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Diffstat (limited to 'lib/ssh/doc/src/ssh_channel.xml')
| -rw-r--r-- | lib/ssh/doc/src/ssh_channel.xml | 300 |
1 files changed, 98 insertions, 202 deletions
diff --git a/lib/ssh/doc/src/ssh_channel.xml b/lib/ssh/doc/src/ssh_channel.xml index c2b7aa94a5..342de97a1b 100644 --- a/lib/ssh/doc/src/ssh_channel.xml +++ b/lib/ssh/doc/src/ssh_channel.xml @@ -1,11 +1,11 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="iso-8859-1" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> <year>2009</year> - <year>2009</year> + <year>2012</year> <holder>Ericsson AB, All Rights Reserved</holder> </copyright> <legalnotice> @@ -22,31 +22,38 @@ The Initial Developer of the Original Code is Ericsson AB. </legalnotice> - <title>ssh_channel</title> - <prepared>Ingela Anderton Andin</prepared> - <responsible></responsible> - <docno></docno> - <approved></approved> - <checked></checked> - <date></date> - <rev></rev> </header> <module>ssh_channel</module> <modulesummary>Generic Ssh Channel Behavior </modulesummary> <description> - <p>Ssh services are implemented as channels that are multiplexed - over an ssh connection and communicates via the ssh connection - protocol. This module provides a callback API that takes care of - generic channel aspects such as flow control and close messages - and lets the callback functions take care of the service specific - parts. + <p>SSH services (clients and servers) are implemented as channels + that are multiplexed over an SSH connection and communicates via + the <url href="http://www.ietf.org/rfc/rfc4254.txt"> SSH + Connection Protocol </url>. This module provides a callback API + that takes care of generic channel aspects such as flow control + and close messages and lets the callback functions take care of + the service (application) specific parts. This behavior also ensures + that the channel process honors the principal of an OTP-process so + that it can be part of a supervisor tree. This is a requirement of + channel processes implementing a subsystem that will be added to + the SSH applications supervisor tree. </p> + + <p>The functions init/1, terminate/2, handle_ssh_msg/2 and + handle_msg/2 are the functions that are required + to provide the implementation for a server side channel, such as + an SSH subsystem channel that can be plugged into the Erlang ssh + daemon see <seealso marker="ssh#daemon-3">ssh:daemon/[2, + 3]</seealso>. + The handle_call/3, handle_cast/2, code_change/3 and enter_loop/1 + functions are only relevant when implementing a client side + channel.</p> </description> <section> - <title>COMMON DATA TYPES </title> + <title>DATA TYPES </title> <p>Type definitions that are used more than once in this module and/or abstractions to indicate the intended use of the data @@ -56,31 +63,31 @@ <p><c>string() = list of ASCII characters</c></p> <p><c>timeout() = infinity | integer() - in milliseconds.</c></p> <p><c>ssh_connection_ref() - opaque to the user returned by - ssh:connect/3 or sent to a ssh channel process</c></p> + ssh:connect/3 or sent to an SSH channel process</c></p> <p><c>ssh_channel_id() = integer() </c></p> <p><c>ssh_data_type_code() = 1 ("stderr") | 0 ("normal") are - currently valid values see RFC 4254 section 5.2.</c></p> + currently valid values see <url href="http://www.ietf.org/rfc/rfc4254.txt">RFC 4254 </url> section 5.2.</c></p> </section> <funcs> <func> <name>call(ChannelRef, Msg) -></name> - <name>call(ChannelRef, Msg, Timeout) -> Reply | {error, Reason}</name> + <name>call(ChannelRef, Msg, timeout()) -> Reply | {error, Reason}</name> <fsummary> Makes a synchronous call to a channel.