path: root/lib/megaco/doc/src/megaco_user.xml

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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2000</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
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      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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    </legalnotice>

    <title>megaco_user</title>
    <prepared>H&aring;kan Mattsson</prepared>
    <responsible>H&aring;kan Mattsson</responsible>
    <docno></docno>
    <approved>H&aring;kan Mattsson</approved>
    <checked></checked>
    <date>2007-06-15</date>
    <rev>%VSN%</rev>
    <file>megaco_user.xml</file>
  </header>
  <module>megaco_user</module>
  <modulesummary>Callback module for users of the Megaco application</modulesummary>
  <description>
    <p>This module defines the callback behaviour of Megaco users.  A
      megaco_user compliant callback module must export the following
      functions: </p>
    <list type="bulleted">
      <item>
        <p><seealso marker="#connect">handle_connect/2,3</seealso></p>
      </item>

      <item>
        <p><seealso marker="#disconnect">handle_disconnect/3</seealso></p>
      </item>

      <item>
        <p><seealso marker="#syntax_error">handle_syntax_error/3,4</seealso></p>
      </item>

      <item>
        <p><seealso marker="#message_error">handle_message_error/3,4</seealso></p>
      </item>

<!--
      <item>
        <p><seealso marker="#segment_error">handle_segment_error/4,5</seealso></p>
      </item>
-->

      <item>
        <p><seealso marker="#trans_request">handle_trans_request/3,4</seealso></p>
      </item>

      <item>
        <p><seealso marker="#trans_long_request">handle_trans_long_request/3,4</seealso></p>
      </item>

      <item>
        <p><seealso marker="#trans_reply">handle_trans_reply/4,5</seealso></p>
      </item>

      <item>
        <p><seealso marker="#trans_ack">handle_trans_ack/4,5</seealso></p>
      </item>

      <item>
        <p><seealso marker="#unexpected_trans">handle_unexpected_trans/3,4</seealso></p>
      </item>

      <item>
        <p><seealso marker="#request_abort">handle_trans_request_abort/4,5</seealso></p>
      </item>

      <item>
        <p><seealso marker="#segment_reply">handle_segment_reply/5,6</seealso></p>
      </item>
    </list>

    <p>The semantics of them and their exact signatures are explained 
      below. </p>
    <p>The <c><![CDATA[user_args]]></c> configuration parameter which may be used to
      extend the argument list of the callback functions. For example,
      the handle_connect function takes by default two arguments:</p>
    <code type="none"><![CDATA[
        handle_connect(Handle, Version)
    ]]></code>
    <p>but if the <c><![CDATA[user_args]]></c> parameter is set to a longer
      list, such as <c><![CDATA[[SomePid,SomeTableRef]]]></c>, the callback
      function is expected to have these (in this case two) extra
      arguments last in the argument list:</p>
    <code type="none"><![CDATA[
        handle_connect(Handle, Version, SomePid, SomeTableRef)
    ]]></code>

    <marker id="extra_argument"></marker>
    <note>
      <p>Must of the functions  below has an optional <c>Extra</c> argument (e.g. 
        <seealso marker="#unexpected_trans">handle_unexpected_trans/4</seealso>). 
        The functions which takes this argument will be called if and only if one 
        of the functions 
        <seealso marker="megaco#receive_message">receive_message/5</seealso> or 
        <seealso marker="megaco#process_received_message">process_received_message/5</seealso> 
        was called with the <c>Extra</c> argument different than 
        <c>ignore_extra</c>. </p>
    </note>

