mid_registrar Module
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   Table of Contents

   1. Admin Guide

        1.1. Overview

              1.1.1. Path Support (RFC 3327)
              1.1.2. GRUU Support (RFC 5627)
              1.1.3. SIP Push Notification Support (RFC 8599)

        1.2. Working modes

              1.2.1. Contact mirroring (default)
              1.2.2. Contact throttling
              1.2.3. AOR throttling

        1.3. Auto-Insertion Into Future SIP Flows
        1.4. Dependencies

              1.4.1. OpenSIPS Modules
              1.4.2. External Libraries or Applications

        1.5. Exported Parameters

              1.5.1. mode (integer)
              1.5.2. contact_id_insertion (integer)
              1.5.3. contact_id_param (string)
              1.5.4. at_escape_str (string)
              1.5.5. outgoing_expires (integer)
              1.5.6. received_avp (string)
              1.5.7. received_param (string)
              1.5.8. extra_contact_params_avp (string)
              1.5.9. attr_avp (string)
              1.5.10. min_expires (integer)
              1.5.11. default_expires (integer)
              1.5.12. max_expires (integer)
              1.5.13. default_q (integer)
              1.5.14. tcp_persistent_flag (string)
              1.5.15. realm_prefix (string)
              1.5.16. case_sensitive (integer)
              1.5.17. expires_max_deviation (integer)
              1.5.18. max_contacts (integer)
              1.5.19. max_username_len (integer)
              1.5.20. max_domain_len (integer)
              1.5.21. max_aor_len (integer)
              1.5.22. max_contact_len (integer)
              1.5.23. retry_after (integer)
              1.5.24. disable_gruu (integer)
              1.5.25. gruu_secret (string)
              1.5.26. pn_enable (boolean)
              1.5.27. pn_providers (string)
              1.5.28. pn_ct_match_params (string)
              1.5.29. pn_pnsreg_interval (integer)
              1.5.30. pn_trigger_interval (integer)
              1.5.31. pn_skip_pn_interval (integer)
              1.5.32. pn_refresh_timeout (integer)
              1.5.33. pn_enable_purr (boolean)

        1.6. Exported Functions

              1.6.1. mid_registrar_save(domain[, flags[, aor[,
                      outgoing_expires[, ownership_tag]]]])

              1.6.2. mid_registrar_lookup(domain[, [flags][,
                      [aor]]])

        1.7. Exported Asynchronous Functions

              1.7.1. pn_process_purr(domain)

   2. Contributors

        2.1. By Commit Statistics
        2.2. By Commit Activity

   3. Documentation

        3.1. Contributors

   List of Tables

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

   2.2. Most recently active contributors^(1) to this module

   List of Examples

   1.1. Setting the mode module parameter
   1.2. Setting the contact_id_insertion module parameter
   1.3. Setting the contact_id_param module parameter
   1.4. Setting the at_escape_str module parameter
   1.5. Setting the outgoing_expires module parameter
   1.6. Setting the received_avp module parameter
   1.7. Setting the received_param module parameter
   1.8. Setting the extra_contact_params_avp module parameter
   1.9. Set attr_avp parameter
   1.10. Setting the min_expires module parameter
   1.11. Setting the default_expires module parameter
   1.12. Setting the max_expires module parameter
   1.13. Setting the default_q module parameter
   1.14. Setting the tcp_persistent_flag module parameter
   1.15. Setting the realm_prefix module parameter
   1.16. Setting the case_sensitive module parameter
   1.17. Setting the expires_max_deviation parameter
   1.18. Set max_contacts parameter
   1.19. Setting the max_username_len module parameter
   1.20. Setting the max_domain_len module parameter
   1.21. Setting the max_aor_len module parameter
   1.22. Setting the max_contact_len module parameter
   1.23. Setting the retry_after module parameter
   1.24. Setting the gruu_secret module parameter
   1.25. Setting the gruu_secret module parameter
   1.26. Setting the pn_enable parameter
   1.27. Setting the pn_providers parameter
   1.28. Setting the pn_ct_match_params parameter
   1.29. Setting the pn_pnsreg_interval parameter
   1.30. Setting the pn_trigger_interval parameter
   1.31. Setting the pn_skip_pn_interval parameter
   1.32. Setting the pn_refresh_timeout parameter
   1.33. Setting the pn_enable_purr parameter
   1.34. mid_registrar_save usage
   1.35. mid_registrar_lookup usage
   1.36. async pn_process_purr() usage

Chapter 1. Admin Guide

1.1. Overview

   The mid_registrar is a mid-component of a SIP platform,
   designed to work between end users and the platform's main
   registration component. It opens up new possibilities for
   leveraging existing infrastructure in order to continue to grow
   (as subscribers and as registration traffic) while keeping an
   existing low-resources registrar server.

   Acting as a registration front-end to the main SIP registrar,
   the mid-registrar is able to:
     * convert incoming high-rate registration traffic into a
       low-rate variant, towards the main registrar layer. With
       proper configuration, it can absorb over 90% of existing
       registration traffic while correctly managing the
       back-end's user location state, effectively reducing
       resource usage at the respective layer.
     * stay synchronized with the main registrar (from a user
       location perspective), by properly accepting the contact
       states and expirations it decides.

