Initial commit

internal/proxy/socks.go

@@ -0,0 +1,95 @@
+package proxy
+
+import (
+	"context"
+	"fmt"
+	"net"
+
+	"github.com/things-go/go-socks5"
+)
+
+// SOCKSProxy is a SOCKS5 proxy server with domain filtering.
+type SOCKSProxy struct {
+	server   *socks5.Server
+	listener net.Listener
+	filter   FilterFunc
+	debug    bool
+	port     int
+}
+
+// NewSOCKSProxy creates a new SOCKS5 proxy with the given filter.
+func NewSOCKSProxy(filter FilterFunc, debug bool) *SOCKSProxy {
+	return &SOCKSProxy{
+		filter: filter,
+		debug:  debug,
+	}
+}
+
+// fenceRuleSet implements socks5.RuleSet for domain filtering.
+type fenceRuleSet struct {
+	filter FilterFunc
+	debug  bool
+}
+
+func (r *fenceRuleSet) Allow(ctx context.Context, req *socks5.Request) (context.Context, bool) {
+	host := req.DestAddr.FQDN
+	if host == "" {
+		host = req.DestAddr.IP.String()
+	}
+	port := req.DestAddr.Port
+
+	allowed := r.filter(host, port)
+	if r.debug {
+		if allowed {
+			fmt.Printf("[fence:socks] Allowed: %s:%d\n", host, port)
+		} else {
+			fmt.Printf("[fence:socks] Blocked: %s:%d\n", host, port)
+		}
+	}
+	return ctx, allowed
+}
+
+// Start starts the SOCKS5 proxy on a random available port.
+func (p *SOCKSProxy) Start() (int, error) {
+	// Create listener first to get a random port
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		return 0, fmt.Errorf("failed to listen: %w", err)
+	}
+	p.listener = listener
+	p.port = listener.Addr().(*net.TCPAddr).Port
+
+	server := socks5.NewServer(
+		socks5.WithRule(&fenceRuleSet{
+			filter: p.filter,
+			debug:  p.debug,
+		}),
+	)
+	p.server = server
+
+	go func() {
+		if err := p.server.Serve(p.listener); err != nil {
+			if p.debug {
+				fmt.Printf("[fence:socks] Server error: %v\n", err)
+			}
+		}
+	}()
+
+	if p.debug {
+		fmt.Printf("[fence:socks] SOCKS5 proxy listening on localhost:%d\n", p.port)
+	}
+	return p.port, nil
+}
+
+// Stop stops the SOCKS5 proxy.
+func (p *SOCKSProxy) Stop() error {
+	if p.listener != nil {
+		return p.listener.Close()
+	}
+	return nil
+}
+
+// Port returns the port the proxy is listening on.
+func (p *SOCKSProxy) Port() int {
+	return p.port
+}