undefined }, res: ServerResponse { _events: [Object: null prototype], _eventsCount: 1, _maxListeners: undefined, outputData: [], outputSize: 0, writable: true, destroyed: false, _last: false, chunkedEncoding: false, shouldKeepAlive: true, maxRequestsOnConnectionReached: false, _defaultKeepAlive: true, useChunkedEncodingByDefault: true, sendDate: true, _removedConnection: false, _removedContLen: false, _removedTE: false, _contentLength: null, _hasBody: true, _trailer: '', finished: false, _headerSent: false, _closed: false, socket: [Socket], _header: null, _keepAliveTimeout: 5000, _onPendingData: [Function: bound updateOutgoingData], req: [IncomingMessage], _sent100: false, _expect_continue: false, locals: [Object: null prototype] {}, flush: [Function: flush], write: [Function: write], end: [Function: end], on: [Function: on], writeHead: [Function: writeHead], body: '{"a":1,"b":2,"c":3}', [Symbol(kCapture)]: false, [Symbol(kNeedDrain)]: false, [Symbol(corked)]: 0, [Symbol(kOutHeaders)]: null }, continueRequest: [Function: next], onError: [Function: onError], _onResponse: [Function: onResponse], matchingRoutes: [ [Object] ], state: { requests: [Object], routes: [Array], pendingEventHandlers: {}, reset: [Function: reset] }, socket: SocketE2E { ensureProp: [Function: ensureProp], supportsRunEvents: true, experimentalSessionAndOrigin: false, ended: false, localBus: [EventEmitter], onTestFileChange: [Function: bound ], testFilePath: 'cypress/e2e/interceptBug.cy.js', onStudioTestFileChange: [Function: bound onStudioTestFileChange], removeOnStudioTestFileChange: [Function: bound removeOnStudioTestFileChange], _io: [SocketIOServer], _sendResetBrowserTabsForNextTestMessage: [AsyncFunction (anonymous)], _sendResetBrowserStateMessage: [AsyncFunction (anonymous)], _sendFocusBrowserMessage: [AsyncFunction (anonymous)], _isRunnerSocketConnected: [Function (anonymous)] }, lastEvent: 'before:request' } } +15ms
  cypress:net-stubbing:server:util sending event to driver { eventName: 'response:callback', data: { eventId: 'event15', subscription: { eventName: 'response:callback', await: false, routeId: '1666797466567-22' }, browserRequestId: '76357.69', requestId: 'interceptedRequest13', data: { headers: [Object], body: '{"a":1,"b":2,"c":3}', url: 'http://localhost:3000/api', method: null, httpVersion: null, statusCode: 200, statusMessage: null } } } +3ms
  cypress:net-stubbing:server:intercept-request request/response finished, cleaning up { requestId: 'interceptedRequest13' } +5ms
  cypress:net-stubbing:server:util sending event to driver { eventName: 'after:response', data: { eventId: 'event16', subscription: { eventName: 'after:response', await: false, routeId: '1666797466567-22' }, browserRequestId: '76357.69', requestId: 'interceptedRequest13', data: {} } } +3ms
    ✓ receives no content-length header when cy.intercept is used to stub (83ms)


  2 passing (4s)
  1 failing

  1) cy.intercept should not change headers
       receives no content-length header when cy.intercept is used to spy:
     AssertionError: Timed out retrying after 4000ms: Expected to find content: 'No Content-Length header' but never did.
      at Context.eval (webpack:///./cypress/e2e/interceptBug.cy.js:16:44)




  (Results)

  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ Tests:        3                                                                                │
  │ Passing:      2                                                                                │
  │ Failing:      1                                                                                │
  │ Pending:      0                                                                                │
  │ Skipped:      0                                                                                │
  │ Screenshots:  1                                                                                │
  │ Video:        true                                                                             │
  │ Duration:     4 seconds                                                                        │
  │ Spec Ran:     interceptBug.cy.js                                                               │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘


  (Screenshots)

  -  /Users/abourgerie/Scratch/cypress-header-bug-minimal/cypress/screenshots/interce     (1280x720)
     ptBug.cy.js/cy.intercept should not change headers -- receives no content-length
      header when cy.intercept is used to spy (failed).png


  (Video)

  -  Started processing:  Compressing to 32 CRF
  -  Finished processing: /Users/abourgerie/Scratch/cypress-header-bug-minimal/cypres    (0 seconds)
                          s/videos/interceptBug.cy.js.mp4


====================================================================================================

  (Run Finished)


       Spec                                              Tests  Passing  Failing  Pending  Skipped
  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ ✖  interceptBug.cy.js                       00:04        3        2        1        -        - │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘
    ✖  1 of 1 failed (100%)                     00:04        3        2        1        -        -

abourgerie@C02G46BXMD6R cypress-header-bug-minimal %

Other

I also observed this on Cypress 10.5.0 and 10.10.0, as I upgraded while trying to debug.
I also observed this on Node v16.15.0, which is the version my company uses in production.

[mschile]

@Bourg, thanks for logging this issue and including the reproduction. It appears we are incorrectly comparing the content-length of the headers without actually verifying the header is populated.

cypress/packages/net-stubbing/lib/server/middleware/request.ts

Lines 124 to 127 in 9ceb95d

	if (before.headers['content-length'] === after.headers['content-length']) {
	// user did not purposely override content-length, let's set it
	after.headers['content-length'] = String(Buffer.from(after.body).byteLength)
	}

I am going to route this issue to the appropriate team.

In the meantime, you could use the deprecated cy.route to spy on the call.

cy.server().route('/api').as('api')
cy.visit("");
cy.wait('@api')

If you are using fetch, you'll also need to set experimentalFetchPolyfill to true (this is not needed when using cy.intercept).

[cypress-bot]

Released in 12.9.0.

This comment thread has been locked. If you are still experiencing this issue after upgrading to
Cypress v12.9.0, please open a new issue.