mirror of https://github.com/vacp2p/nim-webrtc.git
153 lines
5.2 KiB
Nim
153 lines
5.2 KiB
Nim
# Nim-WebRTC
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# Copyright (c) 2023 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, strutils
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import chronos,
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chronicles,
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binary_serialization,
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stew/objects,
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stew/byteutils
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import stun_attributes
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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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msgHeaderSize = 20
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magicCookieSeq = @[ 0x21'u8, 0x12, 0xa4, 0x42 ]
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magicCookie = 0x2112a442
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BindingRequest = 0x0001'u16
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BindingResponse = 0x0101'u16
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proc decode(T: typedesc[RawStunAttribute], cnt: seq[byte]): seq[RawStunAttribute] =
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const pad = @[0, 3, 2, 1]
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var padding = 0
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while padding < cnt.len():
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let attr = Binary.decode(cnt[padding ..^ 1], RawStunAttribute)
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result.add(attr)
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padding += 4 + attr.value.len()
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padding += pad[padding mod 4]
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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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# it.conten.len() + 8 Because the Fingerprint is added after the encoding
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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]
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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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Stun* = object
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proc getAttribute(attrs: seq[RawStunAttribute], typ: uint16): Option[seq[byte]] =
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for attr in attrs:
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if attr.attributeType == typ:
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return some(attr.value)
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return none(seq[byte])
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proc isMessage*(T: typedesc[Stun], msg: seq[byte]): bool =
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msg.len >= msgHeaderSize and msg[4..<8] == magicCookieSeq and bitand(0xC0'u8, msg[0]) == 0'u8
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proc addLength(msgEncoded: var seq[byte], length: uint16) =
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let
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hi = (length div 256'u16).uint8
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lo = (length mod 256'u16).uint8
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msgEncoded[2] = msgEncoded[2] + hi
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if msgEncoded[3].int + lo.int >= 256:
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msgEncoded[2] = msgEncoded[2] + 1
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msgEncoded[3] = ((msgEncoded[3].int + lo.int) mod 256).uint8
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else:
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msgEncoded[3] = msgEncoded[3] + lo
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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*(msg: StunMessage, userOpt: Option[seq[byte]]): 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: magicCookie,
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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 userOpt.isSome():
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let username = string.fromBytes(userOpt.get())
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let usersplit = username.split(":")
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if usersplit.len() == 2 and usersplit[0].startsWith("libp2p+webrtc+v1/"):
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result.addLength(24)
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result.add(Binary.encode(MessageIntegrity.encode(result, toBytes(usersplit[0]))))
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result.addLength(8)
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result.add(Binary.encode(Fingerprint.encode(result)))
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proc getResponse*(T: typedesc[Stun], msg: seq[byte],
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ta: TransportAddress): Option[seq[byte]] =
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if ta.family != AddressFamily.IPv4 and ta.family != AddressFamily.IPv6:
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return none(seq[byte])
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let sm =
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try:
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StunMessage.decode(msg)
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except CatchableError as exc:
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return none(seq[byte])
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if sm.msgType != BindingRequest:
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return none(seq[byte])
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var res = StunMessage(msgType: BindingResponse,
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transactionId: sm.transactionId)
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var unknownAttr: seq[uint16]
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for attr in sm.attributes:
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let typ = attr.attributeType
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if typ.isRequired() and typ notin StunAttributeEnum:
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unknownAttr.add(typ)
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if unknownAttr.len() > 0:
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res.attributes.add(ErrorCode.encode(ECUnknownAttribute))
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res.attributes.add(UnknownAttribute.encode(unknownAttr))
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return some(res.encode(sm.attributes.getAttribute(AttrUsername.uint16)))
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res.attributes.add(XorMappedAddress.encode(ta, sm.transactionId))
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return some(res.encode(sm.attributes.getAttribute(AttrUsername.uint16)))
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proc new*(T: typedesc[Stun]): T =
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result = T()
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