HTable Module

Elena-Ramona Modroiu

Edited by

Elena-Ramona Modroiu

Table of Contents

1. Admin Guide
1.1. Overview
1.2. Dependencies
1.2.1. Kamailio Modules
1.2.2. External Libraries or Applications
1.2.3. Loading from database
1.3. Exported Parameters
1.3.1. htable (str)
1.3.2. db_url (str)
1.3.3. key_name_column (str)
1.3.4. key_type_column (str)
1.3.5. value_type_column (str)
1.3.6. key_value_column (str)
1.3.7. array_size_suffix (str)
1.3.8. fetch_rows (integer)
1.3.9. timer_interval (integer)
1.3.10. timer_mode (integer)
1.4. Exported Functions
1.4.1. sht_print()
1.4.2. sht_rm_name_re(htable=>regexp)
1.4.3. sht_rm_value_re(htable=>regexp)
1.5. Exported pseudo-variables
1.6. Exported MI Functions
1.6.1. sht_reload

List of Examples

1.1. Accessing $sht(htname=>key)
1.2. Dictionary attack limitation
1.3. Set hash_size parameter
1.4. Set db_url parameter
1.5. Set key_name parameter
1.6. Set key_name parameter
1.7. Set value_type parameter
1.8. Set key_value parameter
1.9. Set array_size_suffix parameter
1.10. Set fetch_rows parameter
1.11. Set timer_interval parameter
1.12. Set timer_mode parameter
1.13. sht_print usage
1.14. sht_rm_name_re usage
1.15. sht_rm_value_re usage

Chapter 1. Admin Guide

1.1. Overview

The module adds a hash table container to configuration language. The hash table is stored in shared memory and the access to it can be done via pseudo-variables: $sht(htname=>name).

The “name” can be a static string or can include pseudo- variables that will be replaced at runtime.

Example 1.1. Accessing $sht(htname=>key)

modparam("htable", "htable", "a=>size=4;")
$sht(a=>test) = 1;
$sht(a=>$ci::srcip) = $si;

Next example shows a way to protect against dictionary attacks. If someone fails to authenticate 3 times, it is forbidden for 15min. Authenticatin against database is expensive as it does a select on subscriber table. By disabling the DB auth for 15min, resources on server as saved and time to discover the password is increased substantially. Additional alerting can be done by writing a message to syslog or sending email, etc.

To implement the logic, two hash table variables are user: one counting the failed authentications per user and one for storing the time of last authentication attempt. To ensure unique name per user, the hash table uses a combination of authentication username and text “::auth_count” and “::last_auth”.

Example 1.2. Dictionary attack limitation

modparam("htable", "htable", "a=>size=4;")
		$var(exp) = $Ts - 900;
        if($sht(a=>$au::last_auth) > $var(exp))
            sl_send_reply("403", "Try later");
        } else {
            $sht(a=>$au::auth_count) = 0;
        switch ($retcode) {
            case -1:
                sl_send_reply("403", "Forbidden");
            case -2:
                if($sht(a=>$au::auth_count) == null)
                    $sht(a=>$au::auth_count) = 0;
                $sht(a=>$au::auth_count) = $sht(a=>$au::auth_count) + 1;
                if($sht(a=>$au::auth_count) == 3)
                    xlog("auth failed 3rd time - src ip: $si\n");
                $sht(a=>$au::last_auth) = $Ts;
    $sht(a=>$au::auth_count) = 0;
} else {

1.2. Dependencies

1.2.1. Kamailio Modules

The following modules must be loaded before this module:

  • No dependencies on other Kamailio modules.

1.2.2. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio with this module loaded:

  • None.

1.2.3. Loading from database

The module is able to load values in hash table at startup upon providing a DB URL and table name.

The structure of the table must contain:

  • key name - string containing the name of the key.

  • key type - the type of the key

    • 0 - simple key - the key is added as 'key_name'.

