Python Receive HTTP file via POST

In get_data() you check while b"\r\n\r\n" not in data: so you read only head with headers but not body with posted file.

You have to get value from header Content-Length and use it to read rest of data - body.

But your recv(1024) may already read some part of body and it can make problem. You should read byte-after-byte (recv(1)) until you get b"\r\n\r\n" and later use Content-Length to read rest of data.

Minimal working code with HTML in code so everyone can simply copy and run it.

import socket

class Server():  # PEP8: `CamelCaseName` for classes
    
    def __init__(self):
        #self.host_ip = socket.gethostbyname(socket.gethostname())
        self.host_ip = '0.0.0.0'  # universal IP for server - to connect from other computers
        self.host_port = 8000  # 81 was restricted on my computer

        #self.s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.s = socket.socket()  # default values are `socket.AF_INET, socket.SOCK_STREAM`
        self.s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)  # solution for '[Error 89] Address already in use'. Use before bind()

        self.data_recv_size = 1024

    def get_head(self, conn):
        """ gets headers from client """
        data = b""
        while not data.endswith(b"\r\n\r\n"):
            data += conn.recv(1)
        return data

    def get_body(self, conn, size):
        """ gets the data from client """
        data = b""
        while b"\r\n\r\n" not in data:
            data += conn.recv(self.data_recv_size)
        return data

    def run(self):
        """ main method starts the server """
        print(f"[+] Server: http://{self.host_ip}:{self.host_port}")
        self.s.bind((self.host_ip, self.host_port))
        self.s.listen()
        try:
            while True:
                conn, addr = self.s.accept()
                with conn:
                    head = self.get_head(conn)
                    
                    # todo: parse headers
                    lines = head.strip().splitlines()
                    request = lines[0]
                    headers = lines[1:]
                    headers = list(line.split(b': ') for line in headers)
                    #print(headers)
                    headers = dict(headers)
                    for key, value in headers.items():
                        print(f'{key.decode()}: {value.decode()}')
                    
                    # GET request
                    if request[0:5] == b"GET /":
                        #html = open("index.html", "rb").read()
                        
                        html = '''<form enctype="multipart/form-data" action="" method="POST">
                                    <input type="hidden" name="MAX_FILE_SIZE" value="8000000" />
                                    <input name="uploadedfile" type="file" /><br />
                                    <input type="submit" value="Upload File" />
                                </form>'''

                        conn.sendall(b"HTTP/1.0 200 OK\nContent-Type: text/html\n\n" + html.encode())
                        print("[+] Responded to GET request")
    
                    # POST request
                    elif request[0:4] == b"POST":
                        size = int(headers[b'Content-Length'].decode())
                        body = self.get_body(conn, size)
                        with open("output.txt", "ab") as file:
                            file.write(head)
                            file.write(body)
                        total_size = len(head)+len(body)    
                        print(f"{total_size} bytes received from POST")
                        html = f"OK: {total_size} bytes"
                        conn.sendall(b"HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n" + html.encode())
                        print("[+] Responded to POST request")
    
        except KeyboardInterrupt:
            print("[+] Stopped by Ctrl+C")
        finally:
            self.s.close()

# --- main ---

s = Server()
s.run()

BTW:

I display http://0.0.0.0:8000 in console because in some consoles you can click on URL to open it in browser.

I use universal address 0.0.0.0 so it can recive connections from all NIC (Network Internet Controller/Card?) which means LAN cable, WiFi and other connections at the same time.

PEP 8 -- Style Guide for Python Code

EDIT:

It can be much simpler with Flask

I use form for uploading 3 files at once.

import os
from flask import Flask, request

# create folder for uploaded data
FOLDER = 'uploaded'
os.makedirs(FOLDER, exist_ok=True)

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def index():

    if request.method == 'GET':
        return '''<form enctype="multipart/form-data" action="" method="POST">
    <input type="hidden" name="MAX_FILE_SIZE" value="8000000" />
    <input name="uploadedfile1" type="file" /><br />
    <input name="uploadedfile2" type="file" /><br />
    <input name="uploadedfile3" type="file" /><br />
    <input type="submit" value="Upload File" />
</form>'''
    
    if request.method == 'POST':
        for field, data in request.files.items():
            print('field:', field)
            print('filename:', data.filename)
            if data.filename:
                data.save(os.path.join(FOLDER, data.filename))
        return "OK"

if __name__ == '__main__':
    app.run(port=80)

With the help of furas answer, trial an error, and lots of research online. I was able to create a web server that works. I'm going to post the completed script here, as it will be of use to other people in the future who stumbles across this question, and are also trying to create a file upload server as well.

import socket, re

class Server():
    def __init__(self):
        self.host_ip = "localhost"
        self.host_port = 81
        self.s = socket.socket()
        self.s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.data_recv_size = 1024
        self.form = b"""<form enctype="multipart/form-data" action="" method="POST">
                <input type="hidden" name="MAX_FILE_SIZE" value="8000000" />
                <input name="uploadedfile" type="file" /><br />
                <input type="submit" value="Upload File" />
            </form>"""

    def get_data(self, conn):
        data = b""
        while True:
            chunk = conn.recv(self.data_recv_size)
            if len(chunk) < self.data_recv_size:
                return data + chunk
            else:
                data += chunk

    def save_file(self, packet):
        name = re.compile(b'name="uploadedfile"; filename="(.+)"').search(packet).group(1)
        data = re.compile(b"WebKitFormBoundary((\n|.)*)Content-Type.+\n.+?\n((\n|.)*)([\-]+WebKitFormBoundary)?")
        with open(name, "wb") as file:
            file.write(data.search(packet).group(3))

    def run(self):
        print(f"[+] Server: http://{self.host_ip}:{self.host_port}")
        self.s.bind((self.host_ip, self.host_port))
        self.s.listen()

        while True:
            conn,addr = self.s.accept()
            request = self.get_data(conn)

            # GET request
            if request[0:5] == b"GET /":
                conn.sendall(b"HTTP/1.0 200 OK\nContent-Type: text/html\n\n"+self.form)
                print("[+] Responded to GET request!")

            # POST request
            elif request[0:4] == b"POST":
                packet = self.get_data(conn)
                self.save_file(packet)
                ok_reponse = b"Successfully upload %d bytes to the server!" % len(packet)
                conn.sendall(b"HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n"+ok_reponse)
                print(f"[+] {len(packet)} bytes received from POST!")


s = Server()
s.run()

Here is a screenshot showing the script running

Here is a screenshot of the directory with the image file saved, after it was uploaded via the server.

So it all seems to be working OK now.