1.1.1. Path Support (RFC 3327)

   The mid_registrar module includes SIP Path header field support
   according to RFC 3327, for usage in registrars and
   home-proxies.

   A call to mid_registrar_save() stores, if path support is
   enabled in the mid_registrar module, the values of the Path
   Header(s) along with the Contact information into usrloc. There
   are three modes for building the reply to a REGISTER message
   which includes one or more Path header fields:
     * off - stores the value of the Path headers into usrloc
       without passing it back to the UAC in the reply.
     * lazy - stores the Path header and passes it back to the UAC
       if Path-support is indicated by the “path” param in the
       Supported HF.
     * strict - rejects the registration with “420 Bad Extension”
       if there's a Path header but no support for it is indicated
       by the UAC. Otherwise it's stored and passed back to the
       UAC.

   A call to mid_registrar_lookup() always uses the Path header if
   found, and inserts it as Route HF either in front of the first
   Route HF, or after the last Via HF if no Route is present. It
   also sets the destination URI to the first Path URI, thus
   overwriting the received-URI, because NAT has to be handled at
   the outbound-proxy of the UAC (the first hop after client's
   NAT).

   The whole process is transparent to the user, so no config
   changes are required besides enabling one of the "p0" / "p1" /
   "p2" flags when calling mid_registrar_save().

1.1.2. GRUU Support (RFC 5627)

   The mid_registrar module includes support for Globally Routable
   User Agent URIs according to RFC 5627.

   A call to mid_registrar_save() stores, if the phone supports
   GRUU, the values of the SIP Instance along with the contact
   into usrloc. The module will generate two types of GRUUs:
     * public - exposes the underlying AOR, constructed just by
       attaching the SIP Instance as the ;gr parameter value.
       These are persistent, valid as long as the contact
       registration is valid.
     * temporary - hides the underlying AOR Each new Register
       request leads to the construction of a new temporary GRUU,
       while Register requests with a different Call-ID lead to
       the invalidation of all the previous generated temporary
       GRUUs.

   A call to mid_registrar_lookup() will try to detect if the
   R-URI contains a GRUU. If it does, it will route the request
   just for the Contact that the specific AOR belongs to, without
   appending any other branches.

   Even if the the GRUU handling during the registration process
   is transparent to the user, so no config changes are required,
   you need to take care of the GRUU specifics when handling
   mid-dialog requests.

   As the GRUU will be present in the contact header of the
   initial requests generated byt GRUU enabled devices, you will
   have to also do a lookup() when receiving a mid-dialog request
   with the GRUU indication in the RURI.

1.1.3. SIP Push Notification Support (RFC 8599)

   The mid_registrar module includes support for standards-based
   SIP Push Notifications, per RFC 8599. Support for the basic
   version of the draft can be enabled by switching pn_enable to
   true. The module also includes optional support for sending
   Push Notifications during long-lived dialogs (see RFC section
   6), through the pn_enable_purr switch.

   Essential mechanics behind the Push Notification (PN) support:
     * the PN support is fully compatible with the existing logic
       and enabling it does not impose any limitations, as the
       mid_registrar can simultaneously handle both SIP PN
       compliant and standard SIP User Agents
     * OpenSIPS will raise a E_UL_CONTACT_REFRESH event any time a
       Push Notification needs to be sent to a PN-enabled contact.
       The event includes the PN coordinates of the contact --
       they may be found in the Contact URI ('uri' event
       parameter) and may be extracted using the {uri.param,name}
       transformation. From here onwards, it is up to the script
       developer to trigger the Push Notification (e.g. possibly
       by sending an HTTP POST with the rest_client module), thus
       forcing a re-registration from the device.
     * REGISTER processing is unchanged -- PN-enabled UAs are
       saved just as regular UAs, with the former ones
       additionally having the 4 bitflag set in the "Flags" field
       of any MI listing of contacts, for differentiation purposes
     * initial INVITE processing is barely changed, with the
       mid_registrar_lookup() function now additionally returning
       a value of 2 if the only found contacts were PN-enabled
       contacts, all which required a Push Notification. This
       means that PNs have been triggered for each of them and
       t_relay() is not required, since they are not reachable
       until they re-register!
       Using the event_routing module, OpenSIPS will transparently
       fork a new branch from the current INVITE on each
       re-registration from these contacts within the accepted
       pn_refresh_timeout
     * mid-dialog requests: In some cases (e.g. long-lived
       dialogs), a PN may be required before being able to route a
       mid-dialog request to a SIP UA. The pn_process_purr() async
       function will take care of triggering the PN event and
       resuming the script as soon as a re-registration from the
       concerned contact is received.

   For more information or examples, refer to the documentation of
   the "pn_xxx" module parameters or the OpenSIPS blog posts
   around the "SIP Push Notification" topic.

1.2. Working modes

   The mid_registrar may function in one of several modes:

1.2.1. Contact mirroring (default)

   In "contact mirroring" mode, the mid-registrar will only insert
   itself in the SIP traffic flow between end user and main
   registrar by altering the Contact header field values. See
   section Section 1.3, “Auto-Insertion Into Future SIP Flows” for
   a detailed description of possible Contact-based insertion
   modes. The incoming REGISTER requests will be proxied further
   to the main registrar; the registered contact will be stored in
   the mid-registrar only on 2xx replies, according to the
   information returned by the main registrar.

