func_evalexten.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2021, Naveen Albert
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*! \file
 *
 * \brief Dialplan extension evaluation function
 *
 * \author Naveen Albert <asterisk@phreaknet.org>
 *
 * \ingroup functions
 */
 
/*** MODULEINFO
    <support_level>extended</support_level>
 ***/
 
#include "asterisk.h"
 
#include "asterisk/module.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/utils.h"
#include "asterisk/app.h"
 
/*** DOCUMENTATION
    <function name="EVAL_EXTEN" language="en_US">
        <synopsis>
            Evaluates the contents of a dialplan extension and returns it as a string.
        </synopsis>
        <syntax>
            <parameter name="context" />
            <parameter name="extensions" />
            <parameter name="priority" required="true" />
        </syntax>
        <description>
            <para>The EVAL_EXTEN function looks up a dialplan entry by context,extension,priority,
            evaluates the contents of a Return statement to resolve any variable or function
            references, and returns the result as a string.</para>
            <para>You can use this function to create simple user-defined lookup tables or
            user-defined functions.</para>
            <example title="Custom dialplan functions">
            [call-types]
            exten => _1NNN,1,Return(internal)
            exten => _NXXNXXXXXX,1,Return(external)
 
            [udf]
            exten => calleridlen,1,Return(${LEN(${CALLERID(num)})})
 
            [default]
            exten => _X!,1,Verbose(Call type ${EVAL_EXTEN(call-types,${EXTEN},1)} - ${EVAL_EXTEN(udf,calleridlen,1)})
            </example>
            <para>Any variables in the evaluated data will be resolved in the context of
            that extension. For example, <literal>${EXTEN}</literal> would refer to the
            EVAL_EXTEN extension, not the extension in the context invoking the function.
            This behavior is similar to other applications, e.g. <literal>Gosub</literal>.</para>
            <example title="Choosing which prompt to use">
            same => n,Read(input,${EVAL_EXTEN(prompts,${CALLERID(num)},1)})
 
            [prompts]
            exten => _X!,1,Return(default)
            exten => _20X,1,Return(welcome)
            exten => _2XX,1,Return(${DB(promptsettings/${EXTEN})})
            exten => _3XX,1,Return(${ODBC_MYFUNC(${EXTEN})})
            </example>
            <para>Extensions on which EVAL_EXTEN is invoked are not different from other
            extensions. However, the application at that extension is not executed.
            Only the application data is parsed and evaluated.</para>
            <para>A limitation of this function is that the application at the specified
            extension isn't actually executed, and thus unlike a Gosub, you can't pass
            arguments in the EVAL_EXTEN function.</para>
        </description>
        <see-also>
            <ref type="function">EVAL</ref>
        </see-also>
    </function>
 ***/
 
static int eval_exten_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
{
    char *exten, *pri, *context, *parse;
    int ipri;
    char tmpbuf[len];
 
    if (ast_strlen_zero(data)) {
        ast_log(LOG_WARNING, "The EVAL_EXTEN function requires an extension\n");
        return -1;
    }
 
    parse = ast_strdupa(data);
    /* Split context,exten,pri */
    context = strsep(&parse, ",");
    exten = strsep(&parse, ",");
    pri = strsep(&parse, ",");
 
    if (pbx_parse_location(chan, &context, &exten, &pri, &ipri, NULL, NULL)) {
        return -1;
    }
 
    if (ast_strlen_zero(exten) || ast_strlen_zero(context)) { /* only lock if we really need to */
        ast_channel_lock(chan);
        if (ast_strlen_zero(exten)) {
            exten = ast_strdupa(ast_channel_exten(chan));
        }
        if (ast_strlen_zero(context)) {
            context = ast_strdupa(ast_channel_context(chan));
        }
        ast_channel_unlock(chan);
    }
 
    if (ast_get_extension_data(tmpbuf, len, chan, context, exten, ipri)) {
        return -1; /* EVAL_EXTEN failed */
    }
 
    pbx_substitute_variables_helper_full_location(chan, (chan) ? ast_channel_varshead(chan) : NULL, tmpbuf, buf, len, NULL, context, exten, ipri);
 
    return 0;
}
 
static struct ast_custom_function eval_exten_function = {
    .name = "EVAL_EXTEN",
    .read = eval_exten_read,
};
 
static int unload_module(void)
{
    return ast_custom_function_unregister(&eval_exten_function);
}
 
static int load_module(void)
{
    return ast_custom_function_register(&eval_exten_function);
}
 
AST_MODULE_INFO_STANDARD_EXTENDED(ASTERISK_GPL_KEY, "Extension evaluation function");