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informix-db/docs/CAPTURES/13-py-varchar.socat.log
Ryan Malloy 34ad04a872 Phase 2.x: VARCHAR row decoding works — three byte-level fixes 
Three findings, each caught by a different debugging technique,
documented in DECISION_LOG.md:

1. CURNAME+NFETCH PDU: trailing reserved field is SHORT not INT.
   Caught by byte-diffing our 44-byte PDU against JDBC's 42-byte
   reference under socat. The server tolerated the longer version
   for INT-only SELECTs (silently consuming extra zeros) but
   rejected it for VARCHAR queries. Lesson: server tolerance varies
   by query type — always match JDBC byte-for-byte.

2. SQ_TUPLE payload pads to even byte alignment. An 11-byte
   "syscolumns" VARCHAR payload had a trailing 0x00 between it and
   the next SQ_TUPLE tag. JDBC's IfxRowColumn.readTuple consumes
   this pad silently; we weren't, so any odd-length variable-width
   row desynced the parser.

3. VARCHAR/NCHAR/NVCHAR in tuple data use a SINGLE-byte length
   prefix (max 255 chars — IDS VARCHAR's hard limit). NOT a 2-byte
   short as I'd initially assumed. CHAR is fixed-width per
   encoded_length. LVARCHAR uses a 4-byte int prefix for >255 byte
   values.

Module changes:
  src/informix_db/_resultset.py — _LENGTH_PREFIXED_SHORT_TYPES set,
    branched VARCHAR/NCHAR/NVCHAR (1-byte prefix) vs CHAR (fixed)
    vs LVARCHAR (4-byte prefix); even-byte alignment pad consumed
    after each SQ_TUPLE payload.
  src/informix_db/cursors.py — CURNAME+NFETCH and standalone NFETCH
    PDUs now write_short(0) for the reserved trailing field.

Tests: 40 unit + 18 integration (3 new VARCHAR tests) = 58 total,
all green, ruff clean. New tests cover:
  - VARCHAR single-column SELECT
  - Odd-length VARCHAR row (regression for the pad-byte bug)
  - Mixed INT + VARCHAR + FLOAT three-column SELECT

Sample output:
  SELECT FIRST 5 tabname FROM systables → ('systables',),
    ('syscolumns',), ('sysindices',), ('systabauth',), ('syscolauth',)
  SELECT FIRST 3 tabname, tabid, nrows → ('systables', 1, 276.0), ...

VARCHAR was the last known gap from the Phase 2 commit. Phase 2
now reads INT, BIGINT, REAL, FLOAT, CHAR, VARCHAR end-to-end. Phase
6+ types (DATETIME, INTERVAL, DECIMAL, BLOBs) remain.
2026-05-04 07:55:13 -06:00

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2026/05/04 07:40:07 socat[340723] N listening on AF=2 0.0.0.0:9090
2026/05/04 07:40:07 socat[340723] N accepting connection from AF=2 127.0.0.1:46824 on AF=2 127.0.0.1:9090
2026/05/04 07:40:07 socat[340723] N opening connection to 127.0.0.1:9088
2026/05/04 07:40:07 socat[340723] N opening connection to AF=2 127.0.0.1:9088
2026/05/04 07:40:07 socat[340723] N successfully connected from local address AF=2 127.0.0.1:49596
2026/05/04 07:40:07 socat[340723] N successfully connected to 127.0.0.1:9088
2026/05/04 07:40:07 socat[340723] N starting data transfer loop with FDs [6,6] and [5,5]
> 2026/05/04 07:40:07.516183 length=384 from=0 to=383
01 80 01 3c 00 00 00 64 00 65 00 00 00 3d 00 06 49 45 45 45 4d 00 00 6c 73 71 6c 65 78 65 63 00 00 00 00 00 00 06 39 2e 32 38 30 00 00 0c 52 44 53 23 52 30 30 30 30 30 30 00 00 05 73 71 6c 69 00 00 00 01 3c 00 00 00 00 00 00 00 00 00 01 00 09 69 6e 66 6f 72 6d 69 78 00 00 07 69 6e 34 6d 69 78 00 6f 6c 00 00 00 00 00 00 00 00 00 3d 74 6c 69 74 63 70 00 00 00 00 00 01 00 68 00 0b 00 00 00 03 00 09 69 6e 66 6f 72 6d 69 78 00 00 00 00 00 00 00 00 00 00 00 00 6a 00 06 00 07 44 42 50 41 54 48 00 00 02 2e 00 00 0e 43 4c 49 45 4e 54 5f 4c 4f 43 41 4c 45 00 00 0d 65 6e 5f 55 53 2e 38 38 35 39 2d 31 00 00 11 43 4c 4e 54 5f 50 41 4d 5f 43 41 50 41 42 4c 45 00 00 02 31 00 00 07 44 42 44 41 54 45 00 00 06 59 34 4d 44 2d 00 00 0c 49 46 58 5f 55 50 44 44 45 53 43 00 00 02 31 00 00 09 4e 4f 44 45 46 44 41 43 00 00 03 6e 6f 00 00 6b 00 00 00 00 00 05 33 01 00 00 00 00 00 0b 72 70 6d 2d 62 75 6c 6c 65 74 00 00 00 00 29 2f 68 6f 6d 65 2f 72 70 6d 2f 63 6c 61 75 64 65 2f 69 6e 66 6f 72 6d 69 78 2f 70 79 74 68 6f 6e 2d 6c 69 62 72 61 72 79 00 00 74 00 20 00 00 00 00 00 00 00 00 00 16 69 6e 66 6f 72 6d 69 78 2d 64 62 40 70 69 64 33 34 30 37 33 37 00 00 7f
< 2026/05/04 07:40:07.528122 length=276 from=0 to=275
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> 2026/05/04 07:40:07.528386 length=14 from=384 to=397
00 7e 00 08 ff fc 7f fc 3c 8c aa 97 00 0c
< 2026/05/04 07:40:07.528522 length=16 from=276 to=291
00 7e 00 09 bd be 9f fe 7f b7 ff ef ff 00 00 0c
> 2026/05/04 07:40:07.528584 length=48 from=398 to=445
00 51 00 06 00 26 00 0c 00 04 00 06 44 42 54 45 4d 50 00 04 2f 74 6d 70 00 0b 53 55 42 51 43 41 43 48 45 53 5a 00 00 02 31 30 00 00 00 00 00 0c
< 2026/05/04 07:40:07.528662 length=2 from=292 to=293
00 0c
> 2026/05/04 07:40:07.528681 length=18 from=446 to=463
00 24 00 09 73 79 73 6d 61 73 74 65 72 00 00 00 00 0c
< 2026/05/04 07:40:07.528847 length=28 from=294 to=321
00 0f 00 15 00 00 00 00 00 00 00 00 00 00 00 00 00 37 00 00 00 01 00 00 00 01 00 0c
> 2026/05/04 07:40:07.528893 length=66 from=464 to=529
00 02 00 00 00 00 00 34 53 45 4c 45 43 54 20 46 49 52 53 54 20 32 20 74 61 62 6e 61 6d 65 20 46 52 4f 4d 20 73 79 73 74 61 62 6c 65 73 20 4f 52 44 45 52 20 42 59 20 74 61 62 69 64 00 16 00 31 00 0c
< 2026/05/04 07:40:07.529094 length=84 from=322 to=405
00 08 00 02 00 00 00 00 00 00 00 81 00 01 00 00 00 08 00 00 00 00 00 00 00 00 00 0d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 80 74 61 62 6e 61 6d 65 00 00 0f 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 37 00 00 01 14 00 00 00 25 00 0c
> 2026/05/04 07:40:07.529204 length=44 from=530 to=573
00 04 00 00 00 03 00 12 5f 69 66 78 63 30 30 30 30 30 30 30 30 30 30 30 30 31 00 06 00 04 00 00 00 09 00 00 10 00 00 00 00 00 00 0c
< 2026/05/04 07:40:07.529311 length=66 from=406 to=471
00 0e 00 00 00 00 00 0a 09 73 79 73 74 61 62 6c 65 73 00 0e 00 00 00 00 00 0b 0a 73 79 73 63 6f 6c 75 6d 6e 73 00 00 0f 00 10 00 00 00 02 00 00 03 02 00 00 00 00 00 37 00 00 01 14 00 00 00 25 00 0c
> 2026/05/04 07:40:07.529416 length=2 from=574 to=575
00 38
2026/05/04 07:40:07 socat[340723] N socket 1 (fd 6) is at EOF
2026/05/04 07:40:07 socat[340723] N socket 2 (fd 5) is at EOF
2026/05/04 07:40:07 socat[340723] N exiting with status 0
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