Federico Cabiddu

Giacomo Vacca

Camille Oudot


Edited by

Federico Cabiddu

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. workers (integer)
3.2. connection_timeout (integer)
3.3. hash_size (integer)
3.4. tls_version (integer)
3.5. tls_verify_host (integer)
3.6. tls_verify_peer (integer)
3.7. curl_verbose (integer)
3.8. curl_follow_redirect (integer)
3.9. memory_manager (string)
3.10. tls_client_cert (string)
3.11. tls_client_key (string)
3.12. tls_ca_path (string)
3.13. tcp_keepalive (integer)
3.14. tcp_ka_idle (integer)
3.15. tcp_ka_interval (integer)
4. Functions
4.1. http_async_query(url, route_name)
5. Pseudo Variables
6. Statistics
6.1. requests
6.2. replies
6.3. errors
6.4. timeouts
7. Remarks

List of Examples

1.1. Set workers parameter
1.2. Set connection_timeout parameter
1.3. Set hash_size parameter
1.4. Set tls_version parameter
1.5. Set tls_verify_host parameter
1.6. Set tls_verify_peer parameter
1.7. Set curl_verbose parameter
1.8. Set curl_follow_redirect parameter
1.9. Set memory_manager parameter
1.10. Set tls_client_cert parameter
1.11. Set tls_client_key parameter
1.12. Set tls_ca_path parameter
1.13. Set tcp_keepalive parameter
1.14. Set tcp_ka_idle parameter
1.15. Set tcp_ka_interval parameter
1.16. http_async_query() usage
1.17. $http_req_id variable usage
1.18. $http_req(key) variable usage

Chapter 1. Admin Guide

1. Overview

This module performs asynchronous HTTP queries.

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • tm - Transaction module

  • pv - Pseudo-Variables module

2.2. External Libraries or Applications

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

  • libcurl -

  • libevent -

3. Parameters

3.1. workers (integer)

Number of worker processes to be started to send HTTP requests and asynchronously handle responses.

Default value is 1.

Example 1.1. Set workers parameter

modparam("http_async_client", "workers", 2)

3.2. connection_timeout (integer)

Defines in milliseconds how long Kamailio waits for a response from HTTP server.

Default value is 500ms.

Example 1.2. Set connection_timeout parameter

modparam("http_async_client", "connection_timeout", 1000)

3.3. hash_size (integer)

The size of the hash table internally used to keep the requests. A larger table is much faster but consumes more memory. The hash size must be a power of two, otherwise it will be rounded down to the nearest power of two.

Default value is 2048.

Example 1.3. Set hash_size parameter

modparam("http_async_client", "hash_size", 1024)

3.4. tls_version (integer)

For HTTPS connections, what's the preferred SSL version.

Default value is 0 (default SSL version).

Example 1.4. Set tls_version parameter

modparam("http_async_client", "tls_version", 6)

3.5. tls_verify_host (integer)

For HTTPS connections, whether the client should verify the server host.

Default value is 2 (enabled).

Example 1.5. Set tls_verify_host parameter

modparam("http_async_client", "tls_verify_host", 0)

3.6. tls_verify_peer (integer)

For HTTPS connections, whether the client should verify the server identity.

Default value is 1 (enabled).

Example 1.6. Set tls_verify_peer parameter

modparam("http_async_client", "tls_verify_peer", 0)

3.7. curl_verbose (integer)

If defined to a non-zero value, extra information from cURL (request and response headers) will be included in the kamailio logs, with LM_INFO priority.

Default value is 0 (disabled).

Example 1.7. Set curl_verbose parameter

modparam("http_async_client", "curl_verbose", 1)

3.8. curl_follow_redirect (integer)

If defined to a non-zero value, will tell curl to follow HTTP 3xx redirects.

Default value is 0 (disabled).

Example 1.8. Set curl_follow_redirect parameter

modparam("http_async_client", "curl_follow_redirect", 1)

3.9. memory_manager (string)

Choose the memory manager used by curl:

  • shm: curl will use kamailio's SHM pool and memory manager

  • sys: curl will use the system memory and memory manager (malloc, free, ...)

