REST_CLIENT module

Admin Guide

Overview

The rest_client module provides a means of interacting with an HTTP server by doing RESTful queries, such as GET, POST and PUT.

TCP Connection Reusage

Unless specified otherwise by the server through a “Connection: close” indication, the module will keep and reuse the TCP connections it creates as much as possible, regardless if the script writer performs blocking or asynchronous HTTP requests. These connections are not shared among OpenSIPS workers — each worker maintains its own set of connections.

Dependencies

OpenSIPS Modules

The following modules must be loaded before this module:

• No dependencies on other OpenSIPS modules..

External Libraries or Applications

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

• libcurl.

Exported Parameters

curl_timeout (integer)

The maximum allowed time for any HTTP(S) transfer to complete. This interval is inclusive of the initial connect time window, hence the value of this parameter must be greater than or equal to connection timeout.

Default value is “20” seconds.

Setting the curl_timeout parameter

...
modparam("rest_client", "curl_timeout", 10)
...

connection_timeout (integer)

The maximum allowed time to establish a connection with the server.

Default value is “20” seconds.

Setting the connection_timeout parameter

...
modparam("rest_client", "connection_timeout", 4)
...

connect_poll_interval (integer)

Only relevant with async requests. Allows complete control over how quickly we want to detect libcurl’s completed blocking TCP/TLS handshakes, so the async transfers can be put in the background. A lower connect poll interval may speed up all async HTTP transfers, but will also increase CPU usage.

Default value is “20” milliseconds.

Setting the connect_poll_interval parameter

...
modparam("rest_client", "connect_poll_interval", 2)
...

max_async_transfers (integer)

Maximum number of asynchronous HTTP transfers a single OpenSIPS worker is allowed to run simultaneously. As long as this threshold is reached for a worker, all new async transfers it attempts to perform will be done in a blocking manner, with appropriate logging warnings.

Default value is “100”.

Setting the max_async_transfers parameter

...
modparam("rest_client", "max_async_transfers", 300)
...

max_transfer_size (integer)

The maximum allowed size of a single transfer (download). Reaching this limit during a transfer will cause the transfer to stop immediately, returning error -10 at script level. A value of 0 will disable the check.

Default value is “10240” (KB).

Setting the max_transfer_size parameter

...
modparam("rest_client", "max_transfer_size", 64)
...

ssl_verifypeer (integer)

Set this to 0 in order to disable the verification of the remote peer’s certificate. Verification is done using a default bundle of CA certificates which come with libcurl.

Default value is “1” (enabled).

Setting the ssl_verifypeer parameter

...
modparam("rest_client", "ssl_verifypeer", 0)
...

ssl_verifyhost (integer)

Set this to 0 in order to disable the verification that the remote peer actually corresponds to the server listed in the certificate.

Default value is “1” (enabled).

Setting the ssl_verifyhost parameter

...
modparam("rest_client", "ssl_verifyhost", 0)
...

ssl_capath (integer)

An optional path for CA certificates to be used for host verifications.

Setting the ssl_capath parameter

...
modparam("rest_client", "ssl_capath", "/home/opensips/ca_certificates")
...

curl_http_version (integer)

Use a specific HTTP version for all requests. Possible values:

• 0 (default) - use whatever is deemed fit by libcurl
• 1 - enforce HTTP 1.0 requests
• 2 - enforce HTTP 1.1 requests
• 3 - attempt HTTP 2 requests. Fall back to HTTP 1.1 if HTTP 2 cannot be negotiated with the server. Requires libcurl 7.33.0+.
• 4 - attempt HTTP 2 over TLS (HTTPS) only. Fall back to HTTP 1.1 if HTTP 2 cannot be negotiated with the HTTPS server. For clear text HTTP servers, use HTTP 1.1. Requires libcurl 7.47.0+.
• 5 - Issue non-TLS HTTP requests using HTTP 2 without HTTP 1.1 Upgrade. It requires prior knowledge that the server supports HTTP 2 straight away. HTTPS requests will still do HTTP/2 the standard way with negotiated protocol version in the TLS handshake. Requires libcurl 7.49.0+.

more details here, where the documentation for this setting was inspired (read: pilfered) from

Setting the curl_http_version parameter

...
modparam("rest_client", "curl_http_version", 3)
...

enable_expect_100 (boolean)

Include a “Expect: 100-continue” HTTP header field whenever the body size of a POST or PUT request exceeds 1024 bytes. Once enabled, the timeout for waiting for a “100 Continue” reply from the server is 1 second, after which the body upload will begin.