  </description>

  <section>
    <title>DATA TYPES</title>
    <code type="none"><![CDATA[
action_request() = #'ActionRequest'{}
action_reply() = #'ActionReply'{}
error_desc() = #'ErrorDescriptor'{}
segment_no() = integer()
    ]]></code>
    <code type="none"><![CDATA[
conn_handle() = #megaco_conn_handle{}    ]]></code>
    <p>The record initially returned by <c><![CDATA[megaco:connect/4,5]]></c>. 
      It identifies a "virtual" connection and may be reused after a 
      reconnect (disconnect + connect).</p>
    <code type="none"><![CDATA[
protocol_version() = integer()    ]]></code>
    <p>Is the actual protocol version. In most cases the protocol
      version is retrieved from the processed message, but there
      are exceptions:</p>
    <p></p>
    <list type="bulleted">
      <item>
        <p>When <c><![CDATA[handle_connect/2,3]]></c> is triggered by an 
          explicit call to <c><![CDATA[megaco:connect/4,5]]></c>.</p>
      </item>
      <item>
        <p><c><![CDATA[handle_disconnect/3]]></c></p>
      </item>
      <item>
        <p><c><![CDATA[handle_syntax_error/3]]></c></p>
      </item>
    </list>
    <p>In these cases, the ProtocolVersion default
      version is obtained from the static connection
      configuration:</p>
    <list type="bulleted">
      <item>
        <p><c><![CDATA[megaco:conn_info(ConnHandle, protocol_version)]]></c>.</p>
      </item>
    </list>
    <marker id="connect"></marker>
  </section>

  <funcs>
    <func>
      <name>handle_connect(ConnHandle, ProtocolVersion) -> ok | error | {error,ErrorDescr}</name>
      <name>handle_connect(ConnHandle, ProtocolVersion, Extra]) -> ok | error | {error,ErrorDescr}</name>
      <fsummary>Invoked when a new connection is established</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>ErrorDescr      = error_desc()</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Invoked when a new connection is established</p>
        <p>Connections may either be established by an explicit call to
          megaco:connect/4 or implicitly at the first invocation of
          megaco:receive_message/3.</p>
        <p>Normally a Media Gateway (MG) connects explicitly while a Media
          Gateway Controller (MGC) connects implicitly.</p>
        <p>At the Media Gateway Controller (MGC) side it is possible to reject
          a connection request (and send a message error reply to the gateway)
          by returning <c><![CDATA[{error, ErrorDescr}]]></c> or simply <c><![CDATA[error]]></c> which
          generates an error descriptor with code 402 (unauthorized) and 
          reason "Connection refused by user" (this is also the case for all 
          unknown results, such as exit signals or throw).</p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_message_error/4</c>. </p>

	<p><c><![CDATA[handle_connect/3]]></c> (with <c><![CDATA[Extra]]></c>) 
          can also be called as a result of a call to the 
          <seealso marker="megaco#connect">megaco:connect/5</seealso> function
          (if that function is called with the 
          <c>Extra</c> argument different than <c>ignore_extra</c>. </p>

        <marker id="disconnect"></marker>
      </desc>
    </func>

    <func>
      <name>handle_disconnect(ConnHandle, ProtocolVersion, Reason) -> ok</name>
      <fsummary>Invoked when a connection is teared down</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Invoked when a connection is teared down</p>
        <p>The disconnect may either be made explicitly by a call to
          megaco:disconnect/2 or implicitly when the control process
          of the connection dies.</p>

        <marker id="syntax_error"></marker>
      </desc>
    </func>

    <func>
      <name>handle_syntax_error(ReceiveHandle, ProtocolVersion, DefaultED) -> reply | {reply, ED} | no_reply | {no_reply, ED} </name>
      <name>handle_syntax_error(ReceiveHandle, ProtocolVersion, DefaultED, Extra) -> reply | {reply, ED} | no_reply | {no_reply, ED} </name>
      <fsummary>Invoked when a received message had syntax errors</fsummary>
      <type>
        <v>ReceiveHandle    = receive_handle()</v>
        <v>ProtocolVersion  = protocol_version()</v>
        <v>DefaultED        = error_desc()</v>
        <v>ED               = error_desc()</v>
        <v>Extra            = term()</v>
      </type>
      <desc>
        <p>Invoked when a received message had syntax errors</p>
        <p>Incoming messages is delivered by megaco:receive_message/4
          and normally decoded successfully. But if the decoding
          failed this function is called in order to decide if the
          originator should get a reply message (reply) or if the reply
          silently should be discarded (no_reply).</p>
        <p>Syntax errors are detected locally on this side of the
          protocol and may have many causes, e.g. a malfunctioning
          transport layer, wrong encoder/decoder selected, bad
          configuration of the selected encoder/decoder etc.</p>
        <p>The error descriptor defaults to <c><![CDATA[DefaultED]]></c>,
          but can be overridden with an alternate one by
          returning <c><![CDATA[{reply,ED}]]></c> or <c><![CDATA[{no_reply,ED}]]></c>
          instead of <c><![CDATA[reply]]></c> and <c><![CDATA[no_reply]]></c> respectively.
          </p>
        <p>Any other return values (including exit signals or throw) and the
          <c><![CDATA[DefaultED]]></c> will be used. </p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_syntax_error/4</c>. </p>