   A possible usage of this mode, for example, would be to clone
   registrations on a SIP front-end that extends the main platform
   with new services (like adding IM/messaging routing).

1.2.2. Contact throttling

   In "contact throttling" mode, the mid-registrar can
   significantly reduce the registration rate on the main
   registrar side (between mid-registrar and main registrar),
   while coping with a high registration rate on the end-user side
   (between end-user and mid-registrar). This is useful in
   scenarios were the end-users are very dynamic and short-lived
   (e.g. mobile devices), but the main registrar cannot cope with
   large amounts of registration traffic.

   Traffic conversion is done in a "per-device" manner, according
   to each unique SIP Contact header field value. It is achieved
   by increasing the "expires" parameter value of each contact,
   when relaying registrations to the main registrar. Once such a
   registration is completed, subsequent registrations for the
   same SIP Contact header field value will be continuously
   absorbed by the mid-registrar until, eventually, the lifetime
   of the remote registration will have decreased enough that a
   refresh (i.e. simply forwarding the next REGISTER request) is
   mandatory.

   A common occurence is for some SIP User Agents to lose their
   network connection (especially when dealing with mobile
   devices), hence they do not properly de-register from the
   mid-registrar. In this case, in order to avoid stale
   registrations on the main registrar (which contains SIP
   contacts with greatly extended lifetimes!), the mid-registrar
   will appropriately generate De-REGISTER requests and remove
   these contacts from the main registrar's location service as
   soon as it considers them to have expired.

   The main practical use for this mode is registration traffic
   conversion. By minimizing the strain of processing
   registrations on the main registrar, we allow it to dedicate
   more system resources to critical areas of the platform, such
   as advanced SIP calling features and/or media handling.

1.2.3. AOR throttling

   In "AOR throttling" mode, the mid-registrar helps with handling
   multiple registrations per user/AOR. This is done by
   aggregating all the end-user registered contacts from a single
   AOR under a single registration into the main registrar. This
   can dramatically reduce the incoming rate of registrations (to
   a single registration per AOR), but also helps in dealing with
   registrar servers which are not able to implement parallel
   forking/ringing.

   Traffic conversion is done in a "per-user" manner, according to
   each unique SIP AOR. It is achieved by providing a contact with
   a large "expires" parameter value, when relaying registrations
   to the main registrar. Once such a registration is completed,
   subsequent registrations to the same Address-of-record will be
   continuously absorbed by the mid-registrar until, eventually,
   the lifetime of the remote registration will have decreased
   enough that a refresh (i.e. simply forwarding the next REGISTER
   request) is mandatory.

   A common occurence is for some SIP User Agents to lose their
   network connection (especially when dealing with mobile
   devices), hence they do not properly de-register from the
   mid-registrar. In this case, in order to avoid stale
   registrations on the main registrar (which contains SIP AORs
   with greatly extended lifetimes!), the mid-registrar will
   appropriately generate De-REGISTER requests and remove these
   contacts from the main registrar's location service as soon as
   it considers them to have expired.

   Of all three modes, "AOR throttling" potentially offers the
   best reduction in traffic on the way to the main registrar. By
   aggregating contacts, it also has the added benefit of reducing
   the number of contacts that the main registrar must handle.

   Regarding SIP request mangling in this mode, the module will
   always replace all Contact header field values with a single
   Contact header field value when proxying registrations to the
   main registrar, indicating that the AOR is local to the
   front-end, and its contacts can be found there.

   The main practical uses for this mode are registration traffic
   conversion towards the main registrar, as well as taking over
   its call forking duties. By minimizing the strain of processing
   registrations / forking calls on the main registrar, we allow
   it to dedicate more system resources to critical areas of the
   platform, such as advanced SIP calling features and/or media
   handling.

1.3. Auto-Insertion Into Future SIP Flows

   A defining feature of the mid-registrar is that it must be easy
   to integrate, ideally a "plug-and-play" SIP component. It
   should not impose any "outbound-proxy" configurations on any of
   the platform's layers and automatically insert itself on the
   call flows which follow successful registrations.

   Regardless of its configured working mode, the mid-registrar
   will mangle the Contact header field URIs of all forwarded
   REGISTER requests and replace the original "hostname" and
   "port" parts of a Contact URI with one of its listening
   interfaces.

   Additionally, in modes "0" and "1", each Contact will be
   assigned an unique identifier, which will be utilized in future
   contact-based lookup operations. This information will be
   included in each forwarded Contact URI. The
   contact_id_insertion modparam controls how this information is
   included.

1.4. Dependencies

1.4.1. OpenSIPS Modules

   The following modules must be loaded before this module:
     * usrloc
     * signaling
     * tm
     * event_routing, if pn_enable is set to true.

1.4.2. External Libraries or Applications

   The following libraries or applications must be installed
   before running OpenSIPS with this module loaded:
     * None

1.5. Exported Parameters

1.5.1. mode (integer)

   Working mode of the module. Refer to Section 1.2, “Working
   modes” for more details.

   The following is true for all working modes:
     * when a REGISTER is received, the script writer must call
       mid_registrar_save()
     * the mid-registrar will insert itself on the call flow of
       all registrations according to the contact_id_insertion.
     * registrations forwarded by the mid-registrar will
       transparently result in a user location update only if the
       reply status code from the downstream registrar is 2xx.

