path: root/libmproxy/protocol/http.py

from __future__ import absolute_import
import Cookie
import urllib
import urlparse
import time
import copy
from email.utils import parsedate_tz, formatdate, mktime_tz
import threading
from netlib import http, tcp, http_status
import netlib.utils
from netlib.odict import ODict, ODictCaseless
from .tcp import TCPHandler
from .primitives import KILL, ProtocolHandler, Flow, Error
from ..proxy.connection import ServerConnection
from .. import encoding, utils, controller, stateobject, proxy

HDR_FORM_URLENCODED = "application/x-www-form-urlencoded"
CONTENT_MISSING = 0


class KillSignal(Exception):
    pass


def get_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()
    if line == "":
        raise tcp.NetLibDisconnect()
    return line


def send_connect_request(conn, host, port, update_state=True):
    upstream_request = HTTPRequest(
        "authority",
        "CONNECT",
        None,
        host,
        port,
        None,
        (1, 1),
        ODictCaseless(),
        ""
    )
    conn.send(upstream_request.assemble())
    resp = HTTPResponse.from_stream(conn.rfile, upstream_request.method)
    if resp.code != 200:
        raise proxy.ProxyError(resp.code,
                               "Cannot establish SSL " +
                               "connection with upstream proxy: \r\n" +
                               str(resp.assemble()))
    if update_state:
        conn.state.append(("http", {
            "state": "connect",
            "host": host,
            "port": port}
        ))
    return resp


class decoded(object):
    """
    A context manager that decodes a request or response, and then
    re-encodes it with the same encoding after execution of the block.

    Example:
    with decoded(request):
        request.content = request.content.replace("foo", "bar")
    """

    def __init__(self, o):
        self.o = o
        ce = o.headers.get_first("content-encoding")
        if ce in encoding.ENCODINGS:
            self.ce = ce
        else:
            self.ce = None

    def __enter__(self):
        if self.ce:
            self.o.decode()

    def __exit__(self, type, value, tb):
        if self.ce:
            self.o.encode(self.ce)


class HTTPMessage(stateobject.StateObject):
    """
    Base class for HTTPRequest and HTTPResponse
    """

    def __init__(self, httpversion, headers, content, timestamp_start=None,
                 timestamp_end=None):
        self.httpversion = httpversion
        self.headers = headers
        """@type: ODictCaseless"""
        self.content = content

        self.timestamp_start = timestamp_start
        self.timestamp_end = timestamp_end

    _stateobject_attributes = dict(
        httpversion=tuple,
        headers=ODictCaseless,
        content=str,
        timestamp_start=float,
        timestamp_end=float
    )
    _stateobject_long_attributes = {"content"}

    def get_state(self, short=False):
        ret = super(HTTPMessage, self).get_state(short)
        if short:
            if self.content:
                ret["contentLength"] = len(self.content)
            else:
                ret["contentLength"] = 0
        return ret

    def get_decoded_content(self):
        """
            Returns the decoded content based on the current Content-Encoding
            header.
            Doesn't change the message iteself or its headers.
        """
        ce = self.headers.get_first("content-encoding")
        if not self.content or ce not in encoding.ENCODINGS:
            return self.content
        return encoding.decode(ce, self.content)

    def decode(self):
        """
            Decodes content based on the current Content-Encoding header, then
            removes the header. If there is no Content-Encoding header, no
            action is taken.

            Returns True if decoding succeeded, False otherwise.
        """
        ce = self.headers.get_first("content-encoding")
        if not self.content or ce not in encoding.ENCODINGS:
            return False
        data = encoding.decode(ce, self.content)
        if data is None:
            return False
        self.content = data
        del self.headers["content-encoding"]
        return True

    def encode(self, e):
        """
            Encodes content with the encoding e, where e is "gzip", "deflate"
            or "identity".
        """
        # FIXME: Error if there's an existing encoding header?
        self.content = encoding.encode(e, self.content)
        self.headers["content-encoding"] = [e]

    def size(self, **kwargs):
        """
            Size in bytes of a fully rendered message, including headers and
            HTTP lead-in.
        """
        hl = len(self._assemble_head(**kwargs))
        if self.content:
            return hl + len(self.content)
        else:
            return hl

    def copy(self):
        c = copy.copy(self)
        c.headers = self.headers.copy()
        return c

    def replace(self, pattern, repl, *args, **kwargs):
        """
            Replaces a regular expression pattern with repl in both the headers
            and the body of the message. Encoded content will be decoded
            before replacement, and re-encoded afterwards.

            Returns the number of replacements made.
        """
        with decoded(self):
            self.content, c = utils.safe_subn(
                pattern, repl, self.content, *args, **kwargs
            )
        c += self.headers.replace(pattern, repl, *args, **kwargs)
        return c

    def _assemble_first_line(self):
        """
        Returns the assembled request/response line
        """
        raise NotImplementedError()  # pragma: nocover

    def _assemble_headers(self):
        """
        Returns the assembled headers
        """
        raise NotImplementedError()  # pragma: nocover

    def _assemble_head(self):
        """
        Returns the assembled request/response line plus headers
        """
        raise NotImplementedError()  # pragma: nocover

    def assemble(self):
        """
        Returns the assembled request/response
        """
        raise NotImplementedError()  # pragma: nocover


class HTTPRequest(HTTPMessage):
    """
    An HTTP request.

