path: root/netlib/http.py

from __future__ import (absolute_import, print_function, division)
import collections
import string
import urlparse
import binascii
import sys
from . import odict, utils, tcp, http_status


class HttpError(Exception):

    def __init__(self, code, message):
        super(HttpError, self).__init__(message)
        self.code = code


class HttpErrorConnClosed(HttpError):
    pass


def _is_valid_port(port):
    if not 0 <= port <= 65535:
        return False
    return True


def _is_valid_host(host):
    try:
        host.decode("idna")
    except ValueError:
        return False
    if "\0" in host:
        return None
    return True


def get_request_line(fp):
    """
        Get a line, possibly preceded by a blank.
    """
    line = fp.readline()
    if line == "\r\n" or line == "\n":
        # Possible leftover from previous message
        line = fp.readline()
    return line


def parse_url(url):
    """
        Returns a (scheme, host, port, path) tuple, or None on error.

        Checks that:
            port is an integer 0-65535
            host is a valid IDNA-encoded hostname with no null-bytes
            path is valid ASCII
    """
    try:
        scheme, netloc, path, params, query, fragment = urlparse.urlparse(url)
    except ValueError:
        return None
    if not scheme:
        return None
    if '@' in netloc:
        # FIXME: Consider what to do with the discarded credentials here Most
        # probably we should extend the signature to return these as a separate
        # value.
        _, netloc = string.rsplit(netloc, '@', maxsplit=1)
    if ':' in netloc:
        host, port = string.rsplit(netloc, ':', maxsplit=1)
        try:
            port = int(port)
        except ValueError:
            return None
    else:
        host = netloc
        if scheme == "https":
            port = 443
        else:
            port = 80
    path = urlparse.urlunparse(('', '', path, params, query, fragment))
    if not path.startswith("/"):
        path = "/" + path
    if not _is_valid_host(host):
        return None
    if not utils.isascii(path):
        return None
    if not _is_valid_port(port):
        return None
    return scheme, host, port, path


def read_headers(fp):
    """
        Read a set of headers from a file pointer. Stop once a blank line is
        reached. Return a ODictCaseless object, or None if headers are invalid.
    """
    ret = []
    name = ''
    while True:
        line = fp.readline()
        if not line or line == '\r\n' or line == '\n':
            break
        if line[0] in ' \t':
            if not ret:
                return None
            # continued header
            ret[-1][1] = ret[-1][1] + '\r\n ' + line.strip()
        else:
            i = line.find(':')
            # We're being liberal in what we accept, here.
            if i > 0:
                name = line[:i]
                value = line[i + 1:].strip()
                ret.append([name, value])
            else:
                return None
    return odict.ODictCaseless(ret)


def read_chunked(fp, limit, is_request):
    """
        Read a chunked HTTP body.

        May raise HttpError.
    """
    # FIXME: Should check if chunked is the final encoding in the headers
    # http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-16#section-3.3
    # 3.3 2.
    total = 0
    code = 400 if is_request else 502
    while True:
        line = fp.readline(128)
        if line == "":
            raise HttpErrorConnClosed(code, "Connection closed prematurely")
        if line != '\r\n' and line != '\n':
            try:
                length = int(line, 16)
            except ValueError:
                raise HttpError(
                    code,
                    "Invalid chunked encoding length: %s" % line
                )
            total += length
            if limit is not None and total > limit:
                msg = "HTTP Body too large. Limit is %s," \
                      " chunked content longer than %s" % (limit, total)
                raise HttpError(code, msg)
            chunk = fp.read(length)
            suffix = fp.readline(5)
            if suffix != '\r\n':
                raise HttpError(code, "Malformed chunked body")
            yield line, chunk, '\r\n'
            if length == 0:
                return


def get_header_tokens(headers, key):
    """
        Retrieve all tokens for a header key. A number of different headers
        follow a pattern where each header line can containe comma-separated
        tokens, and headers can be set multiple times.
    """
    toks = []
    for i in headers[key]:
        for j in i.split(","):
            toks.append(j.strip())
    return toks


def has_chunked_encoding(headers):
    return "chunked" in [
        i.lower() for i in get_header_tokens(headers, "transfer-encoding")
    ]


def parse_http_protocol(s):
    """
        Parse an HTTP protocol declaration. Returns a (major, minor) tuple, or
        None.
    """
    if not s.startswith("HTTP/"):
        return None
    _, version = s.split('/', 1)
    if "." not in version:
        return None
    major, minor = version.split('.', 1)
    try:
        major = int(major)
        minor = int(minor)
    except ValueError:
        return None
    return major, minor


def parse_http_basic_auth(s):
    words = s.split()
    if len(words) != 2:
        return None
    scheme = words[0]
    try:
        user = binascii.a2b_base64(words[1])
    except binascii.Error:
        return None
    parts = user.split(':')
    if len(parts) != 2:
        return None
    return scheme, parts[0], parts[1]


