An incomplete WebSocket client based on only socket, ssl, and uuid in Python

04815

A few days ago, I couldn’t get a WebSocket library working with another library on Python 3.10. So to avoid those dependencies, I implemented my WebSocket client on a low-level socket API. I implemented one in Common Lisp first. Then I translated it to Python. My WebSocket client is very far away from being completed, but at least it can run.

The first part is import. I imported only three things that are socket, ssl, and uuid. 

<span>import</span> <span>socket</span>
<span>import</span> <span>ssl</span>
<span>import</span> <span>uuid</span>
<span>import</span> <span>socket</span>
<span>import</span> <span>ssl</span>
<span>import</span> <span>uuid</span>
import socket
import ssl
import uuid

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The second part is based on HTTP headers for telling the server to switch to the WebSocket mode. 

<span>def</span> <span>upgrade</span><span>(</span><span>s</span><span>,</span> <span>conn_info</span><span>):</span>
    <span>with</span> <span>s</span><span>.</span><span>makefile</span><span>(</span><span>mode</span> <span>=</span> <span>'rw'</span><span>,</span> <span>encoding</span> <span>=</span> <span>"ISO-8859-1"</span><span>)</span> <span>as</span> <span>f</span><span>:</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>f</span><span>'GET </span><span>{</span><span>conn_info</span><span>[</span><span>"path"</span><span>]</span><span>}</span><span> HTTP/1.1</span><span>\r\n</span><span>'</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>f</span><span>'Host: </span><span>{</span><span>conn_info</span><span>[</span><span>"host"</span><span>]</span><span>}</span><span>\r\n</span><span>'</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"Connection: Upgrade</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"Upgrade: websocket</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>f</span><span>'Sec-Websocket-Key: </span><span>{</span><span>str</span><span>(</span><span>uuid</span><span>.</span><span>uuid1</span><span>())</span><span>}</span><span>\r\n</span><span>'</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"Sec-WebSocket-Version: 13</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>flush</span><span>()</span>
        <span># reading response </span>        <span>for</span> <span>line</span> <span>in</span> <span>f</span><span>:</span>
            <span>if</span> <span>line</span> <span>==</span> <span>"</span><span>\n</span><span>"</span><span>:</span>
                <span>break</span>
<span>def</span> <span>upgrade</span><span>(</span><span>s</span><span>,</span> <span>conn_info</span><span>):</span>
    <span>with</span> <span>s</span><span>.</span><span>makefile</span><span>(</span><span>mode</span> <span>=</span> <span>'rw'</span><span>,</span> <span>encoding</span> <span>=</span> <span>"ISO-8859-1"</span><span>)</span> <span>as</span> <span>f</span><span>:</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>f</span><span>'GET </span><span>{</span><span>conn_info</span><span>[</span><span>"path"</span><span>]</span><span>}</span><span> HTTP/1.1</span><span>\r\n</span><span>'</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>f</span><span>'Host: </span><span>{</span><span>conn_info</span><span>[</span><span>"host"</span><span>]</span><span>}</span><span>\r\n</span><span>'</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"Connection: Upgrade</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"Upgrade: websocket</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>f</span><span>'Sec-Websocket-Key: </span><span>{</span><span>str</span><span>(</span><span>uuid</span><span>.</span><span>uuid1</span><span>())</span><span>}</span><span>\r\n</span><span>'</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"Sec-WebSocket-Version: 13</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>write</span><span>(</span><span>"</span><span>\r\n</span><span>"</span><span>)</span>
        <span>f</span><span>.</span><span>flush</span><span>()</span>

        <span># reading response </span>        <span>for</span> <span>line</span> <span>in</span> <span>f</span><span>:</span>
            <span>if</span> <span>line</span> <span>==</span> <span>"</span><span>\n</span><span>"</span><span>:</span>
                <span>break</span>
def upgrade(s, conn_info):
    with s.makefile(mode = 'rw', encoding = "ISO-8859-1") as f:
        f.write(f'GET {conn_info["path"]} HTTP/1.1\r\n')
        f.write(f'Host: {conn_info["host"]}\r\n')
        f.write("Connection: Upgrade\r\n")
        f.write("Upgrade: websocket\r\n")
        f.write(f'Sec-Websocket-Key: {str(uuid.uuid1())}\r\n')
        f.write("Sec-WebSocket-Version: 13\r\n")
        f.write("\r\n")
        f.flush()

