Data corruption affecting every Informix version including 15. Two of the
three silently corrupt columns AFTER the offending one, so the damage
shows up far from its cause.
BOOLEAN: described as UDTFIXED(41) with encoded_length=1, but carries the
full UDT envelope on the wire — [1-byte indicator][4-byte length][data],
six bytes for a one-byte value. We read one byte and left five behind.
Captured payload for (INT, BOOLEAN 't', INT, VARCHAR 'tail'):
00 01 b2 07 | 00 00 00 00 01 74 | 00 03 64 0e | 04 74 61 69 6c
Before: (111111, b'\x00', 1, '\x00\x03d\x0e\x04tail')
After: (111111, True, 222222, 'tail')
NCHAR: fixed-width and space-padded like CHAR, but we had it grouped with
the byte-length-prefixed types. NCHAR(10) holding 'nch' read 0x6E ('n') as
a 110-byte length. Silent truncation alone, struct.error with any column
following. NVARCHAR really is length-prefixed and is unchanged; there's a
test guarding both sides now.
INT8/SERIAL8: absent from FIXED_WIDTHS, fell through to the unknown-type
path and surfaced as raw bytes. INT8 is not BIGINT — 10 bytes,
sign-magnitude, halves stored high-last:
bytes 0-1 sign word (0=NULL, 1=pos, 0xFFFF=neg)
bytes 2-5 LOW 32 bits, bytes 6-9 HIGH 32 bits
+n and -n share magnitude bytes, so a two's-complement read is wrong for
every negative while looking correct for every positive.
Not a version bug. Reported against Informix 12, but the same 28-type
round-trip against 12.10.FC12W1DE and 15.0.1.0.3DE produced byte-identical
wire output. It read as version-specific only because INT8/SERIAL8 dominate
12-era schemas while our fixtures use BIGINT.
251 tests missed all three because no fixture used these types. Added
tests/test_type_framing.py (20 integration) and tests/test_int8_unit.py
(14 unit, wire vectors from both servers). Each type is tested twice —
alone, and with trailing columns, since only the latter catches desync.
Verified: 271/271 integration on 15; 241/241 non-smart-LOB on 12.10 (the
LOB tests need an sbspace that image lacks); 20/20 framing tests on both.
Also corrected README and _fastpath docstring, which asserted 12.10
compatibility that had never been tested. The claims held up, but they
were guesses when written and cost a user debugging time.
