Stun protocol encoding / decoding

2023-04-11 14:31:30 +02:00 · 2023-04-11 14:31:30 +02:00 · 2e26deb377
parent 09a664dbad
commit 2e26deb377
3 changed files with 104 additions and 1 deletions
--- a/tests/teststun.nim
+++ b/tests/teststun.nim
@ -0,0 +1,14 @@
+import ../webrtc/stun
+import ./asyncunit
+import binary_serialization
+
+suite "Stun suite":
+  test "Stun encoding/decoding with padding":
+    let msg = @[ 0x00'u8, 0x01, 0x00, 0xa4, 0x21, 0x12, 0xa4, 0x42, 0x75, 0x6a, 0x58, 0x46, 0x42, 0x58, 0x4e, 0x72, 0x6a, 0x50, 0x4d, 0x2b, 0x00, 0x06, 0x00, 0x63, 0x6c, 0x69, 0x62, 0x70, 0x32, 0x70, 0x2b, 0x77, 0x65, 0x62, 0x72, 0x74, 0x63, 0x2b, 0x76, 0x31, 0x2f, 0x62, 0x71, 0x36, 0x67, 0x69, 0x43, 0x75, 0x4a, 0x38, 0x6e, 0x78, 0x59, 0x46, 0x4a, 0x36, 0x43, 0x63, 0x67, 0x45, 0x59, 0x58, 0x58, 0x2f, 0x78, 0x51, 0x58, 0x56, 0x4c, 0x74, 0x39, 0x71, 0x7a, 0x3a, 0x6c, 0x69, 0x62, 0x70, 0x32, 0x70, 0x2b, 0x77, 0x65, 0x62, 0x72, 0x74, 0x63, 0x2b, 0x76, 0x31, 0x2f, 0x62, 0x71, 0x36, 0x67, 0x69, 0x43, 0x75, 0x4a, 0x38, 0x6e, 0x78, 0x59, 0x46, 0x4a, 0x36, 0x43, 0x63, 0x67, 0x45, 0x59, 0x58, 0x58, 0x2f, 0x78, 0x51, 0x58, 0x56, 0x4c, 0x74, 0x39, 0x71, 0x7a, 0x00, 0xc0, 0x57, 0x00, 0x04, 0x00, 0x00, 0x03, 0xe7, 0x80, 0x2a, 0x00, 0x08, 0x86, 0x63, 0xfd, 0x45, 0xa9, 0xe5, 0x4c, 0xdb, 0x00, 0x24, 0x00, 0x04, 0x6e, 0x00, 0x1e, 0xff, 0x00, 0x08, 0x00, 0x14, 0x16, 0xff, 0x70, 0x8d, 0x97, 0x0b, 0xd6, 0xa3, 0x5b, 0xac, 0x8f, 0x4c, 0x85, 0xe6, 0xa6, 0xac, 0xaa, 0x7a, 0x68, 0x27, 0x80, 0x28, 0x00, 0x04, 0x79, 0x5e, 0x03, 0xd8 ]
+    check msg == encode(StunMessage.decode(msg))
+
+  test "Error while encoding":
+    let msgLengthFailed = @[ 0x00'u8, 0x01, 0x00, 0xa4, 0x21, 0x12, 0xa4, 0x42, 0x75, 0x6a, 0x58, 0x46, 0x42, 0x58, 0x4e, 0x72, 0x6a, 0x50, 0x4d ]
+    expect AssertionDefect: discard StunMessage.decode(msgLengthFailed)
+    let msgAttrFailed = @[ 0x00'u8, 0x01, 0x00, 0x08, 0x21, 0x12, 0xa4, 0x42, 0x75, 0x6a, 0x58, 0x46, 0x42, 0x58, 0x4e, 0x72, 0x6a, 0x50, 0x4d, 0x2b, 0x28, 0x00, 0x05, 0x79, 0x5e, 0x03, 0xd8 ]
+    expect AssertionDefect: discard StunMessage.decode(msgAttrFailed)
--- a/webrtc.nimble
+++ b/webrtc.nimble
@ -7,4 +7,5 @@ license = "MIT"

 requires "nim >= 1.2.0",
         "chronicles >= 0.10.2",
-         "chronos >= 3.0.6"
+         "chronos >= 3.0.6",
+         "https://github.com/status-im/nim-binary-serialization.git"
--- a/webrtc/stun.nim
+++ b/webrtc/stun.nim
@ -0,0 +1,88 @@
+import bitops
+import chronos, chronicles
+import binary_serialization
+
+logScope:
+  topics = "webrtc stun"
+
+const
+  msgHeaderSize = 20
+  magicCookieSeq = @[ 0x21'u8, 0x12, 0xa4, 0x42 ]
+  magicCookie = 0x2112a442
+
+type
+# Stun Attribute
+# 0                   1                   2                   3
+# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+# |         Type                  |            Length             |
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+# |                         Value (variable)                ....
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+  StunAttribute* = object 
+    attributeType*: uint16
+    length* {.bin_value: it.value.len.}: uint16
+    value* {.bin_len: it.length.}: seq[byte]
+
+proc decode(T: typedesc[StunAttribute], cnt: seq[byte]): seq[StunAttribute] =
+  const val = @[0, 3, 2, 1]
+  var padding = 0
+  while padding < cnt.len():
+    let attr = Binary.decode(cnt[padding ..^ 1], StunAttribute)
+    result.add(attr)
+    padding += 4 + attr.value.len()
+    padding += val[padding mod 4]
+
+proc seqAttrLen(s: seq[StunAttribute]): uint16 =
+  for it in s:
+    result = it.length + 4
+
+type
+#  Stun Header
+#  0                   1                   2                   3
+#  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+# |0 0|     STUN Message Type     |         Message Length        |
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+# |                         Magic Cookie                          |
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+# |                                                               |
+# |                     Transaction ID (96 bits)                  |
+# |                                                               |
+# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+  StunMessageInner = object
+    msgType: uint16
+    length* {.bin_value: it.content.len().}: uint16
+    magicCookie: uint32
+    transactionId: array[12, byte]
+    content* {.bin_len: it.length.}: seq[byte]
+  
+  StunMessage* = object
+    msgType*: uint16
+    transactionId*: array[12, byte]
+    attributes*: seq[StunAttribute]
+
+  Stun* = object
+
+proc isMessage*(T: typedesc[Stun], msg: seq[byte]): bool =
+  msg.len >= msgHeaderSize and msg[4..<8] == magicCookie and bitand(0xC0'u8, msg[0]) == 0'u8
+
+proc decode*(T: typedesc[StunMessage], msg: seq[byte]): StunMessage =
+  let smi = Binary.decode(msg, StunMessageInner)
+  return T(msgType: smi.msgType,
+           transactionId: smi.transactionId,
+           attributes: StunAttribute.decode(smi.content))
+
+proc encode*(msg: StunMessage): seq[byte] =
+  const val = @[0, 3, 2, 1]
+  var smi = StunMessageInner(msgType: msg.msgType,
+                             magicCookie: magicCookie,
+                             transactionId: msg.transactionId)
+  for attr in msg.attributes:
+    smi.content.add(Binary.encode(attr))
+    smi.content.add(newSeq[byte](val[smi.content.len() mod 4]))
+
+  return Binary.encode(smi)
+
+proc new*(T: typedesc[Stun]): T =
+  result = T()