    Exposes the following attributes:

        method: HTTP method

        scheme: URL scheme (http/https)

        host: Target hostname of the request. This is not neccessarily the
        directy upstream server (which could be another proxy), but it's always
        the target server we want to reach at the end. This attribute is either
        inferred from the request itself (absolute-form, authority-form) or from
        the connection metadata (e.g. the host in reverse proxy mode).

        port: Destination port

        path: Path portion of the URL (not present in authority-form)

        httpversion: HTTP version tuple, e.g. (1,1)

        headers: ODictCaseless object

        content: Content of the request, None, or CONTENT_MISSING if there
        is content associated, but not present. CONTENT_MISSING evaluates
        to False to make checking for the presence of content natural.

        form_in: The request form which mitmproxy has received. The following
        values are possible:

             - relative (GET /index.html, OPTIONS *) (covers origin form and
               asterisk form)
             - absolute (GET http://example.com:80/index.html)
             - authority-form (CONNECT example.com:443)
             Details: http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-25#section-5.3

        form_out: The request form which mitmproxy will send out to the
        destination

        timestamp_start: Timestamp indicating when request transmission started

        timestamp_end: Timestamp indicating when request transmission ended
    """

    def __init__(
        self,
        form_in,
        method,
        scheme,
        host,
        port,
        path,
        httpversion,
        headers,
        content,
        timestamp_start=None,
        timestamp_end=None,
        form_out=None
    ):
        assert isinstance(headers, ODictCaseless) or not headers
        HTTPMessage.__init__(
            self,
            httpversion,
            headers,
            content,
            timestamp_start,
            timestamp_end
        )
        self.form_in = form_in
        self.method = method
        self.scheme = scheme
        self.host = host
        self.port = port
        self.path = path
        self.httpversion = httpversion
        self.form_out = form_out or form_in

        # Have this request's cookies been modified by sticky cookies or auth?
        self.stickycookie = False
        self.stickyauth = False
        # Is this request replayed?
        self.is_replay = False

    _stateobject_attributes = HTTPMessage._stateobject_attributes.copy()
    _stateobject_attributes.update(
        form_in=str,
        method=str,
        scheme=str,
        host=str,
        port=int,
        path=str,
        form_out=str
    )

    @classmethod
    def from_state(cls, state):
        f = cls(None, None, None, None, None, None, None, None, None, None, None)
        f.load_state(state)
        return f

    def __repr__(self):
        return "<HTTPRequest: {0}>".format(
            self._assemble_first_line(self.form_in)[:-9]
        )

    @classmethod
    def from_stream(cls, rfile, include_body=True, body_size_limit=None):
        """
        Parse an HTTP request from a file stream
        """
        httpversion, host, port, scheme, method, path, headers, content, timestamp_start, timestamp_end = (
            None, None, None, None, None, None, None, None, None, None)

        timestamp_start = utils.timestamp()

        if hasattr(rfile, "reset_timestamps"):
            rfile.reset_timestamps()

        request_line = get_line(rfile)

        if hasattr(rfile, "first_byte_timestamp"):
            # more accurate timestamp_start
            timestamp_start = rfile.first_byte_timestamp

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

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

        if include_body:
            content = http.read_http_body(rfile, headers, body_size_limit,
                                          method, None, True)
            timestamp_end = utils.timestamp()

        return HTTPRequest(
            form_in,
            method,
            scheme,
            host,
            port,
            path,
            httpversion,
            headers,
            content,
            timestamp_start,
            timestamp_end
        )

    def _assemble_first_line(self, form=None):
        form = form or self.form_out

        if form == "relative":
            request_line = '%s %s HTTP/%s.%s' % (
                self.method, self.path, self.httpversion[0], self.httpversion[1]
            )
        elif form == "authority":
            request_line = '%s %s:%s HTTP/%s.%s' % (
                self.method, self.host, self.port, self.httpversion[0],
                self.httpversion[1]
            )
        elif form == "absolute":
            request_line = '%s %s://%s:%s%s HTTP/%s.%s' % (
                self.method, self.scheme, self.host,
                self.port, self.path, self.httpversion[0],
                self.httpversion[1]
            )
        else:
            raise http.HttpError(400, "Invalid request form")
        return request_line

    def _assemble_headers(self):
        headers = self.headers.copy()
        for k in ['Proxy-Connection',
                  'Keep-Alive',
                  'Connection',
                  'Transfer-Encoding']:
            del headers[k]
        if headers["Upgrade"] == ["h2c"]:
            # Suppress HTTP2 https://http2.github.io/http2-spec/index.html#discover-http
            del headers["Upgrade"]
        if not 'host' in headers and self.scheme and self.host and self.port:
            headers["Host"] = [utils.hostport(self.scheme,
                                              self.host,
                                              self.port)]

        # If content is defined (i.e. not None or CONTENT_MISSING), we always add a content-length header.
        if self.content or self.content == "":
            headers["Content-Length"] = [str(len(self.content))]

        return str(headers)

    def _assemble_head(self, form=None):
        return "%s\r\n%s\r\n" % (
            self._assemble_first_line(form), self._assemble_headers()
        )

    def assemble(self, form=None):
        """
            Assembles the request for transmission to the server. We make some
            modifications to make sure interception works properly.