   Each working mode behaves differently, as follows:
     * 0 (Contact mirroring mode)
       The module will only insert itself on the call flow.
       Contact expirations are left unchanged.
     * 1 (Contact throttling mode)
       Contact throttling is a first step in lowering registration
       traffic rates. This is possible through the use of the
       outgoing_expires module parameter or the corresponding
       parameter to mid_registrar_save(), which allow the script
       writer to prolong the life of the registrations on the way
       to the main registrar.
       In this mode, the mid-registrar may alter Expires header
       field values or "expires" Contact header field parameters
       found in the initial request when forwarding registrations,
       according to outgoing_expires
     * 2 (AOR throttling mode)
       AOR throttling is a step beyond "Contact throttling", as
       the main registrar is only made aware of the network
       presence of AORs, rather than Contacts. This behaviour is
       also made possible through the outgoing_expires module
       parameter or the corresponding parameter to
       mid_registrar_save(), which allow the script writer to
       prolong the life of the registrations on the way to the
       main registrar.
       In this mode, the mid-registrar will fully replace the
       Contact set of all forwarded registrations with a single
       Contact, advertising that the AOR is available to the main
       registrar. The expiration value for this Contact is given
       by outgoing_expires.

   Default value is 0 (contact mirroring mode)

   Example 1.1. Setting the mode module parameter
modparam("mid_registrar", "mode", 2)

1.5.2. contact_id_insertion (integer)

   Only relevant in a "mirroring" or "contact throttling" mode.
   Controls where the additional unique Contact identification
   information (64-bit, hex-encoded integer) will be placed within
   outgoing Contact header field URIs. Refer to Section 1.3,
   “Auto-Insertion Into Future SIP Flows” for more details.

   Possible values are:
     * "ct-param" (default) - the contact IDs shall be appended to
       outgoing Contact URIs as ";ctid=" parameters.
     * "ct-username" - the contact IDs will substitute the
       "username" parts of outgoing Contact URIs

   Example 1.2. Setting the contact_id_insertion module parameter
modparam("mid_registrar", "contact_id_insertion", "ct-username")

1.5.3. contact_id_param (string)

   Only relevant in a "mirroring" or "contact throttling" mode.
   Specifies the name of the Contact URI parameter which is used
   by the module in order to match contacts and route SIP
   requests.

   Default value is “ctid”

   Example 1.3. Setting the contact_id_param module parameter
modparam("mid_registrar", "contact_id_param", "ctid")

# Example resulting Contact header field:
# Contact: <sip:liviu@10.0.0.10:5060;ctid=619244948763447138>;expires=18
0.

1.5.4. at_escape_str (string)

   Only relevant when in "AoR throttling" mode and with the usrloc
   use_domain setting enabled. This string represents the escape
   sequence for the "@" character, which must be included, in one
   way or another, in mid-registrar's generated Contact URI
   usernames.

   Setting this parameter to a different value may be useful in
   situations where the backend registrar is incompatible with the
   default escape string.

   Default value is “%40”

   Example 1.4. Setting the at_escape_str module parameter
modparam("mid_registrar", "at_escape_str", "___")

# Example Contact header field generated by mid-registrar:
# Contact: <sip:zach%40sipdomain.invalid@127.0.0.1:5060>;expires=120

1.5.5. outgoing_expires (integer)

   Only relevant in Contact/AOR throttling modes. Sets a minimal
   value for the expiration intervals of egressing contacts.

   Default value is 3600 (seconds)

   Example 1.5. Setting the outgoing_expires module parameter
modparam("mid_registrar", "outgoing_expires", 3600)

1.5.6. received_avp (string)

   The module will store the value of the AVP configured by this
   parameter in the received column of the user location table. It
   will leave the column empty if the AVP is empty. The AVP should
   contain a SIP URI consisting of the source IP, port, and
   protocol of the REGISTER message being processed.

Note

   The value of this parameter should be the same as the value of
   corresponding parameter of nathelper module.

   Default value is "NULL" (disabled)

   Example 1.6. Setting the received_avp module parameter
modparam("mid_registrar", "received_avp", "$avp(rcv)")

1.5.7. received_param (string)

   The name of the parameter that will be appended to Contacts of
   200 OK replies if the received URI is set by nathelper module.

Note

   The value of this parameter should be the same as the value of
   corresponding parameter of nathelper module.

   Default value is "received"

   Example 1.7. Setting the received_param module parameter
modparam("mid_registrar", "received_param", "rcv")

1.5.8. extra_contact_params_avp (string)

   An AVP specification. This AVP is evaluated during
   mid_registrar_save(): if it holds a valid string, its content
   will be appended to each new Contact URI built by the
   mid-registrar, for the outgoing request.

   Default value is None (not used)

   Example 1.8. Setting the extra_contact_params_avp module
   parameter
# NB: AVPs are cleared with every new SIP request
modparam("mid_registrar", "extra_contact_params_avp", "$avp(extra_ct_par
ams)")

# setting the AVP during SIP message processing
$avp(extra_ct_params) = ";transport=tls";

1.5.9. attr_avp (string)

   AVP to store specific additional information for each
   registration. This information is read from the AVP and stored
   (in memory, DB or both) at mid_registrar_save(). When the
   mid_registrar_lookup() or 'is_registered()' (registrar)
   functions are called, the attr_avp will be populated with the
   value saved at [re]registration.

