Class | EventMachine::Connection
In: | lib/eventmachine.rb lib/jeventmachine.rb lib/pr_eventmachine.rb
Parent: | Object

EventMachine::Connection is a class that is instantiated by EventMachine‘s processing loop whenever a new connection is created. (New connections can be either initiated locally to a remote server or accepted locally from a remote client.) When a Connection object is instantiated, it mixes in the functionality contained in the user-defined module specified in calls to EventMachine#connect or EventMachine#start_server. User-defined handler modules may redefine any or all of the standard methods defined here, as well as add arbitrary additional code that will also be mixed in.

EventMachine manages one object inherited from EventMachine::Connection (and containing the mixed-in user code) for every network connection that is active at any given time. The event loop will automatically call methods on EventMachine::Connection objects whenever specific events occur on the corresponding connections, as described below.

This class is never instantiated by user code, and does not publish an initialize method. The instance methods of EventMachine::Connection which may be called by the event loop are: post_init, receive_data, and unbind. All of the other instance methods defined here are called only by user code.

### Methods

associate_callback_target associate_callback_target close_connection close_connection_after_writing comm_inactivity_timeout comm_inactivity_timeout= connection_completed detach error? get_outbound_data_size get_peer_cert get_peername get_pid get_sockname get_status post_init receive_data reconnect send_data send_datagram send_file_data set_comm_inactivity_timeout ssl_handshake_completed start_tls stream_file_data unbind

### Attributes

signature | [RW] | EXPERIMENTAL. Added the reconnect methods, which may go away.

### Public Instance methods

associate_callback_target(sig)
associate_callback_target(sig)
close_connection(after_writing = false)

EventMachine::Connection#close_connection is called only by user code, and never by the event loop. You may call this method against a connection object in any callback handler, whether or not the callback was made against the connection you want to close. close_connection schedules the connection to be closed at the next available opportunity within the event loop. You may not assume that the connection is closed when close_connection returns. In particular, the framework will callback the unbind method for the particular connection at a point shortly after you call close_connection. You may assume that the unbind callback will take place sometime after your call to close_connection completes. In other words, the unbind callback will not re-enter your code "inside" of your call to close_connection. However, it‘s not guaranteed that a future version of EventMachine will not change this behavior.

close_connection will silently discard any outbound data which you have sent to the connection using EventMachine::Connection#send_data but which has not yet been sent across the network. If you want to avoid this behavior, use EventMachine::Connection#close_connection_after_writing.

close_connection_after_writing()

EventMachine::Connection#close_connection_after_writing is a variant of close_connection. All of the descriptive comments given for close_connection also apply to close_connection_after_writing, with one exception: If the connection has outbound data sent using send_dat but which has not yet been sent across the network, close_connection_after_writing will schedule the connection to be closed after all of the outbound data has been safely written to the remote peer.

Depending on the amount of outgoing data and the speed of the network, considerable time may elapse between your call to close_connection_after_writing and the actual closing of the socket (at which time the unbind callback will be called by the event loop). During this time, you may not call send_data to transmit additional data (that is, the connection is closed for further writes). In very rare cases, you may experience a receive_data callback after your call to close_connection_after_writing, depending on whether incoming data was in the process of being received on the connection at the moment when you called close_connection_after_writing. Your protocol handler must be prepared to properly deal with such data (probably by ignoring it).

comm_inactivity_timeout()

comm_inactivity_timeout returns the current value (in seconds) of the inactivity-timeout property of network-connection and datagram-socket objects. A nonzero value indicates that the connection or socket will automatically be closed if no read or write activity takes place for at least that number of seconds. A zero value (the default) specifies that no automatic timeout will take place.

comm_inactivity_timeout=(value)

Alias for set_comm_inactivity_timeout.

connection_completed()

connection_completed is called by the event loop when a remote TCP connection attempt completes successfully. You can expect to get this notification after calls to EventMachine#connect. Remember that EventMachine makes remote connections asynchronously, just as with any other kind of network event. connection_completed is intended primarily to assist with network diagnostics. For normal protocol handling, use post_init to perform initial work on a new connection (such as send an initial set of data). post_init will always be called. connection_completed will only be called in case of a successful completion. A connection-attempt which fails will receive a call to unbind after the failure.

detach()

EventMachine::Connection#detach will remove the given connection from the event loop. The connection‘s socket remains open and its file descriptor number is returned

error?()

Returns true if the connection is in an error state, false otherwise. In general, you can detect the occurrence of communication errors or unexpected disconnection by the remote peer by handing the unbind method. In some cases, however, it‘s useful to check the status of the connection using error? before attempting to send data. This function is synchronous: it will return immediately without blocking.

get_outbound_data_size()
get_peer_cert()

If SSL/TLS is active on the connection, get_peer_cert returns the remote X509 certificate as a String, in the popular PEM format. This can then be used for arbitrary validation of a peer‘s certificate in your code.

