Kotlin sockets and Ktor

Integration · Sockets · Messages · Official networking research

src/main/kotlin/Main.kt is a runnable desktop Kotlin/JVM program using the Java SDK. Its local Device and SocketFactory helpers are included under src/main/java.

Install and run

Use JDK 21+, Gradle 8.13+, and the published io.ur:urnetwork-sdk version:

gradle -PsdkVersion=<socket-release-version> run --args=--version
gradle -PsdkVersion=<socket-release-version> run --args=--new-id
gradle -PsdkVersion=<socket-release-version> run --args='https://example.com/'
gradle -PsdkVersion=<socket-release-version> run --args='udp echo.example:9000'

Before first publication, install the JAR/POM built by sdk/java into Maven Local as described in the Java guide. This Gradle project checks Maven Local before Central. Set the Device variables below for live requests. The default local package version is 0.0.1-dev.0.

Replace HTTP connection creation

The DNS placeholder preserves the original hostname for the SDK. TLS is JSSE/OkHttp TLS above a UR TCP stream, with normal certificate verification. The example intentionally chooses the engine whose socket creation can be replaced. Native Kotlin/Multiplatform targets do not use this JVM/JNA artifact. Android Kotlin uses the gomobile AAR and portable Socket methods; platform-specific UI/lifecycle setup is separate.

Sources checked September 14, 2026: Ktor engines, Ktor OkHttpConfig, OkHttp socket factory, Retrofit.

Device setup

The executable creates a local Device with the scoped client JWT issued by your service backend and chooses the best available location. Follow the integration guide: the JWT must contain its assigned client_id; only the backend holds the root JWT. Generate an instance ID once with this program's --new-id mode, save it, and reuse it for this installation.

export URNETWORK_CLIENT_JWT='your-scoped-client-jwt'
export URNETWORK_INSTANCE_ID='your-persisted-instance-uuid'

Keep the network-space manager alive until the Device closes. The sample owns and releases these objects in that order. HTTP proxy modes use the Go proxy's Device instead.

Socket behavior

The destination connection lives in the SDK's user-space network stack and sends packets through the Device's URnetwork connection. It is not a kernel socket: its handle cannot be passed to select, poll, an OS socket option, or a library that requires a native file descriptor. Creating these application sockets does not require installing a system VPN or opening a kernel TUN device.

Pass the hostname unchanged with tcp or udp. The SDK resolves A and AAAA records through its connection and applies Happy Eyeballs; use tcp4/tcp6 or udp4/udp6 to force a family. Plain UDP races the initial application datagram and selects the address that sends the first reply. That initial datagram can be delivered to both addresses. Subsequent writes use the winner; a silent server cannot select a winner, so set a read/write deadline. Use an echo server you control for UDP examples. An empty datagram is data, not stream EOF.

TLS verifies the certificate and destination hostname. TLS-over-TCP and DTLS-over-UDP use the same Device packet path. DTLS needs a DTLS server, not a plain UDP echo server. Deadlines are absolute Unix milliseconds in portable bindings; zero clears them. Close each connection and then its Device. Listener/server sockets are a future API.

These are application integration examples. The core SDK suite separately tests real TCP/UDP packets, IPv4/IPv6, hostname races, TLS/DTLS, deadlines, close, and local/RPC transport behavior. A version/self-test command checks installation without using account credentials; live examples require a working account and provider path.