def assemble_http_basic_auth(scheme, username, password):
    v = binascii.b2a_base64(username + ":" + password)
    return scheme + " " + v


def parse_init(line):
    try:
        method, url, protocol = string.split(line)
    except ValueError:
        return None
    httpversion = parse_http_protocol(protocol)
    if not httpversion:
        return None
    if not utils.isascii(method):
        return None
    return method, url, httpversion


def parse_init_connect(line):
    """
        Returns (host, port, httpversion) if line is a valid CONNECT line.
        http://tools.ietf.org/html/draft-luotonen-web-proxy-tunneling-01 section 3.1
    """
    v = parse_init(line)
    if not v:
        return None
    method, url, httpversion = v

    if method.upper() != 'CONNECT':
        return None
    try:
        host, port = url.split(":")
    except ValueError:
        return None
    try:
        port = int(port)
    except ValueError:
        return None
    if not _is_valid_port(port):
        return None
    if not _is_valid_host(host):
        return None
    return host, port, httpversion


def parse_init_proxy(line):
    v = parse_init(line)
    if not v:
        return None
    method, url, httpversion = v

    parts = parse_url(url)
    if not parts:
        return None
    scheme, host, port, path = parts
    return method, scheme, host, port, path, httpversion


def parse_init_http(line):
    """
        Returns (method, url, httpversion)
    """
    v = parse_init(line)
    if not v:
        return None
    method, url, httpversion = v
    if not utils.isascii(url):
        return None
    if not (url.startswith("/") or url == "*"):
        return None
    return method, url, httpversion


def connection_close(httpversion, headers):
    """
        Checks the message to see if the client connection should be closed
        according to RFC 2616 Section 8.1 Note that a connection should be
        closed as well if the response has been read until end of the stream.
    """
    # At first, check if we have an explicit Connection header.
    if "connection" in headers:
        toks = get_header_tokens(headers, "connection")
        if "close" in toks:
            return True
        elif "keep-alive" in toks:
            return False
    # If we don't have a Connection header, HTTP 1.1 connections are assumed to
    # be persistent
    if httpversion == (1, 1):
        return False
    return True


def parse_response_line(line):
    parts = line.strip().split(" ", 2)
    if len(parts) == 2:  # handle missing message gracefully
        parts.append("")
    if len(parts) != 3:
        return None
    proto, code, msg = parts
    try:
        code = int(code)
    except ValueError:
        return None
    return (proto, code, msg)


def read_http_body(*args, **kwargs):
    return "".join(
        content for _, content, _ in read_http_body_chunked(*args, **kwargs)
    )


def read_http_body_chunked(
    rfile,
    headers,
    limit,
    request_method,
    response_code,
    is_request,
    max_chunk_size=None
):
    """
        Read an HTTP message body:

            rfile: A file descriptor to read from
            headers: An ODictCaseless object
            limit: Size limit.
            is_request: True if the body to read belongs to a request, False
            otherwise
    """
    if max_chunk_size is None:
        max_chunk_size = limit or sys.maxsize

    expected_size = expected_http_body_size(
        headers, is_request, request_method, response_code
    )

    if expected_size is None:
        if has_chunked_encoding(headers):
            # Python 3: yield from
            for x in read_chunked(rfile, limit, is_request):
                yield x
        else:  # pragma: nocover
            raise HttpError(
                400 if is_request else 502,
                "Content-Length unknown but no chunked encoding"
            )
    elif expected_size >= 0:
        if limit is not None and expected_size > limit:
            raise HttpError(
                400 if is_request else 509,
                "HTTP Body too large. Limit is %s, content-length was %s" % (
                    limit, expected_size
                )
            )
        bytes_left = expected_size
        while bytes_left:
            chunk_size = min(bytes_left, max_chunk_size)
            yield "", rfile.read(chunk_size), ""
            bytes_left -= chunk_size
    else:
        bytes_left = limit or -1
        while bytes_left:
            chunk_size = min(bytes_left, max_chunk_size)
            content = rfile.read(chunk_size)
            if not content:
                return
            yield "", content, ""
            bytes_left -= chunk_size
        not_done = rfile.read(1)
        if not_done:
            raise HttpError(
                400 if is_request else 509,
                "HTTP Body too large. Limit is %s," % limit
            )


def expected_http_body_size(headers, is_request, request_method, response_code):
    """
        Returns the expected body length:
         - a positive integer, if the size is known in advance
         - None, if the size in unknown in advance (chunked encoding or invalid
         data)
         - -1, if all data should be read until end of stream.