This should be called in/after the ssl_handshake_completed callback, which indicates that SSL/TLS is active. Using this callback is important, because the certificate may not be available until the time it is executed. Using post_init or connection_completed is not adequate, because the SSL handshake may still be taking place.

get_peer_cert will return nil if:

- EventMachine is not built with OpenSSL support
- SSL/TLS is not active on the connection
- SSL/TLS handshake is not yet complete
- Remote peer for any other reason has not presented a certificate

### Example:

     module Handler

      def post_init
        puts "Starting TLS"
        start_tls
      end

      def ssl_handshake_completed
        puts get_peer_cert
        close_connection
      end

      def unbind
        EventMachine::stop_event_loop
      end

     end

     EM.run {
      EventMachine::connect "mail.google.com", 443, Handler
     }

Output:

     -----BEGIN CERTIFICATE-----
     MIIDIjCCAougAwIBAgIQbldpChBPqv+BdPg4iwgN8TANBgkqhkiG9w0BAQUFADBM
     MQswCQYDVQQGEwJaQTElMCMGA1UEChMcVGhhd3RlIENvbnN1bHRpbmcgKFB0eSkg
     THRkLjEWMBQGA1UEAxMNVGhhd3RlIFNHQyBDQTAeFw0wODA1MDIxNjMyNTRaFw0w
     OTA1MDIxNjMyNTRaMGkxCzAJBgNVBAYTAlVTMRMwEQYDVQQIEwpDYWxpZm9ybmlh
     MRYwFAYDVQQHEw1Nb3VudGFpbiBWaWV3MRMwEQYDVQQKEwpHb29nbGUgSW5jMRgw
     FgYDVQQDEw9tYWlsLmdvb2dsZS5jb20wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJ
     AoGBALlkxdh2QXegdElukCSOV2+8PKiONIS+8Tu9K7MQsYpqtLNC860zwOPQ2NLI
     3Zp4jwuXVTrtzGuiqf5Jioh35Ig3CqDXtLyZoypjZUQcq4mlLzHlhIQ4EhSjDmA7
     Ffw9y3ckSOQgdBQWNLbquHh9AbEUjmhkrYxIqKXeCnRKhv6nAgMBAAGjgecwgeQw
     KAYDVR0lBCEwHwYIKwYBBQUHAwEGCCsGAQUFBwMCBglghkgBhvhCBAEwNgYDVR0f
     BC8wLTAroCmgJ4YlaHR0cDovL2NybC50aGF3dGUuY29tL1RoYXd0ZVNHQ0NBLmNy
     bDByBggrBgEFBQcBAQRmMGQwIgYIKwYBBQUHMAGGFmh0dHA6Ly9vY3NwLnRoYXd0
     ZS5jb20wPgYIKwYBBQUHMAKGMmh0dHA6Ly93d3cudGhhd3RlLmNvbS9yZXBvc2l0
     b3J5L1RoYXd0ZV9TR0NfQ0EuY3J0MAwGA1UdEwEB/wQCMAAwDQYJKoZIhvcNAQEF
     BQADgYEAsRwpLg1dgCR1gYDK185MFGukXMeQFUvhGqF8eT/CjpdvezyKVuz84gSu
     6ccMXgcPQZGQN/F4Xug+Q01eccJjRSVfdvR5qwpqCj+6BFl5oiKDBsveSkrmL5dz
     s2bn7TdTSYKcLeBkjXxDLHGBqLJ6TNCJ3c4/cbbG5JhGvoema94=
     -----END CERTIFICATE-----

You can do whatever you want with the certificate String, such as load it as a certificate object using the OpenSSL library, and check it‘s fields.

get_peername()

get_peername is used with stream-connections to obtain the identity of the remotely-connected peer. If a peername is available, this method returns a sockaddr structure. The method returns nil if no peername is available. You can use Socket#unpack_sockaddr_in and its variants to obtain the values contained in the peername structure returned from get_peername.

get_pid()

Returns the PID (kernel process identifier) of a subprocess associated with this Connection object. For use with EventMachine#popen and similar methods. Returns nil when there is no meaningful subprocess.

get_sockname()

get_sockname is used with stream-connections to obtain the identity of the local side of the connection. If a local name is available, this method returns a sockaddr structure. The method returns nil if no local name is available. You can use Socket#unpack_sockaddr_in and its variants to obtain the values contained in the local-name structure returned from get_sockname.

get_status()

Returns a subprocess exit status. Only useful for popen. Call it in your unbind handler.

post_init()

EventMachine::Connection#post_init is called by the event loop immediately after the network connection has been established, and before resumption of the network loop. This method is generally not called by user code, but is called automatically by the event loop. The base-class implementation is a no-op. This is a very good place to initialize instance variables that will be used throughout the lifetime of the network connection.

receive_data(data)

EventMachine::Connection#receive_data is called by the event loop whenever data has been received by the network connection. It is never called by user code. receive_data is called with a single parameter, a String containing the network protocol data, which may of course be binary. You will generally redefine this method to perform your own processing of the incoming data.

