Options reference

socketOptions { } builds an immutable snapshot. Options are read when the client is created — mutating the builder afterwards changes nothing, and reconfiguring means building new options and reconnecting.

socketOptions {
    path = "/socket.io/"
    transports(Transports.POLLING, Transports.WEBSOCKET)
    upgrade = true

    auth { put("token", jwt) }
    extraHeaders { put("Authorization", listOf("Bearer $jwt")) }

    timeoutMs = 20_000
    ackTimeoutMs = 0

    reconnection = true
    reconnectionAttempts = Int.MAX_VALUE
    reconnectionDelayMs = 1_000
    reconnectionDelayMaxMs = 5_000
    randomizationFactor = 0.5

    multiplex = true
    forceNew = false

    trustAllCerts = false
    httpClient = null
    logger = Logger.NoOp
}

Connection

Option	Default
`path`	`/socket.io/`	Server’s Engine.IO endpoint. Change only if the server did
`transports(…)`	polling, websocket	Allowed transports, in preference order
`upgrade`	`true`	Upgrade polling → websocket when the server offers it
`timeoutMs`	`20_000`	Budget for the initial connection

Transports accept library constants or plain strings — "websocket" works as well as Transports.WEBSOCKET. Unrecognised names are dropped at build(), matching the JavaScript client. An empty list fails fast with IllegalArgumentException.

transports(Transports.WEBSOCKET) alone skips polling entirely: one fewer round trip, at the cost of failing outright on networks where only long-polling survives.

Acknowledgements

Option	Default
`ackTimeoutMs`	`0` — disabled	How long `emitWithAck` waits before failing

Zero means wait forever. Set it to something finite unless you are certain the server always replies. See Acknowledgements.

Reconnection

Covered in Reconnection.

Event buffering

eventBuffer {
    capacity = 64
    overflow = EventBufferOverflow.DROP_OLDEST
}

See Receiving events.

Multiplexing

Option	Default
`multiplex`	`true`	Share one engine per `scheme://host:port`
`forceNew`	`false`	Own engine, not registered

See Namespaces.

Transport and TLS

Option	Default
`httpClient`	`null`	Reuse your own Ktor client — see Sharing an HttpClient
`trustAllCerts`	`false`	Development only — see TLS

Logging

logger defaults to Logger.NoOp. See Logging.

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