   When doing call forking, the AVP will hold multiple values. The
   position of the corresponding attribute information in attr_avp
   is equal to the branch index. An example scenario is given
   below.

   Default value is NULL.

   Example 1.9. Set attr_avp parameter
# reading attributes from the attr_pvar when doing parallel forking
...
modparam("mid_registrar", "attr_avp", "$avp(attr)")

...
if (is_method("REGISTER")) {
        $avp(attr) = "contact_info";
        mid_registrar_save("location");
        exit;
}
...
mid_registrar_lookup("location");
t_on_branch("parallel_fork");
...
branch_route [parallel_fork] {
        xlog("Attributes for branch $T_branch_idx: $(avp(attr)[$T_branch
_idx])\n");
}


1.5.10. min_expires (integer)

   The minimum expires value of a Contact, values lower than this
   minimum will be automatically set to the minimum. Value 0
   disables the checking.

   Default value is 10 (seconds)

   Example 1.10. Setting the min_expires module parameter
modparam("mid_registrar", "min_expires", 600)

1.5.11. default_expires (integer)

   If the processed message contains neither Expires HFs nor
   expires contact parameters, this value will be used as the
   expiration interval of any newly created usrloc records.

   Default value is 3600 (seconds)

   Example 1.11. Setting the default_expires module parameter
modparam("mid_registrar", "default_expires", 1800)

1.5.12. max_expires (integer)

   The maximum expires value of a Contact, values higher than this
   maximum will be automatically set to the maximum. Value 0
   disables the checking.

   Default value is 3600 (seconds)

   Example 1.12. Setting the max_expires module parameter
modparam("mid_registrar", "max_expires", 7200)

1.5.13. default_q (integer)

   Sets the default "q" value for new contacts. Because OpenSIPS
   does not support floating point module parameters, the supplied
   "q" value must be multiplied by 1000. For example, if you want
   default_q to be 0.38, set this parameter to 380.

   Default value is 0

   Example 1.13. Setting the default_q module parameter
modparam("mid_registrar", "default_q", 380)

1.5.14. tcp_persistent_flag (string)

   Specifies the message flag to be used to control the module
   behaviour regarding TCP connections. If the flag is set for a
   REGISTER via TCP containing a TCP contact, the module, via the
   mid_registrar_save() function, will set the lifetime of the TCP
   connection to the contact expire value. By doing this, the TCP
   connection will stay up as long as its contacts are valid.

   Default value is -1 (not set)

   Example 1.14. Setting the tcp_persistent_flag module parameter
modparam("mid_registrar", "tcp_persistent_flag", "TCP_PERSIST_REGISTRATI
ONS")

1.5.15. realm_prefix (string)

   In multi-domain user location scenarios ("use_domain" usrloc
   module parameter set to "1"), this parameter denotes a prefix
   to be automatically stripped from the hostname part of To
   header field URIs when doing a save, or Request-URIs when doing
   a lookup.

   It is meant as an alternative to DNS SRV records (not all SIP
   clients support SRV lookups), a subdomain of the master domain
   can be defined for SIP purposes (like "sip.mydomain.net"
   pointing to same IP address as the SRV record for
   "mydomain.net"). By ignoring the realm_prefix "sip.", at
   registration, "sip.mydomain.net" will be translated to
   "mydomain.net".

   Default value is NULL (none)

   Example 1.15. Setting the realm_prefix module parameter
modparam("mid_registrar", "realm_prefix", "sip.")

1.5.16. case_sensitive (integer)

   If set to 1, then AOR comparison will be case sensitive (as
   RFC3261 instructs), if set to 0 then AOR comparison will be
   case insensitive.

   Default value is 1 (true)

   Example 1.16. Setting the case_sensitive module parameter
modparam("mid_registrar", "case_sensitive", 0)

1.5.17. expires_max_deviation (integer)

   Set this parameter in order to add a random +/- deviation up to
   and including the given value to the expiration interval of a
   newly registered contact. For example, if this parameter is set
   to 100 and a phone registers for 1800 sec, the final expiry
   will be a random number in the [1700, 1900] interval.

   By randomizing the registration lifetimes of the contacts, the
   server is better equipped to deal with a post-restart
   registration storm, when all TCP connections are lost and a
   significant portion of UAs will re-register at the same time.
   Thanks to the contact lifetime randomization, the registration
   storm will only happen once rather than, e.g., every 1800
   seconds following the restart.

   Default value is 0 (no deviation).

   Example 1.17. Setting the expires_max_deviation parameter
...
# add a random +/- 0-100 seconds to each registration lifetime
modparam("mid_registrar", "expires_max_deviation", 100)
...

1.5.18. max_contacts (integer)

   The parameter can be used to limit the number of contacts per
   AOR (Address of Record) in the user location database. Value 0
   disables the check.

   This is the default value and will be used only if no other
   value (for max_contacts) is passed as parameter to the save()
   function. That's it - the function parameter overwride this
   global parameter.

   Default value is 0.

   Example 1.18. Set max_contacts parameter
...
# Allow no more than 10 contacts per AOR
modparam("mid_registrar", "max_contacts", 10)
...

1.5.19. max_username_len (integer)

   The maximum length of the "username" part of an
   Address-of-Record SIP URI.

