packet.py

import functools
import json as _json

import six

(CONNECT, DISCONNECT, EVENT, ACK, ERROR, BINARY_EVENT, BINARY_ACK) = \
    (0, 1, 2, 3, 4, 5, 6)
packet_names = ['CONNECT', 'DISCONNECT', 'EVENT', 'ACK', 'ERROR',
                'BINARY_EVENT', 'BINARY_ACK']


class Packet(object):
    """Socket.IO packet."""

    # the format of the Socket.IO packet is as follows:
    #
    # packet type: 1 byte, values 0-6
    # num_attachments: ASCII encoded, only if num_attachments != 0
    # '-': only if num_attachments != 0
    # namespace: only if namespace != '/'
    # ',': only if namespace and one of id and data are defined in this packet
    # id: ASCII encoded, only if id is not None
    # data: JSON dump of data payload

    json = _json

    def __init__(self, packet_type=EVENT, data=None, namespace=None, id=None,
                 binary=None, encoded_packet=None):
        self.packet_type = packet_type
        self.data = data
        self.namespace = namespace
        self.id = id
        if binary or (binary is None and self._data_is_binary(self.data)):
            if self.packet_type == EVENT:
                self.packet_type = BINARY_EVENT
            elif self.packet_type == ACK:
                self.packet_type = BINARY_ACK
            else:
                raise ValueError('Packet does not support binary payload.')
        self.attachment_count = 0
        self.attachments = []
        if encoded_packet:
            self.attachment_count = self.decode(encoded_packet)

    def encode(self):
        """Encode the packet for transmission.

        If the packet contains binary elements, this function returns a list
        of packets where the first is the original packet with placeholders for
        the binary components and the remaining ones the binary attachments.
        """
        encoded_packet = six.text_type(self.packet_type)
        if self.packet_type == BINARY_EVENT or self.packet_type == BINARY_ACK:
            data, attachments = self._deconstruct_binary(self.data)
            encoded_packet += six.text_type(len(attachments)) + '-'
        else:
            data = self.data
            attachments = None
        needs_comma = False
        if self.namespace is not None and self.namespace != '/':
            encoded_packet += self.namespace
            needs_comma = True
        if self.id is not None:
            if needs_comma:
                encoded_packet += ','
                needs_comma = False
            encoded_packet += six.text_type(self.id)
        if data is not None:
            if needs_comma:
                encoded_packet += ','
            encoded_packet += self.json.dumps(data, separators=(',', ':'))
        if attachments is not None:
            encoded_packet = [encoded_packet] + attachments
        return encoded_packet

    def decode(self, encoded_packet):
        """Decode a transmitted package.

        The return value indicates how many binary attachment packets are
        necessary to fully decode the packet.
        """
        ep = encoded_packet
        try:
            self.packet_type = int(ep[0:1])
        except TypeError:
            self.packet_type = ep
            ep = ''
        self.namespace = None
        self.data = None
        ep = ep[1:]
        dash = ep.find('-')
        attachment_count = 0
        if dash > 0 and ep[0:dash].isdigit():
            attachment_count = int(ep[0:dash])
            ep = ep[dash + 1:]
        if ep and ep[0:1] == '/':
            sep = ep.find(',')
            if sep == -1:
                self.namespace = ep
                ep = ''
            else:
                self.namespace = ep[0:sep]
                ep = ep[sep + 1:]
            q = self.namespace.find('?')
            if q != -1:
                self.namespace = self.namespace[0:q]
        if ep and ep[0].isdigit():
            self.id = 0
            while ep and ep[0].isdigit():
                self.id = self.id * 10 + int(ep[0])
                ep = ep[1:]
        if ep:
            self.data = self.json.loads(ep)
        return attachment_count

    def add_attachment(self, attachment):
        if self.attachment_count <= len(self.attachments):
            raise ValueError('Unexpected binary attachment')
        self.attachments.append(attachment)
        if self.attachment_count == len(self.attachments):
            self.reconstruct_binary(self.attachments)
            return True
        return False

    def reconstruct_binary(self, attachments):
        """Reconstruct a decoded packet using the given list of binary
        attachments.
        """
        self.data = self._reconstruct_binary_internal(self.data,
                                                      self.attachments)

    def _reconstruct_binary_internal(self, data, attachments):
        if isinstance(data, list):
            return [self._reconstruct_binary_internal(item, attachments)
                    for item in data]
        elif isinstance(data, dict):
            if data.get('_placeholder') and 'num' in data:
                return attachments[data['num']]
            else:
                return {key: self._reconstruct_binary_internal(value,
                                                               attachments)
                        for key, value in six.iteritems(data)}
        else:
            return data

    def _deconstruct_binary(self, data):
        """Extract binary components in the packet."""
        attachments = []
        data = self._deconstruct_binary_internal(data, attachments)
        return data, attachments

    def _deconstruct_binary_internal(self, data, attachments):
        if isinstance(data, six.binary_type):
            attachments.append(data)
            return {'_placeholder': True, 'num': len(attachments) - 1}
        elif isinstance(data, list):
            return [self._deconstruct_binary_internal(item, attachments)
                    for item in data]
        elif isinstance(data, dict):
            return {key: self._deconstruct_binary_internal(value, attachments)
                    for key, value in six.iteritems(data)}
        else:
            return data

    def _data_is_binary(self, data):
        """Check if the data contains binary components."""
        if isinstance(data, six.binary_type):
            return True
        elif isinstance(data, list):
            return functools.reduce(
                lambda a, b: a or b, [self._data_is_binary(item)
                                      for item in data], False)
        elif isinstance(data, dict):
            return functools.reduce(
                lambda a, b: a or b, [self._data_is_binary(item)
                                      for item in six.itervalues(data)],
                False)
        else:
            return False