        <marker id="message_error"></marker>
      </desc>
    </func>

    <func>
      <name>handle_message_error(ConnHandle, ProtocolVersion, ErrorDescr) -> ok</name>
      <name>handle_message_error(ConnHandle, ProtocolVersion, ErrorDescr, Extra) -> ok</name>
      <fsummary>Invoked when a received message just contains an error</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>ErrorDescr      = error_desc()</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Invoked when a received message just contains an error
          instead of a list of transactions.</p>
        <p>Incoming messages is delivered by megaco:receive_message/4
          and successfully decoded. Normally a message contains a list
          of transactions, but it may instead contain an
          ErrorDescriptor on top level of the message.</p>
        <p>Message errors are detected remotely on the other side of
          the protocol. And you probably don't want to reply to it,
          but it may indicate that you have outstanding transactions
          that not will get any response (request -&gt; reply; reply -&gt;
          ack).</p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_message_error/4</c>. </p>

<!--        <marker id="segment_error"></marker> -->
        <marker id="trans_request"></marker>
      </desc>
    </func>

<!--
    <func>
      <name>handle_segment_error(ConnHandle, ProtocolVersion, TransId, SegmentError) -> ok</name>
      <name>handle_segment_error(ConnHandle, ProtocolVersion, TransId, SegmentError, Extra) -> ok</name>
      <fsummary>Invoked when a segment error has been detected</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>TransId         = integer()</v>
        <v>SegmentError    = {missing_segments, [integer()]}</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Invoked when a segment error has been detected.</p>
        <p><c><![CDATA[missing_segments]]></c> means that one or more 
          segments of a segmented message was not received in time.</p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_segment_error/5</c>. </p>