   Default value is 64.

   Example 1.19. Setting the max_username_len module parameter
modparam("mid_registrar", "max_username_len", 128)

1.5.20. max_domain_len (integer)

   The maximum length of the "domain" part of an Address-of-Record
   SIP URI.

   Default value is 64.

   Example 1.20. Setting the max_domain_len module parameter
modparam("mid_registrar", "max_domain_len", 128)

1.5.21. max_aor_len (integer)

   The maximum length of an Address-of-Record SIP URI.

   Default value is 256.

   Example 1.21. Setting the max_aor_len module parameter
modparam("mid_registrar", "max_aor_len", 512)

1.5.22. max_contact_len (integer)

   The maximum length of a Contact header field SIP URI.

   Default value is 255.

   Example 1.22. Setting the max_contact_len module parameter
modparam("mid_registrar", "max_contact_len", 512)

1.5.23. retry_after (integer)

   The mid-registrar can generate 5xx replies to registrations in
   various situations. It could, for example, happen when the
   max_contacts parameter is set and the processing of REGISTER
   request would exceed the limit. In this case, OpenSIPS would
   respond with "503 Service Unavailable".

   If you want to add the Retry-After header field in 5xx replies,
   set this parameter to a value greater than zero (0 means: do
   not add the header field). See section 20.33 of RFC3261 for
   more details.

   Default value is 0 (disabled)

   Example 1.23. Setting the retry_after module parameter
modparam("mid_registrar", "retry_after", 30)

1.5.24. disable_gruu (integer)

   Globally disable GRUU handling.

   Default value is 1 (GRUUs will not be handled)

   Example 1.24. Setting the gruu_secret module parameter
modparam("mid_registrar", "disable_gruu", 0)

1.5.25. gruu_secret (string)

   The string that will be used in XORing when generating
   temporary GRUUs.

   Default value is "0p3nS1pS"

   Example 1.25. Setting the gruu_secret module parameter
modparam("mid_registrar", "gruu_secret", "my_secret")

1.5.26. pn_enable (boolean)

   Enable SIP Push Notification support (RFC 8599). If enabled,
   Contact header field URIs which include all pn_ct_match_params
   will be matched against existing bindings using only these
   parameters. Otherwise, the module will attempt to match them as
   usual, using the current usrloc matching_mode.

   Default value is false.

   Example 1.26. Setting the pn_enable parameter
...
modparam("mid_registrar", "pn_enable", true)
...

1.5.27. pn_providers (string)

   A list of supported Push Notification providers. While only
   three possible values are defined by RFC 8599 ("apns", "fcm"
   and "webpush"), non-standard values may be specified as well.

   Default value is NULL (not set).

   Example 1.27. Setting the pn_providers parameter
...
modparam("mid_registrar", "pn_providers", "apns, fcm, webpush")
...

1.5.28. pn_ct_match_params (string)

   The minimally required list of RFC 8599 parameters (custom ones
   are accepted as well) which must be present in a Contact URI
   and identically match an existing binding in order for the
   binding to be refreshed during a SIP re-REGISTER. If at least
   one such parameter is missing from a Contact header field URI,
   the module will fall back to performing regular contact
   matching.

   Note that if all above PN Contact URI parameters match an
   existing binding, the match is considered to be successful
   regardless if other parts of the SIP URI do not match (e.g.
   hostname, port, other URI parameters, etc.).

   After calling mid_registrar_lookup() or pn_process_purr(), the
   above PN-related parameters will be automatically stripped from
   the resulting Request and Contact URI event parameter,
   respectively.

   Default value is "pn-provider, pn-prid, pn-param".

   Example 1.28. Setting the pn_ct_match_params parameter
...
modparam("mid_registrar", "pn_ct_match_params", "pn-provider, pn-prid")
...

1.5.29. pn_pnsreg_interval (integer)

   For devices capable of waking up and refreshing their binding
   on their own (signified by the ";+sip.pnsreg" Contact header
   field parameter), this setting denotes the prior-to-expiration
   interval advertised by the server at which the device should
   issue its binding refresh request.

   Default value is 130 (seconds before expiry).

   Example 1.29. Setting the pn_pnsreg_interval parameter
...
modparam("mid_registrar", "pn_pnsreg_interval", 140)
...

1.5.30. pn_trigger_interval (integer)

   If a binding refresh REGISTER request from a given SIP endpoint
   does not arrive within at least pn_trigger_interval seconds
   prior to expiration (e.g. because the device does not support
   ";+sip.pnsreg" or because of other error conditions), the
   E_UL_CONTACT_REFRESH usrloc event will be triggered.

   Once E_UL_CONTACT_REFRESH is triggered, the script writer
   should use the RFC 8599 parameters from the Contact URI in
   order to generate a Push Notification request to the PN
   provider of the device, in order to cause the device to wake up
   and re-register.

   Default value is 120 (seconds before expiry).

   Example 1.30. Setting the pn_trigger_interval parameter
...
modparam("mid_registrar", "pn_trigger_interval", 130)
...

1.5.31. pn_skip_pn_interval (integer)

   Following a successful (re)registration of a contact, this
   setting denotes a time interval, in seconds, during which the
   contact is assumed to be reachable, so any Push Notifications
   will be skipped.

