Add example for SOCKS proxy chaining

examples/cascadeproxy-socks/README.md

@@ -0,0 +1,29 @@
+# CascadeSocksProxy
+
+`CascadeSocksProxy` is an example that shows an aggregator server that forwards
+the requests to another socks proxy server. This example is written base on `cascadeproxy` example.
+
+Diagram:
+```
+client --> goproxy --> socks5 proxy --> internet
+```
+
+This example starts a HTTP/HTTPS proxy using goproxy that listens on port `8080`, and forward the requests to the socks5 proxy on `socks5://localhost:1080`.
+It uses MITM (Man in the Middle) proxy mode to retriece and parse the request, and then forwards it to the destination using  the socks5 proxy client implemented in the standard Go `net/http` library. 
+
+### Example usage:
+
+Aggregator server that have HTTP proxy server run on port `8080` and forward the requests to socks proxy listens on `socks5://localhost:1080` with no auth
+```shell
+./socks -v -addr ":8080" -socks "localhost:1080"
+``` 
+
+With auth:
+```shell
+./socks -v -addr ":8080" -socks "localhost:1080" -user "bob" -pass "123"
+ ```
+
+You can run the socks proxy server locally for testing with the following command - this will start a socks5 proxy server on port `1080` with no auth:
+```shell
+./socks5proxyserver/socks5proxyserver
+```

examples/cascadeproxy-socks/socks5proxyserver/go.mod

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+module socks5proxyserver
+
+go 1.20
+
+require github.com/things-go/go-socks5 v0.0.5

examples/cascadeproxy-socks/socks5proxyserver/go.sum

@@ -0,0 +1,7 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/things-go/go-socks5 v0.0.5 h1:qvKaGcBkfDrUL33SchHN93srAmYGzb4CxSM2DPYufe8=
+github.com/things-go/go-socks5 v0.0.5/go.mod h1:mtzInf8v5xmsBpHZVbIw2YQYhc4K0jRwzfsH64Uh0IQ=
+golang.org/x/net v0.20.0 h1:aCL9BSgETF1k+blQaYUBx9hJ9LOGP3gAVemcZlf1Kpo=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

examples/cascadeproxy-socks/socks5proxyserver/main.go

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+package main
+
+import (
+	"context"
+	"github.com/things-go/go-socks5"
+	"log"
+	"net"
+	"os"
+)
+
+func main() {
+	// Create a SOCKS5 server
+	server := socks5.NewServer(
+		socks5.WithLogger(socks5.NewLogger(log.New(os.Stdout, "socks5: ", log.LstdFlags))),
+		socks5.WithDialAndRequest(func(ctx context.Context, network, addr string, request *socks5.Request) (net.Conn, error) {
+			log.Printf("Request from %s to %s", request.RemoteAddr, request.DestAddr)
+			return net.Dial(network, addr)
+		}),
+	)
+
+	// Create SOCKS5 proxy on localhost port 1080
+	if err := server.ListenAndServe("tcp", ":1080"); err != nil {
+		panic(err)
+	}
+}

examples/cascadeproxy-socks/socksproxy.go

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+package main
+
+import (
+	"crypto/tls"
+	"flag"
+	"log"
+	"net/http"
+	"net/url"
+
+	"github.com/elazarl/goproxy"
+)
+
+type SocksAuth struct {
+	Username, Password string
+}
+
+func createSocksProxy(socksAddr string, auth SocksAuth) func(r *http.Request) (*url.URL, error) {
+	return func(r *http.Request) (*url.URL, error) {
+		Url := &url.URL{
+			Scheme: "socks5",
+			Host:   socksAddr,
+		}
+		if auth.Username != "" {
+			Url.User = url.UserPassword(auth.Username, auth.Password)
+		}
+		return Url, nil
+	}
+}
+
+func main() {
+	verbose := flag.Bool("v", false, "should every proxy request be logged to stdout")
+	addr := flag.String("addr", ":8080", "proxy listen address")
+	socksAddr := flag.String("socks", "127.0.0.1:1080", "socks proxy address")
+	username := flag.String("user", "", "username for SOCKS5 proxy if auth is required")
+	password := flag.String("pass", "", "password for SOCKS5 proxy")
+	flag.Parse()
+
+	auth := SocksAuth{
+		Username: *username,
+		Password: *password,
+	}
+	proxyServer := goproxy.NewProxyHttpServer()
+
+	proxyServer.OnRequest().DoFunc(func(req *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
+		client := &http.Client{
+			Transport: &http.Transport{
+				Proxy: createSocksProxy(*socksAddr, auth),
+				TLSClientConfig: &tls.Config{
+					InsecureSkipVerify: true,
+				},
+			},
+		}
+
+		// https://stackoverflow.com/questions/19595860/http-request-requesturi-field-when-making-request-in-go
+		req.RequestURI = ""
+
+		resp, err := client.Do(req)
+		if err != nil {
+			ctx.Logf("Failed to forward request: " + err.Error())
+			return nil, nil
+		}
+		ctx.Logf("Succesfully forwarded request to socks proxy")
+		return req, resp
+	})
+
+	proxyServer.OnRequest().HandleConnect(goproxy.AlwaysMitm)
+	proxyServer.Verbose = *verbose
+
+	log.Fatalln(http.ListenAndServe(*addr, proxyServer))
+}