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from __future__ import absolute_import
import base64
import hashlib
import os
import struct
import io

from . import utils, odict, tcp

# Colleciton of utility functions that implement small portions of the RFC6455
# WebSockets Protocol Useful for building WebSocket clients and servers.
#
# Emphassis is on readabilty, simplicity and modularity, not performance or
# completeness
#
# This is a work in progress and does not yet contain all the utilites need to
# create fully complient client/servers #
# Spec: https://tools.ietf.org/html/rfc6455

# The magic sha that websocket servers must know to prove they understand
# RFC6455
websockets_magic = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
VERSION = "13"
MAX_16_BIT_INT = (1 << 16)
MAX_64_BIT_INT = (1 << 64)


OPCODE = utils.BiDi(
    CONTINUE=0x00,
    TEXT=0x01,
    BINARY=0x02,
    CLOSE=0x08,
    PING=0x09,
    PONG=0x0a
)


class Masker:

    """
        Data sent from the server must be masked to prevent malicious clients
        from sending data over the wire in predictable patterns

        Servers do not have to mask data they send to the client.
        https://tools.ietf.org/html/rfc6455#section-5.3
    """

    def __init__(self, key):
        self.key = key
        self.masks = [utils.bytes_to_int(byte) for byte in key]
        self.offset = 0

    def mask(self, offset, data):
        result = ""
        for c in data:
            result += chr(ord(c) ^ self.masks[offset % 4])
            offset += 1
        return result

    def __call__(self, data):
        ret = self.mask(self.offset, data)
        self.offset += len(ret)
        return ret


def client_handshake_headers(key=None, version=VERSION):
    """
        Create the headers for a valid HTTP upgrade request. If Key is not
        specified, it is generated, and can be found in sec-websocket-key in
        the returned header set.

        Returns an instance of ODictCaseless
    """
    if not key:
        key = base64.b64encode(os.urandom(16)).decode('utf-8')
    return odict.ODictCaseless([
        ('Connection', 'Upgrade'),
        ('Upgrade', 'websocket'),
        ('Sec-WebSocket-Key', key),
        ('Sec-WebSocket-Version', version)
    ])


def server_handshake_headers(key):
    """
      The server response is a valid HTTP 101 response.
    """
    return odict.ODictCaseless(
        [
            ('Connection', 'Upgrade'),
            ('Upgrade', 'websocket'),
            ('Sec-WebSocket-Accept', create_server_nonce(key))
        ]
    )


def make_length_code(len):
    """
     A websockets frame contains an initial length_code, and an optional
     extended length code to represent the actual length if length code is
     larger than 125
    """
    if len <= 125:
        return len
    elif len >= 126 and len <= 65535:
        return 126
    else:
        return 127


def check_client_handshake(headers):
    if headers.get_first("upgrade", None) != "websocket":
        return
    return headers.get_first('sec-websocket-key')


def check_server_handshake(headers):
    if headers.get_first("upgrade", None) != "websocket":
        return
    return headers.get_first('sec-websocket-accept')


def create_server_nonce(client_nonce):
    return base64.b64encode(
        hashlib.sha1(client_nonce + websockets_magic).hexdigest().decode('hex')
    )


DEFAULT = object()


class FrameHeader:

    def __init__(
        self,
        opcode=OPCODE.TEXT,
        payload_length=0,
        fin=False,
        rsv1=False,
        rsv2=False,
        rsv3=False,
        masking_key=DEFAULT,
        mask=DEFAULT,
        length_code=DEFAULT
    ):
        if not 0 <= opcode < 2 ** 4:
            raise ValueError("opcode must be 0-16")
        self.opcode = opcode
        self.payload_length = payload_length
        self.fin = fin
        self.rsv1 = rsv1
        self.rsv2 = rsv2
        self.rsv3 = rsv3

        if length_code is DEFAULT:
            self.length_code = make_length_code(self.payload_length)
        else:
            self.length_code = length_code

        if mask is DEFAULT and masking_key is DEFAULT:
            self.mask = False
            self.masking_key = ""
        elif mask is DEFAULT:
            self.mask = 1
            self.masking_key = masking_key
        elif masking_key is DEFAULT:
            self.mask = mask
            self.masking_key = os.urandom(4)
        else:
            self.mask = mask
            self.masking_key = masking_key

        if self.masking_key and len(self.masking_key) != 4:
            raise ValueError("Masking key must be 4 bytes.")

    def human_readable(self):
        vals = [
            "wf:",
            OPCODE.get_name(self.opcode, hex(self.opcode)).lower()