feat: do not modify the Content-Type twice when sending strings by bjohansebas · Pull Request #6991 · expressjs/express

bjohansebas · 2026-01-16T02:44:25Z

We were modifying the Content-Type twice when a manual Content-Type was not set (that is, without res.set('Content-Type', 'text/plain').send('hey')), because it would enter here and then enter here again. This reduces how often we go into the content-type library, adds a small performance improvement, and slightly improves CPU usage, building on all the validations that

express/lib/utils.js

Line 225 in 2cd372e

exports.setCharset = function setCharset(type, charset) {

already did.

For those who do comparisons with a hello-world, this will improve Express’s results, we’re almost catching up to Fastify 😄

The following diffs are based on the simple hello-world example in this repo (https://github.com/expressjs/express/tree/master/examples/hello-world)

diff v4.22.1 vs this pr

diff v4.22.1 vs v5.2.1

ShubhamOulkar

Methodology

Scenario: res.send('<html>...</html>')
Iterations: 100,000
Environment: Windows / Node.js
Metric: Operations per second (ops/sec)

Results

Metric	Before (Current)	After (Optimized)	Improvement
Total Time	~501 ms	~137 ms	~3.6x Faster
Avg Op Time	0.0050 ms	0.0014 ms	-72% overhead
Throughput	~200k ops/sec	~728k ops/sec	+264%

jonchurch

Looks good, just some nits

…ove clarity

Phillip9587

LGTM

…set-twice-content-type

…gs (expressjs#6991)" This reverts commit a479419.

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [express](https://expressjs.com/) ([source](https://github.com/expressjs/express)) | [`5.2.1` → `5.3.0`](https://renovatebot.com/diffs/npm/express/5.2.1/5.3.0) | ![age](https://developer.mend.io/api/mc/badges/age/npm/express/5.3.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/express/5.2.1/5.3.0?slim=true) | --- > ⚠️ **Warning** > > Some dependencies could not be looked up. Check the [Dependency Dashboard](issues/99) for more information. --- ### Release Notes <details> <summary>expressjs/express (express)</summary> ### [`v5.3.0`](https://github.com/expressjs/express/blob/HEAD/History.md#530) [Compare Source](expressjs/express@v5.2.1...v5.3.0) \===== #### 🐞 Bug fixes - Fixed HTTP header conflict between Content-Length and Transfer-Encoding in res.send - by [@YuryShkoda](https://github.com/YuryShkoda) in [#4893](expressjs/express#4893) Fixed the behavior of `res.send()` to prevent conflicts between `Content-Length` and `Transfer-Encoding` HTTP headers in responses. The `Content-Length` header in `res.send()` is now only added when a `Transfer-Encoding` header is not present, complying with the HTTP specification that states both headers should not coexist in the same response. ETag generation is unaffected by the presence of a `Transfer-Encoding` header - by [@cuishuang](https://github.com/cuishuang) in [#7459](expressjs/express#7459) * Upgrade `qs` to `^6.16.0`, which fixes [CVE-2026-2391](https://www.cve.org/CVERecord?id=CVE-2026-2391) ([GHSA-w7fw-mjwx-w883](GHSA-w7fw-mjwx-w883)), [CVE-2026-82417](https://www.cve.org/CVERecord?id=CVE-2026-82417) ([GHSA-4mjr-xmp4-gh2g](GHSA-4mjr-xmp4-gh2g)) and [CVE-2026-82562](https://www.cve.org/CVERecord?id=CVE-2026-82562) ([GHSA-x5fp-wj9c-mxmx](GHSA-x5fp-wj9c-mxmx)): `arrayLimit` bypasses in comma parsing and a denial of service via an attacker-controlled `isBuffer` - by [@davetashner](https://github.com/davetashner) in [#7057](expressjs/express#7057) and [#7478](expressjs/express#7478), and [@cyphercodes](https://github.com/cyphercodes) in [#7305](expressjs/express#7305) * Upgrade `proxy-addr` to `^2.0.8`, which fixes [CVE-2026-90711](https://www.cve.org/CVERecord?id=CVE-2026-90711) - by [@lazerg](https://github.com/lazerg) in [#7474](expressjs/express#7474) #### 🚀 Improvements - Allow conditional revalidation for QUERY requests. `req.fresh` previously only validated freshness for GET and HEAD requests, so QUERY responses never returned 304 despite a matching validator. Since QUERY is a safe, idempotent, and cacheable method that supports conditional requests, it is now included in the freshness check - by [@Cherry](https://github.com/Cherry) in [#7366](expressjs/express#7366) ```js // QUERY /reports with If-None-Match: "12345" app.query('/reports', (req, res) => { res.set('ETag', '"12345"'); res.send(results); // now responds 304 Not Modified }); ``` - Improve HTML structure in `res.redirect()` responses when HTML format is accepted by adding `<!DOCTYPE html>`, `<title>`, and `<body>` tags for better browser compatibility - by [@Bernice55231](https://github.com/Bernice55231) in [#5167](expressjs/express#5167) - When calling `app.render` with options set to null, the locals object is handled correctly, preventing unexpected errors and making the method behave the same as when options is omitted or an empty object is passed - by [AkaHarshit](https://github.com/AkaHarshit) in [#6903](expressjs/express#6903) ```js app.render('index', null, callback); // now works as expected ``` - Upgrade `content-type` to `^2.0.0`, bringing a faster parser (\~1.5x quicker `Content-Type` parsing/formatting in `res.send()`) along with a behavior change: `res.send()` now keeps any existing parameters when adding the charset and no longer throws on a `Content-Type` that fails to parse. `type-is` is upgraded to `^2.1.0` as part of the same change - by [@blakeembrey](https://github.com/blakeembrey) in [#7234](expressjs/express#7234) ```js res.set('Content-Type', 'text/plain; foo=bar').send('hey'); // -> Content-Type: text/plain; foo=bar; charset=utf-8 ``` - The default error handler now logs the full error object instead of only its stack trace, so nested details such as `Error.cause` and library-specific properties (e.g. Sequelize's `parent`/`original`) are no longer swallowed - by [@Nitin-Mohapatra](https://github.com/Nitin-Mohapatra) in [#6464](expressjs/express#6464) - Upgrade `content-disposition` to `^2.0.1`, which changes the `Content-Disposition` header emitted by `res.download()`, `res.attachment()`, and `res.sendFile()`: file names that are valid HTTP tokens are no longer wrapped in quotes. This is equivalent per RFC 6266, but applications asserting on the exact header bytes should update their expectations - by [@blakeembrey](https://github.com/blakeembrey) in [#7233](expressjs/express#7233) ```js res.attachment('user.html'); // before -> Content-Disposition: attachment; filename="user.html" // after -> Content-Disposition: attachment; filename=user.html ``` - Upgrade `body-parser` to `^2.3.0`, which fixes [CVE-2026-12590](https://www.cve.org/CVERecord?id=CVE-2026-12590) ([GHSA-v422-hmwv-36x6](GHSA-v422-hmwv-36x6)): an invalid `limit` option value caused request body size enforcement to be silently disabled (fail-open), allowing a denial of service via arbitrarily large payloads. Invalid `limit` values now throw at parser initialization instead of being ignored - by [@Mayvis](https://github.com/Mayvis) in [#7390](expressjs/express#7390) #### ⚡ Performance - Avoid duplicate Content-Type header processing in `res.send()` when sending string responses without an explicit Content-Type header - by [@bjohansebas](https://github.com/bjohansebas) in [#6991](expressjs/express#6991) </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - "before 9am on tuesday" - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Mend Renovate CLI](https://github.com/renovatebot/renovate).  Reviewed-on: https://code.futo.org/harbor/harbor/pulls/1812