            Raises an Exception if the request cannot be assembled.
        """
        if self.content == CONTENT_MISSING:
            raise proxy.ProxyError(
                502,
                "Cannot assemble flow with CONTENT_MISSING"
            )
        head = self._assemble_head(form)
        if self.content:
            return head + self.content
        else:
            return head

    def __hash__(self):
        return id(self)

    def anticache(self):
        """
            Modifies this request to remove headers that might produce a cached
            response. That is, we remove ETags and If-Modified-Since headers.
        """
        delheaders = [
            "if-modified-since",
            "if-none-match",
        ]
        for i in delheaders:
            del self.headers[i]

    def anticomp(self):
        """
            Modifies this request to remove headers that will compress the
            resource's data.
        """
        self.headers["accept-encoding"] = ["identity"]

    def constrain_encoding(self):
        """
            Limits the permissible Accept-Encoding values, based on what we can
            decode appropriately.
        """
        if self.headers["accept-encoding"]:
            self.headers["accept-encoding"] = [', '.join(
                e for e in encoding.ENCODINGS if e in self.headers["accept-encoding"][0]
            )]

    def update_host_header(self):
        """
            Update the host header to reflect the current target.
        """
        self.headers["Host"] = [self.host]

    def get_form_urlencoded(self):
        """
            Retrieves the URL-encoded form data, returning an ODict object.
            Returns an empty ODict if there is no data or the content-type
            indicates non-form data.
        """
        if self.content and self.headers.in_any("content-type", HDR_FORM_URLENCODED, True):
            return ODict(utils.urldecode(self.content))
        return ODict([])

    def set_form_urlencoded(self, odict):
        """
            Sets the body to the URL-encoded form data, and adds the
            appropriate content-type header. Note that this will destory the
            existing body if there is one.
        """
        # FIXME: If there's an existing content-type header indicating a
        # url-encoded form, leave it alone.
        self.headers["Content-Type"] = [HDR_FORM_URLENCODED]
        self.content = utils.urlencode(odict.lst)

    def get_path_components(self):
        """
            Returns the path components of the URL as a list of strings.

            Components are unquoted.
        """
        _, _, path, _, _, _ = urlparse.urlparse(self.url)
        return [urllib.unquote(i) for i in path.split("/") if i]

    def set_path_components(self, lst):
        """
            Takes a list of strings, and sets the path component of the URL.

            Components are quoted.
        """
        lst = [urllib.quote(i, safe="") for i in lst]
        path = "/" + "/".join(lst)
        scheme, netloc, _, params, query, fragment = urlparse.urlparse(self.url)
        self.url = urlparse.urlunparse(
            [scheme, netloc, path, params, query, fragment]
        )

    def get_query(self):
        """
            Gets the request query string. Returns an ODict object.
        """
        _, _, _, _, query, _ = urlparse.urlparse(self.url)
        if query:
            return ODict(utils.urldecode(query))
        return ODict([])

    def set_query(self, odict):
        """
            Takes an ODict object, and sets the request query string.
        """
        scheme, netloc, path, params, _, fragment = urlparse.urlparse(self.url)
        query = utils.urlencode(odict.lst)
        self.url = urlparse.urlunparse(
            [scheme, netloc, path, params, query, fragment]
        )

    def pretty_host(self, hostheader):
        """
            Heuristic to get the host of the request.

            Note that pretty_host() does not always return the TCP destination
            of the request, e.g. if an upstream proxy is in place

            If hostheader is set to True, the Host: header will be used as
            additional (and preferred) data source. This is handy in transparent
            mode, where only the ip of the destination is known, but not the
            resolved name. This is disabled by default, as an attacker may spoof
            the host header to confuse an analyst.

        """
        host = None
        if hostheader:
            host = self.headers.get_first("host")
        if not host:
            host = self.host
        host = host.encode("idna")
        return host

    def pretty_url(self, hostheader):
        if self.form_out == "authority":  # upstream proxy mode
            return "%s:%s" % (self.pretty_host(hostheader), self.port)
        return utils.unparse_url(self.scheme,
                                 self.pretty_host(hostheader),
                                 self.port,
                                 self.path).encode('ascii')

    @property
    def url(self):
        """
            Returns a URL string, constructed from the Request's URL components.
        """
        return utils.unparse_url(
            self.scheme,
            self.host,
            self.port,
            self.path
        ).encode('ascii')

    @url.setter
    def url(self, url):
        """
            Parses a URL specification, and updates the Request's information
            accordingly.

            Returns False if the URL was invalid, True if the request succeeded.
        """
        parts = http.parse_url(url)
        if not parts:
            raise ValueError("Invalid URL: %s" % url)
        self.scheme, self.host, self.port, self.path = parts

    def get_cookies(self):
        cookie_headers = self.headers.get("cookie")
        if not cookie_headers:
            return None

        cookies = []
        for header in cookie_headers:
            pairs = [pair.partition("=") for pair in header.split(';')]
            cookies.extend((pair[0], (pair[2], {})) for pair in pairs)
        return dict(cookies)

    def replace(self, pattern, repl, *args, **kwargs):
        """
            Replaces a regular expression pattern with repl in the headers, the
            request path and the body of the request. Encoded content will be
            decoded before replacement, and re-encoded afterwards.

