Twisted Example Client: Post RequestsΒΆ

This example is a basic HTTP/2 client written for the Twisted asynchronous networking framework.

This client is fairly simple: it makes a hard-coded POST request to nghttp2.org/httpbin/post and prints out the response data, sending a file that is provided on the command line or the script itself. Its purpose is to demonstrate how to write a HTTP/2 client implementation that handles flow control.

  1# -*- coding: utf-8 -*-
  2"""
  3post_request.py
  4~~~~~~~~~~~~~~~
  5
  6A short example that demonstrates a client that makes POST requests to certain
  7websites.
  8
  9This example is intended to demonstrate how to handle uploading request bodies.
 10In this instance, a file will be uploaded. In order to handle arbitrary files,
 11this example also demonstrates how to obey HTTP/2 flow control rules.
 12
 13Takes one command-line argument: a path to a file in the filesystem to upload.
 14If none is present, uploads this file.
 15"""
 16from __future__ import print_function
 17
 18import mimetypes
 19import os
 20import sys
 21
 22from twisted.internet import reactor, defer
 23from twisted.internet.endpoints import connectProtocol, SSL4ClientEndpoint
 24from twisted.internet.protocol import Protocol
 25from twisted.internet.ssl import optionsForClientTLS
 26from h2.connection import H2Connection
 27from h2.events import (
 28    ResponseReceived, DataReceived, StreamEnded, StreamReset, WindowUpdated,
 29    SettingsAcknowledged,
 30)
 31
 32
 33AUTHORITY = u'nghttp2.org'
 34PATH = '/httpbin/post'
 35
 36
 37class H2Protocol(Protocol):
 38    def __init__(self, file_path):
 39        self.conn = H2Connection()
 40        self.known_proto = None
 41        self.request_made = False
 42        self.request_complete = False
 43        self.file_path = file_path
 44        self.flow_control_deferred = None
 45        self.fileobj = None
 46        self.file_size = None
 47
 48    def connectionMade(self):
 49        """
 50        Called by Twisted when the TCP connection is established. We can start
 51        sending some data now: we should open with the connection preamble.
 52        """
 53        self.conn.initiate_connection()
 54        self.transport.write(self.conn.data_to_send())
 55
 56    def dataReceived(self, data):
 57        """
 58        Called by Twisted when data is received on the connection.
 59
 60        We need to check a few things here. Firstly, we want to validate that
 61        we actually negotiated HTTP/2: if we didn't, we shouldn't proceed!
 62
 63        Then, we want to pass the data to the protocol stack and check what
 64        events occurred.
 65        """
 66        if not self.known_proto:
 67            self.known_proto = self.transport.negotiatedProtocol
 68            assert self.known_proto == b'h2'
 69
 70        events = self.conn.receive_data(data)
 71
 72        for event in events:
 73            if isinstance(event, ResponseReceived):
 74                self.handleResponse(event.headers)
 75            elif isinstance(event, DataReceived):
 76                self.handleData(event.data)
 77            elif isinstance(event, StreamEnded):
 78                self.endStream()
 79            elif isinstance(event, SettingsAcknowledged):
 80                self.settingsAcked(event)
 81            elif isinstance(event, StreamReset):
 82                reactor.stop()
 83                raise RuntimeError("Stream reset: %d" % event.error_code)
 84            elif isinstance(event, WindowUpdated):
 85                self.windowUpdated(event)
 86
 87        data = self.conn.data_to_send()
 88        if data:
 89            self.transport.write(data)
 90
 91    def settingsAcked(self, event):
 92        """
 93        Called when the remote party ACKs our settings. We send a SETTINGS
 94        frame as part of the preamble, so if we want to be very polite we can
 95        wait until the ACK for that frame comes before we start sending our
 96        request.
 97        """
 98        if not self.request_made:
 99            self.sendRequest()
100
101    def handleResponse(self, response_headers):
102        """
103        Handle the response by printing the response headers.
104        """
105        for name, value in response_headers:
106            print("%s: %s" % (name.decode('utf-8'), value.decode('utf-8')))
107
108        print("")
109
110    def handleData(self, data):
111        """
112        We handle data that's received by just printing it.
113        """
114        print(data, end='')
115
116    def endStream(self):
117        """
118        We call this when the stream is cleanly ended by the remote peer. That
119        means that the response is complete.
120
121        Because this code only makes a single HTTP/2 request, once we receive
122        the complete response we can safely tear the connection down and stop