</fsummary> <type> <v>ChannelRef = pid() </v> <d>As returned by start_link/4 </d> <v>Msg = term() </v> - <v>Timeout = timeout() </v> <v>Reply = term() </v> <v>Reason = closed | timeout </v> </type> <desc> <p>Makes a synchronous call to the channel process by sending a message and waiting until a reply arrives or a timeout - occurs. The channel will call - <c>CallbackModule:handle_call/3</c> to handle the message. - If the channel process does not exist <c>{error, closed}</c> is returned. + occurs. The channel will call <seealso mark = + "#CallbackModule:handle_call-3">CallbackModule:handle_call/3</seealso> + to handle the message. If the channel process does not exist + <c>{error, closed}</c> is returned. </p> </desc> </func> @@ -98,32 +105,33 @@ <p>Sends an asynchronous message to the channel process and returns ok immediately, ignoring if the destination node or channel process does not exist. The channel will call - <c>CallbackModule:handle_cast/2</c> to handle the message. + <seealso mark = "#CallbackModule:handle_cast-3">CallbackModule:handle_cast/2</seealso> + to handle the message. </p> </desc> </func> <func> <name>enter_loop(State) -> _ </name> - <fsummary> Makes an existing process into a ssh_channel process. </fsummary> + <fsummary> Makes an existing process an ssh_channel process. </fsummary> <type> - <v> State = term() - as returned by ssh_channel:init/1</v> + <v> State = term() - as returned by <seealso mark = "#init-1">ssh_channel:init/1</seealso></v> </type> <desc> - <p> Makes an existing process into a <c>ssh_channel</c> + <p> Makes an existing process an <c>ssh_channel</c> process. Does not return, instead the calling process will - enter the <c>ssh_channel</c> process receive loop and become a + enter the <c>ssh_channel</c> process receive loop and become an <c>ssh_channel process.</c> The process must have been started using one of the start functions in proc_lib, see <seealso marker="stdlib:proc_lib">proc_lib(3)</seealso>. The user is responsible for any initialization of the process - and needs to call ssh_channel:init/1. + and needs to call <seealso mark = "#init-1">ssh_channel:init/1</seealso> </p> </desc> </func> <func> - <name>init(Options) -> {ok, State} | {ok, State, Timeout} | {stop, Reason} </name> + <name>init(Options) -> {ok, State} | {ok, State, timeout()} | {stop, Reason} </name> <fsummary> Initiates a ssh_channel process.</fsummary> <type> <v> Options = [{Option, Value}]</v> @@ -134,24 +142,27 @@ </p> <taglist> <tag><c><![CDATA[{channel_cb, atom()}]]></c></tag> - <item>The module that implements the channel behavior.</item> + <item>The module that implements the channel behaviour.</item> <tag><c><![CDATA[{init_args(), list()}]]></c></tag> - <item> The list of arguments to the callback modules + <item> The list of arguments to the callback module's init function.</item> <tag><c><![CDATA[{cm, connection_ref()}]]></c></tag> - <item> Reference to the ssh connection.</item> + <item> Reference to the ssh connection as returned by <seealso + marker="ssh#connect-3">ssh:connect/3</seealso></item> <tag><c><![CDATA[{channel_id, channel_id()}]]></c></tag> <item> Id of the ssh channel.</item> </taglist> - <note><p>This function is normally not called by the user, it is - only needed if for some reason the channel process needs - to be started with help of <c>proc_lib</c> instead calling - <c>ssh_channel:start/4</c> or <c>ssh_channel:start_link/4</c> </p> + <note><p>This function is normally not called by the + user. The user only needs to call if for some reason the + channel process needs to be started with help of + <c>proc_lib</c> instead of calling + <c>ssh_channel:start/4</c> or + <c>ssh_channel:start_link/4</c> </p> </note> </desc> </func> @@ -167,12 +178,12 @@ <p>This function can be used by a channel to explicitly send a reply to a client that called <c>call/[2,3]</c> when the reply cannot be defined in the return value of - <c>CallbackModule:handle_call/3</c>.</p> + <seealso marker ="#CallbackModule:handle_call-3">CallbackModule:handle_call/3</seealso>.</p> <p><c>Client</c> must be the <c>From</c> argument provided to the callback function <c>handle_call/3</c>. <c>Reply</c> is an arbitrary term, - which will be given back to the client as the return value of - <c>ssh_channel:call/[2,3].</c></p> + which will be given back to the client as the return value of + <seealso marker="#call-2">ssh_channel:call/[2,3].