More progress.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3849 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/io/FrameReader.as

@@ -0,0 +1,65 @@
+package com.threerings.io {
+
+import flash.events.EventDispatcher;
+import flash.events.ProgressEvent;
+
+import flash.net.Socket;
+
+import flash.util.ByteArray;
+import flash.util.Endian;
+
+/**
+ * Reads socket data until a complete frame is available.
+ * This dispatches a FrameAvailableEvent.FRAME_AVAILABLE once a frame
+ * has been fully read off the socket and is ready for decoding.
+ */
+public class FrameReader extends EventDispatcher
+{
+    public function FrameReader (socket :Socket)
+    {
+        _socket = socket;
+        _socket.addEventListener(ProgressEvent.SOCKET_DATA, socketHasData);
+    }
+
+    /**
+     * Called when our socket has data that we can read.
+     */
+    protected function socketHasData (event :ProgressEvent) :void
+    {
+        if (_curData == null) {
+            if (_socket.bytesAvailable < HEADER_SIZE) {
+                // if there are less bytes available than a header, let's
+                // just leave them on the socket until we can read the length
+                // all at once
+                return;
+            }
+            _length = _socket.readInt();
+            _curData = new ByteArray();
+            _curData.endian = Endian.BIG_ENDIAN;
+        }
+
+        // read bytes: either as much as possible or up to the end of the frame
+        var toRead :int = Math.min(_length - _curData.length,
+            _socket.bytesAvailable);
+        _socket.readBytes(_curData, _curData.length, toRead);
+
+        if (_length === _curData.length) {
+            // we have now read a complete frame, let us dispatch the data
+            _curData.position = 0; // move the read pointer to the beginning
+            dispatchEvent(new FrameAvailableEvent(_curData));
+            _curData = null; // clear, so we know we need to first read length
+
+            // there's a good chance there's more on the socket, recurse
+            // now to read it
+            socketHasData(event);
+        }
+    }
+
+    protected var _socket :Socket;
+    protected var _curData :ByteArray;
+    protected var _length :int;
+
+    /** The number of bytes in the frame header (a 32-bit integer). */
+    protected const HEADER_SIZE :int = 4;
+}
+}