123        the reactor. We do that as cleanly as possible.
124        """
125        self.request_complete = True
126        self.conn.close_connection()
127        self.transport.write(self.conn.data_to_send())
128        self.transport.loseConnection()
129
130    def windowUpdated(self, event):
131        """
132        We call this when the flow control window for the connection or the
133        stream has been widened. If there's a flow control deferred present
134        (that is, if we're blocked behind the flow control), we fire it.
135        Otherwise, we do nothing.
136        """
137        if self.flow_control_deferred is None:
138            return
139
140        # Make sure we remove the flow control deferred to avoid firing it
141        # more than once.
142        flow_control_deferred = self.flow_control_deferred
143        self.flow_control_deferred = None
144        flow_control_deferred.callback(None)
145
146    def connectionLost(self, reason=None):
147        """
148        Called by Twisted when the connection is gone. Regardless of whether
149        it was clean or not, we want to stop the reactor.
150        """
151        if self.fileobj is not None:
152            self.fileobj.close()
153
154        if reactor.running:
155            reactor.stop()
156
157    def sendRequest(self):
158        """
159        Send the POST request.
160
161        A POST request is made up of one headers frame, and then 0+ data
162        frames. This method begins by sending the headers, and then starts a
163        series of calls to send data.
164        """
165        # First, we need to work out how large the file is.
166        self.file_size = os.stat(self.file_path).st_size
167
168        # Next, we want to guess a content-type and content-encoding.
169        content_type, content_encoding = mimetypes.guess_type(self.file_path)
170
171        # Now we can build a header block.
172        request_headers = [
173            (':method', 'POST'),
174            (':authority', AUTHORITY),
175            (':scheme', 'https'),
176            (':path', PATH),
177            ('content-length', str(self.file_size)),
178        ]
179
180        if content_type is not None:
181            request_headers.append(('content-type', content_type))
182
183            if content_encoding is not None:
184                request_headers.append(('content-encoding', content_encoding))
185
186        self.conn.send_headers(1, request_headers)
187        self.request_made = True
188
189        # We can now open the file.
190        self.fileobj = open(self.file_path, 'rb')
191
192        # We now need to send all the relevant data. We do this by checking
193        # what the acceptable amount of data is to send, and sending it. If we
194        # find ourselves blocked behind flow control, we then place a deferred
195        # and wait until that deferred fires.
196        self.sendFileData()
197
198    def sendFileData(self):
199        """
200        Send some file data on the connection.
201        """
202        # Firstly, check what the flow control window is for stream 1.
203        window_size = self.conn.local_flow_control_window(stream_id=1)
204
205        # Next, check what the maximum frame size is.
206        max_frame_size = self.conn.max_outbound_frame_size
207
208        # We will send no more than the window size or the remaining file size
209        # of data in this call, whichever is smaller.
210        bytes_to_send = min(window_size, self.file_size)
211
212        # We now need to send a number of data frames.
213        while bytes_to_send > 0:
214            chunk_size = min(bytes_to_send, max_frame_size)
215            data_chunk = self.fileobj.read(chunk_size)
216            self.conn.send_data(stream_id=1, data=data_chunk)
217
218            bytes_to_send -= chunk_size
219            self.file_size -= chunk_size
220
221        # We've prepared a whole chunk of data to send. If the file is fully
222        # sent, we also want to end the stream: we're done here.
223        if self.file_size == 0:
224            self.conn.end_stream(stream_id=1)
225        else:
226            # We've still got data left to send but the window is closed. Save
227            # a Deferred that will call us when the window gets opened.
228            self.flow_control_deferred = defer.Deferred()
229            self.flow_control_deferred.addCallback(self.sendFileData)
230
231        self.transport.write(self.conn.data_to_send())
232
233
234try:
235    filename = sys.argv[1]
236except IndexError:
237    filename = __file__
238
239options = optionsForClientTLS(
240    hostname=AUTHORITY,
241    acceptableProtocols=[b'h2'],
242)
243
244connectProtocol(
245    SSL4ClientEndpoint(reactor, AUTHORITY, 443, options),
246    H2Protocol(filename)
247)
248reactor.run()