Class: Net::SSH::Connection::Session

Class | Net::SSH::Connection::Session
In: | lib/net/ssh/connection/session.rb
Parent: | Object

A session class representing the connection service running on top of the SSH transport layer. It manages the creation of channels (see open_channel), and the dispatching of messages to the various channels. It also encapsulates the SSH event loop (via loop and process), and serves as a central point-of-reference for all SSH-related services (e.g. port forwarding, SFTP, SCP, etc.).

You will rarely (if ever) need to instantiate this class directly; rather, you‘ll almost always use Net::SSH.start to initialize a new network connection, authenticate a user, and return a new connection session, all in one call.

      Net::SSH.start("localhost", "user") do |ssh|
        # 'ssh' is an instance of Net::SSH::Connection::Session
        ssh.exec! "/etc/init.d/some_process start"
      end

### Methods

[] []= busy? close closed? exec exec! forward host listen_to loop new on_global_request on_open_channel open_channel postprocess preprocess process send_global_request send_message shutdown! stop_listening_to

### Included Modules

Constants Loggable

### Classes and Modules

Class Net::SSH::Connection::Session::NilChannel

### Constants

MAP | = | Constants.constants.inject({}) do |memo, name| value = const_get(name)

### External Aliases

loop | -> | loop_forever
| preserve a reference to Kernel#loop

### Attributes

options | [R] | The map of options that were used to initialize this instance.
properties | [R] | The collection of custom properties for this instance. (See #[] and #[]=).
transport | [R] | The underlying transport layer abstraction (see Net::SSH::Transport::Session).

### Public Class methods

new(transport, options={})

Create a new connection service instance atop the given transport layer. Initializes the listeners to be only the underlying socket object.

### Public Instance methods

[](key)

Retrieves a custom property from this instance. This can be used to store additional state in applications that must manage multiple SSH connections.

[]=(key, value)

Sets a custom property for this instance.

busy?(include_invisible=false)

Returns `true` if there are any channels currently active on this session. By default, this will not include "invisible" channels (such as those created by forwarding ports and such), but if you pass a `true` value for `include_invisible`, then those will be counted.

This can be useful for determining whether the event loop should continue to be run.

      ssh.loop { ssh.busy? }

close()

Closes the session gracefully, blocking until all channels have successfully closed, and then closes the underlying transport layer connection.

closed?()

Returns true if the underlying transport has been closed. Note that this can be a little misleading, since if the remote server has closed the connection, the local end will still think it is open until the next operation on the socket. Nevertheless, this method can be useful if you just want to know if you have closed the connection.

exec(command, &block)

A convenience method for executing a command and interacting with it. If no block is given, all output is printed via $stdout and $stderr. Otherwise, the block is called for each data and extended data packet, with three arguments: the channel object, a symbol indicating the data type (:stdout or :stderr), and the data (as a string).

Note that this method returns immediately, and requires an event loop (see Session#loop) in order for the command to actually execute.

This is effectively identical to calling open_channel, and then Net::SSH::Connection::Channel#exec, and then setting up the channel callbacks. However, for most uses, this will be sufficient.

      ssh.exec "grep something /some/files" do |ch, stream, data|
        if stream == :stderr
          puts "ERROR: #{data}"
        else
          puts data
        end
      end

exec!(command, &block)

Same as exec, except this will block until the command finishes. Also, if a block is not given, this will return all output (stdout and stderr) as a single string.

      matches = ssh.exec!("grep something /some/files")

forward()

Returns a reference to the Net::SSH::Service::Forward service, which can be used for forwarding ports over SSH.

host()

Returns the name of the host that was given to the transport layer to connect to.

listen_to(io, &callback)

Adds an IO object for the event loop to listen to. If a callback is given, it will be invoked when the io is ready to be read, otherwise, the io will merely have its fill method invoked.

Any `io` value passed to this method must have mixed into it the Net::SSH::BufferedIo functionality, typically by calling extend on the object.

The following example executes a process on the remote server, opens a socket to somewhere, and then pipes data from that socket to the remote process’ stdin stream:

      channel = ssh.open_channel do |ch|
        ch.exec "/some/process/that/wants/input" do |ch, success|
          abort "can't execute!" unless success

          io = TCPSocket.new(somewhere, port)
          io.extend(Net::SSH::BufferedIo)
          ssh.listen_to(io)

          ch.on_process do
            if io.available > 0
              ch.send_data(io.read_available)
            end
          end

          ch.on_close do
            ssh.stop_listening_to(io)
            io.close
          end
        end
      end

      channel.wait

loop(wait=nil, &block)

The main event loop. Calls process until process returns false. If a block is given, it is passed to process, otherwise a default proc is used that just returns true if there are any channels active (see busy?). The # `wait` parameter is also passed through to process (where it is interpreted as the maximum number of seconds to wait for IO.select to return).