Default value is “false” (disabled).

Setting the enable_expect_100 parameter

...
modparam("rest_client", "enable_expect_100", true)
...

no_concurrent_connects (boolean)

Set to true in order to only allow one OpenSIPS worker to connect to a given URL hostname at a time. While a worker is connecting, all other workers will receive error code -4 (already connecting) when attempting to perform any rest_client operation to the same hostname, regardless if the operation is sync or async.

For sync transfers, the scope of the worker process serialization extends to the entire cURL transfer (TCP connect + upload + download), as all three phases take place within a single cURL library call.

This parameter may be useful in order to prevent system outages caused by concurrent blocking of all OpenSIPS workers on a failed (hanging) HTTP service, with no more free workers being left to process incoming SIP packets.

Default value is “false” (disabled).

Setting the no_concurrent_connects parameter

...
modparam("rest_client", "no_concurrent_connects", true)
...

curl_conn_lifetime (integer)

Only relevant when no concurrent connects is enabled. By setting this parameter, script developers can leverage the connection reusage capabilities of libcURL and entirely skip the “no concurrent transfers” logic on a given SIP worker, should that worker already be known to have a TCP connection to the target URL hostname (established by a previous rest_xxx() function call).

The parameter denotes the lifetime, in seconds, of TCP connections kept within libcURL for reusage, a setting which is often operating system dependant, and which may also be affected by enabling/disabling keepalives. Consult your operating system’s and/or libcurl’s documentation for further information on the max lifetime of your cURL TCP connections.

Default value is 0 (disabled).

Setting the curl_conn_lifetime parameter

...
modparam("rest_client", "curl_conn_lifetime", 1800)
...

Exported Functions

rest_get(url, body_pv, [ctype_pv], [retcode_pv])

Perform a blocking HTTP GET on the given url and return a representation of the resource.

Parameters:

• url (string)
• body_pv (var) - output variable which will hold the body of the HTTP response.
• ctype_pv (var, optional) - output variable which will contain the value of the “Content-Type:” header of the response.
• retcode_pv (var, optional) - output variable which will retain the status code of the HTTP response. A 0 status code value means no HTTP reply arrived at all.

Return Codes

• 1 - Success
• -1 - Connection Refused.
• -2 - Connection Timeout (the connection timeout was exceeded before a TCP connection could be established)
• -3 - Transfer Timeout (the curl timeout was exceeded before the last byte was received). The retcode_pv may be set to 200 or 0, depending whether a 200 OK was received or not. If it was, the body_pv will contain partially downloaded data, use at your own risk! (we recommend you only use this data for logging / debugging purposes)
• -4 - Already Connecting (another OpenSIPS worker is already connecting to this URL hostname. Consult no concurrent connects for more info).
• -10 - Internal Error (out of memory, unexpected libcurl error, etc.)

This function can be used from any route.

rest_get usage

...
# Example of querying a REST service to get the credit of an account
$var(rc) = rest_get("https://getcredit.org/?account=$fU",
                    $var(credit),
                    $var(ct),
                    $var(rcode));
if ($var(rc) < 0) {
  xlog("rest_get() failed with $var(rc), acc=$fU\n");
  send_reply(500, "Server Internal Error");
  exit;
}

if ($var(rcode) != 200) {
  xlog("L_INFO", "rest_get() rcode=$var(rcode), acc=$fU\n");
  send_reply(403, "Forbidden");
  exit;
}
...

rest_post(url, send_body, [send_ctype], recv_body_pv, [recv_ctype_pv], [retcode_pv])

Perform a blocking HTTP POST on the given url.