        <marker id="trans_request"></marker>
      </desc>
    </func>
-->

    <func>
      <name>handle_trans_request(ConnHandle, ProtocolVersion, ActionRequests) -> pending() | reply() | ignore_trans_request</name>
      <name>handle_trans_request(ConnHandle, ProtocolVersion, ActionRequests, Extra) -> pending() | reply() | ignore_trans_request</name>
      <fsummary>Invoked for each transaction request</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>ActionRequests  = [action_request()]</v>
        <v>Extra           = term()</v>
        <v>pending()       = {pending, req_data()}</v>
        <v>req_data()      = term()</v>
        <v>reply()         = {ack_action(), actual_reply()} | {ack_action(), actual_reply(), send_options()} </v>
        <v>ack_action()    = discard_ack | {handle_ack, ack_data()} | {handle_pending_ack, ack_data()} | {handle_sloppy_ack, ack_data()}</v>
        <v>actual_reply()  = [action_reply()] | error_desc()</v>
        <v>ack_data()      = term()</v>
        <v>send_options()  = [send_option()]</v>
        <v>send_option()   = {reply_timer, megaco_timer()} | {send_handle, term()} | {protocol_version, integer()}</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Invoked for each transaction request</p>
        <p>Incoming messages is delivered by megaco:receive_message/4
          and successfully decoded. Normally a message contains a list
          of transactions and this function is invoked for each
          TransactionRequest in the message.</p>
        <p>This function takes a list of 'ActionRequest' records and
          has three main options:</p>
        <taglist>
          <tag><c><![CDATA[Return ignore_trans_request]]></c></tag>
          <item>
            <p>Decide that these action requests shall be ignored
              completely.</p>
          </item>
          <tag><c><![CDATA[Return pending()]]></c></tag>
          <item>
            <p>Decide that the processing of these action requests
              will take a long time and that the originator should get
              an immediate 'TransactionPending' reply as interim
              response. The actual processing of these action requests
              instead should be delegated to the the
              handle_trans_long_request/3 callback function with the
              req_data() as one of its arguments. </p>
          </item>
          <tag><c><![CDATA[Return reply()]]></c></tag>
          <item>
            <p>Process the action requests and either return an
              error_descr() indicating some fatal error or a list of
              action replies (wildcarded or not). </p>
            <p>If for some reason megaco is unable to deliver the reply,
              the reason for this will be passed to the user via a call
              to the callback function 
              <seealso marker="#trans_ack">handle_trans_ack</seealso>,
              unless <c><![CDATA[ack_action() = discard_ack]]></c>. </p>
            <p>The ack_action() is  either:</p>
            <taglist>
              <tag><c><![CDATA[discard_ack]]></c></tag>
              <item>
                <p>Meaning that you don't care if the reply is
                  acknowledged or not.</p>
              </item>
              <tag><c><![CDATA[{handle_ack, ack_data()} | {handle_ack, ack_data(), send_options()}]]></c></tag>
              <item>
                <p>Meaning that you want an immediate acknowledgement
                  when the other part receives this transaction
                  reply. When the acknowledgement eventually is
                  received, the handle_trans_ack/4 callback function
                  will be invoked with the ack_data() as one of its
                  arguments. ack_data() may be any Erlang term.</p>
              </item>
              <tag><c><![CDATA[{handle_pending_ack, ack_data()} | {handle_pending_ack, ack_data(), send_options()}]]></c></tag>
              <item>
                <p>This has the same effect as the above, 
                  <em>if and only if</em> megaco has sent at least one 
                  pending message for this request (during the processing
                  of the request). If no pending message has been sent, then 
                  immediate acknowledgement will <em>not</em> be 
                  requested. </p>
                <p>Note that this only works as specified if the 
                  <c><![CDATA[sent_pending_limit]]></c> config option has been set to 
                  an integer value. </p>
              </item>
              <tag><c><![CDATA[{handle_sloppy_ack, ack_data()}| {handle_sloppy_ack, ack_data(), send_options()}]]></c></tag>
              <item>
                <p>Meaning that you want an acknowledgement <em>sometime</em>.
                  When the acknowledgement eventually is received, the 
                  handle_trans_ack/4 callback function will be invoked with 
                  the ack_data() as one of its arguments. ack_data() may be 
                  any Erlang term.</p>
              </item>
            </taglist>
          </item>
        </taglist>
        <p>Any other return values (including exit signals or throw) will 
          result in an error descriptor with code 500 (internal gateway error) 
          and the module name (of the callback module) as reason. </p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_trans_request/4</c>. </p>

        <marker id="trans_long_request"></marker>
      </desc>
    </func>

    <func>
      <name>handle_trans_long_request(ConnHandle, ProtocolVersion, ReqData) -> reply()</name>
      <name>handle_trans_long_request(ConnHandle, ProtocolVersion, ReqData, Extra) -> reply()</name>
      <fsummary>Optionally invoked for a time consuming transaction request</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>ReqData         = req_data()</v>
        <v>Extra           = term()</v>
        <v>req_data()      = term()</v>
        <v>reply()         = {ack_action(), actual_reply()} | {ack_action(), actual_reply(), send_options()}</v>
        <v>ack_action()    = discard_ack | {handle_ack, ack_data()} | {handle_sloppy_ack, ack_data()}</v>
        <v>actual_reply()  = [action_reply()] | error_desc()</v>
        <v>ack_data()      = term()</v>
        <v>send_options()  = [send_option()]</v>
        <v>send_option()   = {reply_timer, megaco_timer()} | {send_handle, term()} | {protocol_version, integer()}</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Optionally invoked for a time consuming transaction request</p>
        <p>If this function gets invoked or not is controlled by the
          reply from the preceding call to handle_trans_request/3.
          The handle_trans_request/3 function may decide to process
          the action requests itself or to delegate the processing to
          this function.</p>
        <p>The req_data() argument to this function is the Erlang term
          returned by handle_trans_request/3.</p>
        <p></p>
        <p>Any other return values (including exit signals or throw) will 
          result in an error descriptor with code 500 (internal gateway error)
          and the module name (of the callback module) as reason. </p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_trans_long_request/4</c>. </p>

