websocket 原理

Posted 2021-02-14 追风zz

自己写一个websocket

import socket, hashlib, base64

sock = socket.socket()
sock.bind((‘127.0.0.1‘, 9000))
sock.listen(5)
‘‘‘
b‘GET / HTTP/1.1

Host: 127.0.0.1:9000

Connection: Upgrade

Pragma: no-cache

Cache-Control: no-cache

User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (Khtml, like Gecko) Chrome/69.0.3497.81 Safari/537.36

Upgrade: websocket
   --建立--
Origin: http://localhost:63342

Sec-WebSocket-Version: 13

Accept-Encoding: gzip, deflate, br

Accept-Language: zh-CN,zh;q=0.9

Sec-WebSocket-Key: vNtQ8bVSNRPL5p+xo1X5CA==
  验证 一按钥匙
Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits


‘‘‘
‘‘‘
b‘GET / HTTP/1.1
   -- 单纯http地址栏访问
Host: 127.0.0.1:9000

Connection: keep-alive

Pragma: no-cache

Cache-Control: no-cache

Upgrade-Insecure-Requests: 1

User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.81 Safari/537.36

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8

Accept-Encoding: gzip, deflate, br

Accept-Language: zh-CN,zh;q=0.9

‘
‘‘‘
conn, addr = sock.accept()
data = conn.recv(1024)
# print(data)

def get_header(data): # 获取头部信息
    header_dict = {}
    header_str = data.decode(‘utf8‘)
    for i in header_str.split(‘
‘):
        if str(i).startswith(‘Sec-WebSocket-Key‘):
            header_dict[‘Sec-WebSocket-Key‘] = i.split(‘:‘)[1].strip()
    return header_dict


headers = get_header(data)
magic_string = ‘258EAFA5-E914-47DA-95CA-C5AB0DC85B11‘  # magic_string = 魔法字符串
value = headers[‘Sec-WebSocket-Key‘] + magic_string
print(value)  #mzrsVOiYogmzB8fYcyMBpw==258EAFA5-E914-47DA-95CA-C5AB0DC85B11
ac = base64.b64encode(hashlib.sha1(value.encode(‘utf-8‘)).digest())  # 固定加密算法
print(ac) #b‘0Cu1dAA7U6tFsJS4EVkIDLcvKDU=‘
response_tpl = "HTTP/1.1 101 Switching Protocols
"                "Upgrade:websocket
"                "Connection: Upgrade
"                "Sec-WebSocket-Accept: %s
"                "WebSocket-Location: ws://127.0.0.1:9527

"
response_str = response_tpl % (ac.decode(‘utf-8‘))
conn.send(response_str.encode(‘utf8‘))  # 响应握手信息

while True:
    msg = conn.recv(8096)
    print(msg)

解密过程  分析

hashstr = b‘x81x89xbcxb8,xb5Y6xa5Px12x0bxc8x0f:‘
# b‘x81    x83    xceHxb6x85xffzx85‘

# 将第二个字节也就是 x83 第9-16位 进行与127进行 与位 运算
payload = hashstr[1] & 127
print(payload)
if payload == 127:
    extend_payload_len = hashstr[2:10]  # 顾头不顾尾
    mask = hashstr[10:14]
    decoded = hashstr[14:]
# 当位运算结果等于127时,则第3-10个字节为数据长度
# 第11-14字节为mask 解密所需字符串
# 则数据为第15字节至结尾

if payload == 126:
    extend_payload_len = hashstr[2:4]
    mask = hashstr[4:8]
    decoded = hashstr[8:]
# 当位运算结果等于126时,则第3-4个字节为数据长度  255*255+510=65535 21845汉字
# 第5-8字节为mask 解密所需字符串
# 则数据为第9字节至结尾

if payload <= 125:
    extend_payload_len = None
    mask = hashstr[2:6]
    decoded = hashstr[6:]

# 当位运算结果小于等于125时,则这个数字就是数据的长度
# 第3-6字节为mask 解密所需字符串
# 则数据为第7字节至结尾

str_byte = bytearray()  # 字节流

for i in range(len(decoded)):
    byte = decoded[i] ^ mask[i % 4]  # 异或运算  上下为0就是0  上下有1就是1
    str_byte.append(byte)

print(str_byte.decode("utf8"))  # 主要解决中文  厉害了

# # 1字节 = 8 bit  与位运算
# 01111111
# 11111111  最大255
# 2/4/8/16/32/64/138/256

加密过程 -- 分析

import struct
msg_bytes = "hello".encode("utf8")  #转bytes
token = b"x81"       # 数据标准格式
length = len(msg_bytes)  #第二位就是数据长度

if length < 126:
    token += struct.pack("B", length)
elif length == 126:
    token += struct.pack("!BH", 126, length)
else:
    token += struct.pack("!BQ", 127, length)

msg = token + msg_bytes

print(msg)

总结

WebSocket的工作原理
1.握手
    客户端   Sec-WebSocket-Key
    响应     base64(sha1(Sec-WebSocket-Key + magic_string))
    
2.解密：
    与127 进行"与"位运算 结果是两个数的最小值
    1. == 127 第3-10个字节表示该数据的长度 
    2. == 126 第3-4个字节表示该数据的长度 00000010 00000000
    3. <= 125 当前这个数字就是Websocket发送的数据长度