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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1999</year><year>2021</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.

    </legalnotice>
    <title>ssl</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>ssl_session_cache_api.xml</file>
  </header>
  <module since="OTP R14B">ssl_session_cache_api</module>
  <modulesummary>TLS session cache API</modulesummary>

  <description>
    <p>
      Defines the API for the TLS session cache (pre TLS-1.3) so
      that the data storage scheme can be replaced by
      defining a new callback module implementing this API.
    </p>
  </description>

 <!--
      ================================================================
      =  Data types                                                  =
      ================================================================
  -->

  <datatypes>
    
      <datatype>
	<name name="session_cache_ref"/>
      </datatype>

      <datatype>
	<name name="session_cache_key"/>
	<desc>
	  <p>A key to an entry in the session cache.</p>
	</desc>
      </datatype>

        <datatype>
	  <name name="partial_key"/>
	<desc>
	   <p>The opaque part of the key. Does not need to be handled
	  by the callback.</p>
	</desc>
      </datatype>
      
       <datatype>
	<name name="session"/>
	<desc>
	   <p>The session data that is stored for each session.</p>
	</desc>
      </datatype>  
  </datatypes>

  <funcs>

    <func>
      <name since="OTP R14B">Module:delete(Cache, Key) -> _</name>
      <fsummary>Deletes a cache entry.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
	<v>Key = <seetype marker="#session_cache_key">session_cache_key() </seetype> </v>
      </type>
      <desc>
	<p>Deletes a cache entry. Is only called from the cache
	handling process.
	</p>
      </desc>
    </func>

    <func>
      <name since="OTP R14B">Module:foldl(Fun, Acc0, Cache) -> Acc</name>
      <fsummary></fsummary>
      <type>
	<v>Fun = fun()</v>
	<v>Acc0 = Acc = term()</v>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
      </type>
      <desc>
	<p>Calls <c>Fun(Elem, AccIn)</c> on successive elements of the
	cache, starting with <c>AccIn == Acc0</c>. <c>Fun/2</c> must
	return a new accumulator, which is passed to the next call.
	The function returns the final value of the accumulator.
	<c>Acc0</c> is returned if the cache is empty.
	</p>

	<note><p>Since OTP-23.3 this functions is only used on the client side
	and does not need to implemented for a server cache.
	</p></note>

      </desc>
    </func>

    <func>
      <name since="OTP 18.0">Module:init(Args) -> Cache </name>
      <fsummary>Returns cache reference.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
	<v>Args = <seetype marker="stdlib:proplists#proplist">proplists:proplist()</seetype></v>
      </type>
      <desc>
	<p>Includes property <c>{role, client | server}</c>.
	Currently this is the only predefined property,
	there can also be user-defined properties. See also
	application environment variable
	<seeapp marker="ssl_app">session_cb_init_args</seeapp>.
	</p>
	<p>Performs possible initializations of the cache and returns
	a reference to it that is used as parameter to the other
	API functions. Is called by the cache handling processes
	<c>init</c> function, hence putting the same requirements on it
	as a normal process <c>init</c> function. This function is
	called twice when starting the SSL application, once with
	the role client and once with the role server, as the SSL
	application must be prepared to take on both roles.
	</p>
      </desc>
    </func>

    <func>
      <name since="OTP R14B">Module:lookup(Cache, Key) -> Entry</name>
      <fsummary>Looks up a cache entry.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
	<v>Key = <seetype marker="#session_cache_key">session_cache_key()</seetype> </v>
	<v>Session = <seetype marker="#session">session()</seetype> | undefined</v>
      </type>
      <desc>
	<p>Looks up a cache entry. Is to be callable from any
         process.
         </p>
      </desc>
    </func>

    <func>
      <name since="OTP R14B">Module:select_session(Cache, PartialKey) -> [Session]</name>
      <fsummary>Selects sessions that can be reused.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
	<v>PartialKey = <seetype marker="#partial_key"> partial_key() </seetype></v>
	<v>Session = <seetype marker="#session">session()</seetype></v>
      </type>
      <desc>
	<p>Selects sessions that can be reused, that is sessions that
	include <c>PartialKey</c> in its key. Is to be callable from
	any process.</p>
	<note><p>Since OTP-23.3 This functions is only used on the client side
	and does not need to implemented for a server cache.
	</p></note>
      </desc>
    </func>

    <func>
      <name since="OTP 19.3">Module:size(Cache) -> integer()</name>
      <fsummary>Returns the number of sessions in the cache.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
      </type>
      <desc>
	<p>Returns the number of sessions in the cache. If size
	exceeds the maximum number of sessions, the current cache
	entries will be invalidated regardless of their remaining
	lifetime. Is to be callable from any process.
	</p>
      </desc>
    </func>

    <func>
      <name since="OTP R14B">Module:terminate(Cache) -> _</name>
      <fsummary>Called by the process that handles the cache when it
      is about to terminate.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
	<d>As returned by init/0</d>
      </type>
      <desc>
	<p>Takes care of possible cleanup that is needed when the
	cache handling process terminates.
	</p>
      </desc>
    </func>

    <func>
      <name since="OTP R14B">Module:update(Cache, Key, Session) -> _</name>
      <fsummary>Caches a new session or updates an already cached one.</fsummary>
      <type>
	<v>Cache = <seetype marker="#session_cache_ref"> session_cache_ref() </seetype></v>
	<v>Key = <seetype marker="#session_cache_key">session_cache_key()</seetype> </v>
	<v>Session = <seetype marker="#session">session()</seetype></v>
      </type>
      <desc>
	<p>Caches a new session or updates an already cached one. Is
	only called from the cache handling process.
	</p>
      </desc>
    </func>

  </funcs>

</erlref>
