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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2008</year>
      <year>2020</year>
      <holder>Ericsson AB, All Rights Reserved</holder>
    </copyright>
    <legalnotice>
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
 
      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

  The Initial Developer of the Original Code is Ericsson AB.
    </legalnotice>

    <title>ssh_connection</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module since="">ssh_connection</module>
  <modulesummary>
    This module provides API functions to send SSH Connection Protocol 
    events to the other side of an SSH channel.
  </modulesummary>

  <description>
    <p>The <url href="http://www.ietf.org/rfc/rfc4254.txt">SSH Connection Protocol</url> 
    is used by clients and servers, that is, SSH channels, to communicate over the 
    SSH connection. The API functions in this module send SSH Connection Protocol events,
    which are received as messages by the remote channel handling the remote channel.
    The Erlang format of thoose messages is
    (see also <seetype marker="#event">below</seetype>):
    </p>
    <p><c>{ssh_cm, </c><seetype marker="ssh:ssh#connection_ref">ssh:connection_ref()</seetype><c>, </c><seetype marker="#channel_msg"><c>channel_msg()</c></seetype><c>}</c>
    </p>
    <p>
    If the <seeerl marker="ssh_client_channel">ssh_client_channel</seeerl> behavior is used to
    implement the channel process, these messages are handled by
    <seemfa marker="ssh_client_channel#Module:handle_ssh_msg/2">handle_ssh_msg/2</seemfa>.</p>
  </description>

  <datatypes>
    <datatype>
      <name name="ssh_data_type_code"/>
      <desc>
	<p>The valid values are <c>0</c> ("normal") and <c>1</c> ("stderr"), see
	<url href="https://tools.ietf.org/html/rfc4254#page/8">RFC 4254, Section 5.2</url>.</p>
      </desc>
    </datatype>

    <datatype>
      <name name="result"/>
      <name name="reason"/>
      <desc>
	<p>The result of a call.</p>
	<p>If the request reached the peer, was handled and the response
	reached the requesting node the	<seetype marker="#req_status">req_status()</seetype>
	is the status reported from the peer.</p>
	<p>If not, the <seetype marker="#reason">reason()</seetype> indicates what went wrong:</p>
	<taglist>
	  <tag><c>closed</c></tag>
	  <item>indicates that the channel or connection was closed when trying to send the request
	  </item>
	  <tag><c>timeout</c></tag>
	  <item>indicates that the operation exceeded a time limit
	  </item>
	</taglist>
      </desc>
    </datatype>

    <datatype>
      <name name="req_status"/>
      <desc>
	<p>The status of a request.
	Coresponds to the <c>SSH_MSG_CHANNEL_SUCCESS</c> and <c>SSH_MSG_CHANNEL_FAILURE</c> values in
	<url href="https://tools.ietf.org/html/rfc4254#section-5.4">RFC 4254, Section 5.4</url>.
	</p>
      </desc>
    </datatype>

    <datatype_title>SSH Connection Protocol: General</datatype_title>
    <datatype>
      <name name="event"/>
      <name name="channel_msg"/>
      <desc>
	<p>As mentioned in the introduction, the
	<url href="https://tools.ietf.org/html/rfc4254">SSH Connection Protocol</url>
	events are handled as messages. When writing a channel handling process without using
	the support by the <seeerl marker="ssh_client_channel">ssh_client_channel</seeerl>
	behavior the process must handle thoose messages.
	</p>
      </desc>
    </datatype>

    <datatype>
      <name name="want_reply"/>
      <desc>
      <p>Messages that include a <c>WantReply</c> expect the channel handling
       process to call <seemfa marker="ssh_connection#reply_request/4">
       ssh_connection:reply_request/4</seemfa>
      with the boolean value of <c>WantReply</c> as the second argument.</p>
      </desc>
    </datatype>


    <datatype_title>Data Transfer (RFC 4254, section 5.2)</datatype_title>
    <datatype>
      <name name="data_ch_msg"/>
      <desc>
	<p>Data has arrived on the channel. This event is sent as a result of calling
	<seemfa marker="ssh_connection#send/3"> ssh_connection:send/[3,4,5]</seemfa>.
	</p>
      </desc>
    </datatype>


