mitmproxy/libmproxy/flow.py

"""
    This module provides more sophisticated flow tracking and provides filtering and interception facilities.
"""
from __future__ import absolute_import
from abc import abstractmethod, ABCMeta
import hashlib
import Cookie
import cookielib
import os
import re
import urlparse
import inspect

from netlib import wsgi
from netlib.exceptions import HttpException
from netlib.http import CONTENT_MISSING, Headers, http1
import netlib.http
from . import controller, tnetstring, filt, script, version
from .onboarding import app
from .proxy.config import HostMatcher
from .protocol.http_replay import RequestReplayThread
from .protocol import Kill
from .models import ClientConnection, ServerConnection, HTTPResponse, HTTPFlow, HTTPRequest
from . import contentviews as cv


class PluginError(Exception):
    pass


class AppRegistry:
    def __init__(self):
        self.apps = {}

    def add(self, app, domain, port):
        """
            Add a WSGI app to the registry, to be served for requests to the
            specified domain, on the specified port.
        """
        self.apps[(domain, port)] = wsgi.WSGIAdaptor(
            app,
            domain,
            port,
            version.NAMEVERSION
        )

    def get(self, request):
        """
            Returns an WSGIAdaptor instance if request matches an app, or None.
        """
        if (request.host, request.port) in self.apps:
            return self.apps[(request.host, request.port)]
        if "host" in request.headers:
            host = request.headers["host"]
            return self.apps.get((host, request.port), None)


class ReplaceHooks:
    def __init__(self):
        self.lst = []

    def set(self, r):
        self.clear()
        for i in r:
            self.add(*i)

    def add(self, fpatt, rex, s):
        """
            add a replacement hook.

            fpatt: a string specifying a filter pattern.
            rex: a regular expression.
            s: the replacement string

            returns true if hook was added, false if the pattern could not be
            parsed.
        """
        cpatt = filt.parse(fpatt)
        if not cpatt:
            return False
        try:
            re.compile(rex)
        except re.error:
            return False
        self.lst.append((fpatt, rex, s, cpatt))
        return True

    def get_specs(self):
        """
            Retrieve the hook specifcations. Returns a list of (fpatt, rex, s)
            tuples.
        """
        return [i[:3] for i in self.lst]

    def count(self):
        return len(self.lst)

    def run(self, f):
        for _, rex, s, cpatt in self.lst:
            if cpatt(f):
                if f.response:
                    f.response.replace(rex, s)
                else:
                    f.request.replace(rex, s)

    def clear(self):
        self.lst = []


class SetHeaders:
    def __init__(self):
        self.lst = []

    def set(self, r):
        self.clear()
        for i in r:
            self.add(*i)

    def add(self, fpatt, header, value):
        """
            Add a set header hook.

            fpatt: String specifying a filter pattern.
            header: Header name.
            value: Header value string

            Returns True if hook was added, False if the pattern could not be
            parsed.
        """
        cpatt = filt.parse(fpatt)
        if not cpatt:
            return False
        self.lst.append((fpatt, header, value, cpatt))
        return True

    def get_specs(self):
        """
            Retrieve the hook specifcations. Returns a list of (fpatt, rex, s)
            tuples.
        """
        return [i[:3] for i in self.lst]

    def count(self):
        return len(self.lst)

    def clear(self):
        self.lst = []

    def run(self, f):
        for _, header, value, cpatt in self.lst:
            if cpatt(f):
                if f.response:
                    f.response.headers.pop(header, None)
                else:
                    f.request.headers.pop(header, None)
        for _, header, value, cpatt in self.lst:
            if cpatt(f):
                if f.response:
                    f.response.headers.fields.append((header, value))
                else:
                    f.request.headers.fields.append((header, value))


class StreamLargeBodies(object):
    def __init__(self, max_size):
        self.max_size = max_size

    def run(self, flow, is_request):
        r = flow.request if is_request else flow.response
        expected_size = http1.expected_http_body_size(
            flow.request, flow.response if not is_request else None
        )
        if not (0 <= expected_size <= self.max_size):
            # r.stream may already be a callable, which we want to preserve.
            r.stream = r.stream or True


class ClientPlaybackState:
    def __init__(self, flows, exit):
        self.flows, self.exit = flows, exit
        self.current = None
        self.testing = False  # Disables actual replay for testing.

