answer successfully roundtripped back from snowflake proxy through broker to client (#1)

proxy/broker.coffee

@@ -6,19 +6,25 @@ to get assigned to clients.
 ###
 
 STATUS_OK = 200
+STATUS_GONE = 410
 STATUS_GATEWAY_TIMEOUT = 504
 
+genSnowflakeID = ->
+  Math.random().toString(36).substring(2)
+
 # Represents a broker running remotely.
 class Broker
 
   clients: 0
+  id: null
 
   # When interacting with the Broker, snowflake must generate a unique session
   # ID so the Broker can keep track of which signalling channel it's speaking
   # to.
   constructor: (@url) ->
-    log 'Using Broker at ' + @url
-    clients = 0
+    @clients = 0
+    @id = genSnowflakeID()
+    log 'Contacting Broker at ' + @url + '\nSnowflake ID: ' + @id
 
   # Snowflake registers with the broker using an HTTP POST request, and expects
   # a response from the broker containing some client offer.
@@ -27,7 +33,8 @@ class Broker
     new Promise (fulfill, reject) =>
       xhr = new XMLHttpRequest()
       try
-        xhr.open 'POST', @url
+        xhr.open 'POST', @url + 'proxy'
+        xhr.setRequestHeader('X-Session-ID', @id)
       catch err
         ###
         An exception happens here when, for example, NoScript allows the domain
@@ -47,10 +54,29 @@ class Broker
           else
             log 'Broker ERROR: Unexpected ' + xhr.status +
                 ' - ' + xhr.statusText
-
-      xhr.send 'snowflake-testing'
-      log "Broker: polling for client offer..."
+      xhr.send @id
+      log @id + " - polling for client offer..."
 
   sendAnswer: (answer) ->
-    log 'Sending answer to broker.'
-    log answer
+    log @id + ' - Sending answer back to broker...\n'
+    log answer.sdp
+    xhr = new XMLHttpRequest()
+    try
+      xhr.open 'POST', @url + 'answer'
+      xhr.setRequestHeader('X-Session-ID', @id)
+    catch err
+      log 'Broker: exception while connecting: ' + err.message
+      return
+    xhr.onreadystatechange = ->
+      return if xhr.DONE != xhr.readyState
+      log xhr
+      switch xhr.status
+        when STATUS_OK
+          log 'Broker: Successfully replied with answer.'
+          log xhr.responseText
+        when STATUS_GONE
+          log 'Broker: No longer valid to reply with answer.'
+        else
+          log 'Broker ERROR: Unexpected ' + xhr.status +
+              ' - ' + xhr.statusText
+    xhr.send JSON.stringify(answer)