CN2021/httplib/parser.py

import logging
import re
import urllib
from urllib.parse import urlparse, urlsplit

from httplib.exceptions import InvalidStatusLine, InvalidResponse, BadRequest, InvalidRequestLine


def _is_valid_http_version(http_version: str):
    """
    Returns True if the specified HTTP-version is valid.

    @param http_version: the string to be checked
    @return: True if the specified HTTP-version is valid.
    """
    if len(http_version) < 8 or http_version[4] != "/":
        return False

    (name, version) = http_version[:4], http_version[5:]
    if name != "HTTP" or not re.match(r"1\.[0|1]", version):
        return False

    return True


def parse_status_line(line: str):
    """
    Parses the specified line as an HTTP status-line.

    @param line: the status-line to be parsed
    @raise InvalidStatusLine: if the line couldn't be parsed, if the HTTP-version is invalid or if the status code
    is invalid
    @return: tuple of the HTTP-version, status and reason
    """

    split = list(filter(None, line.strip().split(" ", 2)))
    if len(split) < 3:
        raise InvalidStatusLine(line)

    http_version, status, reason = split

    if not _is_valid_http_version(http_version):
        raise InvalidStatusLine(line)
    version = http_version[:4]

    if not re.match(r"\d{3}", status):
        raise InvalidStatusLine(line)
    status = int(status)
    if status < 100 or status > 999:
        raise InvalidStatusLine(line)

    return version, status, reason


def parse_request_line(line: str):
    """
    Parses the specified line as and HTTP request-line.
    Returns the method, target as ParseResult and HTTP version from the request-line.

    @param line: the request-line to be parsed
    @raise InvalidRequestLine: if the line couldn't be parsed.
    @raise BadRequest: Invalid HTTP method, Invalid HTTP-version or Invalid target
    @return: tuple of the method, target and HTTP-version
    """

    split = list(filter(None, line.rstrip().split(" ", 2)))
    if len(split) < 3:
        raise InvalidRequestLine(line)

    method, target, version = split
    if method not in ("CONNECT", "DELETE", "GET", "HEAD", "OPTIONS", "POST", "PUT", "TRACE"):
        raise BadRequest(f"Invalid method: {method}")

    if not _is_valid_http_version(version):
        logging.debug("[ABRT] request: invalid http-version=%r", version)
        raise BadRequest(f"Invalid HTTP-version: {version}")

    if len(target) == "":
        raise BadRequest()
    parsed_target = urlsplit(target)

    return method, parsed_target, version.split("/")[1]


def parse_headers(lines):
    headers = []

    try:
        # first header after the start-line may not start with a space
        line = next(lines)
        while True:
            if line[0].isspace():
                continue
            else:
                break

        while True:
            if line in ("\r\n", "\n", ""):
                break

            if line[0].isspace():
                headers[-1] = headers[-1].rstrip("\r\n")

            headers.append(line.lstrip())
            line = next(lines)
    except StopIteration:
        # No more lines to be parsed
        pass

    result = {}
    header_str = "".join(headers)
    for line in header_str.splitlines():
        pos = line.find(":")

        if pos <= 0 or pos >= len(line) - 1:
            continue

        (header, value) = map(str.strip, line.split(":", 1))
        check_next_header(result, header, value)
        result[header.lower()] = value.lower()

    return result


def check_next_header(headers, next_header: str, next_value: str):
    if next_header == "content-length":
        if "content-length" in headers:
            logging.error("Multiple content-length headers specified")
            raise InvalidResponse()
        if not next_value.isnumeric() or int(next_value) <= 0:
            logging.error("Invalid content-length value: %r", next_value)
            raise InvalidResponse()


def parse_uri(uri: str):
    parsed = urlsplit(uri)

    # If there is no netloc, the given string is not a valid URI, so split on /
    if parsed.hostname:
        host = parsed.hostname
        path = parsed.path
        if parsed.query != '':
            path = f"{path}?{parsed.query}"
    elif "/" in uri:
        (host, path) = uri.split("/", 1)
    else:
        host = uri
        path = "/"

    if ":" in host:
        host, port = host.split(":", 1)
    elif parsed.scheme == "https":
        port = 443
    else:
        port = 80

    return host, port, path


def get_uri(url: str):
    """
    Returns a valid URI of the specified URL.
    """
    parsed = urlsplit(url)

    result = f"http://{parsed.netloc}{parsed.path}"
    if parsed.query != '':
        result = f"{result}?{parsed.query}"

    return result


def urljoin(base, url):
    """
    Join a base url and a URL to form a absolute url.
    """
    return urllib.parse.urljoin(base, url)