    <datatype_title>Closing a Channel (RFC 4254, section 5.3)</datatype_title>
    <datatype>
      <name name="eof_ch_msg"/>
      <desc>
	<p>Indicates that the other side sends no more data. This event is sent as a result of calling
	<seemfa marker="ssh_connection#send_eof/2"> ssh_connection:send_eof/2</seemfa>.
      </p>
      </desc>
    </datatype>
    <datatype>
      <name name="closed_ch_msg"/>
      <desc>
	<p>This event is sent as a result of calling
	<seemfa marker="ssh_connection#close/2">ssh_connection:close/2</seemfa>.
	Both the handling of this event and sending it are taken care of by the
	<seeerl marker="ssh_client_channel">ssh_client_channel</seeerl> behavior.</p>
      </desc>
    </datatype>


    <datatype_title>Requesting a Pseudo-Terminal (RFC 4254, section 6.2)</datatype_title>
    <datatype>
      <name name="pty_ch_msg"/>
      <name name="term_mode"/>
      <desc>
	<p>A pseudo-terminal has been requested for the
	 session. <c>Terminal</c> is the value of the TERM environment
	 variable value, that is, <c>vt100</c>. Zero dimension parameters must
	 be ignored. The character/row dimensions override the pixel
	 dimensions (when non-zero). Pixel dimensions refer to the
	 drawable area of the window. <c>Opcode</c> in the
	 <c>TerminalModes</c> list is the mnemonic name, represented
	 as a lowercase Erlang atom, defined in
	 <url href="https://tools.ietf.org/html/rfc4254#section/8">RFC 4254</url>, Section 8.
	 It can also be an <c>Opcode</c> if the mnemonic name is not listed in the
	 RFC. Example: <c>OP code: 53, mnemonic name ECHO erlang atom:
	 echo</c>. This event is sent as a result of calling <seemfa
	 marker="ssh_connection#ptty_alloc/4">ssh_connection:ptty_alloc/4</seemfa>.</p>
      </desc>
    </datatype>


    <datatype_title>Environment Variable Passing (RFC 4254, section 6.4)</datatype_title>
    <datatype>
      <name name="env_ch_msg"/>
      <desc>
	<p>Environment variables can be passed to the shell/command
	 to be started later. This event is sent as a result of calling <seemfa
	 marker="ssh_connection#setenv/5"> ssh_connection:setenv/5</seemfa>.
	</p>
      </desc>
    </datatype>


    <datatype_title>Starting a Shell or Command (RFC 4254, section 6.5)</datatype_title>
    <datatype>
      <name name="shell_ch_msg"/>
      <desc>
	<p>This message requests that the user default shell
	 is started at the other end. This event is sent as a result of calling
	 <seemfa marker="ssh_connection#shell/2"> ssh_connection:shell/2</seemfa>.
	</p>
      </desc>
    </datatype>
    <datatype>
      <name name="exec_ch_msg"/>
      <desc>
	<p>This message requests that the server starts
	 execution of the given command. This event is sent as a result of calling <seemfa
	 marker="ssh_connection#exec/4">ssh_connection:exec/4 </seemfa>.
	</p>
      </desc>
    </datatype>


    <datatype_title>Window Dimension Change Message (RFC 4254, section 6.7)</datatype_title>
    <datatype>
      <name name="window_change_ch_msg"/>
      <desc>
	<p>When the window (terminal) size changes on the client
	 side, it <em>can</em> send a message to the server side to inform it of
	the new dimensions. No API function generates this event.</p>
      </desc>
    </datatype>
     
    <datatype_title>Signals (RFC 4254, section 6.9)</datatype_title>
    <datatype>
      <name name="signal_ch_msg"/>
      <desc>
	<p>A signal can be delivered to the remote process/service
	using the following message. Some systems do not support
	signals, in which case they are to ignore this message. There is
	currently no function to generate this event as the signals
	referred to are on OS-level and not something generated by an
	Erlang program.</p>
      </desc>
    </datatype>


    <datatype_title>Returning Exit Status (RFC 4254, section 6.10)</datatype_title>
    <datatype>
      <name name="exit_status_ch_msg"/>
      <desc>
	<p>When the command running at the other end terminates, the
	following message can be sent to return the exit status of the
	command. A zero <c>exit_status</c> usually means that the command
	terminated successfully. This event is sent as a result of calling
	<seemfa marker="ssh_connection#exit_status/3">
	ssh_connection:exit_status/3</seemfa>.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="exit_signal_ch_msg"/>
      <desc>
	<p>A remote execution can terminate violently because of a signal.
	Then this message can be received. For details on valid string
	values, see <url href="https://tools.ietf.org/html/rfc4254#section-6.10">RFC 4254</url>
	Section 6.10, which shows a special case of these signals.</p>
      </desc>
    </datatype>