            Returns the number of replacements made.
        """
        c = HTTPMessage.replace(self, pattern, repl, *args, **kwargs)
        self.path, pc = utils.safe_subn(
            pattern, repl, self.path, *args, **kwargs
        )
        c += pc
        return c


class HTTPResponse(HTTPMessage):
    """
    An HTTP response.

    Exposes the following attributes:

        httpversion: HTTP version tuple, e.g. (1,1)

        code: HTTP response code

        msg: HTTP response message

        headers: ODict object

        content: Content of the request, None, or CONTENT_MISSING if there
        is content associated, but not present. CONTENT_MISSING evaluates
        to False to make checking for the presence of content natural.

        timestamp_start: Timestamp indicating when request transmission started

        timestamp_end: Timestamp indicating when request transmission ended
    """

    def __init__(self, httpversion, code, msg, headers, content, timestamp_start=None,
                 timestamp_end=None):
        assert isinstance(headers, ODictCaseless) or headers is None
        HTTPMessage.__init__(
            self,
            httpversion,
            headers,
            content,
            timestamp_start,
            timestamp_end
        )

        self.code = code
        self.msg = msg

        # Is this request replayed?
        self.is_replay = False
        self.stream = False

    _stateobject_attributes = HTTPMessage._stateobject_attributes.copy()
    _stateobject_attributes.update(
        code=int,
        msg=str
    )

    @classmethod
    def from_state(cls, state):
        f = cls(None, None, None, None, None)
        f.load_state(state)
        return f

    def __repr__(self):
        size = utils.pretty_size(len(self.content)) if self.content else "content missing"
        return "<HTTPResponse: {code} {msg} ({contenttype}, {size})>".format(
            code=self.code,
            msg=self.msg,
            contenttype=self.headers.get_first(
                "content-type", "unknown content type"
            ),
            size=size
        )

    @classmethod
    def from_stream(cls, rfile, request_method, include_body=True, body_size_limit=None):
        """
        Parse an HTTP response from a file stream
        """

        timestamp_start = utils.timestamp()

        if hasattr(rfile, "reset_timestamps"):
            rfile.reset_timestamps()

        httpversion, code, msg, headers, content = http.read_response(
            rfile,
            request_method,
            body_size_limit,
            include_body=include_body)

        if hasattr(rfile, "first_byte_timestamp"):
            # more accurate timestamp_start
            timestamp_start = rfile.first_byte_timestamp

        if include_body:
            timestamp_end = utils.timestamp()
        else:
            timestamp_end = None

        return HTTPResponse(
            httpversion,
            code,
            msg,
            headers,
            content,
            timestamp_start,
            timestamp_end
        )

    def _assemble_first_line(self):
        return 'HTTP/%s.%s %s %s' % \
               (self.httpversion[0], self.httpversion[1], self.code, self.msg)

    def _assemble_headers(self, preserve_transfer_encoding=False):
        headers = self.headers.copy()
        for k in ['Proxy-Connection',
                  'Alternate-Protocol',
                  'Alt-Svc']:
            del headers[k]
        if not preserve_transfer_encoding:
            del headers['Transfer-Encoding']

        # If content is defined (i.e. not None or CONTENT_MISSING), we always add a content-length header.
        if self.content or self.content == "":
            headers["Content-Length"] = [str(len(self.content))]

        return str(headers)

    def _assemble_head(self, preserve_transfer_encoding=False):
        return '%s\r\n%s\r\n' % (
            self._assemble_first_line(),
            self._assemble_headers(
                preserve_transfer_encoding=preserve_transfer_encoding
            )
        )

    def assemble(self):
        """
            Assembles the response for transmission to the client. We make some
            modifications to make sure interception works properly.

            Raises an Exception if the request cannot be assembled.
        """
        if self.content == CONTENT_MISSING:
            raise proxy.ProxyError(
                502,
                "Cannot assemble flow with CONTENT_MISSING"
            )
        head = self._assemble_head()
        if self.content:
            return head + self.content
        else:
            return head

    def _refresh_cookie(self, c, delta):
        """
            Takes a cookie string c and a time delta in seconds, and returns
            a refreshed cookie string.
        """
        c = Cookie.SimpleCookie(str(c))
        for i in c.values():
            if "expires" in i:
                d = parsedate_tz(i["expires"])
                if d:
                    d = mktime_tz(d) + delta
                    i["expires"] = formatdate(d)
                else:
                    # This can happen when the expires tag is invalid.
                    # reddit.com sends a an expires tag like this: "Thu, 31 Dec
                    # 2037 23:59:59 GMT", which is valid RFC 1123, but not
                    # strictly correct according to the cookie spec. Browsers
                    # appear to parse this tolerantly - maybe we should too.
                    # For now, we just ignore this.
                    del i["expires"]
        return c.output(header="").strip()

    def refresh(self, now=None):
        """
            This fairly complex and heuristic function refreshes a server
            response for replay.

