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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2008</year>
      <year>2018</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.
    If the receiving channel is an Erlang process, the
    messages have the format
    <c><![CDATA[{ssh_cm, connection_ref(), ssh_event_msg()}]]></c>.
    If the <seealso marker="ssh_client_channel">ssh_client_channel</seealso> behavior is used to
    implement the channel process, these messages are handled by
    <seealso marker="ssh_client_channel#Module:handle_ssh_msg-2">handle_ssh_msg/2</seealso>.</p>
  </description>

  <section>
    <title>DATA TYPES</title>

    <p>Type definitions that are used more than once in this module,
    or abstractions to indicate the intended use of the data
    type, or both:</p>

    <taglist>
      <tag><c>boolean() =</c></tag>
      <item><p><c>true | false </c></p></item>
      <tag><c>string() =</c></tag>
      <item><p>list of ASCII characters</p></item>
      <tag><c>timeout() =</c></tag>
      <item><p><c>infinity | integer()</c> in milliseconds</p></item>
      <tag><c>connection_ref() =</c></tag>
      <item><p>opaque() -as returned by
      <c>ssh:connect/3</c> or sent to an SSH channel processes</p></item>
      <tag><c>channel_id() =</c></tag>
      <item><p><c>integer()</c></p></item>
      <tag><c>ssh_data_type_code() =</c></tag>
      <item><p><c>1</c> ("stderr") | <c>0</c> ("normal") are
      valid values, see
      <url href="http://www.ietf.org/rfc/rfc4254.txt">RFC 4254</url> Section 5.2.</p></item>
      <tag><c>ssh_request_status() =</c></tag>
      <item><p> <c>success | failure</c></p></item>
      <tag><c>event() =</c></tag>
      <item><p><c>{ssh_cm, connection_ref(), ssh_event_msg()}</c></p></item>
      <tag><c>ssh_event_msg() =</c></tag>
      <item><p><c>data_events() | status_events() | terminal_events()</c></p></item>
      <tag><c>reason() =</c></tag>
      <item><p><c>timeout | closed</c></p></item>
    </taglist>

    <taglist>
      <tag><em>data_events()</em></tag>
       <item>
	 <taglist>
	   <tag><c><![CDATA[{data, channel_id(), ssh_data_type_code(), Data :: binary()}]]></c></tag>
	   <item><p>Data has arrived on the channel. This event is sent as a
	   result of calling <seealso marker="ssh_connection#send-3">
	   ssh_connection:send/[3,4,5]</seealso>.</p></item>

	   <tag><c><![CDATA[{eof, channel_id()}]]></c></tag>
	   <item><p>Indicates that the other side sends no more data.
	   This event is sent as a result of calling <seealso
	   marker="ssh_connection#send_eof-2"> ssh_connection:send_eof/2</seealso>.
	   </p></item>
	 </taglist>
       </item>

       <tag><em>status_events()</em></tag>
       <item>

      <taglist>
	<tag><c><![CDATA[{signal, channel_id(), ssh_signal()}]]></c></tag>
	<item><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></item>

	<tag><c><![CDATA[{exit_signal, channel_id(), ExitSignal :: string(), ErrorMsg ::string(),
	LanguageString :: string()}]]></c></tag>

	<item><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="http://www.ietf.org/rfc/rfc4254.txt">RFC 4254</url>
	Section 6.10, which shows a special case of these signals.</p></item>

	<tag><c><![CDATA[{exit_status, channel_id(), ExitStatus :: integer()}]]></c></tag>
	<item><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
	<seealso marker="ssh_connection#exit_status-3">
	ssh_connection:exit_status/3</seealso>.</p></item>

	<tag><c><![CDATA[{closed, channel_id()}]]></c></tag>
	<item><p>This event is sent as a result of calling
	<seealso marker="ssh_connection#close-2">ssh_connection:close/2</seealso>.
	Both the handling of this event and sending it are taken care of by the
	<seealso marker="ssh_client_channel">ssh_client_channel</seealso> behavior.</p></item>

      </taglist>
     </item>

     <tag><em>terminal_events()</em></tag>

     <item>
       <p>Channels implementing a shell and command execution on the
       server side are to handle the following messages that can be sent by client-
       channel processes.</p>

      <p>Events that include a <c>WantReply</c> expect the event handling
       process to call <seealso marker="ssh_connection#reply_request-4">
       ssh_connection:reply_request/4</seealso>
       with the boolean value of <c>WantReply</c> as the second argument.</p>