  </datatypes>


  <funcs>
   
   <func>
     <name since="" name="adjust_window" arity="3"/>
     <fsummary>Adjusts the SSH flow control window.</fsummary>
     <desc>
	<p>Adjusts the SSH flow control window. This is to be done by both the
	client- and server-side channel processes.</p>
	
	<note><p>Channels implemented with the <seeerl marker="ssh_client_channel"> ssh_client_channel</seeerl>
	behavior do not normally need to call this function as flow control
	is handled by the behavior. The behavior adjusts the window every time
	the callback <seemfa marker="ssh_client_channel#Module:handle_ssh_msg/2">
	handle_ssh_msg/2</seemfa> returns after processing channel data.</p></note>
      </desc>
   </func>
   
   <func>
     <name since="" name="close" arity="2"/>
     <fsummary>Sends a close message on the channel <c>ChannelId</c>.</fsummary>
     <desc>
       <p>A server- or client-channel process can choose to close their session by
       sending a close event.
       </p>
       <note><p>This function is called by the <c>ssh_client_channel</c>
       behavior when the channel is terminated, see <seeerl
       marker="ssh_client_channel"> ssh_client_channel(3)</seeerl>. Thus, channels implemented
       with the behavior are not to call this function explicitly.</p></note>
     </desc>
   </func>
   
   <func>
     <name since="" name="exec" arity="4"/>
     <fsummary>Requests that the server starts the execution of the given command.</fsummary>
     <desc>
       <p>Is to be called by a client-channel process to request that the server starts
       executing the given command. The result is several messages according to the
       following pattern. The last message is a channel close message, as the <c>exec</c>
       request is a one-time execution that closes the channel when it is done.</p>

       <taglist>
	 <tag>N x <seetype marker="#data_ch_msg">data message(s)</seetype></tag>
	 <item><p>The result of executing the command can be only one line
	 or thousands of lines depending on the command.</p></item>

	 <tag>0 or 1 x <seetype marker="#eof_ch_msg">eof message</seetype></tag>
	 <item><p>Indicates that no more data is to be sent.</p></item>

	 <tag>0 or 1 x <seetype marker="#exit_signal_ch_msg">exit signal message</seetype></tag>
	 <item><p>Not all systems send signals. For details on valid string
	 values, see RFC 4254, Section 6.10</p></item>

	 <tag>0 or 1 x <seetype marker="#exit_status_ch_msg">exit status message</seetype></tag>
	 <item><p>It is recommended by the SSH Connection Protocol to send this
	 message, but that is not always the case.</p></item>

	 <tag>1 x <seetype marker="#closed_ch_msg">closed status message</seetype></tag>
	 <item><p>Indicates that the <c>ssh_client_channel</c> started for the
	 execution of the command has now been shut down.</p></item>
       </taglist>
       <p>See the User's Guide section on
       <seeguide marker="using_ssh#one-time-execution">One-Time Execution</seeguide> for examples.
       </p>
     </desc>
   </func>

   <func>
     <name since="" name="exit_status" arity="3"/>
     <fsummary>Sends the exit status of a command to the client.</fsummary>
     <desc>
       <p>Is to be called by a server-channel process to send the exit status of a command
       to the client.</p>
     </desc>
   </func>
   
   <func>
     <name since="OTP 17.5" name="ptty_alloc" arity="3"/>
     <name since="OTP 17.4" name="ptty_alloc" arity="4"/>
       <fsummary>Sends an SSH Connection Protocol <c>pty_req</c>,
       to allocate a pseudo-terminal.</fsummary>
      <desc>
	<p>Sends an SSH Connection Protocol <c>pty_req</c>, to allocate a pseudo-terminal.
	Is to be called by an SSH client process.</p>
	<p>Options:</p>

	<taglist>
	  <tag>{term, string()}</tag>
	  <item><p>Defaults to <em>os:getenv("TERM")</em> or <em>vt100</em>
	  if it is undefined.</p></item>

	  <tag>{width, integer()}</tag>
	  <item><p>Defaults to 80 if <c>pixel_width</c> is not defined.</p></item>

	  <tag>{height, integer()}</tag>
	  <item><p>Defaults to 24 if <c>pixel_height</c> is not defined.</p></item>

	  <tag>{pixel_width, integer()}</tag>
	  <item><p>Is disregarded if <c>width</c> is defined.</p></item>

