One connection to a Thrift server, as a gen_server.

A deliberately simple client: no automatic reconnection. Any failure — connect error, socket close, per-call timeout — fails the affected calls and stops the process, so a supervisor or a pool (poolboy, pooler, a custom supervisor) sees the death immediately and replaces the worker. That makes this process safe to use as a pool worker without extra keep-alive logic.

call/4 sends a CALL envelope with the function's parameter struct, then waits for exactly one REPLY. The reply payload is decoded per the service description: field 0 is the success value, a declared exception field turns into the wire-level {error, {exception, Name, Map}} (generated clients convert it to {error, {exception, Value}} in the value's representation), and a TApplicationException into {error, {application_exception, ...}}. oneway/4 answers as soon as the message is on the wire.

The socket runs in {active, N} delivery mode, so a dead peer is noticed even while the connection is idle. Calls are serialized per connection (one outstanding request at a time); concurrent callers queue inside the client and are served in order, matching the classic Thrift client model.

Pool owners read the per-worker counters with get_stats/1 (#{calls_ok, calls_failed}; get_and_reset_stats/1 zeroes them) — the same accounting the thrift_runtime_reconnecting_client wrapper reports, minus the connection axis a single-connection client does not have.

The generated typed client modules call into this; the same map drives both:

• host, port (required);
• service — module implementing thrift_runtime_service (required);
• transport — framed (default), buffered, or http: each call POSTs one Thrift message to http_path (default "/") over a keep-alive connection and waits for the response whose body is the reply. A oneway waits for the (empty) response too — HTTP is request/response. max_frame_size bounds the response body; a non-200 status fails the call with {error, {http_status, Code}};
• protocol — binary (default), or any thrift_runtime_protocol implementation module (see thrift_runtime:protocol_module/1);
• timeout / connect_timeout — the connect and TLS handshake wait, default 5000 ms (connect_timeout overrides the umbrella; per-call timeouts ride the call/4 argument);
• max_frame_size — framed guard and HTTP body bound, default 64 MiB;
• ssl_opts — a list of ssl:tls_client_option(); presence switches the connection to TLS (verify the server with verify_peer plus cacerts);
• multiplex — the service name of a multiplexed server: outgoing message names are prefixed <<"Service:function">> (the reply keeps the plain function name, so nothing else changes). Only the name on the wire is touched; pass the same plain function names to call/4/oneway/4;
• on_event — an observability callback (undefined by default): a 1-arity fun or {M, F, A} receiving one event map per caller-facing answer — call_ok / call_error, the same accounting get_stats/1 reports; see thrift_runtime_events.