Dylan M. Taylor
34aa8c1cfd
The part layer read every part by local name, so extLst children (x14:, xr:, xm:), mc:AlternateContent and r:id lost their namespaces and could not be written back. Parts are now read with one fixed prefix per namespace (the main namespace unprefixed), mc:Ignorable and mc:Choice/@Requires are rewritten to match, and ns::declare prepares a kept tree for writing. craft-xml: a namespace listed with the empty prefix reads unprefixed.
craft-xlsx
Excel workbooks: .xlsx, .xlsm, .xltx, .xltm (SpreadsheetML in an OPC package,
transitional and strict) and .xlsb (the same package with binary parts). Clean-room, from
ECMA-376 Part 1 (SpreadsheetML), [MS-XLSB] and observed files. No unsafe.
This is the part layer. Package::open opens the container through craft-opc and reads:
| Call | Gives |
|---|---|
workbook() |
Workbook: sheets in tab order (name, id, visibility, kind, part), the 1904 date flag, defined names, the active tab, and the whole part as a tree |
shared_strings() |
StringItems: text, formatted runs, phonetic readings |
styles() |
Styles: number formats, fonts, fills, borders, cell and cell-style formats, named styles, differential formats, the indexed palette, as indexed tables |
sheet(entry, each) |
each Row of Cells to a callback, then a SheetPart: the rest of the worksheet as a tree, its relationships, columns and merged cells |
opc(), read_xml(), optional_xml(), rels() |
any other part |
Every part is read with fixed prefixes (ns::CANONICAL): the SpreadsheetML main namespace
(transitional or strict) unprefixed, the others by ns::NAMESPACES (r:id, mc:AlternateContent,
x14:sparklineGroups, xm:sqref), and the prefixes in mc:Ignorable and mc:Choice/@Requires
rewritten to match. A tree kept from a part goes back out with ns::declare, which declares what
it uses. A name in a namespace that is not listed reads as ?:name and is not written.
A cell keeps the file's terms: a shared-string index, a format index, the formula text as the
file spells it, value and cell metadata indexes. CellValue::resolve gives the value it shows.
Shared formulas are not expanded and formulas are not parsed: that needs a formula grammar.
A binary workbook gives the same Workbook, strings, rows and merged cells, with saved values
only: its formulas are token streams that are not decoded, and its styles are not read (each
cell keeps its format index).
Hostile input
Limits.package: ZIP entries, bytes per part and in all (craft-opc).Limits.xml: one XML part. Rows and shared strings are streamed, so this bounds one row, one string and what is left of a part, not a sheet's length.Limits.binary_records,binary_cells,binary_text: a binary workbook, over all its parts (40 million records, 4 million cells and as many shared strings, 256 MiB of text, ascraft-xlsallows). Fixed caps: 1024 sheets, 100,000 merged ranges per sheet, 64 nested extension blocks.- Cells and rows outside the 1,048,576 × 16,384 grid are dropped and counted.
SpreadsheetML is read leniently: a damaged optional part is a warning, a damaged worksheet keeps the rows before the damage. A binary part that does not parse fails the read, since skipping a record would lose data without a trace.
Shared with craft-xls and craft-ods through craft-sheet: CellRef, Range, Value,
CellError, Visibility, sheet-name quoting, built-in number formats and the palette.