Note: if this module is used in conjunction with another module using libcurl (http_client, utils, xcap, xcap_client), it must be loaded as first one for this parameter to have effect, otherwise curl will likely use the system memory allocator by default. On the other hand if the module is loaded before any other module using libcurl, all the modules will use the memory manager specified by this parameter.

Default value "shm"

Example 1.9. Set memory_manager parameter

modparam("http_async_client", "memory_manager", "sys")

3.10. tls_client_cert (string)

For HTTPS connections, the file path of the TLS client certificate to be used.

Default value is NULL (not used). Default type is PEM.

Example 1.10. Set tls_client_cert parameter

modparam("http_async_client", "tls_client_cert", "/etc/kamailio/ssl/clientcert.pem")

3.11. tls_client_key (string)

For HTTPS connections, the file path of the TLS client certificate key.

Default value is NULL (not used).

Example 1.11. Set tls_client_key parameter

modparam("http_async_client", "tls_client_key", "/etc/kamailio/ssl/clientcert.key")

3.12. tls_ca_path (string)

The path of the directory holding the CA certificates.

Default value is NULL..

Example 1.12. Set tls_ca_path parameter

modparam("http_async_client", "tls_ca_path", "/etc/kamailio/ssl/ca/")

3.13. tcp_keepalive (integer)

If defined to a non-zero value, TCP keepalive will be enabled on cURL connections.

Requires libcurl >= 7.25.0

Default value is 0 (disabled).

Example 1.13. Set tcp_keepalive parameter

modparam("http_async_client", "tcp_keepalive", 1)

3.14. tcp_ka_idle (integer)

TCP keep-alive idle time wait value (in seconds).

Default value is 0 (use cURL default value, 60s).

Example 1.14. Set tcp_ka_idle parameter

modparam("http_async_client", "tcp_ka_idle", 30)

3.15. tcp_ka_interval (integer)

TCP keep-alive interval (in seconds).

Default value is 0 (use cURL default value, 60s).

Example 1.15. Set tcp_ka_interval parameter

modparam("http_async_client", "tcp_ka_interval", 120)

4. Functions

4.1.  http_async_query(url, route_name)

Sends HTTP(S) request asynchronously to the URL given in url parameter, which is a string that may contain pseudo variables.

Parameter route_name defines the route to be executed upon reception of HTTP reply, on error or on timeout. If a transaction exists before calling http_async_query(), it will be paused and resumed in this route, while the routing script execution will be stopped. If executed in a transactionless context, or if $http_req(suspend) is used not to suspend the transaction, the routing script execution will continue and the query result will be available in route_name.

Return value: 0 (stop script execution) on success in transaction context, 1 (continue script execution) in transaction-less context (or if $http_req(suspend) is used), -1 on error.

This function can be used from ANY_ROUTE.

This method is executed asynchronously. The HTTP return code, body and error are returned in the module-specific $http_* PVs (see below). See example on how to retrieve return values.

Example 1.16. http_async_query() usage

# create a transaction to be paused, and resumed in route[HTTP_REPLY]
http_async_query("$rU&f_uri=$fU", "HTTP_REPLY");
$http_req(body) = "{'r_uri':'" + $rU + "', 'f_uri':'" + $fU + "'}";
http_async_query("", "HTTP_REPLY");
route[HTTP_REPLY] {
    if ($http_ok) {
        xlog("L_INFO", "route[HTTP_REPLY]: status $http_rs\n");
        xlog("L_INFO", "route[HTTP_REPLY]: body   $http_rb\n");
    } else {
        xlog("L_INFO", "route[HTTP_REPLY]: error  $http_err)\n");

5. Pseudo Variables

The $http_req_id read-only variable can be used in REQUEST_ROUTE to retrieve the unique identifier for a query after sending it or in the HTTP callback route to retrieve the id of the query the reply belongs to. Useful mainly in non-transactional context.