    def count(self):
        return len(self.flows)

    def done(self):
        if len(self.flows) == 0 and not self.current:
            return True
        return False

    def clear(self, flow):
        """
           A request has returned in some way - if this is the one we're
           servicing, go to the next flow.
        """
        if flow is self.current:
            self.current = None

    def tick(self, master):
        if self.flows and not self.current:
            self.current = self.flows.pop(0).copy()
            if not self.testing:
                master.replay_request(self.current)
            else:
                self.current.reply = controller.DummyReply()
                master.handle_request(self.current)
                if self.current.response:
                    master.handle_response(self.current)


class ServerPlaybackState:
    def __init__(
            self,
            headers,
            flows,
            exit,
            nopop,
            ignore_params,
            ignore_content,
            ignore_payload_params,
            ignore_host):
        """
            headers: Case-insensitive list of request headers that should be
            included in request-response matching.
        """
        self.headers = headers
        self.exit = exit
        self.nopop = nopop
        self.ignore_params = ignore_params
        self.ignore_content = ignore_content
        self.ignore_payload_params = ignore_payload_params
        self.ignore_host = ignore_host
        self.fmap = {}
        for i in flows:
            if i.response:
                l = self.fmap.setdefault(self._hash(i), [])
                l.append(i)

    def count(self):
        return sum(len(i) for i in self.fmap.values())

    def _hash(self, flow):
        """
            Calculates a loose hash of the flow request.
        """
        r = flow.request

        _, _, path, _, query, _ = urlparse.urlparse(r.url)
        queriesArray = urlparse.parse_qsl(query, keep_blank_values=True)

        key = [
            str(r.port),
            str(r.scheme),
            str(r.method),
            str(path),
        ]

        if not self.ignore_content:
            form_contents = r.urlencoded_form or r.multipart_form
            if self.ignore_payload_params and form_contents:
                key.extend(
                    p for p in form_contents
                    if p[0] not in self.ignore_payload_params
                )
            else:
                key.append(str(r.content))

        if not self.ignore_host:
            key.append(r.host)

        filtered = []
        ignore_params = self.ignore_params or []
        for p in queriesArray:
            if p[0] not in ignore_params:
                filtered.append(p)
        for p in filtered:
            key.append(p[0])
            key.append(p[1])

        if self.headers:
            headers = []
            for i in self.headers:
                v = r.headers.get(i)
                headers.append((i, v))
            key.append(headers)
        return hashlib.sha256(repr(key)).digest()

    def next_flow(self, request):
        """
            Returns the next flow object, or None if no matching flow was
            found.
        """
        l = self.fmap.get(self._hash(request))
        if not l:
            return None

        if self.nopop:
            return l[0]
        else:
            return l.pop(0)


class StickyCookieState:
    def __init__(self, flt):
        """
            flt: Compiled filter.
        """
        self.jar = {}
        self.flt = flt

    def ckey(self, m, f):
        """
            Returns a (domain, port, path) tuple.
        """
        return (
            m["domain"] or f.request.host,
            f.request.port,
            m["path"] or "/"
        )

    def domain_match(self, a, b):
        if cookielib.domain_match(a, b):
            return True
        elif cookielib.domain_match(a, b.strip(".")):
            return True
        return False

    def handle_response(self, f):
        for i in f.response.headers.get_all("set-cookie"):
            # FIXME: We now know that Cookie.py screws up some cookies with
            # valid RFC 822/1123 datetime specifications for expiry. Sigh.
            c = Cookie.SimpleCookie(str(i))
            for m in c.values():
                k = self.ckey(m, f)
                if self.domain_match(f.request.host, k[0]):
                    self.jar[k] = m

