feat(pcm): read and write the iXML metadata chunk - #53
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Add read and write support for the WAV iXML chunk, the standardized home for scene, take, project and per-track metadata that recorders write alongside bext. The reader captures the chunk into Decoder.IXML(), and Config.IXML writes one immediately after bext. The implementation mirrors the existing bext handling at every layer: a new idIXML constant, Header.IXML captured in ParseHeader (first-wins, bounded by the reader's in-memory cap), HeaderConfig.IXML written by BuildHeader and counted by HeaderLen, and the encoder threading the payload through both the header build and the RF64-fit decision. Config.IXML is a string rather than a []byte so that Config stays comparable, the same reason Config.Bext is a pointer; iXML is XML text, so a string is also its natural form. The internal riff layer keeps the []byte wire representation. Decoder.IXML() returns the text as stored, or the empty string when the stream carries none. The encoder rejects an iXML larger than the bytes the reader will hold in memory (riff.MaxChunkPayload, exported for this check) rather than writing a file this package could not read back, mirroring how it refuses a sample rate it cannot read. Verified byte-exact against three real recorder files (ZOOM H5studio 16- and 24-bit, iZotope RX 32-bit float): the decoded iXML matches the raw chunk, and a decode/re-encode/decode round trip preserves the audio, iXML and bext. Closes #51 Closes #52
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WalkthroughThe change adds raw iXML support across RIFF parsing and writing, PCM decoding and encoding, size validation, round-trip preservation, tests, and documentation. The decoder exposes iXML through ChangesiXML metadata support
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to This change adds WAV iXML metadata read/write support. A documentation formatting issue may cause Markdown linting to fail until the code span is corrected. Sequence Diagram(s)sequenceDiagram
participant Encoder
participant RIFFWriter
participant RIFFReader
participant Decoder
Encoder->>RIFFWriter: pass Config.IXML
RIFFWriter->>RIFFWriter: write iXML after bext
RIFFReader->>RIFFReader: parse first iXML chunk
RIFFReader->>Decoder: store Header.IXML
Decoder-->>Encoder: expose iXML for read-modify-write
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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In `@README.md`:
- Line 66: Update the README chunk list’s `cue` code span to remove the trailing
space, while preserving the intended displayed spacing by describing it in prose
or using an HTML code span with an explicit space entity.
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📒 Files selected for processing (14)
.golangci.yamlREADME.mdinternal/riff/chunk.gointernal/riff/ixml_test.gointernal/riff/reader.gointernal/riff/writer.gopcm/bext.gopcm/decode_oneshot.gopcm/decoder.gopcm/doc.gopcm/encoder.gopcm/fuzz_test.gopcm/ixml_test.gopcm/pcm.go
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🟢 Approval recommended
The remaining findings are minor (doc/error-message clarity and an avoidable extra allocation) and the functional change is well-contained and covered by tests.
Pull request overview
Adds first-class read/write support for the WAV iXML metadata chunk (commonly paired with bext) so professional recorder metadata can round-trip through go-wav’s PCM encoder/decoder paths.
Changes:
- Introduces
pcm.Config.IXML(string) for writing aniXMLchunk andpcm.Decoder.IXML()for reading it back. - Extends the internal RIFF header parser/builder to capture, size-bound, and emit
iXML(including padding and ordering afterbext). - Adds focused unit tests (riff + pcm) plus a fuzz seed covering the new reader branch; updates lint config for the now-larger
Config.
File summaries
| File | Description |
|---|---|
| README.md | Documents new iXML API and behavior. |
| pcm/pcm.go | Adds Config.IXML and validates its size against the reader cap. |
| pcm/ixml_test.go | Adds round-trip, ordering, reset, first-wins, and size-boundary tests for iXML. |
| pcm/fuzz_test.go | Adds a fuzz seed containing iXML to exercise the new parse path. |
| pcm/encoder.go | Threads iXML into header build and RF64 fit decision. |
| pcm/doc.go | Updates package docs to mention iXML support. |
| pcm/decoder.go | Adds Decoder.IXML() accessor. |
| pcm/decode_oneshot.go | Clarifies one-shot decode does not expose bext/iXML and avoids pooling retention. |
| pcm/bext.go | Updates docs to reflect iXML is now also exposed. |
| internal/riff/writer.go | Adds HeaderConfig.IXML, writes it after bext, and counts it in HeaderLen. |
| internal/riff/reader.go | Exports MaxChunkPayload, captures iXML first-wins, and returns it on Header. |
| internal/riff/ixml_test.go | Adds riff-layer tests for writing/reading iXML, ordering, sizing, and oversize skip. |
| internal/riff/chunk.go | Adds the idIXML chunk ID constant and updates docs to refer to MaxChunkPayload. |
| .golangci.yaml | Adjusts gocritic hugeParam threshold to avoid flagging by-value Config. |
Review details
Suppressed comments (1)
pcm/encoder.go:207
- This
[]byte(cfg.IXML)conversion allocates; in the RF64Auto+framesKnown path the same conversion is also done for the actual header build, resulting in duplicate allocation for large iXML bodies. If you thread precomputedixmlBodybytes into this helper, you can avoid the extra allocation during the size-fit check.
