Module postgres_io 

PostgreSQL logical replication I/O functions.

Provides low-level functions for connecting to PostgreSQL, managing replication slots, and parsing/encoding replication wire messages.

Architecture

• Control-plane connection (connect, ensure_replication_slot): Feature-gated behind postgres-cdc, uses tokio-postgres for slot management and metadata queries.
• Replication streaming: WAL streaming uses pgwire-replication which implements the CopyBoth sub-protocol natively. See build_replication_config() for config conversion.
• Wire format (parse_replication_message, encode_standby_status, build_start_replication_query): Always available, retained as test utilities and protocol documentation.

Wire Format

Replication messages inside CopyData frames:

• XLogData (tag w): 25-byte header + WAL payload
• PrimaryKeepalive (tag k): 18 bytes with WAL position and reply flag
• StandbyStatusUpdate (tag r): 34 bytes sent from client to server

Enums

ReplicationMessage

A message received from the PostgreSQL replication stream.

Functions

build_replication_config

Builds a [pgwire_replication::ReplicationConfig] from a PostgresCdcConfig.

build_start_replication_query

Builds the START_REPLICATION SQL command.

connect

Connects to PostgreSQL as a regular (control-plane) connection.

drop_replication_slot

Drop a PostgreSQL logical replication slot.

encode_standby_status

Encodes a standby status update message.

ensure_replication_slot

Ensures the replication slot exists, creating it if necessary.

parse_replication_message

Parses a raw replication message from byte data.