                - It adjusts date, expires and last-modified headers.
                - It adjusts cookie expiration.
        """
        if not now:
            now = time.time()
        delta = now - self.timestamp_start
        refresh_headers = [
            "date",
            "expires",
            "last-modified",
        ]
        for i in refresh_headers:
            if i in self.headers:
                d = parsedate_tz(self.headers[i][0])
                if d:
                    new = mktime_tz(d) + delta
                    self.headers[i] = [formatdate(new)]
        c = []
        for i in self.headers["set-cookie"]:
            c.append(self._refresh_cookie(i, delta))
        if c:
            self.headers["set-cookie"] = c

    def get_cookies(self):
        cookie_headers = self.headers.get("set-cookie")
        if not cookie_headers:
            return None

        cookies = []
        for header in cookie_headers:
            pairs = [pair.partition("=") for pair in header.split(';')]
            cookie_name = pairs[0][0]  # the key of the first key/value pairs
            cookie_value = pairs[0][2]  # the value of the first key/value pairs
            cookie_parameters = {
                key.strip().lower(): value.strip() for key, sep, value in pairs[1:]
            }
            cookies.append((cookie_name, (cookie_value, cookie_parameters)))
        return dict(cookies)


class HTTPFlow(Flow):
    """
    A HTTPFlow is a collection of objects representing a single HTTP
    transaction. The main attributes are:

        request: HTTPRequest object
        response: HTTPResponse object
        error: Error object
        server_conn: ServerConnection object
        client_conn: ClientConnection object

    Note that it's possible for a Flow to have both a response and an error
    object. This might happen, for instance, when a response was received
    from the server, but there was an error sending it back to the client.

    The following additional attributes are exposed:

        intercepting: Is this flow currently being intercepted?
        live: Does this flow have a live client connection?
    """

    def __init__(self, client_conn, server_conn, live=None):
        super(HTTPFlow, self).__init__("http", client_conn, server_conn, live)
        self.request = None
        """@type: HTTPRequest"""
        self.response = None
        """@type: HTTPResponse"""

        # FIXME: Should that rather be an attribute of Flow?
        self.intercepting = False

    _stateobject_attributes = Flow._stateobject_attributes.copy()
    _stateobject_attributes.update(
        request=HTTPRequest,
        response=HTTPResponse
    )

    @classmethod
    def from_state(cls, state):
        f = cls(None, None)
        f.load_state(state)
        return f

    def __repr__(self):
        s = "<HTTPFlow"
        for a in ("request", "response", "error", "client_conn", "server_conn"):
            if getattr(self, a, False):
                s += "\r\n  %s = {flow.%s}" % (a, a)
        s += ">"
        return s.format(flow=self)

    def copy(self):
        f = super(HTTPFlow, self).copy()
        if self.request:
            f.request = self.request.copy()
        if self.response:
            f.response = self.response.copy()
        return f

    def match(self, f):
        """
            Match this flow against a compiled filter expression. Returns True
            if matched, False if not.

            If f is a string, it will be compiled as a filter expression. If
            the expression is invalid, ValueError is raised.
        """
        if isinstance(f, basestring):
            from .. import filt

            f = filt.parse(f)
            if not f:
                raise ValueError("Invalid filter expression.")
        if f:
            return f(self)
        return True

    def kill(self, master):
        """
            Kill this request.
        """
        self.error = Error("Connection killed")
        self.intercepting = False
        self.reply(KILL)
        self.reply = controller.DummyReply()
        master.handle_error(self)

    def intercept(self):
        """
            Intercept this Flow. Processing will stop until accept_intercept is
            called.
        """
        self.intercepting = True

    def accept_intercept(self):
        """
            Continue with the flow - called after an intercept().
        """
        self.intercepting = False
        self.reply()

    def replace(self, pattern, repl, *args, **kwargs):
        """
            Replaces a regular expression pattern with repl in both request and
            response of the flow. Encoded content will be decoded before
            replacement, and re-encoded afterwards.

            Returns the number of replacements made.
        """
        c = self.request.replace(pattern, repl, *args, **kwargs)
        if self.response:
            c += self.response.replace(pattern, repl, *args, **kwargs)
        return c


class HttpAuthenticationError(Exception):
    def __init__(self, auth_headers=None):
        super(HttpAuthenticationError, self).__init__(
            "Proxy Authentication Required"
        )
        self.headers = auth_headers
        self.code = 407

    def __repr__(self):
        return "Proxy Authentication Required"


class HTTPHandler(ProtocolHandler):
    """
    HTTPHandler implements mitmproxys understanding of the HTTP protocol.

