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Erik JohnstonandClaude Opus 4.8
848100e9ef
Add the Python-facing `Connection` / `Cursor` pair and the `connect` factory, implementing enough of the PEP-249 (DBAPI2) shape for Synapse's needs. A `Connection` owns a single `tokio_postgres::Client`. The client *moves* between the connection and an in-flight cursor rather than being shared: it lives in the connection between interactions, is taken out for the duration of a cursor, and is handed back when the cursor finishes. That single-owner baton (an `Option<Client>` slot on each side) makes it structurally impossible to use the connection mid-transaction or to run two overlapping transactions on one socket — both become a clean "already closed" error. The transaction lifecycle (`cursor` opens with `BEGIN`; `finish` COMMIT/ROLLBACKs and hands the client back; `CursorGuard` rolls back an abandoned transaction on drop) is included here. On any transaction-control error the client is dropped rather than returned, closing the socket — safer than handing a possibly-broken connection back to what will become a connection pool. `connect()` parses a libpq-style DSN, blocks until connected, and spawns the long-lived connection task onto the shared runtime (the libpq default-host fixup is a follow-up). The cursor query methods (`execute` / `fetch_one` / `fetch_all` / `fetch_next_batch` / `rowcount`) delegate to the `CursorQueryState` machine. `run_interaction` — the high-level glue that opens a cursor, runs the callback, and commits/rolls back — follows in the next change, so `cursor`/`finish`/`CursorGuard` carry a transitional `#[allow(dead_code)]` until then. Now that the value/helpers/cursor_state modules are consumed internally, their visibility is tightened from `pub` back to private. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>