   Default value is 0 seconds (always generate Push
   Notifications).

   Example 1.31. Setting the pn_skip_pn_interval parameter
...
modparam("mid_registrar", "pn_skip_pn_interval", 10)
...

1.5.32. pn_refresh_timeout (integer)

   This timeout starts counting following a mid_registrar_lookup()
   or a pn_process_purr() which triggers a Push Notification. The
   value represents the maximum allowed sum of the duration
   required for the Push Notification to be sent and the duration
   required for the corresponding re-registration from the device
   to arrive.

   Once this timeout is exceeded for an initial or a mid-dialog
   request, any further re-registrations which match the pending
   Push Notification will no longer cause the desired effects. For
   example:
     * pending initial INVITE transactions will complete and will
       no longer auto-fork an additional branch for each REGISTER
       sent by the callee side
     * pending BYE messages will time out and OpenSIPS will
       attempt to route them despite not having received a
       confirmation that the target device is actually reachable

   Default value is 6 seconds.

   Example 1.32. Setting the pn_refresh_timeout parameter
...
modparam("mid_registrar", "pn_refresh_timeout", 10)
...

1.5.33. pn_enable_purr (boolean)

   Enable the SIP Push Notification mechanism for long-lived
   dialogs. If enabled, the mid_registrar will include a
   "+sip.pnspurr" Feature-Caps header field tag in 200 OK replies
   to REGISTER requests. This tag represents a unique identifier
   for the registration (PURR - Proxy Unique Registration
   Reference).

   During dialog setup, each UA may include, in its Contact
   header, the PURR value returned by OpenSIPS during
   registration. By including the PURR (e.g. ";pn-purr=XXX"), an
   agent indicates that it expects to be first awoken by a PN
   before being able to receive a mid-dialog request sent by the
   other party.

   When enabling this parameter, make sure to also add logic for
   pn_process_purr().

   Default value is false.

   Example 1.33. Setting the pn_enable_purr parameter
...
modparam("mid_registrar", "pn_enable_purr", true)
...

1.6. Exported Functions

1.6.1.  mid_registrar_save(domain[, flags[, aor[, outgoing_expires[,
ownership_tag]]]])

   Function to be called when handling REGISTER requests. This
   function decides if a REGISTER should be forwarded to the main
   registrar and performs all the necessary changes over the
   registered contacts. The function is also covering the handling
   of the 2xx REGISTER replies - the contacts confirmed by the
   main registrar will be automatically saved in the local user
   location (without any additional scripting).

   In Contact/AOR throttling modes (more info about working modes
   in Section 1.2, “Working modes”), the return value of this
   function indicates whether the script writer must forward the
   REGISTER request to the main registrar, or just wrap up any
   left-over processing and exit script execution, as the current
   REGISTER request has been answered with 200 OK (absorbed at
   mid-registrar level).

   Depending on the current working mode and contact_id_insertion,
   the function may additionally perform the following series of
   transformations when relaying REGISTER requests:

     * in "Contact throttling" mode
          + change the value of the Expires header field to the
            value of outgoing_expires, if given, otherwise the
            value given by the outgoing_expires module parameter.
            The same applies to any ";expires" Contact URI
            parameter.
          + replace the "host:port" part of all Contact URIs of
            the incoming REGISTER request with an OpenSIPS
            listening interface
          + append a parameter to each Contact URI, which will
            allow the module to match the reply contacts and also
            route calls. The name of this URI parameter is
            configurable via contact_id_param
     * in "AOR throttling" mode
          + change the value of the Expires header field to the
            value of outgoing_expires, if given, otherwise the
            value given by the outgoing_expires module parameter.
          + replace all Contact header fields of the request with
            a single Contact header field, which will contain the
            following SIP URI:
            "sip:address-of-record@proxy_ip:proxy_port"

