Use a built in SOCKS 5 server instead of goptlibs.

Differences from my goptlib branch:
 * Instead of exposing a net.Listener, just expose a Handshake() routine
   that takes an existing net.Conn. (#14135 is irrelevant to this socks
   server.
 * There's an extra routine for sending back sensible errors on Dial
   failure instead of "General failure".
 * The code is slightly cleaner (IMO).

Gotchas:
 * If the goptlib pt.Args datatype or external interface changes,
   args.go will need to be updated.

Tested with obfs3 and obfs4, including IPv6.

1 files changed, 105 insertions, 0 deletions

diff --git a/common/socks5/rfc1929.go b/common/socks5/rfc1929.go
new file mode 100644
index 0000000..f8176f1
--- /dev/null
+++ b/common/socks5/rfc1929.go
@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ *  * Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package socks5
+
+import "fmt"
+
+const (
+	authRFC1929Ver     = 0x01
+	authRFC1929Success = 0x00
+	authRFC1929Fail    = 0x01
+)
+
+func (req *Request) authRFC1929() (err error) {
+	sendErrResp := func() {
+		// Swallow write/flush errors, the auth failure is the relevant error.
+		resp := []byte{authRFC1929Ver, authRFC1929Fail}
+		req.rw.Write(resp[:])
+		req.flushBuffers()
+	}
+
+	// The client sends a Username/Password request.
+	//  uint8_t ver (0x01)
+	//  uint8_t ulen (>= 1)
+	//  uint8_t uname[ulen]
+	//  uint8_t plen (>= 1)
+	//  uint8_t passwd[plen]
+
+	if err = req.readByteVerify("auth version", authRFC1929Ver); err != nil {
+		sendErrResp()
+		return
+	}
+
+	// Read the username.
+	var ulen byte
+	if ulen, err = req.readByte(); err != nil {
+		sendErrResp()
+		return
+	} else if ulen < 1 {
+		sendErrResp()
+		return fmt.Errorf("username with 0 length")
+	}
+	var uname []byte
+	if uname, err = req.readBytes(int(ulen)); err != nil {
+		sendErrResp()
+		return
+	}
+
+	// Read the password.
+	var plen byte
+	if plen, err = req.readByte(); err != nil {
+		sendErrResp()
+		return
+	} else if plen < 1 {
+		sendErrResp()
+		return fmt.Errorf("password with 0 length")
+	}
+	var passwd []byte
+	if passwd, err = req.readBytes(int(plen)); err != nil {
+		sendErrResp()
+		return
+	}
+
+	// Pluggable transports use the username/password field to pass
+	// per-connection arguments.  The fields contain ASCII strings that
+	// are combined and then parsed into key/value pairs.
+	argStr := string(uname)
+	if !(plen == 1 && passwd[0] == 0x00) {
+		// tor will set the password to 'NUL', if the field doesn't contain any
+		// actual argument data.
+		argStr += string(passwd)
+	}
+	if req.Args, err = parseClientParameters(argStr); err != nil {
+		sendErrResp()
+		return
+	}
+
+	resp := []byte{authRFC1929Ver, authRFC1929Success}
+	_, err = req.rw.Write(resp[:])
+	return
+}