Here‘s a key point which is essential to understanding the event-driven programming model: EventMachine knows absolutely nothing about the protocol which your code implements. You must not make any assumptions about the size of the incoming data packets, or about their alignment on any particular intra-message or PDU boundaries (such as line breaks). receive_data can and will send you arbitrary chunks of data, with the only guarantee being that the data is presented to your code in the order it was collected from the network. Don‘t even assume that the chunks of data will correspond to network packets, as EventMachine can and will coalesce several incoming packets into one, to improve performance. The implication for your code is that you generally will need to implement some kind of a state machine in your redefined implementation of receive_data. For a better understanding of this, read through the examples of specific protocol handlers given elsewhere in this package. (STUB, WE MUST ADD THESE!)

The base-class implementation of receive_data (which will be invoked if you don‘t redefine it) simply prints the size of each incoming data packet to stdout.

reconnect(server, port)
send_data(data)

EventMachine::Connection#send_data is only called by user code, never by the event loop. You call this method to send data to the remote end of the network connection. send_data is called with a single String argument, which may of course contain binary data. You can call send_data any number of times. send_data is an instance method of an object derived from EventMachine::Connection and containing your mixed-in handler code), so if you call it without qualification within a callback function, the data will be sent to the same network connection that generated the callback. Calling self.send_data is exactly equivalent.

You can also call send_data to write to a connection other than the one whose callback you are calling send_data from. This is done by recording the value of the connection in any callback function (the value self), in any variable visible to other callback invocations on the same or different connection objects. (Need an example to make that clear.)

send_datagram(data, recipient_address, recipient_port)

send_datagram is for sending UDP messages. This method may be called from any Connection object that refers to an open datagram socket (see EventMachine#open_datagram_socket). The method sends a UDP (datagram) packet containing the data you specify, to a remote peer specified by the IP address and port that you give as parameters to the method. Observe that you may send a zero-length packet (empty string). However, you may not send an arbitrarily-large data packet because your operating system will enforce a platform-specific limit on the size of the outbound packet. (Your kernel will respond in a platform-specific way if you send an overlarge packet: some will send a truncated packet, some will complain, and some will silently drop your request). On LANs, it‘s usually OK to send datagrams up to about 4000 bytes in length, but to be really safe, send messages smaller than the Ethernet-packet size (typically about 1400 bytes). Some very restrictive WANs will either drop or truncate packets larger than about 500 bytes.

send_file_data(filename)

Like EventMachine::Connection#send_data, this sends data to the remote end of the network connection. EventMachine::Connection@send_file_data takes a filename as an argument, though, and sends the contents of the file, in one chunk. Contributed by Kirk Haines.

set_comm_inactivity_timeout(value)

comm_inactivity_timeout= allows you to set the inactivity-timeout property for a network connection or datagram socket. Specify a non-negative numeric value in seconds. If the value is greater than zero, the connection or socket will automatically be closed if no read or write activity takes place for at least that number of seconds. Specify a value of zero to indicate that no automatic timeout should take place. Zero is the default value.

ssl_handshake_completed()

ssl_handshake_completed is called by EventMachine when the SSL/TLS handshake has been completed, as a result of calling start_tls to initiate SSL/TLS on the connection.

This callback exists because post_init and connection_completed are not reliable for indicating when an SSL/TLS connection is ready to have it‘s certificate queried for.

See get_peer_cert for application and example.

start_tls(args={})

Call start_tls at any point to initiate TLS encryption on connected streams. The method is smart enough to know whether it should perform a server-side or a client-side handshake. An appropriate place to call start_tls is in your redefined post_init method, or in the connection_completed handler for an outbound connection.

start_tls takes an optional parameter hash that allows you to specify certificate and other options to be used with this Connection object. Here are the currently-supported options: :cert_chain_file : takes a String, which is interpreted as the name of a readable file in the

      local filesystem. The file is expected to contain a chain of X509 certificates in
      PEM format, with the most-resolved certificate at the top of the file, successive
      intermediate certs in the middle, and the root (or CA) cert at the bottom.

:private_key_file : tales a String, which is interpreted as the name of a readable file in the

      local filesystem. The file must contain a private key in PEM format.

stream_file_data(filename, args={})

Open a file on the filesystem and send it to the remote peer. This returns an object of type EventMachine::Deferrable. The object‘s callbacks will be executed on the reactor main thread when the file has been completely scheduled for transmission to the remote peer. Its errbacks will be called in case of an error (such as file-not-found). stream_file_data employs various strategems to achieve the fastest possible performance, balanced against minimum consumption of memory.

You can control the behavior of stream_file_data with the optional arguments parameter. Currently-supported arguments are: :http_chunks, a boolean flag which defaults false. If true, this flag streams the file data in a format compatible with the HTTP chunked-transfer encoding.

Warning: this feature has an implicit dependency on an outboard extension, evma_fastfilereader. You must install this extension in order to use stream_file_data with files larger than a certain size (currently 8192 bytes).

unbind()

EventMachine::Connection#unbind is called by the framework whenever a connection (either a server or client connection) is closed. The close can occur because your code intentionally closes it (see close_connection and close_connection_after_writing), because the remote peer closed the connection, or because of a network error. You may not assume that the network connection is still open and able to send or receive data when the callback to unbind is made. This is intended only to give you a chance to clean up associations your code may have made to the connection object while it was open.

[Validate]