Preliminary support padding, log on panic.

This adds preliminary support for data padding by adding another layer
of encapsulation inside each AEAD frame containing a type and length.
For now, data is still sent unpadded, but the infrastructure for
supporting it is mostly there.

Additionally, use log.Panic[f]() instead of panic through out the code
so that some panics are logged.

1 files changed, 111 insertions, 0 deletions

diff --git a/packet.go b/packet.go
new file mode 100644
index 0000000..7a6b3fb
--- /dev/null
+++ b/packet.go
@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2014, 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 obfs4
+
+import (
+	"encoding/binary"
+	"fmt"
+	"log"
+
+	"github.com/yawning/obfs4/framing"
+)
+
+const (
+	packetOverhead         = 2 + 1
+	maxPacketPayloadLength = framing.MaximumFramePayloadLength - packetOverhead
+	maxPacketPaddingLength = maxPacketPayloadLength
+)
+
+const (
+	packetTypePayload = iota
+	packetTypePrngSeed
+)
+
+// InvalidPacketLengthError is the error returned when decodePacket detects a
+// invalid packet length/
+type InvalidPacketLengthError int
+
+func (e InvalidPacketLengthError) Error() string {
+	return fmt.Sprintf("packet: Invalid packet length: %d", int(e))
+}
+
+// InvalidPacketLengthError is the error returned when decodePacket rejects the
+// payload length.
+type InvalidPayloadLengthError int
+
+func (e InvalidPayloadLengthError) Error() string {
+	return fmt.Sprintf("packet: Invalid payload length: %d", int(e))
+}
+
+var zeroPadBytes [maxPacketPaddingLength]byte
+
+func makePacket(pkt []byte, pktType uint8, data []byte, padLen uint16) int {
+	pktLen := packetOverhead + len(data) + int(padLen)
+
+	if len(data)+int(padLen) > maxPacketPayloadLength {
+		log.Panicf("BUG: makePacket() len(data) + padLen > maxPacketPayloadLength: %d + %d > %d",
+			len(data), padLen, maxPacketPayloadLength)
+	}
+
+	// Packets are:
+	//   uint8_t type      packetTypePayload (0x00)
+	//   uint16_t length   Length of the payload (Big Endian).
+	//   uint8_t[] payload Data payload.
+	//   uint8_t[] padding Padding.
+
+	pkt[0] = pktType
+	binary.BigEndian.PutUint16(pkt[1:], uint16(len(data)))
+	copy(pkt[3:], data[:])
+	copy(pkt[3+len(data):], zeroPadBytes[:padLen])
+
+	return pktLen
+}
+
+func (c *Obfs4Conn) decodePacket(pkt []byte) error {
+	if len(pkt) < packetOverhead {
+		return InvalidPacketLengthError(len(pkt))
+	}
+
+	pktType := pkt[0]
+	payloadLen := binary.BigEndian.Uint16(pkt[1:])
+	if int(payloadLen) > len(pkt)-packetOverhead {
+		return InvalidPayloadLengthError(int(payloadLen))
+	}
+
+	payload := pkt[3 : 3+payloadLen]
+	switch pktType {
+	case packetTypePayload:
+		// packetTypePayload
+		c.receiveDecodedBuffer.Write(payload)
+	default:
+		// Ignore unrecognised packet types.
+		log.Printf("[INFO] - Ignoring packet type: %d", pktType)
+	}
+
+	return nil
+}