Getting Started

This document explains how to get started using wsproto to connect to WebSocket servers as well as how to write your own.

We assume some level of familiarity with writing Python and networking code. If you’re not familiar with these we highly recommend you read up on these first. It may also be helpful to study Sans-I/O, which describes the ideas behind writing a network protocol library that doesn’t do any network I/O.


The main class you’ll be working with is the WSConnection object. This object represents a connection to a WebSocket peer. This class can handle both WebSocket clients and WebSocket servers.

wsproto provides two layers of abstractions. You need to write code that interfaces with both of these layers. The following diagram illustrates how your code is like a sandwich around wsproto.





Network Layer

wsproto does not do perform any network I/O, so NETWORK GLUE represents the code you need to write to glue wsproto to an actual network, for example using Python’s socket module. The WSConnection class provides two methods for this purpose. When data has been received on a network socket, you should feed this data into a connection instance by calling WSConnection.receive_data(). When you want to communicate with the remote peer, e.g. send a message, ping, or close the connection, you should create an instance of one of the subclasses and pass it to WSConnection.send() to get the corresponding bytes that need to be sent. Your code is responsible for actually sending that data over the network.


If the connection drops, a standard Python socket.recv() will return zero bytes. You should call receive_data(None) to update the internal wsproto state to indicate that the connection has been closed.

Internally, wsproto processes the raw network data you feed into it and turns it into higher level representations of WebSocket events. In APPLICATION GLUE, you need to write code to process these events. Incoming data is exposed though the generator method, which yields WebSocket events. Each event is an instance of an events.Event subclass.

WebSocket Clients

Begin by instantiating a connection object in client mode and then create a instance. The Request must specify host and target arguments. If the WebSocket server is located at, then you would instantiate the connection as follows:

from wsproto import ConnectionType, WSConnection
from import Request
ws = WSConnection(ConnectionType.CLIENT)
request = Request(host="", target='foo')
data = ws.send(request)

Keep in mind that wsproto does not do any network I/O. Instead, WSConnection.send() returns data that you must send to the remote peer. Here is an example using a standard Python socket:

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect(("", 80))

To receive communications from the peer, you must pass the data received from the peer into the connection instance:

data = sock.recv(4096)

The connection instance parses the received data and determines if any high-level events have occurred, such as receiving a ping or a message. To retrieve these events, use the generator function

for event in
    if isinstance(event, AcceptConnection):
        print('Connection established')
    elif isinstance(event, RejectConnection):
        print('Connection rejected')
    elif isinstance(event, CloseConnection):
        print('Connection closed: code={} reason={}'.format(
            event.code, event.reason
    elif isinstance(event, Ping):
        print('Received Ping frame with payload {}'.format(event.payload))
    elif isinstance(event, TextMessage):
        print('Received TEXT data: {}'.format(
        if event.message_finished:
            print('Message finished.')
    elif isinstance(event, BytesMessage):
        print('Received BINARY data: {}'.format(
        if event.message_finished:
            print('BINARY Message finished.')
        print('Unknown event: {!r}'.format(event))

The method events() returns a generator which will yield events for all of the data currently in the wsproto internal buffer and then exit. Therefore, you should iterate over this generator after receiving new network data.

For a more complete example, see

WebSocket Servers

A WebSocket server is similar to a client, but it uses a different wsproto.ConnectionType constant.

from wsproto import ConnectionType, WSConnection
from import Request
ws = WSConnection(ConnectionType.SERVER)

A server also needs to explicitly send an AcceptConnection after it receives a Request event:

for event in
    if isinstance(event, Request):
        print('Accepting connection request')

Alternatively a server can explicitly reject the connection by sending RejectConnection after receiving a Request event.

For a more complete example, see

Protocol Errors

Protocol errors relating to either incorrect data or incorrect state changes are raised when the connection receives data or when events are sent. A LocalProtocolError is raised if the local actions are in error whereas a RemoteProtocolError is raised if the remote actions are in error.


WebSockets are closed with a handshake that requires each endpoint to send one frame and receive one frame. Sending a CloseConnection instance sets the state to LOCAL_CLOSING. When a close frame is received, it yields a CloseConnection event, sets the state to REMOTE_CLOSING and requires a reply to be sent. This reply should be a CloseConnection event. To aid with this the CloseConnection class has a response() method to create the appropriate reply. For example,

if isinstance(event, CloseConnection):

When the reply has been received by the initiator, it will also yield a CloseConnection event.

Regardless of which endpoint initiates the closing handshake, the server is responsible for tearing down the underlying connection. When a CloseConnection event is generated, it should send pending any wsproto data and then tear down the underlying connection.


Both client and server connections must remember to reply to CloseConnection events initiated by the remote party.

Ping Pong

The WSConnection class supports sending WebSocket ping and pong frames via sending Ping and Pong. When a Ping frame is received it requires a reply, this reply should be a Pong event. To aid with this the Ping class has a response() method to create the appropriate reply. For example,

if isinstance(event, Ping):


Both client and server connections must remember to reply to Ping events initiated by the remote party.