Proxy

Ktor HTTP client allows you to configure proxy settings in multiplatform projects. There are two supported types of proxies: HTTP and SOCKS.

Supported engines

The table below shows supported proxy types for specific engines:

Engine	HTTP proxy	SOCKS proxy
Apache	✅	✖️
Java	✅	✖️
Jetty	✖️	✖️
CIO	✅	✖️
Android	✅	✅
OkHttp	✅	✅
JavaScript	✖️	✖️
Darwin	✅	✅
Curl	✅	✅

Add dependencies

To configure the proxy in the client, you don't need to add a specific dependency. The required dependencies are:

Configure proxy

To configure proxy settings, call the engine function inside a client configuration block and then use the proxy property. This property accepts the ProxyConfig instance that can be created using the ProxyBuilder factory.

val client = HttpClient() {
    engine {
        proxy = // Create proxy configuration
    }
}

HTTP proxy

The example below shows how to configure HTTP proxy using ProxyBuilder:

val client = HttpClient() {
    engine {
        proxy = ProxyBuilder.http("http://sample-proxy-server:3128/")
    }
}

On JVM, ProxyConfig is mapped to the Proxy class, so you can configure the proxy as follows:

val client = HttpClient() {
    engine {
        proxy = Proxy(Proxy.Type.HTTP, InetSocketAddress("sample-proxy-server", 3128))
    }
}

SOCKS proxy

The example below shows how to configure SOCKS proxy using ProxyBuilder:

val client = HttpClient() {
    engine {
        proxy = ProxyBuilder.socks(host = "sample-proxy-server", port = 1080)
    }
}

As for the HTTP proxy, on JVM you can use Proxy to configure proxy settings:

val client = HttpClient() {
    engine {
        proxy = Proxy(Proxy.Type.SOCKS, InetSocketAddress("sample-proxy-server", 1080))
    }
}

Proxy authentication and authorization

Proxy authentication and authorization are engine-specific and should be handled manually. For example, to authenticate a Ktor client to an HTTP proxy server using basic authentication, append the Proxy-Authorization header to each request as follows:

val client = HttpClient() {
    defaultRequest {
        val credentials = Base64.getEncoder().encodeToString("jetbrains:foobar".toByteArray())
        header(HttpHeaders.ProxyAuthorization, "Basic $credentials")
    }
}

To authenticate a Ktor client to a SOCKS proxy on JVM, you can use the java.net.socks.username and java.net.socks.password system properties.

Last modified: 25 November 2022