Example 1.17. $http_req_id variable usage

$http_req(suspend) = 0;

http_async_query("", "HTTP_REPLY");

xlog("L_INFO", "Query id: $http_req_id");
route[HTTP_REPLY] {
xlog("L_INFO", "received reply for query $http_req_id\n");

The $http_req(key) write-only variable can be used to set custom parameters before sending a HTTP query

key can be one of:

  • all: if set to $null, resets all the parameters to their default value (the ones defined in modparam)

  • hdr: sets/modifies/removes a HTTP header. N.B.: setting this variable multiple times will add several headers to the query.

  • body: sets/modifies/removes the request body

  • method: sets the HTTP method: either "GET", "POST", "PUT" or "DELETE" (these are the supported methods). (Note: if the method is not set, curl will use GET, or POST if a body is specified)

  • timeout: sets the HTTP timeout. (Note, this timeout should be normally less than tm.fr_timer timeout, because transaction timeout has a higher priority over HTTP timeout)

  • tls_client_cert: sets the client certificate to use

  • tls_client_key: sets the client certificate key to use

  • tls_ca_path: sets the CA certificate path to use

  • authmethod: Sets the preferred authentication mode for HTTP/HTTPS requests. The value is a bitmap and multiple methods can be used. Note that in this case, the CURL library will make an extra request to discover server-supported authentication methods. You may want to use a specific value.

    Valid values are:

    • 1 - BASIC authentication

    • 2 - HTTP Digest authentication

    • 4 - GSS-Negotiate authentication

    • 8 - NTLM authentication

    • 16 - HTTP Digest with IE flavour

    Default value is 3 - BASIC and Digest authentication.

  • username: sets the username to use for authenticated requests

  • password: sets the password to use for authenticated requests

  • suspend: if set to 0 it doesn't suspend the current transaction before performing the query

  • tcp_keepalive: enable TCP keepalive

  • tcp_ka_idle: set TCP keepalive idle time wait

  • tcp_ka_interval: set TCP keepalive interval

  • follow_redirect: if defined to a non-zero value, will tell curl to follow HTTP 3xx redirects. Defaults to curl_follow_redirect global parameter.

Example 1.18. $http_req(key) variable usage

$http_req(all) = $null;                    # reset the parameters
$http_req(timeout) = 100;                  # 100 ms
$http_req(method) = "DELETE";
$http_req(hdr) = "X-Sip-Call-Id: " + $ci;
$http_req(hdr) = "X-Foo: bar";             # add a 2nd header
$http_req(suspend) = 0;             # don't suspend the transaction, continue routing script's execution
# the following request will use the above parameters
http_async_query("", "HTTP_REPLY");

The following read-only pseudo variables can only be used in the callback routes executed by http_async_query()

  • $http_ok: 1 if cURL executed the request successfully, 0 otherwise (check $http_err for details)

  • $http_err: cURL error string if an error occurred, $null otherwise

  • $http_rs: http status

  • $http_rr: http reason phrase

  • $http_hdr(Name): value of the Name header (the $(http_hdr(Name)[N]) syntax can also be used, check the SIP $hdr() PV documentation for details)

  • $http_mb and $http_ml: HTTP response buffer (including headers) and length

  • $http_rb and $http_bs: HTTP response body and body length

  • $http_time: provides access to broken-down transfer time in microseconds calculated by cURL (

    'name' can be:

    • total - total time for the transfer

    • lookup - name lookup time

    • connect - time from the start until the connection to the remote host (or proxy) was completed.

    • appconnect - time from start until SSL/SSH handshake completed

    • pretransfer - time from start until just before the transfer begins

    • starttransfer - time from start until just when the first byte is received

    • redirect - time taken for all redirect steps before the final transfer.

6. Statistics

6.1. requests

The number of http requests sent.

6.2. replies

The number of received http replies.

6.3. errors

The number of errors.

6.4. timeouts

The number of timed out requests.

7. Remarks

Note: libcurl leak in CentOS 6 - this module uses libcurl library and in case if you are using CentOS 6, be aware that standard libcurl-7.19.7-52 has a memory leak. To fix this memory, install libcurl from city-fan repository. More details at: