cursor.execute("SELECT 1 FROM systables WHERE tabid = 1")
cursor.fetchone() == (1,)
To my knowledge, this is the first time a pure-Python implementation
has read data from Informix without wrapping IBM's CSDK or JDBC.
Three breakthroughs in this commit:
1. Login PDU's database field is BROKEN. Passing a database name there
makes the server reject subsequent SQ_DBOPEN with sqlcode -759
("database not available"). JDBC always sends NULL in the login
PDU's database slot — we now do the same. The user-supplied database
opens via SQ_DBOPEN in _init_session.
2. Post-login session init dance: SQ_PROTOCOLS (8-byte feature mask
replayed verbatim from JDBC) → SQ_INFO with INFO_ENV + env vars
(48-byte PDU replayed verbatim — DBTEMP=/tmp, SUBQCACHESZ=10) →
SQ_DBOPEN. Without all three steps in this exact order, the server
silently ignores SELECTs.
3. SQ_DESCRIBE per-column block has 10 fields per column (not the
simple "name + type" my best-effort parser assumed): fieldIndex,
columnStartPos, columnType, columnExtendedId, ownerName,
extendedName, reference, alignment, sourceType, encodedLength.
The string table at the end is offset-indexed (fieldIndex points
into it), which is how JDBC handles disambiguation.
Cursor lifecycle implementation in cursors.py mirrors JDBC exactly:
PREPARE+NDESCRIBE+WANTDONE → DESCRIBE+DONE+COST+EOT
CURNAME+NFETCH(4096) → TUPLE*+DONE+COST+EOT
NFETCH(4096) → DONE+COST+EOT (drain)
CLOSE → EOT
RELEASE → EOT
Five round trips per SELECT — same as JDBC.
Module changes:
src/informix_db/connections.py — added _init_session(), _send_protocols(),
_send_dbopen(), _drain_to_eot(), _raise_sq_err(); login PDU now
forces database=None always; SQ_INFO PDU replayed verbatim from
JDBC capture (offsets-indexed env-var format too gnarly to derive
in MVP).
src/informix_db/cursors.py — full rewrite: real PDU builders for
PREPARE/CURNAME+NFETCH/NFETCH/CLOSE/RELEASE; tag-dispatched
response readers; cursor-name generator matching JDBC's "_ifxc"
convention.
src/informix_db/_resultset.py — proper SQ_DESCRIBE parser per
JDBC's receiveDescribe (USVER mode); offset-indexed string table
with name lookup by fieldIndex; ColumnInfo dataclass with raw
type-code preserved for null-flag extraction.
src/informix_db/_messages.py — added SQ_NDESCRIBE=22, SQ_WANTDONE=49.
Test coverage: 40 unit + 15 integration tests (7 smoke + 8 new SELECT)
= 55 total, all green, ruff clean. New tests cover:
- SELECT 1 returns (1,)
- cursor.description shape per PEP 249
- Multi-row INT SELECT
- Multi-column mixed types (INT + FLOAT)
- Iterator protocol (for row in cursor)
- fetchmany(n)
- Re-executing on same cursor resets state
- Two cursors on one connection (sequential)
Known gap: VARCHAR row decoding doesn't yet handle the variable-width
on-wire encoding correctly. Phase 2.x will address — for now NotImpl
errors surface raw bytes in the row tuple.
This commit takes informix-db from documentation-only (Phase 0 spike)
to a functional connect() / close() against a real Informix server.
To our knowledge, this is the first pure-socket Informix client in any
language — no CSDK, no JVM, no native libraries.
Layered architecture per the plan, mirroring PyMySQL's shape:
src/informix_db/
__init__.py — PEP 249 surface (connect, exceptions, paramstyle="numeric")
exceptions.py — full PEP 249 hierarchy declared up front
_socket.py — raw socket I/O (read_exact, write_all, timeouts)
_protocol.py — IfxStreamReader / IfxStreamWriter framing primitives
(big-endian, 16-bit-aligned variable payloads,
length-prefixed nul-terminated strings)
_messages.py — SQ_* tags from IfxMessageTypes + ASF/login markers
_auth.py — pluggable auth handlers; plain-password is the
only Phase-1 implementation
connections.py — Connection class: builds the binary login PDU
(SLheader + PFheader byte-for-byte per
PROTOCOL_NOTES.md §3), sends it, parses the
server response, wires up close()
Phase 1 design decisions locked in DECISION_LOG.md:
- paramstyle = "numeric" (matches Informix ESQL/C convention)
- Python >= 3.10
- autocommit defaults to off (PEP 249 implicit)
- License: MIT
- Distribution name: informix-db (verified PyPI-available)
Test coverage: 34 unit tests (codec round-trips against synthetic byte
streams; observed login-PDU values from the spike captures asserted as
exact byte literals) + 6 integration tests (connect, idempotent close,
context manager, bad-password → OperationalError, bad-host →
OperationalError, cursor() raises NotImplementedError).
pytest — runs 34 unit tests, no Docker needed
pytest -m integration — runs 6 integration tests against the
Developer Edition container (pinned by digest
in tests/docker-compose.yml)
pytest -m "" — runs everything
ruff is clean across src/ and tests/.
One bug found during smoke testing: threading.get_ident() can exceed
signed 32-bit on some processes, overflowing struct.pack("!i"). Fixed
the same way the JDBC reference does — clamp to signed 32-bit, fall
back to 0 if out of range. The field is diagnostic only.
One protocol-level observation that AMENDED the JDBC source reading:
the "capability section" in the login PDU is three independently
negotiated 4-byte ints (Cap_1=1, Cap_2=0x3c000000, Cap_3=0), not one
int + 8 reserved zero bytes as my CFR decompile read suggested. The
server echoes them back identically. Trust the wire over the
decompiler.
Phase 1 verification matrix (from PROTOCOL_NOTES.md §12):
- Login byte layout: confirmed (server accepts our pure-Python PDU)
- Disconnection: confirmed (SQ_EXIT round-trip works)
- Framing primitives: confirmed (34 unit tests)
- Error path: bad password → OperationalError, bad host → OperationalError
Phase 2 (Cursor / SELECT / basic types) is the next phase. The hard
unknowns there — exact column-descriptor layout, statement-time error
format — were called out as bounded gaps in Phase 0 and have existing
captures (02-select-1.socat.log, 02-dml-cycle.socat.log) to characterize
against.
