streaming parser base class

will be used for BGP-4.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

ryu/lib/packet/stream_parser.py

@@ -0,0 +1,77 @@
+# Copyright (C) 2013 Nippon Telegraph and Telephone Corporation.
+# Copyright (C) 2013 YAMAMOTO Takashi <yamamoto at valinux co jp>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from abc import ABCMeta, abstractmethod
+
+
+class StreamParser(object):
+    """Streaming parser base class.
+
+    An instance of a subclass of this class is used to extract messages
+    from a raw byte stream.
+
+    It's designed to be used for data read from a transport which doesn't
+    preserve message boundaries.  A typical example of such a transport
+    is TCP.
+
+    """
+
+    __metaclass__ = ABCMeta
+
+    class TooSmallException(Exception):
+        pass
+
+    def __init__(self):
+        self._q = bytearray()
+
+    def parse(self, data):
+        """Tries to extract messages from a raw byte stream.
+
+        The data argument would be python bytes newly read from the input
+        stream.
+
+        Returns an ordered list of extracted messages.
+        It can be an empty list.
+
+        The rest of data which doesn't produce a complete message is
+        kept internally and will be used when more data is come.
+        I.e. next time this method is called again.
+        """
+        self._q.append(data)
+        msgs = []
+        while True:
+            try:
+                msg, self._q = self.try_parse(self._q)
+            except self.TooSmallException:
+                break
+            msgs.append(msg)
+        return msgs
+
+    @abstractmethod
+    def try_parse(self, q):
+        """Try to extract a message from the given bytes.
+
+        This is an override point for subclasses.
+
+        This method tries to extract a message from bytes given by the
+        argument.
+
+        Raises TooSmallException if the given data is not enough to
+        extract a complete message but there's still a chance to extract
+        a message if more data is come later.
+        """
+        pass