Initial import: n2usenet HTTPS/Nym Usenet gateway

1 files changed, 131 insertions, 0 deletions

diff --git a/internal/socks5/dialer.go b/internal/socks5/dialer.go
new file mode 100644
index 0000000..8f74840
--- /dev/null
+++ b/internal/socks5/dialer.go
@@ -0,0 +1,131 @@
+package socks5
+
+import (
+	"context"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"net"
+	"strconv"
+	"time"
+)
+
+type Dialer struct {
+	ProxyAddr string
+	Timeout   time.Duration
+}
+
+func (d Dialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
+	if network != "tcp" {
+		return nil, fmt.Errorf("socks5 only supports tcp, got %s", network)
+	}
+	host, portText, err := net.SplitHostPort(address)
+	if err != nil {
+		return nil, fmt.Errorf("split target address: %w", err)
+	}
+	port, err := strconv.Atoi(portText)
+	if err != nil || port < 1 || port > 65535 {
+		return nil, fmt.Errorf("invalid target port")
+	}
+	if len(host) == 0 || len(host) > 255 {
+		return nil, fmt.Errorf("invalid target host length")
+	}
+	timeout := d.Timeout
+	if timeout <= 0 {
+		timeout = 90 * time.Second
+	}
+	conn, err := (&net.Dialer{Timeout: timeout}).DialContext(ctx, "tcp", d.ProxyAddr)
+	if err != nil {
+		return nil, fmt.Errorf("connect socks proxy: %w", err)
+	}
+	if deadline, ok := ctx.Deadline(); ok {
+		_ = conn.SetDeadline(deadline)
+	} else {
+		_ = conn.SetDeadline(time.Now().Add(timeout))
+	}
+	if err := handshake(conn, host, uint16(port)); err != nil {
+		_ = conn.Close()
+		return nil, err
+	}
+	_ = conn.SetDeadline(time.Time{})
+	return conn, nil
+}
+
+func handshake(conn net.Conn, host string, port uint16) error {
+	if _, err := conn.Write([]byte{0x05, 0x01, 0x00}); err != nil {
+		return fmt.Errorf("write socks greeting: %w", err)
+	}
+	var greeting [2]byte
+	if _, err := io.ReadFull(conn, greeting[:]); err != nil {
+		return fmt.Errorf("read socks greeting: %w", err)
+	}
+	if greeting[0] != 0x05 || greeting[1] != 0x00 {
+		return fmt.Errorf("socks proxy rejected no-auth method")
+	}
+
+	req := make([]byte, 0, 7+len(host))
+	req = append(req, 0x05, 0x01, 0x00, 0x03, byte(len(host)))
+	req = append(req, []byte(host)...)
+	var p [2]byte
+	binary.BigEndian.PutUint16(p[:], port)
+	req = append(req, p[:]...)
+	if _, err := conn.Write(req); err != nil {
+		return fmt.Errorf("write socks connect: %w", err)
+	}
+
+	var head [4]byte
+	if _, err := io.ReadFull(conn, head[:]); err != nil {
+		return fmt.Errorf("read socks response: %w", err)
+	}
+	if head[0] != 0x05 {
+		return fmt.Errorf("invalid socks response version")
+	}
+	if head[1] != 0x00 {
+		return fmt.Errorf("socks connect failed: %s", replyText(head[1]))
+	}
+	var skip int
+	switch head[3] {
+	case 0x01:
+		skip = 4 + 2
+	case 0x03:
+		var l [1]byte
+		if _, err := io.ReadFull(conn, l[:]); err != nil {
+			return fmt.Errorf("read socks bind host length: %w", err)
+		}
+		skip = int(l[0]) + 2
+	case 0x04:
+		skip = 16 + 2
+	default:
+		return fmt.Errorf("unsupported socks bind address type")
+	}
+	if skip > 0 {
+		buf := make([]byte, skip)
+		if _, err := io.ReadFull(conn, buf); err != nil {
+			return fmt.Errorf("read socks bind address: %w", err)
+		}
+	}
+	return nil
+}
+
+func replyText(code byte) string {
+	switch code {
+	case 0x01:
+		return "general failure"
+	case 0x02:
+		return "connection not allowed"
+	case 0x03:
+		return "network unreachable"
+	case 0x04:
+		return "host unreachable"
+	case 0x05:
+		return "connection refused"
+	case 0x06:
+		return "ttl expired"
+	case 0x07:
+		return "command not supported"
+	case 0x08:
+		return "address type not supported"
+	default:
+		return fmt.Sprintf("unknown code %d", code)
+	}
+}