forward proxy support for client websocket connections

.gitignore

@@ -1,3 +1,4 @@
 /.idea/
 /deps
 /.gobin/
+/vendor/

client/side_channel_creds.go

@@ -15,8 +15,12 @@
 package client
 
 import (
+	"bufio"
 	"context"
+	"fmt"
 	"net"
+	"net/http"
+	"net/url"
 	"sync"
 
 	"google.golang.org/grpc/credentials"
@@ -47,7 +51,24 @@ func (c *sideChannelCreds) ClientHandshake(ctx context.Context, authority string
 		return rawConn, c.authInfo, nil
 	}
 
-	sideChannelConn, err := (&net.Dialer{}).DialContext(ctx, "tcp", c.endpoint)
+	// check if c.endpoint is reached via proxy
+	destReq, err := http.NewRequest("GET", "http://"+c.endpoint, nil)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to determine proxy URL for %s: %w", c.endpoint, err)
+	}
+	proxyURL, err := http.ProxyFromEnvironment(destReq)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to determine proxy URL for %s: %w", c.endpoint, err)
+	}
+
+	var sideChannelConn net.Conn
+	if proxyURL != nil {
+		// net dial via HTTP CONNECT tunnel if using proxy
+		sideChannelConn, err = dialViaCONNECT(ctx, c.endpoint, proxyURL)
+	} else {
+		sideChannelConn, err = new(net.Dialer).DialContext(ctx, "tcp", c.endpoint)
+	}
+
 	if err != nil {
 		return nil, nil, err
 	}
@@ -61,3 +82,28 @@ func (c *sideChannelCreds) ClientHandshake(ctx context.Context, authority string
 	c.authInfo = authInfo
 	return rawConn, authInfo, nil
 }
+
+// dialViaCONNECT tunnels a tcp connection to addr through proxy using HTTP CONNECT
+func dialViaCONNECT(ctx context.Context, addr string, proxy *url.URL) (net.Conn, error) {
+	proxyAddr := proxy.Host
+	if proxy.Port() == "" {
+		proxyAddr = net.JoinHostPort(proxyAddr, "80")
+	}
+	conn, err := new(net.Dialer).DialContext(ctx, "tcp", proxyAddr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to dial proxy %s: %w", proxyAddr, err)
+	}
+	fmt.Fprintf(conn, "CONNECT %s HTTP/1.1\r\nHost: %s\r\n\r\n", addr, proxy.Hostname())
+	rr := bufio.NewReader(conn)
+	res, err := http.ReadResponse(rr, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read response from HTTP CONNECT to %s via proxy %s: %w", addr, proxyAddr, err)
+	}
+	if res.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to dial %s via %s. response status: %v", addr, proxyAddr, res.Status)
+	}
+	if rr.Buffered() > 0 {
+		return nil, fmt.Errorf("CONNECT response from %s resulted in %d bytes of unexpected data", proxyAddr, rr.Buffered())
+	}
+	return conn, nil
+}

client/ws_proxy.go

@@ -299,6 +299,7 @@ func createClientWSProxy(endpoint string, tlsClientConf *tls.Config) (*http.Serv
 		httpClient: &http.Client{
 			Transport: &http.Transport{
 				TLSClientConfig: tlsClientConf,
+				Proxy:           http.ProxyFromEnvironment,
 			},
 		},
 	}