        <marker id="trans_reply"></marker>
      </desc>
    </func>

    <func>
      <name>handle_trans_reply(ConnHandle, ProtocolVersion, UserReply, ReplyData) -> ok</name>
      <name>handle_trans_reply(ConnHandle, ProtocolVersion, UserReply, ReplyData, Extra) -> ok</name>
      <fsummary>Optionally invoked for a transaction reply</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>UserReply       = success() | failure()</v>
        <v>success()       = {ok, result()} </v>
        <v>result()        = transaction_result() | segment_result()</v>
        <v>transaction_result() = action_reps()</v>
        <v>segment_result() = {segment_no(), last_segment(), action_reps()}</v>
        <v>action_reps()   = [action_reply()]</v>
        <v>failure()       = {error, reason()}</v>
        <v>reason()  = transaction_reason() | segment_reason() | user_cancel_reason() | send_reason() | other_reason()</v>
        <v>transaction_reason() = error_desc()</v>
        <v>segment_reason() = {segment_no(), last_segment(), error_desc()}</v>
        <v>other_reason()   =  timeout | {segment_timeout, missing_segments()} | exceeded_recv_pending_limit | term()</v>
        <v>last_segment()  = bool()</v>
        <v>missing_segments() = [segment_no()]</v>
        <v>user_cancel_reason() = {user_cancel, reason_for_user_cancel()}</v>
        <v>reason_for_user_cancel() = term()</v>
        <v>send_reason() = send_cancelled_reason() | send_failed_reason()</v>
        <v>send_cancelled_reason() = {send_message_cancelled, reason_for_send_cancel()}</v>
        <v>reason_for_send_cancel() = term()</v>
        <v>send_failed_reason() = {send_message_failed, reason_for_send_failure()}</v>
        <v>reason_for_send_failure() = term()</v>
        <v>ReplyData       = reply_data()</v>
        <v>reply_data()    = term()</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Optionally invoked for a transaction reply</p>
        <p>The sender of a transaction request has the option of
          deciding, whether the originating Erlang process should
          synchronously wait (<c><![CDATA[megaco:call/3]]></c>) for a reply or if the
          message should be sent asynchronously (<c><![CDATA[megaco:cast/3]]></c>) and
          the processing of the reply should be delegated this
          callback function.</p>
        <p>Note that if the reply is segmented (split into several smaller 
          messages; segments), then some extra info, segment number and 
          an indication if all segments of a reply has been received or
          not, is also included in the <c><![CDATA[UserReply]]></c>. </p>
        <p>The <c><![CDATA[ReplyData]]></c> defaults to 
          <c><![CDATA[megaco:lookup(ConnHandle, reply_data)]]></c>, 
          but may be explicitely overridden by a
          <c><![CDATA[megaco:cast/3]]></c> option in order to forward info about the
          calling context of the originating process.</p>
        <p>At <c><![CDATA[success()]]></c>, the <c><![CDATA[UserReply]]></c> either contains:</p>
        <list type="bulleted">
          <item>
            <p>A list of 'ActionReply' records possibly containing 
              error indications.</p>
          </item>
          <item>
            <p>A tuple of size three containing: 
              the segment number, 
              the <c><![CDATA[last segment indicator]]></c> and finally 
              a list of 'ActionReply' records possibly containing error 
              indications. This is of course only possible if the 
              reply was segmented. </p>
          </item>
        </list>
        <p><c><![CDATA[failure()]]></c> indicates an local or external error and
          can be one of the following: </p>
        <list type="bulleted">
          <item>
            <p>A <c><![CDATA[transaction_reason()]]></c>, indicates that the remote 
              user has replied with an explicit transactionError.</p>
          </item>
          <item>
            <p>A <c><![CDATA[segment_reason()]]></c>, indicates that the remote user 
              has replied with an explicit transactionError for this 
              segment. This is of course only possible if the reply was 
              segmented. </p>
          </item>
          <item>
            <p>A <c><![CDATA[user_cancel_reason()]]></c>, indicates that the request 
              has been canceled by the user. <c><![CDATA[reason_for_user_cancel()]]></c> 
              is the reason given in the call to the 
              <seealso marker="megaco#cancel">cancel</seealso>
              function.</p>
          </item>
          <item>
            <p>A <c><![CDATA[send_reason()]]></c>, indicates that the transport module
              <seealso marker="megaco_transport#send_message">send_message</seealso>
              function did not send the message. The reason for this can be: </p>
            <list type="bulleted">
              <item>
                <p><c><![CDATA[send_cancelled_reason()]]></c> - the message sending was 
                  deliberately cancelled. <c><![CDATA[reason_for_send_cancel()]]></c> 
                  is the reason given in the <c><![CDATA[cancel]]></c> return
                  from the 
                  <seealso marker="megaco_transport#send_message">send_message</seealso> 
                  function. </p>
              </item>
              <item>
                <p><c><![CDATA[send_failed_reason()]]></c> - an error occurred while attempting to 
                  send the message. </p>
              </item>
            </list>
          </item>
          <item>
            <p>An <c><![CDATA[other_reason()]]></c>, indicates some other error such 
              as: </p>
            <list type="bulleted">
              <item>
                <p><c><![CDATA[timeout]]></c> - the reply failed to arrive before the 
                  request timer expired.</p>
              </item>
              <item>
                <p><c><![CDATA[{segment_timeout, missing_segments()}]]></c> - 
                  one or more segments
                  was not delivered before the expire of the segment 
                  timer.</p>
              </item>
              <item>
                <p><c><![CDATA[exceeded_recv_pending_limit]]></c> - the pending
                  limit was exceeded for this request.</p>
              </item>
            </list>
          </item>
        </list>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_trans_reply/5</c>. </p>

