asyncore.dispatcher

class asyncore.dispatcher

The dispatcher class is a thin wrapper around a low-level socket object. To make it more useful, it has a few methods for event-handling which are called from the asynchronous loop. Otherwise, it can be treated as a normal non-blocking socket object.

The firing of low-level events at certain times or in certain connection states tells the asynchronous loop that certain higher-level events have taken place. For example, if we have asked for a socket to connect to another host, we know that the connection has been made when the socket becomes writable for the first time (at this point you know that you may write to it with the expectation of success). The implied higher-level events are:

Event	Description
handle_connect()	Implied by the first read or write event
handle_close()	Implied by a read event with no data available
handle_accepted()	Implied by a read event on a listening socket

During asynchronous processing, each mapped channel’s readable() and writable() methods are used to determine whether the channel’s socket should be added to the list of channels select()ed or poll()ed for read and write events.

Thus, the set of channel events is larger than the basic socket events. The full set of methods that can be overridden in your subclass follows:

handle_read()

Called when the asynchronous loop detects that a read() call on the channel’s socket will succeed.

handle_write()

Called when the asynchronous loop detects that a writable socket can be written. Often this method will implement the necessary buffering for performance. For example:

def handle_write(self):
    sent = self.send(self.buffer)
    self.buffer = self.buffer[sent:]

handle_expt()

Called when there is out of band (OOB) data for a socket connection. This will almost never happen, as OOB is tenuously supported and rarely used.

handle_connect()

Called when the active opener’s socket actually makes a connection. Might send a “welcome” banner, or initiate a protocol negotiation with the remote endpoint, for example.

handle_close()

Called when the socket is closed.

handle_error()

Called when an exception is raised and not otherwise handled. The default version prints a condensed traceback.

handle_accept()

Called on listening channels (passive openers) when a connection can be established with a new remote endpoint that has issued a connect() call for the local endpoint. Deprecated in version 3.2; use handle_accepted() instead.

Deprecated since version 3.2.

handle_accepted(sock, addr)

Called on listening channels (passive openers) when a connection has been established with a new remote endpoint that has issued a connect() call for the local endpoint. sock is a new socket object usable to send and receive data on the connection, and addr is the address bound to the socket on the other end of the connection.

New in version 3.2.

readable()

Called each time around the asynchronous loop to determine whether a channel’s socket should be added to the list on which read events can occur. The default method simply returns True, indicating that by default, all channels will be interested in read events.

writable()

Called each time around the asynchronous loop to determine whether a channel’s socket should be added to the list on which write events can occur. The default method simply returns True, indicating that by default, all channels will be interested in write events.

In addition, each channel delegates or extends many of the socket methods. Most of these are nearly identical to their socket partners.

create_socket(family=socket.AF_INET, type=socket.SOCK_STREAM)

This is identical to the creation of a normal socket, and will use the same options for creation. Refer to the socket documentation for information on creating sockets.

Changed in version 3.3: family and type arguments can be omitted.

connect(address)

As with the normal socket object, address is a tuple with the first element the host to connect to, and the second the port number.

send(data)

Send data to the remote end-point of the socket.

recv(buffer_size)

Read at most buffer_size bytes from the socket’s remote end-point. An empty bytes object implies that the channel has been closed from the other end.

Note that recv() may raise BlockingIOError , even though select.select() or select.poll() has reported the socket ready for reading.

listen(backlog)

Listen for connections made to the socket. The backlog argument specifies the maximum number of queued connections and should be at least 1; the maximum value is system-dependent (usually 5).

bind(address)

Bind the socket to address. The socket must not already be bound. (The format of address depends on the address family — refer to the socket documentation for more information.) To mark the socket as re-usable (setting the SO_REUSEADDR option), call the dispatcher object’s set_reuse_addr() method.

accept()

Accept a connection. The socket must be bound to an address and listening for connections. The return value can be either None or a pair (conn, address) where conn is a new socket object usable to send and receive data on the connection, and address is the address bound to the socket on the other end of the connection. When None is returned it means the connection didn’t take place, in which case the server should just ignore this event and keep listening for further incoming connections.

close()

Close the socket. All future operations on the socket object will fail. The remote end-point will receive no more data (after queued data is flushed). Sockets are automatically closed when they are garbage-collected.