feat: do not modify the Content-Type twice when sending strings #6991
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ShubhamOulkar
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ShubhamOulkar
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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
requested changes
Jan 16, 2026
| if (typeof type === "string") { | ||
| this.set('Content-Type', setCharset(type, 'utf-8')); | ||
| } else { | ||
| this.type('html'); |
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We are no longer setting charset now when using the fallback html content type
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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 thecontent-typelibrary, adds a small performance improvement, and slightly improves CPU usage, building on all the validations thatexpress/lib/utils.js
Line 225 in 2cd372e
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