       <taglist>
	 <tag><c><![CDATA[{env, channel_id(), WantReply :: boolean(),
	 Var ::string(), Value :: string()}]]></c></tag>
	 <item><p>Environment variables can be passed to the shell/command
	 to be started later. This event is sent as a result of calling <seealso
	 marker="ssh_connection#setenv-5"> ssh_connection:setenv/5</seealso>.
	 </p></item>

	 <tag><c><![CDATA[{pty, channel_id(),
	 WantReply :: boolean(), {Terminal :: string(), CharWidth :: integer(),
	 RowHeight :: integer(), PixelWidth :: integer(), PixelHeight :: integer(),
	 TerminalModes :: [{Opcode  :: atom() | integer(),
	 Value :: integer()}]}}]]></c></tag>
	 <item><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="http://www.ietf.org/rfc/rfc4254.txt">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 <seealso
	 marker="ssh_connection#ptty_alloc/4">ssh_connection:ptty_alloc/4</seealso>.</p></item>

	 <tag><c><![CDATA[{shell, WantReply :: boolean()}]]></c></tag>
	 <item><p>This message requests that the user default shell
	 is started at the other end. This event is sent as a result of calling
	 <seealso marker="ssh_connection#shell-2"> ssh_connection:shell/2</seealso>.
	 </p></item>

	 <tag><c><![CDATA[{window_change, channel_id(), CharWidth() :: integer(),
	 RowHeight :: integer(), PixWidth :: integer(), PixHeight :: integer()}]]></c></tag>
	 <item><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></item>
     
	 <tag><c><![CDATA[{exec, channel_id(),
	 WantReply :: boolean(), Cmd :: string()}]]></c></tag>
	 <item><p>This message requests that the server starts
	 execution of the given command. This event is sent as a result of calling <seealso
	 marker="ssh_connection#exec-4">ssh_connection:exec/4 </seealso>.
	 </p></item>
       </taglist>
     </item>
   </taglist>
 </section>

  <funcs>
   
   <func>
     <name since="">adjust_window(ConnectionRef, ChannelId, NumOfBytes) -> ok</name>
     <fsummary>Adjusts the SSH flow control window.</fsummary>
     <type>
       <v>ConnectionRef = connection_ref()</v>
       <v>ChannelId = channel_id()</v>
       <v>NumOfBytes = integer()</v>
     </type>
      <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 <seealso marker="ssh_client_channel"> ssh_client_channel</seealso>
	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 <seealso marker="ssh_client_channel#Module:handle_ssh_msg-2">
	handle_ssh_msg/2</seealso> returns after processing channel data.</p></note>
      </desc>
   </func>
   
   <func>
     <name since="">close(ConnectionRef, ChannelId) -> ok</name>
     <fsummary>Sends a close message on the channel <c>ChannelId</c>.</fsummary>
     <type>
       <v>ConnectionRef = connection_ref()</v>
       <v>ChannelId = channel_id()</v>
     </type>
     <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 <seealso
       marker="ssh_client_channel"> ssh_client_channel(3)</seealso>. Thus, channels implemented
       with the behavior are not to call this function explicitly.</p></note>
     </desc>
   </func>
   
   <func>
     <name since="">exec(ConnectionRef, ChannelId, Command, TimeOut) -> ssh_request_status() |
     {error, reason()}</name>
     <fsummary>Requests that the server starts the execution of the given command.</fsummary>
     <type>
       <v>ConnectionRef = connection_ref()</v>
       <v>ChannelId = channel_id()</v>
       <v>Command = string()</v>
       <v>Timeout = timeout()</v>
     </type>
     <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><c>N x {ssh_cm, connection_ref(),
	 {data, channel_id(), ssh_data_type_code(), Data :: binary()}}</c></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><c>0 or 1 x {ssh_cm, connection_ref(), {eof, channel_id()}}</c></tag>
	 <item><p>Indicates that no more data is to be sent.</p></item>

	 <tag><c>0 or 1 x {ssh_cm,
	 connection_ref(), {exit_signal,
	 channel_id(), ExitSignal :: string(), ErrorMsg :: string(), LanguageString :: string()}}</c></tag>
	 <item><p>Not all systems send signals. For details on valid string
	 values, see RFC 4254, Section 6.10</p></item>
	 
	  <tag><c>0 or 1 x {ssh_cm, connection_ref(), {exit_status,
	  channel_id(), ExitStatus :: integer()}}</c></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><c>1 x {ssh_cm, connection_ref(),
	  {closed, channel_id()}}</c></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>
     </desc>
   </func>