    def handle_request(self, f):
        l = []
        if f.match(self.flt):
            for i in self.jar.keys():
                match = [
                    self.domain_match(f.request.host, i[0]),
                    f.request.port == i[1],
                    f.request.path.startswith(i[2])
                ]
                if all(match):
                    l.append(self.jar[i].output(header="").strip())
        if l:
            f.request.stickycookie = True
            f.request.headers.set_all("cookie",l)


class StickyAuthState:
    def __init__(self, flt):
        """
            flt: Compiled filter.
        """
        self.flt = flt
        self.hosts = {}

    def handle_request(self, f):
        host = f.request.host
        if "authorization" in f.request.headers:
            self.hosts[host] = f.request.headers["authorization"]
        elif f.match(self.flt):
            if host in self.hosts:
                f.request.headers["authorization"] = self.hosts[host]


class FlowList(object):
    __metaclass__ = ABCMeta

    def __iter__(self):
        return iter(self._list)

    def __contains__(self, item):
        return item in self._list

    def __getitem__(self, item):
        return self._list[item]

    def __nonzero__(self):
        return bool(self._list)

    def __len__(self):
        return len(self._list)

    def index(self, f):
        return self._list.index(f)

    @abstractmethod
    def _add(self, f):
        return

    @abstractmethod
    def _update(self, f):
        return

    @abstractmethod
    def _remove(self, f):
        return


class FlowView(FlowList):
    def __init__(self, store, filt=None):
        self._list = []
        if not filt:
            filt = lambda flow: True
        self._build(store, filt)

        self.store = store
        self.store.views.append(self)

    def _close(self):
        self.store.views.remove(self)

    def _build(self, flows, filt=None):
        if filt:
            self.filt = filt
        self._list = list(filter(self.filt, flows))

    def _add(self, f):
        if self.filt(f):
            self._list.append(f)

    def _update(self, f):
        if f not in self._list:
            self._add(f)
        elif not self.filt(f):
            self._remove(f)

    def _remove(self, f):
        if f in self._list:
            self._list.remove(f)

    def _recalculate(self, flows):
        self._build(flows)


class FlowStore(FlowList):
    """
    Responsible for handling flows in the state:
    Keeps a list of all flows and provides views on them.
    """

    def __init__(self):
        self._list = []
        self._set = set()  # Used for O(1) lookups
        self.views = []
        self._recalculate_views()

    def get(self, flow_id):
        for f in self._list:
            if f.id == flow_id:
                return f

    def __contains__(self, f):
        return f in self._set

    def _add(self, f):
        """
        Adds a flow to the state.
        The flow to add must not be present in the state.
        """
        self._list.append(f)
        self._set.add(f)
        for view in self.views:
            view._add(f)

    def _update(self, f):
        """
        Notifies the state that a flow has been updated.
        The flow must be present in the state.
        """
        if f in self:
            for view in self.views:
                view._update(f)

    def _remove(self, f):
        """
        Deletes a flow from the state.
        The flow must be present in the state.
        """
        self._list.remove(f)
        self._set.remove(f)
        for view in self.views:
            view._remove(f)

    # Expensive bulk operations

    def _extend(self, flows):
        """
        Adds a list of flows to the state.
        The list of flows to add must not contain flows that are already in the state.
        """
        self._list.extend(flows)
        self._set.update(flows)
        self._recalculate_views()

    def _clear(self):
        self._list = []
        self._set = set()
        self._recalculate_views()

    def _recalculate_views(self):
        """
        Expensive operation: Recalculate all the views after a bulk change.
        """
        for view in self.views:
            view._recalculate(self)

    # Utility functions.
    # There are some common cases where we need to argue about all flows
    # irrespective of filters on the view etc (i.e. on shutdown).

    def active_count(self):
        c = 0
        for i in self._list:
            if not i.response and not i.error:
                c += 1
        return c