bjohansebas added 2 commits January 15, 2026 17:10

fix: improve content-type handling in res.send method

2e24588

fix: ensure content-type is a string before setting charset in res.send

51caad2

bjohansebas added 5.x semver-patch This change is a semver patch performance ⚡ labels Jan 16, 2026

bjohansebas requested review from a team and wesleytodd January 16, 2026 02:47

ShubhamOulkar reviewed Jan 16, 2026

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fix: refactor content-type handling in res.send to use const and impr…

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…ove clarity

bjohansebas commented Jan 16, 2026

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bjohansebas requested a review from jonchurch January 16, 2026 21:16

jonchurch approved these changes Jan 18, 2026

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ShubhamOulkar suggested changes Jan 19, 2026

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UlisesGascon approved these changes Jan 19, 2026

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Phillip9587 approved these changes Jan 19, 2026

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ShubhamOulkar approved these changes Jan 19, 2026

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bjohansebas added 2 commits January 19, 2026 09:49

Merge branch 'master' of github.com:expressjs/express into bsebas/no-…

9bc5398

…set-twice-content-type

docs: update History.md

7990883

bjohansebas merged commit a479419 into master Jan 19, 2026
28 checks passed

bjohansebas deleted the bsebas/no-set-twice-content-type branch January 19, 2026 14:56

krzysdz mentioned this pull request May 8, 2026

const declaration inside switch case without block in res.send() (no-case-declarations) #7223

Closed

kkennethlau12393 mentioned this pull request Sep 6, 2026

chore: recreate expressjs/express#6991 kkennethlau12393/expressjs__express#1

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kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 6, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

6e7daa9

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 7, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

807e0c2

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 7, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

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…gs (expressjs#6991)" This reverts commit a479419.

UlisesGascon mentioned this pull request Sep 14, 2026

Release: 5.3.0 #7468

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kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 14, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

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…gs (expressjs#6991)" This reverts commit a479419.

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Revert "feat: do not modify the Content-Type twice when sending strin…

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…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 14, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

35c1c6a

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 14, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

a90f1a8

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

5ae84b8

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

6701ad7

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

f64e2dd

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

c3c1aaf

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

55b6692

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

2692ce7

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

5f20bfb

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

3bad57b

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

48ce854

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

c63e87f

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

13b910a

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

dba96e0

…gs (expressjs#6991)" This reverts commit a479419.

kkennethlau12393 pushed a commit to kkennethlau12393/expressjs__express that referenced this pull request Sep 15, 2026

Revert "feat: do not modify the Content-Type twice when sending strin…

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…gs (expressjs#6991)" This reverts commit a479419.

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feat: do not modify the Content-Type twice when sending strings - #6991

feat: do not modify the Content-Type twice when sending strings#6991
bjohansebas merged 6 commits into
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bjohansebas commented Jan 16, 2026 •

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bjohansebas commented Jan 16, 2026 •

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