        <marker id="trans_ack"></marker>
      </desc>
    </func>

    <func>
      <name>handle_trans_ack(ConnHandle, ProtocolVersion, AckStatus, AckData) -> ok</name>
      <name>handle_trans_ack(ConnHandle, ProtocolVersion, AckStatus, AckData, Extra) -> ok</name>
      <fsummary>Optionally invoked for a transaction acknowledgement</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>AckStatus       = ok | {error, reason()}</v>
        <v>reason() = user_cancel_reason() | send_reason() | other_reason()</v>
        <v>user_cancel_reason() = {user_cancel, reason_for_user_cancel()}</v>
        <v>send_reason()   = send_cancelled_reason() | send_failed_reason()</v>
        <v>send_cancelled_reason() = {send_message_cancelled, reason_for_send_cancel()}</v>
        <v>reason_for_send_cancel() = term()</v>
        <v>send_failed_reason() = {send_message_failed, reason_for_send_failure()}</v>
        <v>reason_for_send_failure() = term()</v>
        <v>other_reason()   = term()</v>
        <v>AckData          = ack_data()</v>
        <v>ack_data()       = term()</v>
        <v>Extra            = term()</v>
      </type>
      <desc>
        <p>Optionally invoked for a transaction acknowledgement</p>
        <p>If this function gets invoked or not, is controlled by the
          reply from the preceding call to handle_trans_request/3.
          The handle_trans_request/3 function may decide to return
          {handle_ack, ack_data()} or {handle_sloppy_ack, ack_data()} 
          meaning that you need an immediate acknowledgement of the 
          reply and that this function should be invoked to handle the 
          acknowledgement.</p>
        <p>The ack_data() argument to this function is the Erlang term
          returned by handle_trans_request/3.</p>
        <p></p>
        <p>If the AckStatus is ok, it is indicating that this is a
          true acknowledgement of the transaction reply.</p>
        <p>If the AckStatus is {error, Reason}, it is an indication that the
          acknowledgement or even the reply (for which this is an 
          acknowledgement) was not delivered, but there is no point in
          waiting any longer for it to arrive. This happens when: </p>
        <taglist>
          <tag><c><![CDATA[reply_timer]]></c></tag>
          <item>
            <p>The <c><![CDATA[reply_timer]]></c> eventually times out.</p>
          </item>
          <tag>reply send failure</tag>
          <item>
            <p>When megaco fails to send the reply (see
              <seealso marker="#trans_reply">handle_trans_reply</seealso>), 
              for whatever reason. </p>
          </item>
          <tag>cancel</tag>
          <item>
            <p>The user has explicitly cancelled the wait 
              (megaco:cancel/2).</p>
          </item>
        </taglist>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_trans_ack/5</c>. </p>

