# Vert.x Http Proxy

Vert.x Http Proxy is a reverse proxy based on Vert.x, it aims to implement reusable reverse proxy logic to focus on higher concerns.

| This module has Tech Preview status, this means the API can change between versions.

## Using Vert.x Http Proxy

To use Vert.x Http Proxy, add the following dependency to the dependencies section of your build descriptor:

- Maven (in your `pom.xml`):

    <dependency>
      <groupId>io.vertx</groupId>
      <artifactId>vertx-http-proxy</artifactId>
      <version>5.0.0.CR1</version>
    </dependency>

- Gradle (in your `build.gradle` file):

    dependencies {
      compile 'io.vertx:vertx-http-proxy:5.0.0.CR1'
    }

## Reverse proxy server

In order to accomplish a reverse proxy with Vert.x Http Proxy you need the following:

1. Proxy Server that handles user-agent requests and forward them to the origin server

2. Origin Server that handles requests from the proxy server and respond accordingly

You can create a proxy server that listens to port `8080` and implement reverse proxy logic

    HttpClient proxyClient = vertx.createHttpClient();

    HttpProxy proxy = HttpProxy.reverseProxy(proxyClient);
    proxy.origin(7070, "origin");

    HttpServer proxyServer = vertx.createHttpServer();

    proxyServer.requestHandler(proxy).listen(8080);

All user-agent requests are forwarded to the origin server conveniently.

### Origin server routing

You can create a proxy that forwards all the traffic to a single server like seen before

You can set an origin selector to route the traffic to a given server

    proxy.originSelector(request -> Future.succeededFuture(resolveOriginAddress(request)));

You can set a function to create the client request to the origin server for ultimate flexibility

    proxy.originRequestProvider((request, client) -> client.request(resolveOriginOptions(request)));

### Headers forwarding

End-to-end headers are forwarded by the proxy, hop-by-hop headers are ignored.

#### Request authority

As a transparent proxy, the request authority (`Host` header for HTTP/1.1, `:authority` pseudo header for HTTP/2) is preserved.

You can override the request authority

    proxy.addInterceptor(new ProxyInterceptor() {
      @Override
      public Future<ProxyResponse> handleProxyRequest(ProxyContext context) {
        ProxyRequest proxyRequest = context.request();
        proxyRequest.setAuthority(HostAndPort.create("example.com", 80));
        return ProxyInterceptor.super.handleProxyRequest(context);
      }
    });

When the request authority is overridden, the `x-forwarded-host` header is set on the request to the origin server with the original authority value.

| changing the request authority can have undesirable side effects and can affect the proxied web server that might rely on the original request authority to handle cookies, URL redirects and such.

### WebSockets

The proxy supports WebSocket by default.

WebSocket handshake requests are forwarded to the origin server (including the `connection` header) and the handshake happens between the user agent and the origin server.

You can configure WebSocket support with `setSupportWebSocket`.

### Proxy caching

By default the proxy does not cache response and ignores most cache directives, you can enable caching by setting the cache options.

    HttpProxy proxy = HttpProxy.reverseProxy(new ProxyOptions().setCacheOptions(new CacheOptions()), proxyClient);

### Proxy interception

Interception is a powerful way to extend the proxy withg new features.

You can implement `handleProxyRequest` to perform any operation on the proxy request

    proxy.addInterceptor(new ProxyInterceptor() {
      @Override
      public Future<ProxyResponse> handleProxyRequest(ProxyContext context) {
        ProxyRequest proxyRequest = context.request();

        filter(proxyRequest.headers());

        // Continue the interception chain
        return context.sendRequest();
      }
    });

Likewise with the proxy response

    proxy.addInterceptor(new ProxyInterceptor() {
      @Override
      public Future<Void> handleProxyResponse(ProxyContext context) {
        ProxyResponse proxyResponse = context.response();

        filter(proxyResponse.headers());

        // Continue the interception chain
        return context.sendResponse();
      }
    });

Interceptors will not apply to WebSocket handshake packets by default. While in some use cases (e.g. changing the WebSocket request path), you can overwrite `allowApplyToWebSocket` method to allow interceptors apply to WebSocket.

#### Body filtering

You can filter body by simply replacing the original `Body` with a new one

    proxy.addInterceptor(new ProxyInterceptor() {
      @Override
      public Future<Void> handleProxyResponse(ProxyContext context) {
        ProxyResponse proxyResponse = context.response();

        // Create a filtered body
        Body filteredBody = filter(proxyResponse.getBody());

        // And then let the response use it
        proxyResponse.setBody(filteredBody);

        // Continue the interception chain
        return context.sendResponse();
      }
    });

#### Interception control

`sendRequest` and `sendResponse` continue the current interception chain and then send the result to the origin server or the user-agent.

You can change the control, e.g you can send a response immediately to the user-agent without even requesting the origin server

    proxy.addInterceptor(new ProxyInterceptor() {
      @Override
      public Future<ProxyResponse> handleProxyRequest(ProxyContext context) {

        ProxyRequest proxyRequest = context.request();

        // Release the underlying resources
        proxyRequest.release();

        // Create a response and populate it
        ProxyResponse proxyResponse = proxyRequest.response()
          .setStatusCode(200)
          .putHeader("content-type", "text/plain")
          .setBody(Body.body(Buffer.buffer("Hello World")));

        return Future.succeededFuture(proxyResponse);
      }
    });

#### Header interceptor

You can apply header interceptors to change headers from the request and response with common operations:

    proxy.addInterceptor(
      HeadersInterceptor.filterResponseHeaders(shouldRemove));

Check out the `HeadersInterceptor` class for details about the available methods.

#### Query interceptor

You can use query interceptors to update or remove the query parameters:

    proxy.addInterceptor(
      QueryInterceptor.setQueryParam(key, value));

You can also refer to `QueryInterceptor` for more information.

#### Body interceptor

You can use body interceptor to create body transformations for common data types, like `JsonObject`:

    proxy.addInterceptor(
      BodyInterceptor.modifyResponseBody(
        BodyTransformer.transformJsonObject(
          jsonObject -> removeSomeFields(jsonObject)
        )
      ));

Please check the `BodyTransformer` for other supported transformations.

#### WebSocket interceptor

You can use WebSocket interceptor to wrap an interceptor to let it allow WebSocket handling:

    proxy.addInterceptor(
      WebSocketInterceptor.allow(PathInterceptor.addPrefix("/api"))
    );