    # TODO: Should accept_all operate on views or on all flows?
    def accept_all(self, master):
        for f in self._list:
            f.accept_intercept(master)

    def kill_all(self, master):
        for f in self._list:
            f.kill(master)


class State(object):
    def __init__(self):
        self.flows = FlowStore()
        self.view = FlowView(self.flows, None)

        # These are compiled filt expressions:
        self.intercept = None

    @property
    def limit_txt(self):
        return getattr(self.view.filt, "pattern", None)

    def flow_count(self):
        return len(self.flows)

    # TODO: All functions regarding flows that don't cause side-effects should
    # be moved into FlowStore.
    def index(self, f):
        return self.flows.index(f)

    def active_flow_count(self):
        return self.flows.active_count()

    def add_flow(self, f):
        """
            Add a request to the state.
        """
        self.flows._add(f)
        return f

    def update_flow(self, f):
        """
            Add a response to the state.
        """
        self.flows._update(f)
        return f

    def delete_flow(self, f):
        self.flows._remove(f)

    def load_flows(self, flows):
        self.flows._extend(flows)

    def set_limit(self, txt):
        if txt == self.limit_txt:
            return
        if txt:
            f = filt.parse(txt)
            if not f:
                return "Invalid filter expression."
            self.view._close()
            self.view = FlowView(self.flows, f)
        else:
            self.view._close()
            self.view = FlowView(self.flows, None)

    def set_intercept(self, txt):
        if txt:
            f = filt.parse(txt)
            if not f:
                return "Invalid filter expression."
            self.intercept = f
        else:
            self.intercept = None

    @property
    def intercept_txt(self):
        return getattr(self.intercept, "pattern", None)

    def clear(self):
        self.flows._clear()

    def accept_all(self, master):
        self.flows.accept_all(master)

    def backup(self, f):
        f.backup()
        self.update_flow(f)

    def revert(self, f):
        f.revert()
        self.update_flow(f)

    def killall(self, master):
        self.flows.kill_all(master)


class Plugins(object):
    def __init__(self):
        self._view_plugins = {}

    def __iter__(self):
        for plugin_type in ('view_plugins',):
            yield (plugin_type, getattr(self, '_' + plugin_type))

    def __getitem__(self, key):
        if key in ('view_plugins',):
            return getattr(self, '_' + key)
        else:
            return None

    def register_view(self, id, **kwargs):
        if self._view_plugins.get(id):
            raise PluginError("Duplicate view registration for %s" % (id, ))

        if not kwargs.get('class_ref') or not \
                callable(kwargs['class_ref']) or not \
                isinstance(kwargs['class_ref'], type):
            raise PluginError("No custom content view class passed for view %s" % (id, ))

        script_path = inspect.stack()[1][1]

        view_plugin = {
            'title': kwargs.get('title') or id,
            'class_ref': kwargs['class_ref'],
            'script_path': script_path,
        }
        self._view_plugins[id] = view_plugin

        cv.add(kwargs['class_ref']())

        print("Registered view plugin %s from script %s" % (kwargs['title'], script_path))


class FlowMaster(controller.Master):
    def __init__(self, server, state):
        controller.Master.__init__(self, server)
        self.state = state
        self.server_playback = None
        self.client_playback = None
        self.kill_nonreplay = False
        self.scripts = []
        self.pause_scripts = False

        self.stickycookie_state = False
        self.stickycookie_txt = None

        self.stickyauth_state = False
        self.stickyauth_txt = None

        self.anticache = False
        self.anticomp = False
        self.stream_large_bodies = False
        self.refresh_server_playback = False
        self.replacehooks = ReplaceHooks()
        self.setheaders = SetHeaders()
        self.replay_ignore_params = False
        self.replay_ignore_content = None
        self.replay_ignore_host = False

        self.stream = None
        self.apps = AppRegistry()

        self.plugins = Plugins()

    def start_app(self, host, port):
        self.apps.add(
            app.mapp,
            host,
            port
        )