</seealso>></p> </desc> </func> @@ -180,11 +191,12 @@ <name>start(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> </name> <name>start_link(SshConnection, ChannelId, ChannelCb, CbInitArgs) -> {ok, ChannelRef} | {error, Reason}</name> - <fsummary> Starts a processes that handles a ssh channel. </fsummary> + <fsummary> Starts a processes that handles a SSH channel. </fsummary> <type> <v>SshConnection = ssh_connection_ref()</v> <v>ChannelId = ssh_channel_id() </v> - <d> As returned by ssh_connection:session_channel/[2,4]</d> + <d> As returned by cannot be defined in the return value of + <seealso marker ="ssh_connection#session_channel/2">ssh_connection:session_channel/[2,4]</seealso></d> <v>ChannelCb = atom()</v> <d> The name of the module implementing the service specific parts of the channel.</d> @@ -193,10 +205,10 @@ <v>ChannelRef = pid()</v> </type> <desc> - <p>Starts a processes that handles a ssh channel. Will be - called internally by the ssh daemon or explicitly by the ssh - client implementations. A channel process traps exit signals - by default. + <p>Starts a processes that handles an SSH channel. It will be + called internally by the SSH daemon or explicitly by the SSH + client implementations. The behavior will set the + <c>trap_exit</c> flag to true. </p> </desc> </func> @@ -204,28 +216,13 @@ </funcs> <section> - <title>CALLBACK FUNCTIONS</title> - - <p>The functions init/1, terminate/2, handle_ssh_msg/2 and - handle_msg/2 are the functions that are required to provide the - implementation for a server side channel, such as a ssh subsystem - channel that can be plugged into the erlang ssh daemon see - <seealso marker="ssh">ssh:daemon/[2, 3]</seealso>. The - handle_call/3, handle_cast/2 code_change/3 and enter_loop/1 - functions are only relevant when implementing a client side - channel.</p> - </section> - - <section> <marker id="cb_timeouts"></marker> <title> CALLBACK TIMEOUTS</title> - <p> If an integer timeout value is provided in a return value of - one of the callback functions, a timeout will occur unless a - message is received within <c>Timeout</c> milliseconds. A timeout - is represented by the atom <c>timeout</c> which should be handled - by the <seealso marker="#handle_msg">handle_msg/2</seealso> - callback function. The atom infinity can be used to wait - indefinitely, this is the default value. </p> + + <p>The timeout values that may be returned by the callback functions + has the same semantics as in a <seealso marker="stdlib#gen_server">gen_server</seealso> + If the timout occurs <seealso marker="#handle_msg">handle_msg/2</seealso> + will be called as <c>handle_msg(timeout, State). </c></p> </section> <funcs> @@ -242,18 +239,19 @@ upgrade/downgrade, i.e. when the instruction <c>{update,Module,Change,...}</c> where <c>Change={advanced,Extra}</c> is given in the <c>appup</c> - file. See <seealso - marker="doc/design_principles:release_handling#instr">OTP - Design Principles</seealso> for more information. Any new - connection will benefit from a server side upgrade but - already started connections on the server side will not be - affected. + file. See <seealso marker="doc/design_principles:release_handling#instr">OTP + Design Principles</seealso> for more information. </p> - <note><p>If there are long lived ssh connections and more - than one upgrade in a short time this may cause the old - connections to fail as only two versions of the code may - be loaded simultaneously.</p></note> + <note><p>Soft upgrade according to the OTP release concept + is not straight forward for the server side, as subsystem + channel processes are spawned by the SSH application and + hence added to its supervisor tree. It could be possible to + upgrade the subsystem channels, when upgrading the user + application, if the callback functions can handle two + versions of the state, but this function can not be used in + the normal way.</p> + </note> <p>In the case of an upgrade, <c>OldVsn</c> is <c>Vsn</c>, and in the case of a downgrade, <c>OldVsn</c> is @@ -269,7 +267,7 @@ </func> <func> - <name>CallbackModule:init(Args) -> {ok, State} | {ok, State, Timeout} | + <name>CallbackModule:init(Args) -> {ok, State} | {ok, State, timeout()} | {stop, Reason}</name> <fsummary> Makes necessary initializations and returns the initial channel state if the initializations succeed.</fsummary> @@ -277,7 +275,6 @@ <v> Args = term() </v> <d> Last argument to ssh_channel:start_link/4.