   <func>
     <name since="">exit_status(ConnectionRef, ChannelId, Status) -> ok</name>
     <fsummary>Sends the exit status of a command to the client.</fsummary>
     <type>
       <v>ConnectionRef = connection_ref() </v>
       <v>ChannelId = channel_id()</v>
       <v>Status = integer()</v>
     </type>
     <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">ptty_alloc(ConnectionRef, ChannelId, Options) -></name>
     <name since="OTP 17.4">ptty_alloc(ConnectionRef, ChannelId, Options, Timeout) ->  > ssh_request_status() |
     {error, reason()}</name>
       <fsummary>Sends an SSH Connection Protocol <c>pty_req</c>,
       to allocate a pseudo-terminal.</fsummary>
      <type>
	<v>ConnectionRef = connection_ref()</v>
	<v>ChannelId = channel_id()</v>
	<v>Options = proplists:proplist()</v>
      </type>
      <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="">reply_request(ConnectionRef, WantReply, Status, ChannelId) -> ok</name>
       <fsummary>Sends status replies to requests that want such replies.</fsummary>
      <type>
	<v>ConnectionRef = connection_ref()</v>
	<v>WantReply =  boolean()</v>
	<v>Status = ssh_request_status()</v>
	<v>ChannelId = channel_id()</v>
      </type>
      <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, timeout} | {error, closed}</name>
       <fsummary>Sends channel data.</fsummary>
       <type>
	<v>ConnectionRef = connection_ref()</v>
	<v>ChannelId = channel_id()</v>
	<v>Data = iodata()</v>
	<v>Type = ssh_data_type_code()</v>
	<v>Timeout = timeout()</v>
       </type>
       <desc>
	 <p>Is to be called by client- and server-channel processes to send data to each other.
	 </p>
	 <p>The function <seealso marker="ssh:ssh_connection#subsystem/4">subsystem/4</seealso> and subsequent
	 calls of <c>send/3,4,5</c> must be executed in the same process.
	 </p>
       </desc>
     </func>
     
     <func>
       <name since="">send_eof(ConnectionRef, ChannelId) -> ok | {error, closed}</name>
       <fsummary>Sends EOF on channel <c>ChannelId</c>.</fsummary>
       <type>
	<v>ConnectionRef = connection_ref()</v>
	<v>ChannelId = channel_id()</v>
       </type>
       <desc>
	 <p>Sends EOF on channel <c>ChannelId</c>.</p>
       </desc>
     </func>

     <func>
       <name since="">session_channel(ConnectionRef, Timeout) -></name>
       <name since="">session_channel(ConnectionRef, InitialWindowSize,
       MaxPacketSize, Timeout) -> {ok, channel_id()} | {error, reason()}</name>
       <fsummary>Opens a channel for an SSH session.</fsummary>
       <type>
	 <v>ConnectionRef = connection_ref()</v>
	 <v>InitialWindowSize = integer()</v>
	 <v>MaxPacketSize = integer()</v>
	 <v>Timeout = timeout()</v>
	 <v>Reason = term()</v>
       </type>
       <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="">setenv(ConnectionRef, ChannelId, Var, Value, TimeOut) -> ssh_request_status() |
      {error, reason()}</name>
      <fsummary>Environment variables can be passed to the
      shell/command to be started later.</fsummary>
      <type>
	<v>ConnectionRef = connection_ref()</v>
	<v>ChannelId = channel_id()</v>
	<v>Var = string()</v>
	<v>Value = string()</v>
	<v>Timeout = timeout()</v>
      </type>
      <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="">shell(ConnectionRef, ChannelId) -> ok | failure | {error, closed}
      </name>
      <fsummary>Requests that the user default shell (typically defined in
      /etc/passwd in Unix systems) is to be executed at the server end.</fsummary>
       <type>
	 <v>ConnectionRef = connection_ref()</v>
	 <v>ChannelId = channel_id()</v>
       </type>
       <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="">subsystem(ConnectionRef, ChannelId, Subsystem, Timeout) -> ssh_request_status() |
      {error, reason()}</name>
      <fsummary>Requests to execute a predefined subsystem on the server.</fsummary>
       <type>
	 <v>ConnectionRef = connection_ref()</v>
	 <v>ChannelId = channel_id()</v>
	 <v>Subsystem = string()</v>
	 <v>Timeout = timeout()</v>
       </type>
       <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 
	 <seealso marker="ssh:ssh_connection#send/3">send/3,4,5</seealso> must be executed in the same process.
	 </p>
       </desc>
    </func>
    
  </funcs>
  
</erlref>