Note

The send_body parameter can also accept a format-string but it cannot be larger than 1024 bytes. For larger messages, you must build them in a pseudo-variable and pass it to the function.

Parameters:

• url (string)
• send_body (string) - The request body.
• send_ctype (string, optional) - The MIME Content-Type header for the request. The default is “application/x-www-form-urlencoded”
• recv_body_pv (var) - output variable which will hold the body of the HTTP response.
• recv_ctype_pv (var, optional) - output variable which will contain the value of the “Content-Type” header of the response
• retcode_pv (var, optional) - output variable which will retain the status code of the HTTP response. A 0 status code value means no HTTP reply arrived at all.

Return Codes

• 1 - Success
• -1 - Connection Refused.
• -2 - Connection Timeout (the connection timeout was exceeded before a TCP connection could be established)
• -3 - Transfer Timeout (the curl timeout was exceeded before the last byte was received). The retcode_pv may be set to 200 or 0, depending whether a 200 OK was received or not. If it was, the body_pv will contain partially downloaded data, use at your own risk! (we recommend you only use this data for logging / debugging purposes)
• -4 - Already Connecting (another OpenSIPS worker is already connecting to this URL hostname. Consult no concurrent connects for more info).
• -10 - Internal Error (out of memory, unexpected libcurl error, etc.)

This function can be used from any route.

rest_post usage

...
# Creating a resource using a RESTful service with an HTTP POST request
$var(rc) = rest_post("https://myserver.org/register_user",
                     $fU, , $var(body), $var(ct), $var(rcode));
if ($var(rc) < 0) {
  xlog("rest_post() failed with $var(rc), user=$fU\n");
  send_reply(500, "Server Internal Error 1");
  exit;
}

if ($var(rcode) != 200) {
  xlog("rest_post() rcode=$var(rcode), user=$fU\n");
  send_reply(500, "Server Internal Error 2");
  exit;
}
...

rest_put(url, send_body, [send_ctype], recv_body_pv[, [recv_ctype_pv][, [retcode_pv]]])

Perform a blocking HTTP PUT on the given url.

Similar to rest post, the send_body_pv parameter can also accept a format-string but it cannot be larger than 1024 bytes. For larger messages, you must build them in a pseudo-variable and pass it to the function.

Parameters:

• url (string)
• send_body (string) - The request body.
• send_ctype (string, optional) - The MIME Content-Type header for the request. The default is “application/x-www-form-urlencoded”
• recv_body_pv (var) - output variable which will hold the body of the HTTP response.
• recv_ctype_pv (var, optional) - output variable which will contain the value of the “Content-Type” header of the response
• retcode_pv (var, optional) - output variable which will retain the status code of the HTTP response. A 0 status code value means no HTTP reply arrived at all.

Return Codes

• 1 - Success
• -1 - Connection Refused.
• -2 - Connection Timeout (the connection timeout was exceeded before a TCP connection could be established)
• -3 - Transfer Timeout (the curl timeout was exceeded before the last byte was received). The retcode_pv may be set to 200 or 0, depending whether a 200 OK was received or not. If it was, the body_pv will contain partially downloaded data, use at your own risk! (we recommend you only use this data for logging / debugging purposes)
• -4 - Already Connecting (another OpenSIPS worker is already connecting to this URL hostname. Consult no concurrent connects for more info).
• -10 - Internal Error (out of memory, unexpected libcurl error, etc.)

This function can be used from any route.

rest_put usage

...
# Creating/Updating a resource using a RESTful service with an HTTP PUT request
$var(rc) = rest_put("https://myserver.org/users/$fU",
                    $var(userinfo), , $var(body), $var(ct), $var(rcode));
if ($var(rc) < 0) {
  xlog("rest_put() failed with $var(rc), user=$fU\n");
  send_reply(500, "Server Internal Error 3");
  exit;
}

if ($var(rcode) != 200) {
  xlog("rest_put() rcode=$var(rcode), user=$fU\n");
  send_reply(500, "Server Internal Error 4");
  exit;
}
...

rest_append_hf(txt)

Append txt to the HTTP headers of the subsequent request. Multiple headers can be appended by making multiple calls before executing a request.

