问题

尝试为支持Python3的应用程序创建一个网络前端.该应用程序将需要双向流,听起来像是一个很好的机会来查看websockets.

我的第一个想法是使用已经存在的东西,来自 mod-pywebsocket 的示例应用程序已被证明是有价值的.不幸的是,他们的API似乎不容易适用于扩展,它是Python2.

围绕博客圈,许多人已经为早期版本的websocket协议编写了​​自己的websocket服务器,大多数不实现安全密钥哈希,所以不工作.

阅读 RFC 6455 我决定自己尝试一下,并提出以下建议:

#!/usr/bin/env python3

"""
A partial implementation of RFC 6455
http://tools.ietf.org/pdf/rfc6455.pdf
Brian Thorne 2012
"""

import socket
import threading
import time
import base64
import hashlib

def calculate_websocket_hash(key):
    magic_websocket_string = b"258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
    result_string = key + magic_websocket_string
    sha1_digest = hashlib.sha1(result_string).digest()
    response_data = base64.encodestring(sha1_digest)
    response_string = response_data.decode('utf8')
    return response_string

def is_bit_set(int_type, offset):
    mask = 1 << offset
    return not 0 == (int_type & mask)

def set_bit(int_type, offset):
    return int_type | (1 << offset)

def bytes_to_int(data):
    # note big-endian is the standard network byte order
    return int.from_bytes(data, byteorder='big')


def pack(data):
    """pack bytes for sending to client"""
    frame_head = bytearray(2)

    # set final fragment
    frame_head[0] = set_bit(frame_head[0], 7)

    # set opcode 1 = text
    frame_head[0] = set_bit(frame_head[0], 0)

    # payload length
    assert len(data) < 126, "haven't implemented that yet"
    frame_head[1] = len(data)

    # add data
    frame = frame_head + data.encode('utf-8')
    print(list(hex(b) for b in frame))
    return frame

def receive(s):
    """receive data from client"""

    # read the first two bytes
    frame_head = s.recv(2)

    # very first bit indicates if this is the final fragment
    print("final fragment: ", is_bit_set(frame_head[0], 7))

    # bits 4-7 are the opcode (0x01 -> text)
    print("opcode: ", frame_head[0] & 0x0f)

    # mask bit, from client will ALWAYS be 1
    assert is_bit_set(frame_head[1], 7)

    # length of payload
    # 7 bits, or 7 bits + 16 bits, or 7 bits + 64 bits
    payload_length = frame_head[1] & 0x7F
    if payload_length == 126:
        raw = s.recv(2)
        payload_length = bytes_to_int(raw)
    elif payload_length == 127:
        raw = s.recv(8)
        payload_length = bytes_to_int(raw)
    print('Payload is {} bytes'.format(payload_length))

    """masking key
    All frames sent from the client to the server are masked by a
    32-bit nounce value that is contained within the frame
    """
    masking_key = s.recv(4)
    print("mask: ", masking_key, bytes_to_int(masking_key))

    # finally get the payload data:
    masked_data_in = s.recv(payload_length)
    data = bytearray(payload_length)

    # The ith byte is the XOR of byte i of the data with
    # masking_key[i % 4]
    for i, b in enumerate(masked_data_in):
        data[i] = b ^ masking_key[i%4]

    return data

def handle(s):
    client_request = s.recv(4096)

    # get to the key
    for line in client_request.splitlines():
        if b'Sec-WebSocket-Key:' in line:
            key = line.split(b': ')[1]
            break
    response_string = calculate_websocket_hash(key)

    header = '''HTTP/1.1 101 Switching Protocols\r
Upgrade: websocket\r
Connection: Upgrade\r
Sec-WebSocket-Accept: {}\r
\r
'''.format(response_string)
    s.send(header.encode())

    # this works
    print(receive(s))

    # this doesn't
    s.send(pack('Hello'))

    s.close()

s = socket.socket( socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(('', 9876))
s.listen(1)

while True:
    t,_ = s.accept()
    threading.Thread(target=handle, args = (t,)).start()

使用这个基本测试页(与mod-pywebsocket一起使用):

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>Web Socket Example</title>
    <meta charset="UTF-8">
</head>
<body>
    <div id="serveroutput"></div>
    <form id="form">
        <input type="text" value="Hello World!" id="msg" />
        <input type="submit" value="Send" onclick="sendMsg()" />
    </form>
<script>
    var form = document.getElementById('form');
    var msg = document.getElementById('msg');
    var output = document.getElementById('serveroutput');
    var s = new WebSocket("ws://"+window.location.hostname+":9876");
    s.onopen = function(e) {
        console.log("opened");
        out('Connected.');
    }
    s.onclose = function(e) {
        console.log("closed");
        out('Connection closed.');
    }
    s.onmessage = function(e) {
        console.log("got: " + e.data);
        out(e.data);
    }
    form.onsubmit = function(e) {
        e.preventDefault();
        msg.value = '';
        window.scrollTop = window.scrollHeight;
    }
    function sendMsg() {
        s.send(msg.value);
    }
    function out(text) {
        var el = document.createElement('p');
        el.innerHTML = text;
        output.appendChild(el);
    }
    msg.focus();
</script>
</body>
</html>

这会正确接收资料并解除封锁,但我无法让传输路径正常工作.

作为向套接字写"Hello"的测试,上面的程序计算要写入套接字的字节:

['0x81', '0x5', '0x48', '0x65', '0x6c', '0x6c', '0x6f']

这与RFC的第5.7节中给出的十六进制值相匹配.不幸的是,该框架从未显示在Chrome的开发人员工具中.

任何想法我错过了什么?还是目前正在使用的Python3 websocket示例?



解决方法

当我尝试在Lion上使用Safari 6.0.1与您的Python代码交谈时,我得到

Unexpected LF in Value at ...

在Javascript控制台中.我还从Python代码中得到一个 IndexError 异常.

当我跟你的Python版本24.0.1290.1开发者的Python代码,我没有得到任何Javascript错误.在javascript中,调用 onopen() onclose()方法,但不调用 onmessage(). python代码不会抛出任何异常,似乎有收到消息,并发送它的响应,即完全你看到的行为.

由于Safari不喜欢您标题中的尾随LF,因此我尝试删除它,即

header = '''HTTP/1.1 101 Switching Protocols\r
Upgrade: websocket\r
Connection: Upgrade\r
Sec-WebSocket-Accept: {}\r
'''.format(response_string)

进行此更改时,Chrome可以看到您的回复邮件,即

got: Hello

会显示在javascript控制台中.

Safari仍然无法运作.现在,当我尝试发送邮件时,它引发了一个不同的问题.

websocket.html:36 INVALID_STATE_ERR: DOM Exception 11: An attempt was made to use an object that is not, or is no longer, usable.

javascript websocket事件处理程序都没有发生,我仍然看到来自python的 IndexError 异常.

总之.您的Python代码无法使用Chrome,因为您的标头响应中有一个额外的LF.还有其他问题,因为与Chrome配合使用的代码无法在Safari中使用.

Update

我已经解决了基本问题,现在有示例在Safari和Chrome中使用.

base64.encodestring() always adds a trailing \n to it's return. This is the source of the LF that Safari was complaining about.

calculate_websocket_hash 的返回值上调用 .strip(),并使用原始标题模板在Safari和Chrome上正常工作.




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