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fix(res.send): add Content-Length only if Transfer-Encoding is not present #7485

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fix(res.send): add Content-Length only if Transfer-Encoding is not present #7485

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fix(res.send): add Content-Length only if Transfer-Encoding is not pr…
hktitof Sep 24, 2026
a308170
test(res.send): cover the other Transfer-Encoding values from #4893
hktitof Oct 5, 2026
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6 changes: 5 additions & 1 deletion lib/response.js
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Original file line number Diff line number Diff line change
Expand Up @@ -195,7 +195,11 @@ res.send = function send(body) {
len = chunk.length
}

this.set('Content-Length', len);
// Because Content-Length and Transfer-Encoding can't be present in the response headers together,
// Content-Length should be added only if there is no Transfer-Encoding header
if (!this.get('Transfer-Encoding')) {
this.set('Content-Length', len);
}
}

// populate ETag
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33 changes: 33 additions & 0 deletions test/res.send.js
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Expand Up @@ -597,5 +597,38 @@ describe('res', function(){
.expect(200, done);
})
})

describe('when Transfer-Encoding is set', function () {

@kgeminicdev kgeminicdev Oct 5, 2026

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Could this also carry over the tests from #4893? They cover an empty body (send('')) and the other Transfer-Encoding values (compress, deflate, gzip), which this test doesn't:

describe('when Transfer-Encoding header is present', function(){
  ['chunked', 'compress', 'deflate', 'gzip'].forEach(function(encoding){
    it('should not add Content-Length header if Transfer-Encoding header is equal to ' + encoding, function(done){
      var app = express();
      app.use(function(_, res){
        res.status(200).set('Transfer-Encoding', encoding).send('');
      });
      request(app)
        .get('/')
        .expect(utils.shouldNotHaveHeader('Content-Length'))
        .expect(utils.shouldHaveHeader('Transfer-Encoding'))
        .expect(200, '', done);
    })
  });
})

I ran them against this branch unchanged and all 4 pass, so it's just for coverage parity with master.

@hktitof hktitof Oct 5, 2026

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good idea @kgeminicdev, i ported the four encoding cases from #4893 so chunked, compress, deflate and gzip are all covered now, and i reverted lib/response.js on the branch to be sure they bite, all five fail with the same Content-Length and Transfer-Encoding parse error without the fix, then pass with it, full test/res.send.js run is 76 passing and the whole test folder is 1222 passing, pushed as a separate commit a308170 so the sha you reviewed is still the one you tested

['chunked', 'compress', 'deflate', 'gzip'].forEach(function (encoding) {
it('should not add Content-Length header if Transfer-Encoding header is equal to ' + encoding, function (done) {
var app = express();

app.use(function (_, res) {
res.status(200).set('Transfer-Encoding', encoding).send('');
});

request(app)
.get('/')
.expect(utils.shouldNotHaveHeader('Content-Length'))
.expect(utils.shouldHaveHeader('Transfer-Encoding'))
.expect(200, '', done);
})
})

it('should not set Content-Length and still generate an ETag', function (done) {
var app = express();

app.use(function (req, res) {
res.set('Transfer-Encoding', 'chunked').send('hello');
});

request(app)
.get('/')
.expect(utils.shouldNotHaveHeader('Content-Length'))
.expect(utils.shouldHaveHeader('Transfer-Encoding'))
.expect('ETag', 'W/"5-qvTGHdzF6KLavt4PO0gs2a6pQ00"')
.expect(200, 'hello', done);
})
})
})
})