    def add_event(self, e, level="info"):
        """
            level: debug, info, error
        """
        pass

    def unload_scripts(self):
        for s in self.scripts[:]:
            self.unload_script(s)

    def unload_script(self, script_obj):
        try:
            script_obj.unload()
        except script.ScriptError as e:
            self.add_event("Script error:\n" + str(e), "error")
        self.scripts.remove(script_obj)

    def load_script(self, command):
        """
            Loads a script. Returns an error description if something went
            wrong.
        """
        try:
            s = script.Script(command, self)
        except script.ScriptError as v:
            return v.args[0]
        self.scripts.append(s)

    def _run_single_script_hook(self, script_obj, name, *args, **kwargs):
        if script_obj and not self.pause_scripts:
            try:
                script_obj.run(name, *args, **kwargs)
            except script.ScriptError as e:
                self.add_event("Script error:\n" + str(e), "error")

    def run_script_hook(self, name, *args, **kwargs):
        for script_obj in self.scripts:
            self._run_single_script_hook(script_obj, name, *args, **kwargs)

    def get_ignore_filter(self):
        return self.server.config.check_ignore.patterns

    def set_ignore_filter(self, host_patterns):
        self.server.config.check_ignore = HostMatcher(host_patterns)

    def get_tcp_filter(self):
        return self.server.config.check_tcp.patterns

    def set_tcp_filter(self, host_patterns):
        self.server.config.check_tcp = HostMatcher(host_patterns)

    def set_stickycookie(self, txt):
        if txt:
            flt = filt.parse(txt)
            if not flt:
                return "Invalid filter expression."
            self.stickycookie_state = StickyCookieState(flt)
            self.stickycookie_txt = txt
        else:
            self.stickycookie_state = None
            self.stickycookie_txt = None

    def set_stream_large_bodies(self, max_size):
        if max_size is not None:
            self.stream_large_bodies = StreamLargeBodies(max_size)
        else:
            self.stream_large_bodies = False

    def set_stickyauth(self, txt):
        if txt:
            flt = filt.parse(txt)
            if not flt:
                return "Invalid filter expression."
            self.stickyauth_state = StickyAuthState(flt)
            self.stickyauth_txt = txt
        else:
            self.stickyauth_state = None
            self.stickyauth_txt = None

    def start_client_playback(self, flows, exit):
        """
            flows: List of flows.
        """
        self.client_playback = ClientPlaybackState(flows, exit)

    def stop_client_playback(self):
        self.client_playback = None

    def start_server_playback(
            self,
            flows,
            kill,
            headers,
            exit,
            nopop,
            ignore_params,
            ignore_content,
            ignore_payload_params,
            ignore_host):
        """
            flows: List of flows.
            kill: Boolean, should we kill requests not part of the replay?
            ignore_params: list of parameters to ignore in server replay
            ignore_content: true if request content should be ignored in server replay
            ignore_payload_params: list of content params to ignore in server replay
            ignore_host: true if request host should be ignored in server replay
        """
        self.server_playback = ServerPlaybackState(
            headers,
            flows,
            exit,
            nopop,
            ignore_params,
            ignore_content,
            ignore_payload_params,
            ignore_host)
        self.kill_nonreplay = kill

    def stop_server_playback(self):
        if self.server_playback.exit:
            self.shutdown()
        self.server_playback = None

    def do_server_playback(self, flow):
        """
            This method should be called by child classes in the handle_request
            handler. Returns True if playback has taken place, None if not.
        """
        if self.server_playback:
            rflow = self.server_playback.next_flow(flow)
            if not rflow:
                return None
            response = HTTPResponse.from_state(rflow.response.get_state())
            response.is_replay = True
            if self.refresh_server_playback:
                response.refresh()
            flow.reply(response)
            if self.server_playback.count() == 0:
                self.stop_server_playback()
            return True
        return None

