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fix(v10/react-router): Carry multi-byte UTF-8 across SSR stream chunk boundaries - #23421
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… boundaries Backport of: #23307
logaretm
marked this pull request as ready for review
August 13, 2026 16:02
logaretm
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chargome and s1gr1d
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a teamAugust 13, 2026 16:02
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Cursor Bugbot has reviewed your changes and found 1 potential issue.
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| } | ||
| const encoder = new TextEncoder(); | ||
| const html = value instanceof Uint8Array ? new TextDecoder().decode(value) : String(value); |
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Streaming decoder not flushed at end
Low Severity
A streaming TextDecoder with { stream: true } holds incomplete UTF-8 until a later chunk or a final flush. injectTraceMetaTags closes on done without a final decoder.decode(), and getMetaTagTransformer has no Transform flush, so leftover bytes at end-of-stream are dropped instead of emitted.
Additional Locations (1)
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Comment on lines
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+26
| const htmlMetaTagTransformer = new Transform({ | ||
| transform(chunk, _encoding, callback) { | ||
| const html = Buffer.isBuffer(chunk) ? chunk.toString() : String(chunk); | ||
| const html = Buffer.isBuffer(chunk) ? decoder.decode(chunk, { stream: true }) : String(chunk); | ||
| if (html.includes(headClosingTag)) { | ||
| const modifiedHtml = html.replace(headClosingTag, `${getTraceMetaTags()}${headClosingTag}`); | ||
| callback(null, modifiedHtml); | ||
| return; | ||
| } | ||
| callback(null, chunk); | ||
| callback(null, html); |
Contributor
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Bug: The streaming TextDecoder is not flushed when the stream ends, which can cause data loss if the stream terminates with an incomplete multi-byte character.
Severity: LOW
Suggested Fix
In getMetaTagTransformer.ts, add a flush(callback) method to the Transform stream options and call callback(null, decoder.decode()) within it. In cloudflare/index.ts, before calling controller.close(), enqueue the result of the final decoder.decode() call to flush any remaining buffered data.
Prompt for AI Agent
Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.
Location: packages/react-router/src/server/getMetaTagTransformer.ts#L18-L26
Potential issue: When using `TextDecoder` with the `{ stream: true }` option, a final
call to `decoder.decode()` without arguments is required to flush any buffered bytes,
such as those from an incomplete multi-byte character at the end of the stream. This
final flushing call is missing in two locations. In `getMetaTagTransformer.ts`, the
Node.js `Transform` stream is missing a `flush` callback to handle the end of the
stream. In `cloudflare/index.ts`, the stream is closed via `controller.close()` without
a final decode. This can lead to data loss if an input stream happens to end with an
incomplete UTF-8 character sequence, which is rare but possible.
Also affects:
packages/react-router/src/cloudflare/index.ts:28~31
Did we get this right? 👍 / 👎 to inform future reviews.
Contributor
size-limit report 📦
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nicohrubec
approved these changes
Aug 13, 2026
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Backport of: #23307