Connection pooling
CurlHttpClient keeps one cURL handle alive across requests — HTTP keep-alive and TLS session resumption work out of the box.
OPC UA HTTPS sends one POST per service call. Without keep-alive, that means a full TCP + TLS handshake every time — easily 200+ ms per call on a typical link.
Built-in behaviour
CurlHttpClient reuses a single CurlHandle for every post() call.
cURL persists the underlying TCP connection (HTTP keep-alive) and the
TLS session, so subsequent requests skip the handshake.
The handle is owned by the client instance and released by:
- explicit
$httpClient->close() - destructor (
__destruct) $transport->close()(which delegates to$httpClient->close())
One transport per client
Keep one HttpsTransport instance alive for as long as the OPC UA
Client is in use. Creating a new transport per call defeats
keep-alive and burns ~100 ms on every read.
Multiple clients sharing one HTTP backend
The same HttpClientInterface instance can back several transports —
useful when an application connects to a fleet of servers and wants a
shared connection pool. The default cURL handle is single-threaded so
this is safe only when calls are sequential.
For concurrent calls against the same HttpClientInterface, supply a
dedicated CurlHttpClient per worker / thread / fiber.
Tuning timeouts
HttpsTransport(timeoutSeconds: …) applies to both connect and read.
For long-running History reads, bump the budget:
new HttpsTransport(
httpClient: $httpClient,
encoding: new BinaryHttpsEncoding(),
endpointUrl: 'opc.https://srv:443/UA/',
timeoutSeconds: 120.0,
);A separate per-request timeout is not exposed at the moment — open an issue if you need it.