    """

    def __init__(self, c):
        super(HTTPHandler, self).__init__(c)
        self.expected_form_in = c.config.mode.http_form_in
        self.expected_form_out = c.config.mode.http_form_out
        self.skip_authentication = False

    def handle_messages(self):
        while self.handle_flow():
            pass

    def get_response_from_server(self, flow):
        self.c.establish_server_connection()
        request_raw = flow.request.assemble()

        for attempt in (0, 1):
            try:
                self.c.server_conn.send(request_raw)
                # Only get the headers at first...
                flow.response = HTTPResponse.from_stream(
                    self.c.server_conn.rfile, flow.request.method,
                    body_size_limit=self.c.config.body_size_limit,
                    include_body=False
                )
                break
            except (tcp.NetLibDisconnect, http.HttpErrorConnClosed), v:
                self.c.log(
                    "error in server communication: %s" % repr(v),
                    level="debug"
                )
                if attempt == 0:
                    # In any case, we try to reconnect at least once. This is
                    # necessary because it might be possible that we already
                    # initiated an upstream connection after clientconnect that
                    # has already been expired, e.g consider the following event
                    # log:
                    # > clientconnect (transparent mode destination known)
                    # > serverconnect
                    # > read n% of large request
                    # > server detects timeout, disconnects
                    # > read (100-n)% of large request
                    # > send large request upstream
                    self.c.server_reconnect()
                else:
                    raise

        # call the appropriate script hook - this is an opportunity for an
        # inline script to set flow.stream = True
        flow = self.c.channel.ask("responseheaders", flow)
        if flow == KILL:
            raise KillSignal()
        else:
            # now get the rest of the request body, if body still needs to be
            # read but not streaming this response
            if flow.response.stream:
                flow.response.content = CONTENT_MISSING
            else:
                flow.response.content = http.read_http_body(
                    self.c.server_conn.rfile, flow.response.headers,
                    self.c.config.body_size_limit,
                    flow.request.method, flow.response.code, False
                )
        flow.response.timestamp_end = utils.timestamp()

    def handle_flow(self):
        flow = HTTPFlow(self.c.client_conn, self.c.server_conn, self.live)
        try:
            try:
                req = HTTPRequest.from_stream(
                    self.c.client_conn.rfile,
                    body_size_limit=self.c.config.body_size_limit
                )
            except tcp.NetLibDisconnect:
                # don't throw an error for disconnects that happen
                # before/between requests.
                return False
            self.c.log(
                "request",
                "debug",
                [req._assemble_first_line(req.form_in)]
            )
            ret = self.process_request(flow, req)
            if ret is not None:
                return ret

            # Be careful NOT to assign the request to the flow before
            # process_request completes. This is because the call can raise an
            # exception. If the request object is already attached, this results
            # in an Error object that has an attached request that has not been
            # sent through to the Master.
            flow.request = req
            request_reply = self.c.channel.ask("request", flow)
            self.process_server_address(flow)  # The inline script may have changed request.host

            if request_reply is None or request_reply == KILL:
                raise KillSignal()

            if isinstance(request_reply, HTTPResponse):
                flow.response = request_reply
            else:
                self.get_response_from_server(flow)

            # no further manipulation of self.c.server_conn beyond this point
            # we can safely set it as the final attribute value here.
            flow.server_conn = self.c.server_conn

            self.c.log("response", "debug", [flow.response._assemble_first_line()])
            response_reply = self.c.channel.ask("response", flow)
            if response_reply is None or response_reply == KILL:
                raise KillSignal()

            self.send_response_to_client(flow)

            if self.check_close_connection(flow):
                return False

            # We sent a CONNECT request to an upstream proxy.
            if flow.request.form_in == "authority" and flow.response.code == 200:
                # TODO: Possibly add headers (memory consumption/usefulness
                # tradeoff) Make sure to add state info before the actual
                # processing of the CONNECT request happens. During an SSL
                # upgrade, we may receive an SNI indication from the client,
                # which resets the upstream connection. If this is the case, we
                # must already re-issue the CONNECT request at this point.
                self.c.server_conn.state.append(
                    (
                        "http", {
                            "state": "connect",
                            "host": flow.request.host,
                            "port": flow.request.port
                        }
                    )
                )
                if not self.process_connect_request((flow.request.host, flow.request.port)):
                    return False

            # If the user has changed the target server on this connection,
            # restore the original target server
            flow.live.restore_server()

            return True  # Next flow please.
        except (
                HttpAuthenticationError,
                http.HttpError,
                proxy.ProxyError,
                tcp.NetLibError,
        ), e:
            self.handle_error(e, flow)
        except KillSignal:
            self.c.log("Connection killed", "info")
        finally:
            flow.live = None  # Connection is not live anymore.
        return False

    def handle_server_reconnect(self, state):
        if state["state"] == "connect":
            send_connect_request(
                self.c.server_conn,
                state["host"],
                state["port"],
                update_state=False
            )
        else:  # pragma: nocover
            raise RuntimeError("Unknown State: %s" % state["state"])

    def handle_error(self, error, flow=None):

        message = repr(error)
        message_debug = None

        if isinstance(error, tcp.NetLibDisconnect):
            message = None
            message_debug = "TCP connection closed unexpectedly."
        elif "tlsv1 alert unknown ca" in message:
            message = "TLSv1 Alert Unknown CA: The client does not trust the proxy's certificate."
        elif "handshake error" in message:
            message_debug = message
            message = "SSL handshake error: The client may not trust the proxy's certificate."