    def tick(self, q, timeout):
        if self.client_playback:
            e = [
                self.client_playback.done(),
                self.client_playback.exit,
                self.state.active_flow_count() == 0
            ]
            if all(e):
                self.shutdown()
            self.client_playback.tick(self)
            if self.client_playback.done():
                self.client_playback = None

        return super(FlowMaster, self).tick(q, timeout)

    def duplicate_flow(self, f):
        return self.load_flow(f.copy())

    def create_request(self, method, scheme, host, port, path):
        """
            this method creates a new artificial and minimalist request also adds it to flowlist
        """
        c = ClientConnection.from_state(dict(
            address=dict(address=(host, port), use_ipv6=False),
            clientcert=None
        ))

        s = ServerConnection.from_state(dict(
            address=dict(address=(host, port), use_ipv6=False),
            state=[],
            source_address=None,
            # source_address=dict(address=(host, port), use_ipv6=False),
            cert=None,
            sni=host,
            ssl_established=True
        ))
        f = HTTPFlow(c, s)
        headers = Headers()

        req = HTTPRequest(
            "absolute",
            method,
            scheme,
            host,
            port,
            path,
            b"HTTP/1.1",
            headers,
            None,
            None,
            None,
            None)
        f.request = req
        return self.load_flow(f)

    def load_flow(self, f):
        """
            Loads a flow, and returns a new flow object.
        """

        if self.server and self.server.config.mode == "reverse":
            f.request.host = self.server.config.upstream_server.address.host
            f.request.port = self.server.config.upstream_server.address.port
            f.request.scheme = re.sub("^https?2", "", self.server.config.upstream_server.scheme)

        f.reply = controller.DummyReply()
        if f.request:
            self.handle_request(f)
        if f.response:
            self.handle_responseheaders(f)
            self.handle_response(f)
        if f.error:
            self.handle_error(f)
        return f

    def load_flows(self, fr):
        """
            Load flows from a FlowReader object.
        """
        cnt = 0
        for i in fr.stream():
            cnt += 1
            self.load_flow(i)
        return cnt

    def load_flows_file(self, path):
        path = os.path.expanduser(path)
        try:
            f = file(path, "rb")
            freader = FlowReader(f)
        except IOError as v:
            raise FlowReadError(v.strerror)
        return self.load_flows(freader)

    def process_new_request(self, f):
        if self.stickycookie_state:
            self.stickycookie_state.handle_request(f)
        if self.stickyauth_state:
            self.stickyauth_state.handle_request(f)

        if self.anticache:
            f.request.anticache()
        if self.anticomp:
            f.request.anticomp()

        if self.server_playback:
            pb = self.do_server_playback(f)
            if not pb:
                if self.kill_nonreplay:
                    f.kill(self)
                else:
                    f.reply()

    def process_new_response(self, f):
        if self.stickycookie_state:
            self.stickycookie_state.handle_response(f)

    def replay_request(self, f, block=False, run_scripthooks=True):
        """
            Returns None if successful, or error message if not.
        """
        if f.live and run_scripthooks:
            return "Can't replay live request."
        if f.intercepted:
            return "Can't replay while intercepting..."
        if f.request.content == CONTENT_MISSING:
            return "Can't replay request with missing content..."
        if f.request:
            f.backup()
            f.request.is_replay = True
            if "Content-Length" in f.request.headers:
                f.request.headers["Content-Length"] = str(len(f.request.content))
            f.response = None
            f.error = None
            self.process_new_request(f)
            rt = RequestReplayThread(
                self.server.config,
                f,
                self.masterq if run_scripthooks else False,
                self.should_exit
            )
            rt.start()  # pragma: no cover
            if block:
                rt.join()

    def handle_log(self, l):
        self.add_event(l.msg, l.level)
        l.reply()

    def handle_clientconnect(self, root_layer):
        self.run_script_hook("clientconnect", root_layer)
        root_layer.reply()

    def handle_clientdisconnect(self, root_layer):
        self.run_script_hook("clientdisconnect", root_layer)
        root_layer.reply()

