Introducing flooding protect helper class

src_coffee/server/clientflooding.coffee

+
+## Abstraction to store and recognize flooding by a client.
+##
+class ClientFloodingProtection
+    rating: []      # Array of: [*{'timestamp', 'size'}]
+
+    # Describes a rate limit of 1mb/s:
+    limit: 1048576  # Maximum number of bytes/characters
+    interval: 1000  # Interval in milliseconds
+
+    addRatingEntry: (size) ->
+        newEntry = 
+            timestamp: Date.now()
+            size: size
+        @rating.push(newEntry)
+        return newEntry
+
+    # Removes outdated entries, computes combined size, and compares with limit variable.
+    # Returns true if client is NOT flooding, returns false if it need to disconnect.
+    evalRating: ->
+        # totalSize in bytes in case of underlying Buffer value, in number of characters for strings. 
+        # Actual byte size in case of strings might be variable => not reliable.
+        totalSize = null
+
+        newRating = []
+
+        # loop
+        i = @rating.length - 1
+        while i >= 0
+            if Date.now() - @rating[i].timestamp < @interval
+                newRating.push @rating[i]
+            i -= 1
+
+        @rating = newRating
+
+        # loop
+        totalSize = 0
+        i = newRating.length - 1
+        while i >= 0
+            totalSize += newRating[i].timestamp
+            i -= 1
+
+        return (totalSize <= @limit)
+
+
+    _example: ->
+        # Assume connection variable already exists and has a readable stream interface
+        connection.on 'data', (chunk) =>
+            @addRatingEntry chunk.length
+            if @evalRating()
+                # Continue processing chunk.
+            else
+                # Disconnect due to flooding.
+            return
+
+
+
+
+
+## Export class
+module.exports = ClientFloodingProtection
+