        if message:
            self.c.log(message, level="info")
        if message_debug:
            self.c.log(message_debug, level="debug")

        if flow:
            # TODO: no flows without request or with both request and response
            # at the moment.
            if flow.request and not flow.response:
                flow.error = Error(message or message_debug)
                self.c.channel.ask("error", flow)
        try:
            code = getattr(error, "code", 502)
            headers = getattr(error, "headers", None)

            html_message = message or ""
            if message_debug:
                html_message += "<pre>%s</pre>" % message_debug
            self.send_error(code, html_message, headers)
        except:
            pass

    def send_error(self, code, message, headers):
        response = http_status.RESPONSES.get(code, "Unknown")
        html_content = """
            <html>
                <head>
                    <title>%d %s</title>
                </head>
                <body %s</body>
            </html>
        """ % (code, response, message)
        self.c.client_conn.wfile.write("HTTP/1.1 %s %s\r\n" % (code, response))
        self.c.client_conn.wfile.write(
            "Server: %s\r\n" % self.c.config.server_version
        )
        self.c.client_conn.wfile.write("Content-type: text/html\r\n")
        self.c.client_conn.wfile.write(
            "Content-Length: %d\r\n" % len(html_content)
        )
        if headers:
            for key, value in headers.items():
                self.c.client_conn.wfile.write("%s: %s\r\n" % (key, value))
        self.c.client_conn.wfile.write("Connection: close\r\n")
        self.c.client_conn.wfile.write("\r\n")
        self.c.client_conn.wfile.write(html_content)
        self.c.client_conn.wfile.flush()

    def process_request(self, flow, request):
        """
        @returns:
        True, if the request should not be sent upstream
        False, if the connection should be aborted
        None, if the request should be sent upstream
        (a status code != None should be returned directly by handle_flow)
        """

        if not self.skip_authentication:
            self.authenticate(request)

        # Determine .scheme, .host and .port attributes
        # For absolute-form requests, they are directly given in the request.
        # For authority-form requests, we only need to determine the request scheme.
        # For relative-form requests, we need to determine host and port as well.
        if not request.scheme:
            request.scheme = "https" if flow.server_conn and flow.server_conn.ssl_established else "http"
        if not request.host:
            # Host/Port Complication: In upstream mode, use the server we CONNECTed to,
            # not the upstream proxy.
            if flow.server_conn:
                for s in flow.server_conn.state:
                    if s[0] == "http" and s[1]["state"] == "connect":
                        request.host, request.port = s[1]["host"], s[1]["port"]
            if not request.host and flow.server_conn:
                request.host, request.port = flow.server_conn.address.host, flow.server_conn.address.port

        # Now we can process the request.
        if request.form_in == "authority":
            if self.c.client_conn.ssl_established:
                raise http.HttpError(
                    400,
                    "Must not CONNECT on already encrypted connection"
                )

            if self.c.config.mode == "regular":
                self.c.set_server_address((request.host, request.port))
                # Update server_conn attribute on the flow
                flow.server_conn = self.c.server_conn
                self.c.establish_server_connection()
                self.c.client_conn.send(
                    'HTTP/1.1 200 Connection established\r\n' +
                    'Content-Length: 0\r\n' +
                    ('Proxy-agent: %s\r\n' % self.c.config.server_version) +
                    '\r\n'
                )
                return self.process_connect_request(self.c.server_conn.address)
            elif self.c.config.mode == "upstream":
                return None
            else:
                # CONNECT should never occur if we don't expect absolute-form
                # requests
                pass

        elif request.form_in == self.expected_form_in:

            request.form_out = self.expected_form_out

            if request.form_in == "absolute":
                if request.scheme != "http":
                    raise http.HttpError(
                        400,
                        "Invalid request scheme: %s" % request.scheme
                    )
                if self.c.config.mode == "regular":
                    # Update info so that an inline script sees the correct
                    # value at flow.server_conn
                    self.c.set_server_address((request.host, request.port))
                    flow.server_conn = self.c.server_conn

            return None
        raise http.HttpError(
            400, "Invalid HTTP request form (expected: %s, got: %s)" % (
                self.expected_form_in, request.form_in
            )
        )

    def process_server_address(self, flow):
        # Depending on the proxy mode, server handling is entirely different
        # We provide a mostly unified API to the user, which needs to be
        # unfiddled here
        # ( See also: https://github.com/mitmproxy/mitmproxy/issues/337 )
        address = netlib.tcp.Address((flow.request.host, flow.request.port))

        ssl = (flow.request.scheme == "https")

        if self.c.config.mode == "upstream":
            # The connection to the upstream proxy may have a state we may need
            # to take into account.
            connected_to = None
            for s in flow.server_conn.state:
                if s[0] == "http" and s[1]["state"] == "connect":
                    connected_to = tcp.Address((s[1]["host"], s[1]["port"]))

            # We need to reconnect if the current flow either requires a
            # (possibly impossible) change to the connection state, e.g. the
            # host has changed but we already CONNECTed somewhere else.
            needs_server_change = (
                ssl != self.c.server_conn.ssl_established
                or
                # HTTP proxying is "stateless", CONNECT isn't.
                (connected_to and address != connected_to)
            )

            if needs_server_change:
                # force create new connection to the proxy server to reset state
                self.live.change_server(self.c.server_conn.address, force=True)
                if ssl:
                    send_connect_request(
                        self.c.server_conn,
                        address.host,
                        address.port
                    )
                    self.c.establish_ssl(server=True)
        else:
            # If we're not in upstream mode, we just want to update the host and
            # possibly establish TLS. This is a no op if the addresses match.
            self.live.change_server(address, ssl=ssl)

        flow.server_conn = self.c.server_conn

    def send_response_to_client(self, flow):
        if not flow.response.stream:
            # no streaming:
            # we already received the full response from the server and can send
            # it to the client straight away.
            self.c.client_conn.send(flow.response.assemble())
        else:
            # streaming:
            # First send the headers and then transfer the response
            # incrementally:
            h = flow.response._assemble_head(preserve_transfer_encoding=True)
            self.c.client_conn.send(h)
            for chunk in http.read_http_body_chunked(self.c.server_conn.rfile,
                                                     flow.response.headers,
                                                     self.c.config.body_size_limit, flow.request.method,
                                                     flow.response.code, False, 4096):
                for part in chunk:
                    self.c.client_conn.wfile.write(part)
                self.c.client_conn.wfile.flush()
            flow.response.timestamp_end = utils.timestamp()

    def check_close_connection(self, flow):
        """
            Checks if the connection should be closed depending on the HTTP
            semantics. Returns True, if so.
        """
        close_connection = (
            http.connection_close(flow.request.httpversion, flow.request.headers) or
            http.connection_close(flow.response.httpversion, flow.response.headers) or
            http.expected_http_body_size(flow.response.headers, False, flow.request.method,
                                         flow.response.code) == -1)
        if close_connection:
            if flow.request.form_in == "authority" and flow.response.code == 200:
                # Workaround for https://github.com/mitmproxy/mitmproxy/issues/313:
                # Some proxies (e.g. Charles) send a CONNECT response with HTTP/1.0 and no Content-Length header
                pass
            else:
                return True
        return False

    def process_connect_request(self, address):
        """
        Process a CONNECT request.
        Returns True if the CONNECT request has been processed successfully.
        Returns False, if the connection should be closed immediately.
        """
        address = tcp.Address.wrap(address)
        if self.c.config.check_ignore(address):
            self.c.log("Ignore host: %s:%s" % address(), "info")
            TCPHandler(self.c, log=False).handle_messages()
            return False
        else:
            self.expected_form_in = "relative"
            self.expected_form_out = "relative"
            self.skip_authentication = True

            # In practice, nobody issues a CONNECT request to send unencrypted HTTP requests afterwards.
            # If we don't delegate to TCP mode, we should always negotiate a SSL connection.
            should_establish_ssl = (
                address.port in self.c.config.ssl_ports
                or
                not self.c.config.check_tcp(address)
            )

            if should_establish_ssl:
                self.c.log("Received CONNECT request to SSL port. Upgrading to SSL...", "debug")
                self.c.establish_ssl(server=True, client=True)
                self.c.log("Upgrade to SSL completed.", "debug")

            if self.c.config.check_tcp(address):
                self.c.log("Generic TCP mode for host: %s:%s" % address(), "info")
                TCPHandler(self.c).handle_messages()
                return False

            return True

    def authenticate(self, request):
        if self.c.config.authenticator:
            if self.c.config.authenticator.authenticate(request.headers):
                self.c.config.authenticator.clean(request.headers)
            else:
                raise HttpAuthenticationError(
                    self.c.config.authenticator.auth_challenge_headers())
        return request.headers


class RequestReplayThread(threading.Thread):
    name = "RequestReplayThread"

    def __init__(self, config, flow, masterq, should_exit):
        self.config, self.flow, self.channel = config, flow, controller.Channel(masterq, should_exit)
        threading.Thread.__init__(self)

    def run(self):
        r = self.flow.request
        form_out_backup = r.form_out
        try:
            self.flow.response = None
            request_reply = self.channel.ask("request", self.flow)
            if request_reply is None or request_reply == KILL:
                raise KillSignal()
            elif isinstance(request_reply, HTTPResponse):
                self.flow.response = request_reply
            else:
                # In all modes, we directly connect to the server displayed
                if self.config.mode == "upstream":
                    server_address = self.config.mode.get_upstream_server(self.flow.client_conn)[2:]
                    server = ServerConnection(server_address)
                    server.connect()
                    if r.scheme == "https":
                        send_connect_request(server, r.host, r.port)
                        server.establish_ssl(self.config.clientcerts, sni=self.flow.server_conn.sni)
                        r.form_out = "relative"
                    else:
                        r.form_out = "absolute"
                else:
                    server_address = (r.host, r.port)
                    server = ServerConnection(server_address)
                    server.connect()
                    if r.scheme == "https":
                        server.establish_ssl(self.config.clientcerts, sni=self.flow.server_conn.sni)
                    r.form_out = "relative"

                server.send(r.assemble())
                self.flow.server_conn = server
                self.flow.response = HTTPResponse.from_stream(server.rfile, r.method,
                                                              body_size_limit=self.config.body_size_limit)
            response_reply = self.channel.ask("response", self.flow)
            if response_reply is None or response_reply == KILL:
                raise KillSignal()
        except (proxy.ProxyError, http.HttpError, tcp.NetLibError) as v:
            self.flow.error = Error(repr(v))
            self.channel.ask("error", self.flow)
        except KillSignal:
            self.channel.tell("log", proxy.Log("Connection killed", "info"))
        finally:
            r.form_out = form_out_backup