Latest v1.17.1 update breaks ExpressJS req.get

[jayschwane]

Context

Express v5 (source) and v4 (source) request objects have a get method - a case-insensitive way to get a request header. req.get is a widely used method for safely getting request headers.

Issue

As of v1.17.1 I have failing unit tests with:

TypeError: mockRequest.headers.get is not a function

Previous version v1.17.0 did not exhibit this issue. In v1.17.0, mockRequest.getHeader was a standalone method (did not call mockRequest.headers.get).

As of v1.17.1, mockRequest.getHeader was refactored to call mockRequest.headers.get (source). As far as I can tell, objects returned from createHeaders should have get methods.

[eugef]

Hi @jayschwane

Thanks for reporting, but I cannot reproduce the issue.

The following code works as expected without any errors:

const req = httpMocks.createRequest();
req.headers['Content-Type'] = 'application/json';

console.log(req.get('Content-Type'));

const req = httpMocks.createRequest({
    headers: {
         'Content-Type': 'application/json',
    }
});

console.log(req.get('Content-Type'));

Please provide a code snippet that throws an error for you.
Also specify the node version you are using.

[jayschwane]

Node v22.15.0 (npm v10.9.2)

In constructing a code sample to recreate the issue, I think see what's happening. Some of our unit tests create a mockRequest in a beforeEach hook, and then customize the instance's headers in individual unit tests. Tests that reassign to the headers object are broken - obviously - we've completely over-written the "rich" headers object we get with v1.17.1. I'm going to refactor our tests to work around this for now.

But any logic that reassigns to req.headers would experience this; I have no idea how widespread reassigning headers is in reality.

Contrived middleware that reassigns headers:

import type { RequestHandler } from 'express'

const testMiddleware: RequestHandler = (req, _res, next) => {
  req.headers = {
    'user-agent': req.get('user-agent') ?? 'unknown', // req.get still works here ...
    'some-meta-data': req.get('some-meta-data')
  }
  const header = req.get('user-agent') // ... but not any more -> TypeError

  console.log({ header })

  next()
}

Sample that more-closely resembles my unit tests (assumes Jest)

import type { RequestHandler, Request } from 'express'
import { createRequest } from 'node-mocks-http'

const testMiddleware: RequestHandler = (req, _res, next) => {
  const header = req.get('user-agent')  // -> TypeError
  console.log({ header })
  next()
}

describe('createRequest', () => {
  let mockRequest!: Request

  beforeEach(() => {
    mockRequest = createRequest()
  })

  it('should work', () => {
    mockRequest.headers = {
      'user-agent': 'UA',
      'some-meta-data': 'value'
    }

    testMiddleware(mockRequest, {} as any, jest.fn())
  })
})

[eugef]

Thanks for the examples.

I was able to reproduce an issue with a code:

const req = httpMock.createRequest();
req.headers = { 'Content-Type': 'application/json' };

console.log(req.get('Content-Type'));

The fix is available in #321

[eugef]

@jayschwane fix is released in 1.17.2

[jayschwane]

Can confirm - v1.17.2 un-breaks our unit tests ✅

Thanks for the quick response!