    • 1 - array key - the key is added as 'key_name[n]'. n is incremented for each key with this name to build an array in hash table.

  • value type - the type of the key value

    • 0 - value is string.

    • 1 - value is integer.

  • key value - string containing the value of the key.

1.3. Exported Parameters

1.3.1. htable (str)

The definition of a hash table. The value of the parameter must have the following format:

  • "htname=>size=_number_;autoexpire=_number_;dbtable=_string_"

The parameter can be set multiple times to get more hash tables in same configuration file.

  • htname - string specifying the name of the hash table. This string is used by $sht(...) to refer to the hash table.

  • size - number specifying the size of hash table. The number of entries in the table is 2^size

  • autoexpire -time in seconds to delete an item from hash table if no update was done to it. If is missing or set to 0, the items won't expire.

  • dbtable - name of database to be loaded at startup in hash table. If empty or missing, no data will be loaded.

Default value is NULL.

Example 1.3. Set hash_size parameter

modparam("htable", "htable", "a=>size=4;autoexpire=7200;dbtable=htable_a;")
modparam("htable", "htable", "a=>size=4;autoexpire=7200;dbtable=htable_a;")

1.3.2. db_url (str)

The URL to connect to database for loading values in hash table at start up.

Default value is NULL (do not connect).

Example 1.4. Set db_url parameter

modparam("htable", "db_url", "mysql://openser:openserrw@localhost/openser")

1.3.3. key_name_column (str)

The name of the column containing hash table key name.

Default value is 'key_name'.

Example 1.5. Set key_name parameter

modparam("htable", "key_name_column", "kname")

1.3.4. key_type_column (str)

The name of the column containing hash table key type.

Default value is 'key_type'.

Example 1.6. Set key_name parameter

modparam("htable", "key_type_column", "ktype")

1.3.5. value_type_column (str)

The name of the column containing hash table value type.

Default value is 'value_type'.

Example 1.7. Set value_type parameter

modparam("htable", "value_type", "vtype")

1.3.6. key_value_column (str)

The name of the column containing hash table key value.

Default value is 'key_value'.

Example 1.8. Set key_value parameter

modparam("htable", "key_value", "kvalue")

1.3.7. array_size_suffix (str)

The suffix to be added to store the number of items in an array.

Default value is '::size'.

Example 1.9. Set array_size_suffix parameter

modparam("htable", "array_size_suffix", "-count")

1.3.8. fetch_rows (integer)

How many rows to fetch at once from database.

Default value is 100.

Example 1.10. Set fetch_rows parameter

modparam("htable", "fetch_rows", 1000)

1.3.9. timer_interval (integer)

Interval in seconds to check for expired htable values.

Default value is 20.

Example 1.11. Set timer_interval parameter

modparam("htable", "timer_interval", 10)

1.3.10. timer_mode (integer)

If set to 1, will start a new timer process. If set to 0 will use default timer process to check for expired htable values.

Default value is 0.

Example 1.12. Set timer_mode parameter

modparam("htable", "timer_mode", 1)

1.4. Exported Functions

1.4.1.  sht_print()

Dump content of hash table to L_ERR log level. Intended for debug purposes.


Example 1.13. sht_print usage


1.4.2.  sht_rm_name_re(htable=>regexp)

Delete all entries in the htable that match the name against regular expression.


Example 1.14. sht_rm_name_re usage


1.4.3.  sht_rm_value_re(htable=>regexp)

Delete all entries in the htable that match the value against regular expression.


Example 1.15. sht_rm_value_re usage


1.5. Exported pseudo-variables

  • $sht(htable=>key)

  • $shtex(htable=>key)

Exported pseudo-variables are documented at

1.6. Exported MI Functions

1.6.1.  sht_reload

Reload a hash table from database.

Name: sht_reload

Parameters: _hash_table_name_ - the name of hash table to reload.

MI FIFO Command Format: