web-app-from-scratch-1-13.py

import mimetypes
import os
import socket
import typing

SERVER_ROOT = os.path.abspath("www")

FILE_RESPONSE_TEMPLATE = """\
HTTP/1.1 200 OK
Content-type: {content_type}
Content-length: {content_length}

""".replace("\n", "\r\n")


def serve_file(sock: socket.socket, path: str) -> None:
    """Given a socket and the relative path to a file (relative to
    SERVER_SOCK), send that file to the socket if it exists.  If the
    file doesn't exist, send a "404 Not Found" response.
    """
    if path == "/":
        path = "/index.html"

    abspath = os.path.normpath(os.path.join(SERVER_ROOT, path.lstrip("/")))
    if not abspath.startswith(SERVER_ROOT):
        sock.sendall(NOT_FOUND_RESPONSE)
        return

    try:
        with open(abspath, "rb") as f:
            stat = os.fstat(f.fileno())
            content_type, encoding = mimetypes.guess_type(abspath)
            if content_type is None:
                content_type = "application/octet-stream"

            if encoding is not None:
                content_type += f"; charset={encoding}"

            response_headers = FILE_RESPONSE_TEMPLATE.format(
                content_type=content_type,
                content_length=stat.st_size,
            ).encode("ascii")

            sock.sendall(response_headers)
            sock.sendfile(f)
    except FileNotFoundError:
        sock.sendall(NOT_FOUND_RESPONSE)
        return