[dmythro]

Builds on #618. Its commit is the first one on this branch and drops out once #618 merges; only the second commit is this PR.

.xls had no streaming reader. CSV, NDJSON, ODS, XLSX and XML each have one. So reading a large .xls meant holding the whole sheet as a Workbook, every row a dense array, whatever the caller did with the rows next.

streamXlsRows(input, options?) yields one sheet's rows on the contract the other stream readers keep:

• One sheet. The first, or the one sheet names by index or by name; a sheet that isn't there yields nothing. range and maxRows mean what they mean for streamXlsxRows, whose implementation the two now share in src/_stream-rows.ts. Reading stops as soon as nothing more can be emitted.
• Rows. An empty row is skipped, and index is the row's own; values run to the row's last cell with nulls in between.
• Options. maxInputBytes, codepage and dateSystem work as they do for readXls.

The values come from readXls's own code. The globals pass (readGlobals) and one record's cell decoding (decodeCells) are split out of reader.ts, and readXls uses them too. Its output is unchanged: the suite and the real-file goldens pass, and a hash over every value of a 17 MB workbook matches.

Two decisions a streaming BIFF reader has to make:

• The input is read whole. A CFB container's directory and allocation tables can sit anywhere in the file, so it needs random access. What is never held is the sheet: memory follows the file and its shared strings.
• Rows have to come in order. A BIFF cell carries its own row. Excel writes them ascending, as do all eight .xls fixtures here, but nothing forces a writer to. A header-only pre-scan checks that no value record goes back a row. If one does, that sheet is buffered and yielded in order, so no row comes out twice or split in two, under the same maxTotalCells bound readXls applies. On the streamed path there is nothing for maxTotalCells to bound.

Measured on a 17 MB BIFF8 workbook (one sheet, ~38k rows × 25 columns), Node 24.22 on macOS arm64, one process per run, three runs each, with #618 in both:

	time	peak RSS	most heap seen
readXls	~142 ms	194 MB	57 MB
streamXlsRows	~173 ms	148 MB	32 MB

The stream spends about 30 ms more on async iteration over the 38k rows. What it saves is the rows themselves, so the saving grows with the sheet; on a file whose size is mostly shared strings it saves less.

Tests:

• Parity with readXls over the BIFF8 and BIFF5 builders (dates, a redefined FORMAT id, the 1904 system, code-page text, RSTRING, a string formula) and over every real .xls fixture: Excel's two and the six SheetJS files.
• Sheet by index, by name and missing; range masking; range and maxRows stopping before a damaged record that a full read reports; empty rows.
• The out-of-order fallback and its maxTotalCells bound; damage before the first row and mid-sheet, both a ParseError; a column past the bounds; ReadableStream input with maxInputBytes; a generator abandoned after one row.

Every new case fails against main, where the function doesn't exist. Two deliberate breakages fail three of them: the pre-scan always answering "in order" fails two, and no early stop past the range fails one. bun run test is green, and bun run size stays within budget.

The README's Streaming and XLS sections and the API table name it, and PARITY.md's paragraph on the stream readers now includes it.

Not verified: I measured on macOS only. The out-of-order fallback is exercised by hand-built files alone; I have no real file written that way.

Summary by CodeRabbit

• New Features

  • Added streamXlsRows for reading legacy .xls files row by row.
  • Supports sheet selection, range filtering, row limits, multiple input types, and cancellation.
  • Exposed the feature through the main and hucre/xlsx entry points.

• Documentation

  • Documented XLS streaming behavior, filtering, sheet handling, and row ordering.

• Bug Fixes

  • Improved handling of long and multi-part XLS strings, malformed records, and out-of-order rows.

• Tests

  • Added comprehensive coverage for XLS streaming, filtering, limits, errors, and real-world files.

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📝 Walkthrough

The change adds streamXlsRows for BIFF5/BIFF8 workbooks. It streams selected rows, applies range and row-count options, and buffers out-of-order cells under a cell limit. BIFF parsing now uses a record cursor, and XLSX streaming uses shared range and sheet-selection utilities.

Changes: Legacy XLS streaming

Layer / File(s)	Summary
BIFF record cursor and string decoding src/xls/biff.ts	BIFF records are traversed lazily with RecordCursor. Character decoding processes chunks and retains fallback handling for incomplete character boundaries.
Cursor-based XLS workbook parsing src/xls/reader.ts, test/xls.test.ts	The XLS reader parses workbook globals and sheets from stream offsets. Cell decoding and bounds checks use reusable helpers. Tests cover string continuation, long strings, and invalid sheet offsets.
Shared range and sheet utilities src/_stream-rows.ts, src/xlsx/stream-reader.ts	Range parsing, row filtering, and target-sheet resolution are shared by the XLS and XLSX streaming readers.
XLS row-streaming API and validation src/xls/stream-reader.ts, src/index.ts, src/xlsx.ts, test/_xls-stream.ts, test/exports.test.ts, test/real-files.test.ts, test/xls.test.ts, README.md, docs/PARITY.md	streamXlsRows streams rows directly when value records are ordered by row and buffers cells otherwise. The API is exported and documented. Tests cover selection, filtering, limits, errors, and fixture comparisons.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant streamXlsRows
  participant openWorkbookStream
  participant RecordCursor
  participant applyRangeFilter
  Caller->>streamXlsRows: input and options
  streamXlsRows->>openWorkbookStream: open workbook stream
  openWorkbookStream-->>streamXlsRows: workbook stream
  streamXlsRows->>RecordCursor: scan BIFF records
  RecordCursor-->>streamXlsRows: BIFF records
  streamXlsRows->>applyRangeFilter: filter decoded row
  applyRangeFilter-->>streamXlsRows: selected row or null
  streamXlsRows-->>Caller: StreamRow

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Merge Risk: ⚪ Minimal · up to dab39

The documented streaming behavior now includes the buffering exception, and no actionable merge risk is established.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 28 functions across 11 files. (1 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely identifies the main change: adding streamXlsRows to stream rows from XLS sheets.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 28 functions across 11 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @README.md:
- Around line 367-369: Update the README text describing legacy .xls streaming
to qualify the memory claim: row-ordered sheets are not held whole, but sheets
whose records go back to an earlier row are buffered under maxTotalCells before
ordered yielding. Preserve the existing sheet, range, maxRows, and CFB
random-access context.

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📒 Files selected for processing: 13

• README.md
• docs/PARITY.md
• src/_stream-rows.ts
• src/index.ts
• src/xls/biff.ts
• src/xls/reader.ts
• src/xls/stream-reader.ts
• src/xlsx.ts
• src/xlsx/stream-reader.ts
• test/_xls-stream.ts
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• test/xls.test.ts

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