Pluggable Client Transports / HTTP(S) proxy Support

The client side infrastructure has support to plug different transport mechanisms underneath. A client side transport is represented by an instance of akka.http.scaladsl.ClientTransportakka.http.javadsl.ClientTransport:

Scala

copysourcetrait ClientTransport {
  def connectTo(host: String, port: Int, settings: ClientConnectionSettings)(implicit system: ActorSystem): Flow[ByteString, ByteString, Future[OutgoingConnection]]
}

Java

copysourceabstract class ClientTransport {
  def connectTo(host: String, port: Int, settings: ClientConnectionSettings, system: ActorSystem): Flow[ByteString, ByteString, CompletionStage[OutgoingConnection]]
}

A transport implementation defines how the client infrastructure should communicate with a given host.

Configuring Client Transports

A ClientTransportClientTransport can be configured in the ClientConnectionSettingsClientConnectionSettings. Right now, this is not possible through config files but only by code. First, use ClientConnectionSettings.withTransport to configure a transport, then use ConnectionPoolSettings.withConnectionSettings. ClientConnectionSettingsClientConnectionSettings can be passed to all client-side entry points in HttpHttp.

Predefined Transports

TCP

The default transport is ClientTransport.TCP which simply opens a TCP connection to the target host.

HTTP(S) Proxy

A transport that connects to target servers via an HTTP(S) proxy. An HTTP(S) proxy uses the HTTP CONNECT method (as specified in RFC 7231 Section 4.3.6) to create tunnels to target servers. The proxy itself should transparently forward data to the target servers so that end-to-end encryption should still work (if TLS breaks, then the proxy might be fussing with your data).

This approach is commonly used to securely proxy requests to HTTPS endpoints. In theory it could also be used to proxy requests targeting HTTP endpoints, but we have not yet found a proxy that in fact allows this.

Instantiate the HTTP(S) proxy transport using ClientTransport.httpsProxy(proxyAddress).

The proxy transport can also be setup using ClientTransport.httpsProxy() or ClientTransport.httpsProxy(basicHttpCredentials) In order to define the transport as such, you will need to set the proxy host / port in your conf file like the following.

akka.http.client.proxy {
 https {
   host = ""
   port = 443
 }
}

If host is left as "" and you attempt to setup an httpsProxy transport, an exception will be thrown.

Use HTTP(S) proxy with Http().singleRequestHttp.get(...).singleRequest

To make use of an HTTP proxy when using the singleRequest API you simply need to configure the proxy and pass the appropriate settings object when calling the single request method.

Scala

copysourceimport java.net.InetSocketAddress

import akka.actor.ActorSystem
import akka.http.scaladsl.{ ClientTransport, Http }

implicit val system = ActorSystem()

val proxyHost = "localhost"
val proxyPort = 8888

val httpsProxyTransport = ClientTransport.httpsProxy(InetSocketAddress.createUnresolved(proxyHost, proxyPort))

val settings = ConnectionPoolSettings(system)
  .withConnectionSettings(ClientConnectionSettings(system)
    .withTransport(httpsProxyTransport))
Http().singleRequest(HttpRequest(uri = "https://google.com"), settings = settings)

Java

copysource
final ActorSystem system = ActorSystem.create();

ClientTransport proxy = ClientTransport.httpsProxy(InetSocketAddress.createUnresolved("192.168.2.5", 8080));
ConnectionPoolSettings poolSettingsWithHttpsProxy = ConnectionPoolSettings.create(system)
    .withConnectionSettings(ClientConnectionSettings.create(system).withTransport(proxy));

final CompletionStage<HttpResponse> responseFuture =
    Http.get(system)
        .singleRequest(
              HttpRequest.create("https://github.com"),
              Http.get(system).defaultClientHttpsContext(),
              poolSettingsWithHttpsProxy, // <- pass in the custom settings here
              system.log());

Use HTTP(S) proxy that requires authentication

In order to use an HTTP(S) proxy that requires authentication, you need to provide HttpCredentialsHttpCredentials that will be used when making the CONNECT request to the proxy:

Scala

copysourceimport akka.http.scaladsl.model.headers

val proxyAddress = InetSocketAddress.createUnresolved(proxyHost, proxyPort)
val auth = headers.BasicHttpCredentials("proxy-user", "secret-proxy-pass-dont-tell-anyone")

val httpsProxyTransport = ClientTransport.httpsProxy(proxyAddress, auth)

val settings = ConnectionPoolSettings(system)
  .withConnectionSettings(ClientConnectionSettings(system)
    .withTransport(httpsProxyTransport))
Http().singleRequest(HttpRequest(uri = "http://akka.io"), settings = settings)

Java

copysourceInetSocketAddress proxyAddress =
  InetSocketAddress.createUnresolved("192.168.2.5", 8080);
HttpCredentials credentials =
  HttpCredentials.createBasicHttpCredentials("proxy-user", "secret-proxy-pass-dont-tell-anyone");

