HTable Module

Elena-Ramona Modroiu

Edited by

Elena-Ramona Modroiu

Edited by

Alex Balashov

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
2.3. Loading from database
3. Parameters
3.1. htable (str)
3.2. db_url (str)
3.3. key_name_column (str)
3.4. key_type_column (str)
3.5. value_type_column (str)
3.6. key_value_column (str)
3.7. expires_column (str)
3.8. array_size_suffix (str)
3.9. fetch_rows (integer)
3.10. timer_interval (integer)
3.11. timer_mode (integer)
3.12. db_expires (integer)
4. Functions
4.1. sht_print()
4.2. sht_rm_name_re(htable=>regexp)
4.3. sht_rm_value_re(htable=>regexp)
5. Exported pseudo-variables
6. MI Commands
6.1. sht_reload
6.2. sht_dump
6.3. sht_delete
7. Exported RPC Commands
7.1. htable.get htable key
7.2. htable.delete htable key
7.3. htable.dump htable
7.4. htable.listTables
8. Event routes
8.1. htable:mod-init

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_column parameter
1.6. Set key_type_column parameter
1.7. Set value_type_column parameter
1.8. Set key_value_column parameter
1.9. Set expires_column parameter
1.10. Set array_size_suffix parameter
1.11. Set fetch_rows parameter
1.12. Set timer_interval parameter
1.13. Set timer_mode parameter
1.14. Set db_expires parameter
1.15. sht_print usage
1.16. sht_rm_name_re usage
1.17. sht_rm_value_re usage

Chapter 1. Admin Guide

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 module supports definition of many hash tables and can load values at startup from a database table.

A typical use case for the SIP server is to implement a cache system in configuration file - if a value is not found in hash table, load it from database and store it in hash table so next time the access to it is very fast. In the definition of the table you can define the default expiration time of cached items. The expiration time can be adjusted per itme via assignment operation at runtime.

You can read more about hash tables at:

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=8;")
$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=8;")
		$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;
    if(!www_authenticate("$td", "subscriber"))
        switch ($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 {

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • No dependencies on other Kamailio modules.

2.2. External Libraries or Applications

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

  • None.

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.

3. Parameters

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. Larger value means less collisions. The number of entries (aka slots or buckets) in the table is 2^size. The possible range for this value is from 2 to 14, smaller or larger values will be increased or decreased respectivly.

  • 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.

  • dbmode - if set to 1, the content of hash table is written to database table when the SIP server is stopped (i.e., ensure persistency over restarts). Default value is 0 (no write back to db table).

  • initval - the integer value to be returned instead of $null when a requested key is not set.

  • updateexpire - if set to 1 (default), the time until expiration of an item is reset when that item is updated. Certain uses of htable may dictate that updates should not reset the expiration timeout, however, in which case this attribute can be set to 0.

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", "b=>size=5;")
modparam("htable", "htable", "c=>size=4;autoexpire=7200;initval=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://kamailio:kamailiorw@localhost/kamailio")

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_column parameter

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

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_type_column parameter

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

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_column parameter

modparam("htable", "value_type_column", "vtype")

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_column parameter

modparam("htable", "key_value_column", "kvalue")

3.7. expires_column (str)

The name of the column containing expires type.

Default value is 'expires'.

Example 1.9. Set expires_column parameter

modparam("htable", "expires", "expiry")

3.8. array_size_suffix (str)

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

Default value is '::size'.

Example 1.10. Set array_size_suffix parameter

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

3.9. fetch_rows (integer)

How many rows to fetch at once from database.

Default value is 100.

Example 1.11. Set fetch_rows parameter

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

3.10. timer_interval (integer)

Interval in seconds to check for expired htable values.

Default value is 20.

Example 1.12. Set timer_interval parameter

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

3.11. 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 1.13. Set timer_mode parameter

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

3.12. db_expires (integer)

If set to 1, will load/save the expires values of the items in hash table fromm/to database. It applies only to hash tables that have auto-expires attribute defined.

Default value is 0.

Example 1.14. Set db_expires parameter

modparam("htable", "db_expires", 1)

4. Functions

4.1.  sht_print()

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


Example 1.15. sht_print usage


4.2.  sht_rm_name_re(htable=>regexp)

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


Example 1.16. sht_rm_name_re usage


4.3.  sht_rm_value_re(htable=>regexp)

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


Example 1.17. sht_rm_value_re usage


5. Exported pseudo-variables

  • $sht(htable=>key)

  • $shtex(htable=>key)

  • $shtcn(htable=>key)

  • $shtcv(htable=>key)

  • $shtinc(htable=>key)

  • $shtval(htable=>key)

Exported pseudo-variables are documented at

6. MI Commands

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:


6.2.  sht_dump

Dump content of a hash table via MI.

Name: sht_dump

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

MI FIFO Command Format:


6.3.  sht_delete

Delete a key from a hash table via MI.

Name: sht_delete


  • _hash_table_name: The table name to delete the key from

  • _key_name: The key to delete from the htable

MI FIFO Command Format:


Example (note the quoting when executing it via FIFO):

		kamctl fifo sht_delete auth '""'

7. Exported RPC Commands

7.1.  htable.get htable key

Lists one value in a hash table

Name: htable.get


  • htable : Name of the hash table to dump

  • key : Key name of the hash table value to dump


# Dump $sht(students=>daniel)
kamcmd htable.get students daniel

7.2.  htable.delete htable key

Delete one value in a hash table

Name: htable.delete


  • htable : Name of the hash table to delete

  • key : Key name of the hash table value to delete


# Delete $sht(students=>anna)
kamcmd htable.get students anna

7.3.  htable.dump htable

Lists all the values in a hash table

Name: dhtable.dump


  • htable : Name of the hash table to dump


kamcmd htable.dump ipban

7.4.  htable.listTables

Lists all defined tables

Name: dhtable.listTables


  • None


kamcmd htable.listTables

8. Event routes

8.1.  htable:mod-init

When defined, the module calls event_route[htable:mod-init] after all modules have been initialized. A typical use case is to initialise items in hash tables. The event route is executed only once, after core and module initialization, but before Kamailio forks any child processes.

event_route[htable:mod-init] {
    $sht(a=>x) = 1;