    def handle_serverconnect(self, server_conn):
        self.run_script_hook("serverconnect", server_conn)
        server_conn.reply()

    def handle_serverdisconnect(self, server_conn):
        self.run_script_hook("serverdisconnect", server_conn)
        server_conn.reply()

    def handle_next_layer(self, top_layer):
        self.run_script_hook("next_layer", top_layer)
        top_layer.reply()

    def handle_error(self, f):
        self.state.update_flow(f)
        self.run_script_hook("error", f)
        if self.client_playback:
            self.client_playback.clear(f)
        f.reply()
        return f

    def handle_request(self, f):
        if f.live:
            app = self.apps.get(f.request)
            if app:
                err = app.serve(
                    f,
                    f.client_conn.wfile,
                    **{"mitmproxy.master": self}
                )
                if err:
                    self.add_event("Error in wsgi app. %s" % err, "error")
                f.reply(Kill)
                return
        if f not in self.state.flows:  # don't add again on replay
            self.state.add_flow(f)
        self.replacehooks.run(f)
        self.setheaders.run(f)
        self.run_script_hook("request", f)
        self.process_new_request(f)
        return f

    def handle_responseheaders(self, f):
        self.run_script_hook("responseheaders", f)

        try:
            if self.stream_large_bodies:
                self.stream_large_bodies.run(f, False)
        except HttpException:
            f.reply(Kill)
            return

        f.reply()
        return f

    def handle_response(self, f):
        self.state.update_flow(f)
        self.replacehooks.run(f)
        self.setheaders.run(f)
        self.run_script_hook("response", f)
        if self.client_playback:
            self.client_playback.clear(f)
        self.process_new_response(f)
        if self.stream:
            self.stream.add(f)
        return f

    def handle_intercept(self, f):
        self.state.update_flow(f)

    def handle_accept_intercept(self, f):
        self.state.update_flow(f)

    def shutdown(self):
        self.unload_scripts()
        controller.Master.shutdown(self)
        if self.stream:
            for i in self.state.flows:
                if not i.response:
                    self.stream.add(i)
            self.stop_stream()

    def start_stream(self, fp, filt):
        self.stream = FilteredFlowWriter(fp, filt)

    def stop_stream(self):
        self.stream.fo.close()
        self.stream = None


def read_flows_from_paths(paths):
    """
    Given a list of filepaths, read all flows and return a list of them.
    From a performance perspective, streaming would be advisable -
    however, if there's an error with one of the files, we want it to be raised immediately.

    If an error occurs, a FlowReadError will be raised.
    """
    try:
        flows = []
        for path in paths:
            path = os.path.expanduser(path)
            with file(path, "rb") as f:
                flows.extend(FlowReader(f).stream())
    except IOError as e:
        raise FlowReadError(e.strerror)
    return flows


class FlowWriter:
    def __init__(self, fo):
        self.fo = fo

    def add(self, flow):
        d = flow.get_state()
        tnetstring.dump(d, self.fo)


class FlowReadError(Exception):
    @property
    def strerror(self):
        return self.args[0]


class FlowReader:
    def __init__(self, fo):
        self.fo = fo

    def stream(self):
        """
            Yields Flow objects from the dump.
        """
        off = 0
        try:
            while True:
                data = tnetstring.load(self.fo)
                if tuple(data["version"][:2]) != version.IVERSION[:2]:
                    v = ".".join(str(i) for i in data["version"])
                    raise FlowReadError(
                        "Incompatible serialized data version: %s" % v
                    )
                off = self.fo.tell()
                yield HTTPFlow.from_state(data)
        except ValueError as v:
            # Error is due to EOF
            if self.fo.tell() == off and self.fo.read() == '':
                return
            raise FlowReadError("Invalid data format.")


class FilteredFlowWriter:
    def __init__(self, fo, filt):
        self.fo = fo
        self.filt = filt

    def add(self, f):
        if self.filt and not f.match(self.filt):
            return
        d = f.get_state()
        tnetstring.dump(d, self.fo)