ClientTransport proxy = ClientTransport.httpsProxy(proxyAddress, credentials); // include credentials
ConnectionPoolSettings poolSettingsWithHttpsProxy = ConnectionPoolSettings.create(system)
    .withConnectionSettings(ClientConnectionSettings.create(system).withTransport(proxy));

final CompletionStage<HttpResponse> responseFuture =
    Http.get(system)
        .singleRequest(
              HttpRequest.create("https://github.com"),
              Http.get(system).defaultClientHttpsContext(),
              poolSettingsWithHttpsProxy, // <- pass in the custom settings here
              system.log());

Use HTTP(S) proxy with Http().singleWebSocketRequestHttp.get(…).singleWebSocketRequest

Making use of an HTTP proxy when using the singleWebSocketRequest is done like using singleRequest, except you set ClientConnectionSettings instead of ConnectionPoolSettings:

Scala

copysourceimport java.net.InetSocketAddress

import akka.actor.ActorSystem
import akka.NotUsed
import akka.http.scaladsl.{ ClientTransport, Http }
import akka.http.scaladsl.settings.ClientConnectionSettings
import akka.http.scaladsl.model.ws._
import akka.stream.scaladsl._

implicit val system = ActorSystem()

val flow: Flow[Message, Message, NotUsed] =
  Flow.fromSinkAndSource(
    Sink.foreach(println),
    Source.single(TextMessage("hello world!")))

val proxyHost = "localhost"
val proxyPort = 8888

val httpsProxyTransport = ClientTransport.httpsProxy(InetSocketAddress.createUnresolved(proxyHost, proxyPort))

val settings = ClientConnectionSettings(system).withTransport(httpsProxyTransport)
Http().singleWebSocketRequest(WebSocketRequest(uri = "wss://example.com:8080/some/path"), clientFlow = flow, settings = settings)

Java

copysource
final ActorSystem system = ActorSystem.create();
final Materializer materializer = SystemMaterializer.get(system).materializer();

final Flow<Message, Message, NotUsed> flow =
  Flow.fromSinkAndSource(
    Sink.foreach(System.out::println),
    Source.single(TextMessage.create("hello world")));

ClientTransport proxy = ClientTransport.httpsProxy(InetSocketAddress.createUnresolved("192.168.2.5", 8080));
ClientConnectionSettings clientSettingsWithHttpsProxy = ClientConnectionSettings.create(system)
  .withTransport(proxy);

Http.get(system)
  .singleWebSocketRequest(
    WebSocketRequest.create("wss://example.com:8080/some/path"),
    flow,
    Http.get(system).defaultClientHttpsContext(),
    null,
    clientSettingsWithHttpsProxy, // <- pass in the custom settings here
    system.log(),
    materializer);

Use HTTP(S) proxy that requires authentication for Web Sockets

Here is an example for Web Socket:

Scala

copysourceimport akka.http.scaladsl.model.headers

val proxyAddress = InetSocketAddress.createUnresolved(proxyHost, proxyPort)
val auth = headers.BasicHttpCredentials("proxy-user", "secret-proxy-pass-dont-tell-anyone")

val httpsProxyTransport = ClientTransport.httpsProxy(proxyAddress, auth)

val settings = ClientConnectionSettings(system).withTransport(httpsProxyTransport)
Http().singleWebSocketRequest(WebSocketRequest(uri = "wss://example.com:8080/some/path"), clientFlow = flow, settings = settings)

Java

copysourceInetSocketAddress proxyAddress =
  InetSocketAddress.createUnresolved("192.168.2.5", 8080);
HttpCredentials credentials =
  HttpCredentials.createBasicHttpCredentials("proxy-user", "secret-proxy-pass-dont-tell-anyone");

ClientTransport proxy = ClientTransport.httpsProxy(proxyAddress, credentials); // include credentials
ClientConnectionSettings clientSettingsWithHttpsProxy = ClientConnectionSettings.create(system)
  .withTransport(proxy);

Http.get(system)
  .singleWebSocketRequest(
    WebSocketRequest.create("wss://example.com:8080/some/path"),
    flow,
    Http.get(system).defaultClientHttpsContext(),
    null,
    clientSettingsWithHttpsProxy, // <- pass in the custom settings here
    system.log(),
    materializer);

Custom Host Name Resolution Transport

You can use ClientTransport.withCustomResolverClientTransport.withCustomResolver to customize host name resolution. The given resolution function will be called for every connection attempt to resolve a hostname / port combination (potentially asynchronously) to an InetSocketAddress.

As a backend to implement the resolution function you can use Akka’s Async DNS Resolution.

Potential use cases:

• in a managed setting this can be used to query for SRV DNS records that contain both address and port for a service.
• if the DNS server returns multiple addresses, you can implement a load balancing algorithm to select a different target address for each connection

Implementing Custom Transports

Implement ClientTransport.connectTo to implement a custom client transport.

Here are some ideas for custom (or future predefined) transports:

• SSH tunnel transport: connects to the target host through an SSH tunnel
• Per-host configurable transport: allows choosing transports per target host