      # loop for as long as there are any channels active
      ssh.loop

      # loop for as long as there are any channels active, but make sure
      # the event loop runs at least once per 0.1 second
      ssh.loop(0.1)

      # loop until ctrl-C is pressed
      int_pressed = false
      trap("INT") { int_pressed = true }
      ssh.loop(0.1) { not int_pressed }

on_global_request(type, &block)

Registers a handler to be invoked when the server sends a global request of the given type. The callback receives the request data as the first parameter, and true/false as the second (indicating whether a response is required). If the callback sends the response, it should return :sent. Otherwise, if it returns true, REQUEST_SUCCESS will be sent, and if it returns false, REQUEST_FAILURE will be sent.

on_open_channel(type, &block)

Registers a handler to be invoked when the server wants to open a channel on the client. The callback receives the connection object, the new channel object, and the packet itself as arguments, and should raise ChannelOpenFailed if it is unable to open the channel for some reason. Otherwise, the channel will be opened and a confirmation message sent to the server.

This is used by the Net::SSH::Service::Forward service to open a channel when a remote forwarded port receives a connection. However, you are welcome to register handlers for other channel types, as needed.

open_channel(type="session", *extra, &on_confirm)

Requests that a new channel be opened. By default, the channel will be of type "session", but if you know what you‘re doing you can select any of the channel types supported by the SSH protocol. The `extra` parameters must be even in number and conform to the same format as described for Net::SSH::Buffer.from. If a callback is given, it will be invoked when the server confirms that the channel opened successfully. The sole parameter for the callback is the channel object itself.

In general, you‘ll use open_channel without any arguments; the only time you‘d want to set the channel type or pass additional initialization data is if you were implementing an SSH extension.

      channel = ssh.open_channel do |ch|
        ch.exec "grep something /some/files" do |ch, success|
          ...
        end
      end

      channel.wait

postprocess(readers, writers)

This is called internally as part of process. It loops over the given arrays of reader IO‘s and writer IO‘s, processing them as needed, and then calls Net::SSH::Transport::Session#rekey_as_needed to allow the transport layer to rekey. Then returns true.

preprocess() {|self| ...}

This is called internally as part of process. It dispatches any available incoming packets, and then runs Net::SSH::Connection::Channel#process for any active channels. If a block is given, it is invoked at the start of the method and again at the end, and if the block ever returns false, this method returns false. Otherwise, it returns true.

process(wait=nil, &block)

The core of the event loop. It processes a single iteration of the event loop. If a block is given, it should return false when the processing should abort, which causes process to return false. Otherwise, process returns true. The session itself is yielded to the block as its only argument.

If `wait` is nil (the default), this method will block until any of the monitored IO objects are ready to be read from or written to. If you want it to not block, you can pass 0, or you can pass any other numeric value to indicate that it should block for no more than that many seconds. Passing 0 is a good way to poll the connection, but if you do it too frequently it can make your CPU quite busy!

This will also cause all active channels to be processed once each (see Net::SSH::Connection::Channel#on_process).

      # process multiple Net::SSH connections in parallel
      connections = [
        Net::SSH.start("host1", ...),
        Net::SSH.start("host2", ...)
      ]

      connections.each do |ssh|
        ssh.exec "grep something /in/some/files"
      end

      condition = Proc.new { |s| s.busy? }

      loop do
        connections.delete_if { |ssh| !ssh.process(0.1, &condition) }
        break if connections.empty?
      end

send_global_request(type, *extra, &callback)

Send a global request of the given type. The `extra` parameters must be even in number, and conform to the same format as described for Net::SSH::Buffer.from. If a callback is not specified, the request will not require a response from the server, otherwise the server is required to respond and indicate whether the request was successful or not. This success or failure is indicated by the callback being invoked, with the first parameter being true or false (success, or failure), and the second being the packet itself.

Generally, Net::SSH will manage global requests that need to be sent (e.g. port forward requests and such are handled in the Net::SSH::Service::Forward class, for instance). However, there may be times when you need to send a global request that isn‘t explicitly handled by Net::SSH, and so this method is available to you.

      ssh.send_global_request("keep-alive@openssh.com")

send_message(message)

Enqueues a message to be sent to the server as soon as the socket is available for writing. Most programs will never need to call this, but if you are implementing an extension to the SSH protocol, or if you need to send a packet that Net::SSH does not directly support, you can use this to send it.

     ssh.send_message(Buffer.from(:byte, REQUEST_SUCCESS).to_s)

shutdown!()

Performs a "hard" shutdown of the connection. In general, this should never be done, but it might be necessary (in a rescue clause, for instance, when the connection needs to close but you don‘t know the status of the underlying protocol‘s state).

stop_listening_to(io)

Removes the given io object from the listeners collection, so that the event loop will no longer monitor it.

[Validate]