mirror of https://github.com/vacp2p/nim-webrtc.git
110 lines
3.8 KiB
Nim
110 lines
3.8 KiB
Nim
# Nim-WebRTC
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# Copyright (c) 2024 Status Research & Development GmbH
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# Licensed under either of
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# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
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# * MIT license ([LICENSE-MIT](LICENSE-MIT))
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# at your option.
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# This file may not be copied, modified, or distributed except according to
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# those terms.
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import bitops
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import chronos,
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bearssl,
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chronicles,
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binary_serialization
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import stun_attributes, ../errors
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export binary_serialization
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logScope:
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topics = "webrtc stun"
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const
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StunMsgHeaderSize = 20
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StunMagicCookieSeq = @[ 0x21'u8, 0x12, 0xa4, 0x42 ]
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StunMagicCookie = 0x2112a442
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proc isStunMessage*(msg: seq[byte]): bool =
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msg.len >= StunMsgHeaderSize and
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msg[4..<8] == StunMagicCookieSeq and
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bitand(0xC0'u8, msg[0]) == 0'u8
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type
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# Stun Header
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# 0 1 2 3
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# 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
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# |0 0| STUN Message Type | Message Length |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | Magic Cookie |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | |
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# | Transaction ID (96 bits) |
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# | |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# Message type:
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# 0x0001: Binding Request
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# 0x0101: Binding Response
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# 0x0111: Binding Error Response
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# 0x0002: Shared Secret Request
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# 0x0102: Shared Secret Response
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# 0x0112: Shared Secret Error Response
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RawStunMessage = object
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msgType: uint16
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length* {.bin_value: it.content.len().}: uint16
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magicCookie: uint32
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transactionId: array[12, byte] # Down from 16 to 12 bytes in RFC5389
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content* {.bin_len: it.length.}: seq[byte]
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StunMessage* = object
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msgType*: uint16
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transactionId*: array[12, byte]
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attributes*: seq[RawStunAttribute]
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proc getAttribute*[T](self: StunMessage, typ: typedesc[T]): Option[T] =
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let attributeTyp = attributeType(typ)
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for attr in self.attributes:
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if attr.attributeType == attributeTyp.uint16:
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return some(T.decode(attr))
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return none(T)
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proc addLength(msgEncoded: var seq[byte], toAddLength: uint16) =
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# Add length to an already encoded message. It is necessary because
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# some attributes (such as Message Integrity or Fingerprint) need
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# the encoded message to be computed.
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let
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currentLength: uint16 = msgEncoded[2].uint16 * 256'u16 + msgEncoded[3].uint16
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totalLength = currentLength + toAddLength
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if totalLength < currentLength:
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raise newException(WebRtcError, "Stun - Try to encode a message larger than uint16 max")
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msgEncoded[2] = (totalLength div 256'u16).uint8
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msgEncoded[3] = (totalLength mod 256'u16).uint8
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proc decode*(T: typedesc[StunMessage], msg: seq[byte]): StunMessage =
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let smi = Binary.decode(msg, RawStunMessage)
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return T(msgType: smi.msgType,
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transactionId: smi.transactionId,
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attributes: RawStunAttribute.decode(smi.content))
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proc encode*(
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msg: StunMessage,
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messageIntegrityPassword: seq[byte]
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): seq[byte] =
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const pad = @[0, 3, 2, 1]
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var smi = RawStunMessage(msgType: msg.msgType,
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magicCookie: StunMagicCookie,
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transactionId: msg.transactionId)
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for attr in msg.attributes:
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smi.content.add(Binary.encode(attr))
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smi.content.add(newSeq[byte](pad[smi.content.len() mod 4]))
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result = Binary.encode(smi)
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if messageIntegrityPassword != @[]:
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result.addLength(24)
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result.add(Binary.encode(MessageIntegrity.encode(result, messageIntegrityPassword)))
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result.addLength(8)
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result.add(Binary.encode(Fingerprint.encode(result)))
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