fix(fetcher): nil-safe charset lookup#1276
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decodeReaderWithCharset called ianaindex.IANA.Encoding(charset) and on
failure fell back to ianaindex.IANA.Encoding("utf-8") while discarding
the second error. The library can return (nil, nil) for charset names
it recognizes but has no implementation for, so encoding could be nil
when we chained .NewDecoder(), panicking.
Extract a lookupCharsetEncoding helper that tries the requested charset,
falls back to utf-8 via ianaindex, and ultimately falls back to
encoding/unicode.UTF8 so it always returns a non-nil encoding.
decodeHeader's CharsetReader had the same nil-after-success edge case;
guard it explicitly with a clear error message.
Regression tests cover an unknown charset and the helper's contract.
Signed-off-by: say <say.apm35@gmail.com>
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Hi @SAY-5! Please fix the following issues with your PR:
- Title: Is too long (64 characters). The PR title must be strictly under 40 characters.
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Fixes #896.
What?
decodeReaderWithCharsetanddecodeHeader'sCharsetReaderinfetcher/fetcher.gocould nil-deref becauseianaindex.IANA.Encodingis allowed to return(nil, nil)for charset names it recognizes but has no implementation for. The previous code chained.NewDecoder()on that nil encoding.Refactor: introduce
lookupCharsetEncodingthat always returns a non-nilencoding.Encodingby trying the requested charset, thenianaindex's "utf-8", thenencoding/unicode.UTF8as final guarantee. Use it fromdecodeReaderWithCharset. Guard thedecodeHeaderpath explicitly so the nil-after-success case surfaces as a clean error.Why?
Without the guard, a real message with an unusual charset header can panic the fetcher. The fix is minimal, has no behavior change for the common path (a valid charset still resolves the same way), and is covered by two new tests:
TestDecodeReaderWithCharsetSurvivesUnknownCharset(issue regression)TestLookupCharsetEncodingAlwaysReturnsNonNil(table-driven contract)go test ./fetcher/...passes locally;go vet ./fetcher/...clean;gofmtclean.