        # reading response         for line in f:
            if line == "\n":
                break

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The third part is reading a content length. I assume that the server keep sending text contents. In read_payload_len(), s.recv(1) read a byte from the socket s. & 0x7F is for masking only 7 bits. If length is 127, the length is in the next 4 bytes instead. If length is 126, the length is in the next 2 bytes. Otherwise the function just returns the length. 

<span>def</span> <span>read_payload_len</span><span>(</span><span>s</span><span>):</span>
    <span>match</span> <span>s</span><span>.</span><span>recv</span><span>(</span><span>1</span><span>)[</span><span>0</span><span>]</span> <span>&</span> <span>0x7F</span><span>:</span>
        <span>case</span> <span>127</span><span>:</span>
            <span>return</span> <span>read_extra_len</span><span>(</span><span>s</span><span>,</span> <span>4</span><span>)</span>
        <span>case</span> <span>126</span><span>:</span>
            <span>return</span> <span>read_extra_len</span><span>(</span><span>s</span><span>,</span> <span>2</span><span>)</span>
        <span>case</span> <span>l</span><span>:</span>
            <span>return</span> <span>l</span>
<span>def</span> <span>read_payload_len</span><span>(</span><span>s</span><span>):</span>
    <span>match</span> <span>s</span><span>.</span><span>recv</span><span>(</span><span>1</span><span>)[</span><span>0</span><span>]</span> <span>&</span> <span>0x7F</span><span>:</span>
        <span>case</span> <span>127</span><span>:</span>
            <span>return</span> <span>read_extra_len</span><span>(</span><span>s</span><span>,</span> <span>4</span><span>)</span>
        <span>case</span> <span>126</span><span>:</span>
            <span>return</span> <span>read_extra_len</span><span>(</span><span>s</span><span>,</span> <span>2</span><span>)</span>
        <span>case</span> <span>l</span><span>:</span>
            <span>return</span> <span>l</span>
def read_payload_len(s):
    match s.recv(1)[0] & 0x7F:
        case 127:
            return read_extra_len(s, 4)
        case 126:
            return read_extra_len(s, 2)
        case l:
            return l

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The read_extra_len reads bytes and turn them to integer. 

<span>def</span> <span>read_extra_len</span><span>(</span><span>s</span><span>,</span> <span>num_of_bytes</span><span>):</span>
    <span>buf</span> <span>=</span> <span>s</span><span>.</span><span>recv</span><span>(</span><span>num_of_bytes</span><span>)</span>
    <span>len</span> <span>=</span> <span>0</span>
    <span>for</span> <span>i</span> <span>in</span> <span>range</span><span>(</span><span>num_of_bytes</span><span>):</span>
        <span>len</span> <span>+=</span> <span>buf</span><span>[</span><span>i</span><span>]</span> <span><<</span> <span>(</span><span>8</span> <span>*</span> <span>(</span><span>num_of_bytes</span> <span>-</span> <span>i</span> <span>-</span> <span>1</span><span>))</span>
    <span>return</span> <span>len</span>
<span>def</span> <span>read_extra_len</span><span>(</span><span>s</span><span>,</span> <span>num_of_bytes</span><span>):</span>
    <span>buf</span> <span>=</span> <span>s</span><span>.</span><span>recv</span><span>(</span><span>num_of_bytes</span><span>)</span>
    <span>len</span> <span>=</span> <span>0</span>
    <span>for</span> <span>i</span> <span>in</span> <span>range</span><span>(</span><span>num_of_bytes</span><span>):</span>
        <span>len</span> <span>+=</span> <span>buf</span><span>[</span><span>i</span><span>]</span> <span><<</span> <span>(</span><span>8</span> <span>*</span> <span>(</span><span>num_of_bytes</span> <span>-</span> <span>i</span> <span>-</span> <span>1</span><span>))</span>
    <span>return</span> <span>len</span>
def read_extra_len(s, num_of_bytes):
    buf = s.recv(num_of_bytes)
    len = 0
    for i in range(num_of_bytes):
        len += buf[i] << (8 * (num_of_bytes - i - 1))
    return len

