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Fixtures

All fixtures are synthetic. jet4.mdb and ace.accdb are written by MakeFixtures.java (Jackcess 4.0.7, Apache-2.0); encrypted.mdb is synthesized from jet4.mdb by make_encrypted.py. Reruns are not byte-identical (the format embeds creation timestamps), but the logical content below is fixed.

Access files cannot be tiny: a freshly created database is a few hundred KB of system tables and allocation maps before the first user row. These are as small as the format allows.

Every value below was verified cell-by-cell against Jackcess reading the same files (via a canonical TSV dump and a byte-level reference reader) before the M implementation was written; the M reader implements exactly the validated logic.

jet4.mdb (Jet 4 / Access 2000 format, version byte 0x01)

Navigation table must list exactly: Empty, Many, Types, Unicode, Wide. With [IncludeSystemObjects = true] the MSys* tables appear as well.

Types, 4 rows

One column per data type. Proves fixed and variable columns, the null bitmap, booleans stored in the null bitmap, LVAL memo storage (inline, single-page, and multi-page), GUID formatting, Decimal sign and scale, and OLE date handling including a pre-1900 date (negative OLE date, fraction read as magnitude).

Id 1 2 3 4
TByte 7 null 255 0
TInt -12345 null 32767 0
TLong 123456789 null -2147483648 0
TCurrency 1234.5678 null -0.0001 0
TFloat 1.5 null -3.25 0
TDouble 2.75 null -10000000000 0
TDate 2026-07-15 13:45:30 null 1899-12-25 06:00:00 1899-12-30 00:00:00
TText hello null Ünïcødé テスト (empty string)
TMemo short memo null "0123456789" repeated 2000 times (20,000 chars) (empty string)
TBool true false true false
TGuid {00112233-4455-6677-8899-AABBCCDDEEFF} null {FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF} null
TNumeric 1234.5678 null -9999.9999 0.0001
TBinary 01 02 03 04 null 200 bytes: 00 01 .. C7 0-byte binary
TOle 10,000 bytes: (i * 7) mod 256 null null null

Notes:

  • TByte row 3 is 255: Access Byte is unsigned 0..255. Jackcess reports Java's signed byte (-1); 255 is correct.
  • The 20,000-char memo exceeds one 4 KB page, proving the multi-page LVAL chain. short memo proves the small-value path; the empty memo proves length 0.
  • Row 2 proves every type's null path in one null bitmap.

Empty, 0 rows

Columns Id, Note. Proves a table with no data pages materializes as an empty typed table.

Many, 2999 rows

Columns Id (Long), Val (Text). 3000 rows row-0001..row-3000 were inserted, then:

  • Id = 77 was deleted: its slot carries the deleted flag and must be skipped. The row is absent and the total is 2999.
  • Id = 42 was grown to "grown " repeated 40 times and trimmed (239 chars). The row no longer fits its page, so its home slot became a 4-byte pointer to an overflow page (flag 0x4000) and the target slot is flagged 0x8000. Exactly one row with Id = 42 must be present, with the 239-char value: this proves pointer-following without double counting.

Also proves multi-page data (about 24 data pages) driven by the usage map.

Unicode, 5 rows

Id Txt
1 plain ascii
2 日本語テキスト
3 mix: ascii + Ωμέγα + 中文
4 (empty string)
5 null

Proves the Jet 4 Unicode compression scheme: row 1 is fully compressed (one byte per char), row 2 is fully uncompressed UTF-16LE, row 3 toggles between modes mid-string, row 4 distinguishes empty from null.

Wide, 2 rows

150 Text columns C001..C150. The column definitions and names do not fit one 4 KB page, proving multi-page table definitions. Row 1 holds v001..v150 (also proves a 150-entry variable-offset table); row 2 is all nulls.

ace.accdb (ACE / Access 2016 format, version byte 0x05)

Same tables and expectations as jet4.mdb, with two differences:

  • Types has one extra column TBigInt (Big Integer, ACE 2016+ only): 42, null, 4503599627370496, -1. The third value is 2^52 and exact; larger magnitudes would lose precision in M doubles.
  • Many holds 1000 inserted rows, minus the same deleted Id = 77 (999 rows), with the same grown Id = 42.

Proves the ACE branch: Standard ACE DB signature, version byte 0x05, and the unchanged Jet 4 page layout.

encrypted.mdb

A copy of the first 8 pages of jet4.mdb with a non-zero database key written into the RC4-masked header region and every page after page 0 scrambled, which is what a key-encoded Jet database looks like without the key. The reader must refuse it with a DataFormat.Error that names encryption as the reason, before touching any table. (Real Access 2007+ password encryption also scrambles page 2, which the reader detects the same way.)