	  <tag>{pixel_height, integer()}</tag>
	  <item><p>Is disregarded if <c>height</c> is defined.</p></item>

	  <tag>{pty_opts, [{posix_atom(), integer()}]}</tag>
	  <item><p>Option can be an empty list. Otherwise, see possible <em>POSIX</em> names
	  in Section 8 in <url href="http://www.ietf.org/rfc/rfc4254.txt"> RFC 4254</url>.</p>
	  </item>
	 </taglist>
      </desc>
     </func>

     <func>
       <name since="" name="reply_request" arity="4"/>
       <fsummary>Sends status replies to requests that want such replies.</fsummary>
      <desc>
	<p>Sends status replies to requests where the requester has
	stated that it wants a status report, that is, <c>WantReply = true</c>.
	If <c>WantReply</c> is <c>false</c>, calling this function becomes a
	"noop". Is to be called while handling an SSH Connection
	Protocol message containing a <c>WantReply</c> boolean value.</p>
      </desc>
     </func>
    
     <func>
       <name since="">send(ConnectionRef, ChannelId, Data) -></name>
       <name since="">send(ConnectionRef, ChannelId, Data, Timeout) -></name>
       <name since="">send(ConnectionRef, ChannelId, Type, Data) -></name>
       <name since="">send(ConnectionRef, ChannelId, Type, Data, TimeOut) ->
       ok | Error</name>
       <fsummary>Sends channel data.</fsummary>
       <type>
	<v>ConnectionRef = <seetype marker="ssh:ssh#connection_ref">ssh:connection_ref()</seetype></v>
	<v>ChannelId = <seetype marker="ssh:ssh#channel_id">ssh:channel_id()</seetype></v>
	<v>Data = iodata()</v>
	<v>Type = <seetype marker="#ssh_data_type_code">ssh_data_type_code()</seetype></v>
	<v>Timeout = timeout()</v>
	<v>Error = {error, <seetype marker="#reason">reason()</seetype>}</v>
       </type>
       <desc>
	 <p>Is to be called by client- and server-channel processes to send data to each other.
	 </p>
	 <p>The function <seemfa marker="ssh:ssh_connection#subsystem/4">subsystem/4</seemfa> and subsequent
	 calls of <c>send/3,4,5</c> must be executed in the same process.
	 </p>
       </desc>
     </func>
     
     <func>
       <name since="" name="send_eof" arity="2"/>
       <fsummary>Sends EOF on channel <c>ChannelId</c>.</fsummary>
       <desc>
	 <p>Sends EOF on channel <c>ChannelId</c>.</p>
       </desc>
     </func>

     <func>
       <name since="" name="session_channel" arity="2"/>
       <name since="" name="session_channel" arity="4"/>
       <fsummary>Opens a channel for an SSH session.</fsummary>
       <desc>
	 <p>Opens a channel for an SSH session. The channel id returned from this function
	 is the id used as input to the other functions in this module.</p>
       </desc>
     </func>

    <func>
      <name since="" name="setenv" arity="5"/>
      <fsummary>Environment variables can be passed to the
      shell/command to be started later.</fsummary>
      <desc>
	<p>Environment variables can be passed before starting the
	shell/command. Is to be called by a client channel processes.</p>
      </desc>
    </func>
    
    <func>
      <name since="" name="shell" arity="2"/>
      <fsummary>Requests that the user default shell (typically defined in
      /etc/passwd in Unix systems) is to be executed at the server end.</fsummary>
       <desc>
	 <p>Is to be called by a client channel process to request that the user default
	 shell (typically defined in /etc/passwd in Unix systems) is executed
	 at the server end.</p>
	 <p>Note: the return value is <c>ok</c> instead of <c>success</c> unlike in other
	 functions in this module. This is a fault that was introduced so long ago that
	 any change would break a large number of existing software.
	 </p>
       </desc>
    </func>

    <func>
      <name since="" name="subsystem" arity="4"/>
      <fsummary>Requests to execute a predefined subsystem on the server.</fsummary>
       <desc>
	 <p>Is to be called by a client-channel process for requesting to execute a predefined
	 subsystem on the server.
	 </p>
	 <p>The function <c>subsystem/4</c> and subsequent calls of 
	 <seemfa marker="ssh:ssh_connection#send/3">send/3,4,5</seemfa> must be executed in the same process.
	 </p>
       </desc>
    </func>
    
  </funcs>
  
</erlref>
