wip

internal/socks5/usernamepassword.go

@@ -0,0 +1,69 @@
+package socks5
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+var (
+	ErrSubnegotiationVersionNotSupported = errors.New("subnegotiation version not supported")
+	ErrUsernameNotValid                  = errors.New("username not valid")
+	ErrPasswordNotValid                  = errors.New("password not valid")
+)
+
+// See https://datatracker.ietf.org/doc/html/rfc1929#section-2
+func usernamePasswordSubnegotiate(conn io.ReadWriter, username, password string) (err error) {
+	status := byte(1)
+	const defaultVersion = byte(1)
+
+	const headerLength = 2
+	var header [headerLength]byte
+	_, err = io.ReadFull(conn, header[:])
+	if err != nil {
+		_, _ = conn.Write([]byte{defaultVersion, status})
+		return fmt.Errorf("reading header: %w", err)
+	}
+
+	if header[0] != authUsernamePasswordSubNegotiation1 {
+		_, _ = conn.Write([]byte{defaultVersion, status})
+		return fmt.Errorf("%w: %d", ErrSubnegotiationVersionNotSupported, header[0])
+	}
+	version := header[0]
+
+	usernameBytes := make([]byte, header[1])
+	_, err = io.ReadFull(conn, usernameBytes)
+	if err != nil {
+		_, _ = conn.Write([]byte{version, status})
+		return fmt.Errorf("reading username bytes: %w", err)
+	} else if username != string(usernameBytes) {
+		_, _ = conn.Write([]byte{version, status})
+		return fmt.Errorf("%w: %s", ErrUsernameNotValid, string(usernameBytes))
+	}
+
+	const passwordHeaderLength = 1
+	passwordHeader := make([]byte, passwordHeaderLength)
+	_, err = io.ReadFull(conn, passwordHeader[:])
+	if err != nil {
+		_, _ = conn.Write([]byte{version, status})
+		return fmt.Errorf("reading password length: %w", err)
+	}
+
+	passwordBytes := make([]byte, passwordHeader[0])
+	_, err = io.ReadFull(conn, passwordBytes)
+	if err != nil {
+		_, _ = conn.Write([]byte{version, status})
+		return fmt.Errorf("reading password bytes: %w", err)
+	} else if password != string(passwordBytes) {
+		_, _ = conn.Write([]byte{version, status})
+		return fmt.Errorf("%w: %s", ErrPasswordNotValid, string(passwordBytes))
+	}
+
+	status = 0
+	_, err = conn.Write([]byte{version, status})
+	if err != nil {
+		return fmt.Errorf("writing success status: %w", err)
+	}
+
+	return nil
+}