        <marker id="unexpected_trans"></marker>
        <marker id="handle_unexpected_trans"></marker>
      </desc>
    </func>

    <func>
      <name>handle_unexpected_trans(ConnHandle, ProtocolVersion, Trans) -> ok</name>
      <name>handle_unexpected_trans(ConnHandle, ProtocolVersion, Trans, Extra) -> ok</name>
      <fsummary>Invoked when an unexpected message is received</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>Trans           = #'TransactionPending'{} | #'TransactionReply'{} | #'TransactionResponseAck'{}</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Invoked when a unexpected message is received</p>
        <p>If a reply to a request is not received in time, the
          megaco stack removes all info about the request from
          its tables. If a reply should arrive after this has been
          done the app has no way of knowing where to send this message.
          The message is delivered to the "user" by calling this
          function on the local node (the node which has the link).</p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_unexpected_trans/4</c>. </p>

        <marker id="request_abort"></marker>
      </desc>
    </func>

    <func>
      <name>handle_trans_request_abort(ConnHandle, ProtocolVersion, TransNo, Pid) -> ok</name>
      <name>handle_trans_request_abort(ConnHandle, ProtocolVersion, TransNo, Pid, Extra) -> ok</name>
      <fsummary>Invoked when an transaction request has been aborted</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>TransNo         = integer()</v>
        <v>Pid             = undefined | pid()</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>Invoked when a transaction request has been aborted</p>
        <p>This function is invoked if the originating pending limit
          has been exceeded. This usually means that a request has taken 
          abnormally long time to complete.</p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_trans_request_abort/5</c>. </p>

        <marker id="segment_reply"></marker>
      </desc>
    </func>

    <func>
      <name>handle_segment_reply(ConnHandle, ProtocolVersion, TransNo, SegNo, SegCompl) -> ok</name>
      <name>handle_segment_reply(ConnHandle, ProtocolVersion, TransNo, SegNo, SegCompl, Extra) -> ok</name>
      <fsummary>Segment Reply Indication</fsummary>
      <type>
        <v>ConnHandle      = conn_handle()</v>
        <v>ProtocolVersion = protocol_version()</v>
        <v>TransNo         = integer()</v>
        <v>SegNo           = integer()</v>
        <v>SegCompl        = asn1_NOVALUE | 'NULL'</v>
        <v>Extra           = term()</v>
      </type>
      <desc>
        <p>This function is called when a segment reply has been received
          if the 
          <seealso marker="megaco#conn_info">segment_reply_ind</seealso> 
          config option has been set to true.</p>
        <p>This is in effect a progress report.</p>

	<p>See <seealso marker="#extra_argument">note</seealso> 
          above about the <c>Extra</c> argument in 
          <c>handle_segment_reply/6</c>. </p>

      </desc>
    </func>
  </funcs>

</erlref>