</d> <v> State = term() </v> - <v>Timeout = timeout() </v> <v> Reason = term() </v> </type> <desc> @@ -298,17 +295,16 @@ <v>From = opaque to the user should be used as argument to ssh_channel:reply/2</v> <v>State = term()</v> - <v>Result = {reply, Reply, NewState} | {reply, Reply, NewState, Timeout} - | {noreply, NewState} | {noreply , NewState, Timeout} + <v>Result = {reply, Reply, NewState} | {reply, Reply, NewState, timeout()} + | {noreply, NewState} | {noreply , NewState, timeout()} | {stop, Reason, Reply, NewState} | {stop, Reason, NewState} </v> <v>Reply = term() - will be the return value of ssh_channel:call/[2,3]</v> - <v>Timeout = timeout() </v> - <v>NewState = term() - a possible updated version of State</v> + <v>NewState = term()</v> <v>Reason = term()</v> </type> <desc> <p>Handles messages sent by calling - <c>ssh_channel:call/[2,3]</c> + <seealso marker="#call-2">ssh_channel:call/[2,3]</seealso> </p> <p>For more detailed information on timeouts see the section <seealso marker="#cb_timeouts">CALLBACK TIMEOUTS</seealso>. </p> @@ -322,10 +318,9 @@ <type> <v>Msg = term()</v> <v>State = term()</v> - <v>Result = {noreply, NewState} | {noreply, NewState, Timeout} + <v>Result = {noreply, NewState} | {noreply, NewState, timeout()} | {stop, Reason, NewState}</v> - <v>NewState = term() - a possible updated version of State</v> - <v>Timeout = timeout() </v> + <v>NewState = term() </v> <v>Reason = term()</v> </type> <desc> @@ -359,14 +354,14 @@ <taglist> <tag><c><![CDATA[{ssh_channel_up, ssh_channel_id(), ssh_connection_ref()}]]></c></tag> - <item>This is the first messages that will be received - by the channel, it is sent just before - the ssh_channel:init/1 function returns successfully. - This is especially useful if the server wants - to send a message to the client without first receiving - a message from the client. If the message is not useful - for your particular problem just ignore it by immediately - returning {ok, State}. + <item>This is the first messages that will be received by + the channel, it is sent just before the <seealso + marker="#init-2">ssh_channel:init/1</seealso> function + returns successfully. This is especially useful if the + server wants to send a message to the client without first + receiving a message from it. If the message is not + useful for your particular scenario just ignore it by + immediately returning {ok, State}. </item> </taglist> </desc> @@ -377,118 +372,19 @@ ssh_channel_id(), State}</name> <fsummary> Handles ssh connection protocol messages. </fsummary> <type> - <v>Msg = {ssh_cm, ssh_connection_ref(), SshMsg}</v> - <v> SshMsg = tuple() - see message list below</v> + <v>Msg = <seealso marker="ssh_connection"> ssh_connection:event() </seealso> </v> <v>State = term()</v> </type> <desc> <p> Handles ssh connection protocol messages that may need service specific attention. </p> - - <p> All channels should handle the following messages. For - channels implementing subsystems the handle_ssh_msg-callback - will not be called for any other messages. </p> - - <taglist> - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {data, ssh_channel_id(), - ssh_data_type_code(), binary() = Data}}]]></c></tag> - <item> Data has arrived on the channel. When the callback - for this message returns the channel behavior will adjust - the ssh flow control window.</item> - - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {eof, - ssh_channel_id()}}]]></c></tag> - <item>Indicteas that the other side will not send any more - data.</item> - - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {signal, - ssh_channel_id(), ssh_signal()}} ]]></c></tag> - <item>A signal can be delivered to the remote - process/service using the following message. Some systems - may not implement signals, in which case they should ignore - this message.</item> - - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), - {exit_signal, ssh_channel_id(), string() = exit_signal, - string() = ErrorMsg, string() = - LanguageString}}]]></c></tag> - <item>A remote execution may terminate violently due to a - signal then this message may be received. For details on valid string - values see RFC 4254 section 6.10</item> - - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {exit_status, - ssh_channel_id(), integer() = ExitStatus}}]]></c></tag> - <item> 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 'exit_status' usually means that the - command terminated successfully.