mirror of
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake.git
synced 2025-10-13 20:11:19 -04:00
137 lines
4.1 KiB
CoffeeScript
137 lines
4.1 KiB
CoffeeScript
###
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A Coffeescript WebRTC snowflake proxy
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Uses WebRTC from the client, and Websocket to the server.
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Assume that the webrtc client plugin is always the offerer, in which case
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this proxy must always act as the answerer.
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TODO: More documentation
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###
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# Minimum viable snowflake for now - just 1 client.
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class Snowflake
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relayAddr: null
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proxyPairs: []
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rateLimit: null
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state: MODE.INIT
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retries: 0
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# Prepare the Snowflake with a Broker (to find clients) and optional UI.
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constructor: (@broker, @ui) ->
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rateLimitBytes = undefined
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if 'off' != query['ratelimit']
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rateLimitBytes = Params.getByteCount(query, 'ratelimit',
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DEFAULT_RATE_LIMIT)
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if undefined == rateLimitBytes
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@rateLimit = new DummyRateLimit()
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else
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@rateLimit = new BucketRateLimit(rateLimitBytes * RATE_LIMIT_HISTORY,
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RATE_LIMIT_HISTORY)
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@retries = 0
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# Set the target relay address spec, which is expected to be websocket.
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# TODO: Should potentially fetch the target from broker later, or modify
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# entirely for the Tor-independent version.
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setRelayAddr: (relayAddr) ->
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@relayAddr = relayAddr
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log 'Using ' + relayAddr.host + ':' + relayAddr.port + ' as Relay.'
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return true
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# Initialize WebRTC PeerConnection, which requires beginning the signalling
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# process. |pollBroker| automatically arranges signalling.
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beginWebRTC: ->
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@state = MODE.WEBRTC_CONNECTING
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for i in [1..CONNECTIONS_PER_CLIENT]
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@makeProxyPair @relayAddr
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log 'ProxyPair Slots: ' + @proxyPairs.length
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log 'Snowflake IDs: ' + (@proxyPairs.map (p) -> p.id).join ' | '
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@pollBroker()
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# Regularly poll Broker for clients to serve until this snowflake is
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# serving at capacity, at which point stop polling.
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pollBroker: ->
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# Temporary countdown. TODO: Simplify
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countdown = (msg, sec, skip) =>
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if not skip then dbg msg
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if sec > 0
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@ui?.setStatus msg + ' (Polling in ' + sec + ' seconds...)'
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sec--
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setTimeout((-> countdown(msg, sec, true)), 1000)
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else
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@ui?.setStatus msg
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findClients()
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# Poll broker for clients.
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findClients = =>
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pair = @nextAvailableProxyPair()
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if !pair
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log 'At client capacity.'
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# Do nothing until a new proxyPair is available.
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return
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msg = 'Polling for client ... '
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msg += '[retries: ' + @retries + ']' if @retries > 0
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@ui?.setStatus msg
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recv = @broker.getClientOffer pair.id
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recv.then (desc) =>
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@receiveOffer pair, desc
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countdown('Serving 1 new client.', DEFAULT_BROKER_POLL_INTERVAL / 1000)
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, (err) ->
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countdown(err, DEFAULT_BROKER_POLL_INTERVAL / 1000)
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@retries++
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findClients()
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# Returns the first ProxyPair that's available to connect.
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nextAvailableProxyPair: ->
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return @proxyPairs.find (pp, i, arr) -> return !pp.active
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# Receive an SDP offer from some client assigned by the Broker,
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# |pair| - an available ProxyPair.
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receiveOffer: (pair, desc) =>
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console.assert !pair.active
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try
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offer = JSON.parse desc
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dbg 'Received:\n\n' + offer.sdp + '\n'
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sdp = new SessionDescription offer
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@sendAnswer pair if pair.receiveWebRTCOffer sdp
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catch e
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log 'ERROR: Unable to receive Offer: ' + e
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sendAnswer: (pair) ->
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next = (sdp) ->
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dbg 'webrtc: Answer ready.'
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pair.pc.setLocalDescription sdp
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fail = ->
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dbg 'webrtc: Failed to create Answer'
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pair.pc.createAnswer()
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.then next
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.catch fail
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makeProxyPair: (relay) ->
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pair = new ProxyPair relay, @rateLimit
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@proxyPairs.push pair
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pair.onCleanup = (event) =>
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# Delete from the list of active proxy pairs.
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@proxyPairs.splice(@proxyPairs.indexOf(pair), 1)
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@pollBroker()
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pair.begin()
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# Stop all proxypairs.
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cease: ->
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while @proxyPairs.length > 0
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@proxyPairs.pop().close()
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disable: ->
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log 'Disabling Snowflake.'
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@cease()
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die: ->
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log 'Snowflake died.'
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@cease()
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# Close all existing ProxyPairs and begin finding new clients from scratch.
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reset: ->
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@cease()
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log 'Snowflake resetting...'
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@retries = 0
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@beginWebRTC()
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