The contents of txt should adhere to the specification for HTTP headers (ex. Field: Value)

Parameters

• txt (string)

This function can be used from any route.

rest_append_hf usage

...
# Example of querying a REST service requiring additional headers

rest_append_hf("Authorization: Bearer mF_9.B5f-4.1JqM");
$var(rc) = rest_get("http://getcredit.org/?account=$fU", $var(credit));
...

rest_init_client_tls(tls_client_domain)

Force a specific TLS domain to be used at most once, during the next GET/POST/PUT request. Refer to the tls_mgm module for additional info regarding TLS client domains.

If using this function, you must also ensure that tls_mgm is loaded and properly configured.

Parameters

• tls_client_domain (string)

This function can be used from any route.

rest_init_client_tls usage

...
rest_init_client_tls("dom1");
if (!rest_get("https://example.com"))
    xlog("query failed\n");
...

Exported Asynchronous Functions

rest_get(url, body_pv[, [ctype_pv][, [retcode_pv]]])

Perform an asynchronous HTTP GET. This function behaves exactly the same as rest get (in terms of input, output and processing), but in a non-blocking manner. Script execution is suspended until the entire content of the HTTP response is available.

async rest_get usage

route {
  ...
  async(rest_get("http://getcredit.org/?account=$fU",
                 $var(credit), , $var(rcode)), resume);
}

route [resume] {
  $var(rc) = $rc;
  if ($var(rc) < 0) {
    xlog("async rest_get() failed with $var(rc), acc=$fU\n");
    send_reply(500, "Server Internal Error");
    exit;
  }

  if ($var(rcode) != 200) {
    xlog("L_INFO", "async rest_get() rcode=$var(rcode), acc=$fU\n");
    send_reply(403, "Forbidden");
    exit;
  }

  ...
}

rest_post(url, send_body_pv, [send_ctype_pv], recv_body_pv[, [recv_ctype_pv][, [retcode_pv]]])

Perform an asynchronous HTTP POST. This function behaves exactly the same as rest post (in terms of input, output and processing), but in a non-blocking manner. Script execution is suspended until the entire content of the HTTP response is available.

async rest_post usage

route {
  ...
  async(rest_post("http://myserver.org/register_user",
                  $fU, , $var(body), $var(ct), $var(rcode)), resume);
}

route [resume] {
  $var(rc) = $rc;
  if ($var(rc) < 0) {
    xlog("async rest_post() failed with $var(rc), user=$fU\n");
    send_reply(500, "Server Internal Error 1");
    exit;
  }
  if ($var(rcode) != 200) {
    xlog("async rest_post() rcode=$var(rcode), user=$fU\n");
    send_reply(500, "Server Internal Error 2");
    exit;
  }

  ...
}

rest_put(url, send_body_pv, [send_ctype_pv], recv_body_pv[, [recv_ctype_pv][, [retcode_pv]]])

Perform an asynchronous HTTP PUT. This function behaves exactly the same as rest put (in terms of input, output and processing), but in a non-blocking manner. Script execution is suspended until the entire content of the HTTP response is available.

async rest_put usage

route {
  ...
  async(rest_put("http://myserver.org/users/$fU", $var(userinfo), ,
                 $var(body), $var(ct), $var(rcode)), resume);
}

route [resume] {
  $var(rc) = $rc;
  if ($var(rc) < 0) {
    xlog("async rest_put() failed with $var(rc), user=$fU\n");
    send_reply(500, "Server Internal Error 3");
    exit;
  }
  if ($var(rcode) != 200) {
    xlog("async rest_put() rcode=$var(rcode), user=$fU\n");
    send_reply(500, "Server Internal Error 4");
    exit;
  }

  ...
}

Exported script transformations

The module also provides a way for encoding and decoding parameters contained in an arbitrary script variable, in accordance with RFC3986. This is done by applying a transformation to a script variable containing the data to be encoded. The value of the original variable is not altered and a corresponding string value is returned. The transformation is performed through libcurl API method curl_easy_escape (or curl_escape for libcurl < 7.15.4).