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In the fourth part, we read a web socket frame. The program determine a frame type from opcode, which in the last 4 bits of the header. I should implement PING-PONG part but I didn’t. According to RFC6455, which I forgot to mention before, opcode == 0x1 means the frame is a text frame. So the program reads payload length and reads the payload. 

<span>def</span> <span>read_frame</span><span>(</span><span>s</span><span>):</span>
    <span>header0</span> <span>=</span> <span>s</span><span>.</span><span>recv</span><span>(</span><span>1</span><span>)[</span><span>0</span><span>]</span>
    <span>opcode</span> <span>=</span> <span>header0</span> <span>&</span> <span>0x0F</span>
    <span>match</span> <span>opcode</span><span>:</span>
        <span>case</span> <span>0x1</span><span>:</span>
            <span>payload_len</span> <span>=</span> <span>read_payload_len</span><span>(</span><span>s</span><span>)</span>
            <span>print</span><span>(</span><span>s</span><span>.</span><span>recv</span><span>(</span><span>payload_len</span><span>))</span>
        <span>case</span> <span>0x9</span><span>:</span>
            <span>print</span><span>(</span><span>"PING"</span><span>)</span>
        <span>case</span> <span>0xA</span><span>:</span>
            <span>print</span><span>(</span><span>"PONG"</span><span>)</span>
<span>def</span> <span>read_frame</span><span>(</span><span>s</span><span>):</span>
    <span>header0</span> <span>=</span> <span>s</span><span>.</span><span>recv</span><span>(</span><span>1</span><span>)[</span><span>0</span><span>]</span>
    <span>opcode</span> <span>=</span> <span>header0</span> <span>&</span> <span>0x0F</span>
    <span>match</span> <span>opcode</span><span>:</span>
        <span>case</span> <span>0x1</span><span>:</span>
            <span>payload_len</span> <span>=</span> <span>read_payload_len</span><span>(</span><span>s</span><span>)</span>
            <span>print</span><span>(</span><span>s</span><span>.</span><span>recv</span><span>(</span><span>payload_len</span><span>))</span>
        <span>case</span> <span>0x9</span><span>:</span>
            <span>print</span><span>(</span><span>"PING"</span><span>)</span>
        <span>case</span> <span>0xA</span><span>:</span>
            <span>print</span><span>(</span><span>"PONG"</span><span>)</span>
def read_frame(s):
    header0 = s.recv(1)[0]
    opcode = header0 & 0x0F
    match opcode:
        case 0x1:
            payload_len = read_payload_len(s)
            print(s.recv(payload_len))
        case 0x9:
            print("PING")
        case 0xA:
            print("PONG")

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The last part is for opening connections and SSL/TLS wrapper. The function created a socket and wrapped it with TLS/SSL wrapper. The sending upgrade message to ask the server to switch to Websocket mode and the keep reading frames. 