</item> - </taglist> - - <p> Channels implementing a shell and command execution on the server side - should also handle the following messages. </p> - - <taglist> - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {env, ssh_channel_id(), - boolean() = WantReply, string() = Var, string() = Value}}]]></c></tag> - <item> Environment variables may be passed to the - shell/command to be started later. Note that before the - callback returns it should call the function - ssh_connection:reply_request/4 with the boolean value of <c> - WantReply</c> as the second argument. - </item> - - <tag><c><![CDATA[{ssh_cm, ConnectionRef, {exec, ssh_channel_id(), - boolean() = WantReply, string() = Cmd}}]]></c></tag> - <item> This message will request that the server start the - execution of the given command. Note that before the - callback returns it should call the function - ssh_connection:reply_request/4 with the boolean value of <c> - WantReply</c> as the second argument.</item> - - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {pty, ssh_channel_id(), - boolean() = WantReply, {string() = Terminal, integer() = CharWidth, - integer() = RowHeight, integer() = PixelWidth, integer() = PixelHight, - [{atom() | integer() = Opcode, - integer() = Value}] = TerminalModes}}}]]></c></tag> - <item>A pseudo-terminal has been requested for the - session. Terminal is the value of the TERM environment - variable value (e.g., vt100). Zero dimension parameters must - be ignored. The character/row dimensions override the pixel - dimensions (when nonzero). Pixel dimensions refer to the - drawable area of the window. The <c>Opcode</c> in the - <c>TerminalModes</c> list is the mnemonic name, represented - as an lowercase erlang atom, defined in RFC 4254 section 8, - or the opcode if the mnemonic name is not listed in the - RFC. Example <c>OP code: 53, mnemonic name ECHO erlang atom: - echo</c>. Note that before the callback returns it should - call the function ssh_connection:reply_request/4 with the - boolean value of <c> WantReply</c> as the second - argument.</item> - - <tag><c><![CDATA[{ssh_cm, ConnectionRef, {shell, boolean() = - WantReply}}]]></c></tag> - <item> This message will request that the user's default - shell be started at the other end. Note that before the - callback returns it should call the function - ssh_connection:reply_request/4 with the value of <c> - WantReply</c> as the second argument. - </item> - - <tag><c><![CDATA[ {ssh_cm, ssh_connection_ref(), {window_change, - ssh_channel_id(), integer() = CharWidth, integer() = RowHeight, - integer() = PixWidth, integer() = PixHeight}}]]></c></tag> - <item> When the window (terminal) size changes on the client - side, it MAY send a message to the other side to inform it - of the new dimensions.</item> - </taglist> <p> The following message is completely taken care of by the ssh channel behavior</p> <taglist> - <tag><c><![CDATA[{ssh_cm, ssh_connection_ref(), {closed, - ssh_channel_id()}}]]></c></tag> + <tag><c><![CDATA[{closed, ssh_channel_id()}]]></c></tag> <item> The channel behavior will send a close message to the other side if such a message has not already been sent and then terminate the channel with reason normal.</item> @@ -505,12 +401,12 @@ </type> <desc> <p>This function is called by a channel process when it is - about to terminate. Before this function is called ssh_connection:close/2 - will be called if it has not been called earlier. - This function should be the opposite of <c>CallbackModule:init/1</c> - and do any necessary cleaning up. When it returns, the - channel process terminates with reason <c>Reason</c>. The return value is - ignored. + about to terminate. Before this function is called <seealso + marker="ssh_connection#close-2"> ssh_connection:close/2 + </seealso> will be called if it has not been called earlier. + This function should do any necessary cleaning + up. When it returns, the channel process terminates with + reason <c>Reason</c>. The return value is ignored. </p> </desc> </func> |