Format: formatOf(cfg),
Container: wav.ContainerRIFF,
Bext: bextBody,
IXML: []byte(cfg.IXML),
}, dataSize)
- Files reviewed: 14/14 changed files
- Comments generated: 3
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| Frames: cfg.TotalFrames, | ||
| Bext: bextBody, | ||
| IXML: []byte(cfg.IXML), | ||
| }) |
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Good catch. Fixed in 10960b7: the encoder now converts Config.IXML to []byte once in reset and threads that ixmlBody through plan/fitsPlainRIFF and BuildHeader, so the frames-known path no longer allocates it twice. This mirrors how bextBody is already threaded.
| // IXML, when non-empty, writes an iXML chunk immediately after bext, | ||
| // ahead of fact and data. The chunk carries free-form XML metadata (scene, | ||
| // take, track names and the like); this package writes the text verbatim | ||
| // rather than modelling the schema. The zero value, the empty string, | ||
| // writes no iXML chunk at all. |
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Fixed in 10960b7. The doc now reads "immediately after bext, or after fmt when no bext is written", so the placement is clear when Bext is nil.
| if int64(len(c.IXML)) > int64(riff.MaxChunkPayload) { | ||
| return fmt.Errorf( | ||
| "go-wav/pcm: %s: %w: iXML chunk of %d bytes exceeds the %d this package will read back", | ||
| op, wav.ErrTooLarge, len(c.IXML), riff.MaxChunkPayload) |
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Fixed in 10960b7: the message now reads "exceeds the %d bytes this package will read back".
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- encoder: convert Config.IXML to a []byte once and thread it through plan and fitsPlainRIFF, so the frames-known path no longer allocates the iXML body a second time, mirroring how bextBody is threaded (Copilot). - pcm: note in the Config.IXML doc that the chunk lands after fmt when no bext is written, and name the unit in the oversize error message (Copilot). - tests: cover Decoder.IXML() reporting the empty string after a failed Reset, so the stale-header guard is exercised.
The new iXML branch in ParseHeader opened coverage the FuzzParseHeader corpus did not seed, so on a slow CI runner the fuzzer was still discovering it at the fuzztime deadline and the engine reported a context-deadline-exceeded failure at the boundary. Seed the bext and iXML branches (including first-wins) so the corpus starts with them and the run reaches steady state well before the deadline. Test-only; no behavior change.
Summary
Adds read and write support for the WAV
iXMLchunk, the standardized home for scene, take, project and per-track metadata that professional recorders write alongsidebext.Config.IXMLwrites the chunk immediately afterbext, andDecoder.IXML()reads it back.The implementation mirrors the existing
bexthandling at every layer: a newidIXMLconstant,Header.IXMLcaptured inParseHeader(first-wins, bounded by the reader's in-memory cap),HeaderConfig.IXMLwritten byBuildHeaderand counted byHeaderLen, and the encoder threading the payload through both the header build and the RF64-fit decision. WithConfig.IXMLunset the encoder output is byte-for-byte identical to before.Config.IXML(andDecoder.IXML()) are astringrather than a[]byte, so thatConfigstays comparable, the same reasonConfig.Bextis a pointer;iXMLis XML text, so a string is also its natural form. The internalrifflayer keeps the[]bytewire representation. The encoder rejects aniXMLlarger than the bytes the reader will hold in memory (riff.MaxChunkPayload, now exported for this check) rather than writing a file this package could not read back, mirroring how it already refuses a sample rate it cannot read.Related Issues
Closes #51
Closes #52
Test Plan
bext,HeaderLenaccounting, decoder round-trip (int and float streams, with and withoutbext), first-wins, absent,Resetclearing, and the size boundary (exactlyMaxChunkPayloadaccepted,+1rejected withwav.ErrTooLarge).FuzzDecodeseed carrying aniXMLchunk exercises the new reader branch.go build,go vet,go test -race ./...,golangci-lint run ./...all clean; total coverage 96.8%.iXMLmatches the raw chunk, and a decode/re-encode/decode round trip preserves the audio,iXML, andbext.Summary by CodeRabbit
New Features
Config.IXMLfor embedding metadata andDecoder.IXML()for retrieving it.Documentation