<span>def</span> <span>connect</span><span>(</span><span>conn_info</span><span>):</span>
    <span>ctx</span> <span>=</span> <span>ssl</span><span>.</span><span>create_default_context</span><span>()</span>
    <span>with</span> <span>socket</span><span>.</span><span>create_connection</span><span>((</span><span>conn_info</span><span>[</span><span>"host"</span><span>],</span> <span>conn_info</span><span>[</span><span>"port"</span><span>]))</span> <span>as</span> <span>s</span><span>:</span>
        <span>with</span> <span>ctx</span><span>.</span><span>wrap_socket</span><span>(</span><span>s</span><span>,</span> <span>server_hostname</span> <span>=</span> <span>conn_info</span><span>[</span><span>"host"</span><span>])</span> <span>as</span> <span>ss</span><span>:</span>
            <span>upgrade</span><span>(</span><span>ss</span><span>,</span> <span>conn_info</span><span>)</span>
            <span>while</span> <span>True</span><span>:</span>
                <span>read_frame</span><span>(</span><span>ss</span><span>)</span>
<span>def</span> <span>connect</span><span>(</span><span>conn_info</span><span>):</span>
    <span>ctx</span> <span>=</span> <span>ssl</span><span>.</span><span>create_default_context</span><span>()</span>
    <span>with</span> <span>socket</span><span>.</span><span>create_connection</span><span>((</span><span>conn_info</span><span>[</span><span>"host"</span><span>],</span> <span>conn_info</span><span>[</span><span>"port"</span><span>]))</span> <span>as</span> <span>s</span><span>:</span>
        <span>with</span> <span>ctx</span><span>.</span><span>wrap_socket</span><span>(</span><span>s</span><span>,</span> <span>server_hostname</span> <span>=</span> <span>conn_info</span><span>[</span><span>"host"</span><span>])</span> <span>as</span> <span>ss</span><span>:</span>
            <span>upgrade</span><span>(</span><span>ss</span><span>,</span> <span>conn_info</span><span>)</span>
            <span>while</span> <span>True</span><span>:</span>
                <span>read_frame</span><span>(</span><span>ss</span><span>)</span>
def connect(conn_info):
    ctx = ssl.create_default_context()
    with socket.create_connection((conn_info["host"], conn_info["port"])) as s:
        with ctx.wrap_socket(s, server_hostname = conn_info["host"]) as ss:
            upgrade(ss, conn_info)
            while True:
                read_frame(ss)

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In the final part, I cannot find any public Websocket endpoint besides ones from cryptocurrency exchanges. So I put Bitkub API. 

<span>connect</span><span>({</span><span>"host"</span><span>:</span> <span>"api.bitkub.com"</span><span>,</span>
         <span>"port"</span><span>:</span> <span>443</span><span>,</span>
         <span>"path"</span><span>:</span> <span>"/websocket-api/market.trade.thb_btc"</span><span>})</span>
<span>connect</span><span>({</span><span>"host"</span><span>:</span> <span>"api.bitkub.com"</span><span>,</span>
         <span>"port"</span><span>:</span> <span>443</span><span>,</span>
         <span>"path"</span><span>:</span> <span>"/websocket-api/market.trade.thb_btc"</span><span>})</span>
connect({"host": "api.bitkub.com",
         "port": 443,
         "path": "/websocket-api/market.trade.thb_btc"})

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And it works, but if you are unlucky, you will get PING instead. 

> python3.10 http_ex.py 
b'{"amt":0.00004661,"bid":86911896,"rat":2140000,"sid":82187323,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078574"}\n{"amt":0.23306074,"bid":86912246,"rat":2140000,"sid":82187325,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078576"}'
b'{"amt":0.00466121,"bid":86912014,"rat":2140000,"sid":82187324,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078575"}'
> python3.10 http_ex.py 
b'{"amt":0.00004661,"bid":86911896,"rat":2140000,"sid":82187323,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078574"}\n{"amt":0.23306074,"bid":86912246,"rat":2140000,"sid":82187325,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078576"}'
b'{"amt":0.00466121,"bid":86912014,"rat":2140000,"sid":82187324,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078575"}'
> python3.10 http_ex.py 
b'{"amt":0.00004661,"bid":86911896,"rat":2140000,"sid":82187323,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078574"}\n{"amt":0.23306074,"bid":86912246,"rat":2140000,"sid":82187325,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078576"}'
b'{"amt":0.00466121,"bid":86912014,"rat":2140000,"sid":82187324,"stream":"market.trade.thb_btc","sym":"THB_BTC","ts":1636729677,"txn":"BTCSELL0011078575"}'

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原文链接：An incomplete WebSocket client based on only socket, ssl, and uuid in Python

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