        May raise HttpError.
    """
    # Determine response size according to
    # http://tools.ietf.org/html/rfc7230#section-3.3
    if request_method:
        request_method = request_method.upper()

    if (not is_request and (
            request_method == "HEAD" or
            (request_method == "CONNECT" and response_code == 200) or
            response_code in [204, 304] or
            100 <= response_code <= 199)):
        return 0
    if has_chunked_encoding(headers):
        return None
    if "content-length" in headers:
        try:
            size = int(headers["content-length"][0])
            if size < 0:
                raise ValueError()
            return size
        except ValueError:
            return None
    if is_request:
        return 0
    return -1


Request = collections.namedtuple(
    "Request",
    [
        "form_in",
        "method",
        "scheme",
        "host",
        "port",
        "path",
        "httpversion",
        "headers",
        "content"
    ]
)


def read_request(rfile, include_body=True, body_size_limit=None, wfile=None):
    """
    Parse an HTTP request from a file stream

    Args:
        rfile (file): Input file to read from
        include_body (bool): Read response body as well
        body_size_limit (bool): Maximum body size
        wfile (file): If specified, HTTP Expect headers are handled
        automatically, by writing a HTTP 100 CONTINUE response to the stream.

    Returns:
        Request: The HTTP request

    Raises:
        HttpError: If the input is invalid.
    """
    httpversion, host, port, scheme, method, path, headers, content = (
        None, None, None, None, None, None, None, None)

    request_line = get_request_line(rfile)
    if not request_line:
        raise tcp.NetLibDisconnect()

    request_line_parts = parse_init(request_line)
    if not request_line_parts:
        raise HttpError(
            400,
            "Bad HTTP request line: %s" % repr(request_line)
        )
    method, path, httpversion = request_line_parts

    if path == '*' or path.startswith("/"):
        form_in = "relative"
        if not utils.isascii(path):
            raise HttpError(
                400,
                "Bad HTTP request line: %s" % repr(request_line)
            )
    elif method.upper() == 'CONNECT':
        form_in = "authority"
        r = parse_init_connect(request_line)
        if not r:
            raise HttpError(
                400,
                "Bad HTTP request line: %s" % repr(request_line)
            )
        host, port, _ = r
        path = None
    else:
        form_in = "absolute"
        r = parse_init_proxy(request_line)
        if not r:
            raise HttpError(
                400,
                "Bad HTTP request line: %s" % repr(request_line)
            )
        _, scheme, host, port, path, _ = r

    headers = read_headers(rfile)
    if headers is None:
        raise HttpError(400, "Invalid headers")

    expect_header = headers.get_first("expect", "").lower()
    if expect_header == "100-continue" and httpversion >= (1, 1):
        wfile.write(
            'HTTP/1.1 100 Continue\r\n'
            '\r\n'
        )
        wfile.flush()
        del headers['expect']

    if include_body:
        content = read_http_body(
            rfile, headers, body_size_limit, method, None, True
        )

    return Request(
        form_in,
        method,
        scheme,
        host,
        port,
        path,
        httpversion,
        headers,
        content
    )


Response = collections.namedtuple(
    "Response",
    [
        "httpversion",
        "code",
        "msg",
        "headers",
        "content"
    ]
)


def read_response(rfile, request_method, body_size_limit, include_body=True):
    """
        Return an (httpversion, code, msg, headers, content) tuple.

        By default, both response header and body are read.
        If include_body=False is specified, content may be one of the
        following:
        - None, if the response is technically allowed to have a response body
        - "", if the response must not have a response body (e.g. it's a
        response to a HEAD request)
    """
    line = rfile.readline()
    # Possible leftover from previous message
    if line == "\r\n" or line == "\n":
        line = rfile.readline()
    if not line:
        raise HttpErrorConnClosed(502, "Server disconnect.")
    parts = parse_response_line(line)
    if not parts:
        raise HttpError(502, "Invalid server response: %s" % repr(line))
    proto, code, msg = parts
    httpversion = parse_http_protocol(proto)
    if httpversion is None:
        raise HttpError(502, "Invalid HTTP version in line: %s" % repr(proto))
    headers = read_headers(rfile)
    if headers is None:
        raise HttpError(502, "Invalid headers.")

    if include_body:
        content = read_http_body(
            rfile,
            headers,
            body_size_limit,
            request_method,
            code,
            False
        )
    else:
        # if include_body==False then a None content means the body should be
        # read separately
        content = None
    return Response(httpversion, code, msg, headers, content)


def request_preamble(method, resource, http_major="1", http_minor="1"):
    return '%s %s HTTP/%s.%s' % (
        method, resource, http_major, http_minor
    )


def response_preamble(code, message=None, http_major="1", http_minor="1"):
    if message is None:
        message = http_status.RESPONSES.get(code)
    return 'HTTP/%s.%s %s %s' % (http_major, http_minor, code, message)