wip

internal/socks5/response.go

@@ -0,0 +1,103 @@
+package socks5
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/netip"
+)
+
+// See https://datatracker.ietf.org/doc/html/rfc1928#section-6
+func (c *socksConn) encodeFailedResponse(writer io.Writer, socksVersion byte, reply replyCode) {
+	_, err := writer.Write([]byte{
+		socksVersion,
+		byte(reply),
+		0, // RSV byte
+		// TODO do we need to set the bind addr type to 0??
+	})
+	if err != nil {
+		c.logger.Warnf("failed writing failed response: %s", err)
+	}
+}
+
+// See https://datatracker.ietf.org/doc/html/rfc1928#section-6
+func (c *socksConn) encodeSuccessResponse(writer io.Writer, socksVersion byte,
+	reply replyCode, bindAddrType addrType, bindAddress string,
+	bindPort uint16) (err error) {
+	bindData, err := encodeBindData(bindAddrType, bindAddress, bindPort)
+	if err != nil { // TODO encode with below block if this changes
+		return err
+	}
+
+	const initialPacketLength = 3
+	capacity := initialPacketLength + len(bindData)
+	packet := make([]byte, initialPacketLength, capacity)
+	packet[0] = socksVersion
+	packet[1] = byte(reply)
+	packet[2] = 0 // RSV byte
+	packet = append(packet, bindData...)
+
+	_, err = writer.Write(packet)
+	if err != nil {
+		c.logger.Warnf("failed writing success response: %s", err)
+	}
+	return nil
+}
+
+var (
+	ErrIPVersionUnexpected = errors.New("ip version is unexpected")
+	ErrDomainNameTooLong   = errors.New("domain name is too long")
+)
+
+func encodeBindData(addrType addrType, address string, port uint16) (
+	data []byte, err error) {
+	capacity := bindDataLength(addrType, address)
+	data = make([]byte, 0, capacity)
+
+	data = append(data, byte(addrType))
+	switch addrType {
+	case ipv4, ipv6:
+		ip, err := netip.ParseAddr(address)
+		if err != nil {
+			return nil, fmt.Errorf("parsing IP address: %w", err)
+		}
+
+		switch {
+		case addrType == ipv4 && !ip.Is4():
+			return nil, fmt.Errorf("%w: expected IPv4 for %s", ErrIPVersionUnexpected, ip)
+		case addrType == ipv6 && !ip.Is6():
+			return nil, fmt.Errorf("%w: expected IPv6 for %s", ErrIPVersionUnexpected, ip)
+		}
+		data = append(data, ip.AsSlice()...)
+	case domainName:
+		const maxDomainNameLength = 255
+		if len(address) > maxDomainNameLength {
+			return nil, fmt.Errorf("%w: %s", ErrDomainNameTooLong, address)
+		}
+		data = append(data, byte(len(address)))
+		data = append(data, []byte(address)...)
+	default:
+		panic(fmt.Sprintf("unsupported address type %d", addrType))
+	}
+	data = binary.BigEndian.AppendUint16(data, port)
+	return data, nil
+}
+
+func bindDataLength(addrType addrType, address string) (maxLength int) {
+	maxLength++ // address type
+	switch addrType {
+	case ipv4:
+		maxLength += net.IPv4len
+	case domainName:
+		maxLength++ // domain name length
+		maxLength += len([]byte(address))
+	case ipv6:
+		maxLength += net.IPv6len
+	default:
+		panic("unsupported address type: " + fmt.Sprint(addrType))
+	}
+	maxLength += 2 // port
+	return maxLength
+}