{rest.escape}

The result of this transformation is to produce percent encoded string value which can be safely used in URI construction.

There are no parameters for this transformation.

rest.escape usage

...
# This example would produce log entry: "Output: call%40example.com%26safe%3Dfalse"
$var(tmp) = "call@example.com&safe=false";
xlog("Output: $(var(tmp){rest.escape})\n");

# Encode call ID before transmission:
$var(rc) = rest_get("https://call-info.org/?id=$(ci{rest.escape})", $var(body_pv));
...

{rest.unescape}

The result of this transformation is to decode percent encoded string values.

There are no parameters for this transformation.

rest.unescape usage

...
# This example would produce log entry: "Output: 1+1=2!"
$var(tmp) = "1%2B1%3D2%21";
xlog("Output: $(var(tmp){rest.unescape})\n");

# This example would produce log entry: "OpenSIPs, tastes better with every SIP!"
$var(tmp) = "OpenSIPs%2C%20tastes%20better%20with%20every%20SIP%21";
xlog("$(var(tmp){rest.unescape})\n");
...

Contributors

By Commit Statistics

Top contributors by DevScore⁽¹⁾, authored commits⁽²⁾ and lines added/removed⁽³⁾

#	Name	DevScore	Commits	Lines++	Lines—
1.	Liviu Chircu (@liviuchircu)	159	87	4309	2060
2.	Ionut Ionita (@ionutrazvanionita)	23	12	668	267
3.	Razvan Crainea (@razvancrainea)	19	16	43	71
4.	Vlad Patrascu (@rvlad-patrascu)	17	8	341	350
5.	Stefan Darius	15	4	916	160
6.	Bogdan-Andrei Iancu (@bogdan-iancu)	9	6	122	55
7.	Jarrod Baumann (@jarrodb)	6	3	136	37
8.	Agalya Ramachandran (@AgalyaR)	6	2	357	4
9.	Callum Guy (@spacetourist)	6	2	295	22
10.	Peter Lemenkov (@lemenkov)	5	3	9	9

All remaining contributors: Ryan Bullock (@rrb3942), Aron Podrigal (@ar45), Maksym Sobolyev (@sobomax), John Burke (@john08burke), Vlad Paiu (@vladpaiu), Andrey Vorobiev (@andrey-vorobiev).

(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)

(2) including any documentation-related commits, excluding merge commits

(3) ignoring whitespace edits, renamed files and auto-generated files

By Commit Activity

#	Name	Commit Activity
1.	Stefan Darius	Jun 2026 - Jul 2026
2.	Razvan Crainea (@razvancrainea)	Aug 2015 - Jun 2026
3.	Bogdan-Andrei Iancu (@bogdan-iancu)	Oct 2014 - Apr 2026
4.	Liviu Chircu (@liviuchircu)	Mar 2013 - Feb 2026
5.	Vlad Paiu (@vladpaiu)	Nov 2025 - Nov 2025
6.	Peter Lemenkov (@lemenkov)	Jun 2018 - Oct 2025
7.	Aron Podrigal (@ar45)	Sep 2024 - Sep 2024
8.	Maksym Sobolyev (@sobomax)	Oct 2020 - Feb 2023
9.	Vlad Patrascu (@rvlad-patrascu)	May 2017 - May 2021
10.	John Burke (@john08burke)	Apr 2021 - Apr 2021

All remaining contributors: Callum Guy (@spacetourist), Ionut Ionita (@ionutrazvanionita), Andrey Vorobiev (@andrey-vorobiev), Ryan Bullock (@rrb3942), Agalya Ramachandran (@AgalyaR), Jarrod Baumann (@jarrodb).

(1) including any documentation-related commits, excluding merge commits

Documentation

Contributors

Last edited by: Razvan Crainea (@razvancrainea), Liviu Chircu (@liviuchircu), Callum Guy (@spacetourist), Vlad Patrascu (@rvlad-patrascu), Peter Lemenkov (@lemenkov), Agalya Ramachandran (@AgalyaR), Jarrod Baumann (@jarrodb), Bogdan-Andrei Iancu (@bogdan-iancu).

License

All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0