   Meaning of the parameters is as follows:
     * domain (static string) - logical domain within the
       registrar. If a database is used, then this must be name of
       the usrloc table which stores the contacts
     * flags (string, optional) - string composed of one or more
       of the following flags, comma-separated:
          + 'memory-only' - (old m flag) save the contacts only in
            memory cache without no DB operation;
          + 'no-reply' - (old r flag) do not generate a SIP reply
            to the current REGISTER request.
          + 'max-contacts=[int]' - (old c flag) this flag can be
            used to limit the number of contacts for this AOR
            (Address of Record) in the user location database.
            Value 0 disables the check. This parameter overrides
            the global "max_contacts" module parameter.
          + 'force-registration' - (old f flag) this flag can be
            used to force the registration of NEW contacts even if
            the maximum number of contacts is reached. In such a
            case, older contacts will be removed to make space to
            the new ones, without exceeding the maximum allowed
            number. This flag makes sense only if "max-contacts"
            is used.
          + 'matching-mode=[val]' - (old M flag) How the matching
            should be performed between the uploaded contacts (by
            the currently handled REGISTER) and the already know
            contacts (in memory or DB). This options will be used
            only for the current operation and can be:
               o '0' - contact URI matching only
               o '1' - contact URI and SIP Call-ID matching
               o '<param_name>' - only the value of the given URI
                 param will be used for matching (for example
                 <rinstance>)
          + 'path-off' - (old p0 flag) (Path support - 'off' mode)
            - The Path header is saved into usrloc, but is never
            included in the reply.
          + 'path-lazy' - (old p1 flag) (Path support - lazy mode)
            The Path header is saved into usrloc, but is only
            included in the reply if path support is indicated in
            the registration request by the “path” option of the
            “Supported” header.
          + 'path-strict' - (old p2 flag) (Path support - strict
            mode) - The path header is only saved into usrloc, if
            path support is indicated in the registration request
            by the “path” option of the “Supported” header. If no
            path support is indicated, the request is rejected
            with “420 - Bad Extension” and the header
            “Unsupported: path” is included in the reply along
            with the received “Path” header. This mode is the one
            recommended by RFC-3327.
          + 'path-received' - (old v flag) if set, the “received”
            parameter of the first Path URI of a registration is
            set as received-uri and the NAT branch flag is set for
            this contact. This is useful if the registrar is
            placed behind a SIP loadbalancer, which passes the
            nat'ed UAC address as “received” parameter in it's
            Path uri.
          + 'only-request-contacts' - (old o flag) Only include
            the REGISTER request's Contacts in the 200 OK reply,
            in case the registration is successful. While this is
            against RFC 3261, it may be useful in certain
            scenarios.
     * aor (string, optional) - a custom Address-of-Record. If not
       given, the AOR will be taken from the To header URI
     * outgoing_expires (int, optional) - only relevant in
       Contact/AOR throttling modes, this is a custom value for
       the contact expiration interval of the outgoing REGISTER
       request, which overrides the default outgoing_expires
       module parameter.
     * ownership_tag (string, optional) - a cluster-shared tag
       (see the clusterer module documentation for more details)
       which will be attached to each contact saved from the
       current request. This tag is only relevant in clustered
       user location scenarios and helps determine the current
       logical owner node of a contact. This, in turn, is useful
       in order to restrict nodes which are not currently
       responsible for this contact from performing certain
       actions (for example: incorrectly originating pings from a
       non-owned virtual IP address in highly-available setups).

   Return value
     * 1 (success) - current REGISTER request must be dispatched
       by the script writer over to the main registrar
     * 2 (success) - current REGISTER request has been absorbed by
       the mid-registrar; a 200 OK reply has been sent upstream
     * -1 (error) - generic error code; the logs should provide
       more help

   This function can only be used from the request route.

   Example 1.34. mid_registrar_save usage
...
if (is_method("REGISTER")) {
        mid_registrar_save("location");
        switch ($retcode) {
        case 1:
                xlog("L_INFO", "forwarding REGISTER to main registrar...
\n");
                $ru = "sip:10.0.0.3:5070";
                if (!t_relay()) {
                        send_reply(500, "Server Internal Error 1");
                }

                break;
        case 2:
                xlog("L_INFO", "REGISTER has been absorbed!\n");
                break;
        default:
                xlog("L_ERR", "mid-registrar error!\n");
                send_reply(500, "Server Internal Error 2");
        }

        exit;
}
...

1.6.2.  mid_registrar_lookup(domain[, [flags][, [aor]]])

   Function to be called when receiving requests from the main
   registrar (to be routed to the end-user). It performs the local
   lookup (in user location) and the necessary RURI processing in
   order to route the requests further to the end-user registered
   contacts (note that multiple branches/destinations may result
   after the lookup).

   Depending on the current working mode, the function will behave
   as follows:

     * in "mirror" mode
          + extract the username (Address-of-Record) from the
            Request-URI and look up all of its contact bindings
            stored in the user location. The Request-URI ($ru
            variable) will be overwritten with the highest q-value
            contact, with additional branches for each contact
            being optionally created. (depending on the flags
            parameter)
     * in "Contact throttling" mode
          + extract the contact_id_param from the Request-URI,
            derive the actual SIP URI of the destination from it
            and set it as the new Request-URI of the INVITE ($ru
            variable).
     * in "AOR throttling" mode
          + extract the username (Address-of-Record) from the
            Request-URI and look up all of its contact bindings
            stored in the user location. The Request-URI ($ru
            variable) will be overwritten with the highest q-value
            contact, with additional branches for each contact
            being optionally created. (depending on the flags
            parameter)

   Meaning of the parameters is as follows:
     * domain (static string) - logical domain within the
       registrar. If a database is used, then this must be name of
       the usrloc table which stores the contacts
     * flags (string, optional) - string composed of one or more
       of the following flags, comma-separated:
          + 'no-branches' - (old b flag) this flag controls how
            the mid_registrar_lookup() function processes multiple
            contacts. If there are multiple contacts for the given
            username in usrloc and this flag is not set,
            Request-URI will be overwritten with the highest-q
            rated contact and the rest will be appended to sip_msg
            structure and can be later used by tm for forking. If
            the flag is set, only Request-URI will be overwritten
            with the highest-q rated contact and the rest will be
            left unprocessed.
          + 'to-branches-only' - (old B flag) this flags forces
            all found contacts to be uploaded only as branches (in
            the destination set) and not at all in the R-URI of
            the current message. Using this option allows the
            mid_registrar_lookup() function to also be used in the
            context of a SIP reply.
          + 'branch' - (old r flag) this flag enables searching
            through existing branches for aor's and expanding them
            to contacts. For example, you have got AOR A in your
            ruri but you also want to forward your calls to AOR B.
            In order to do this, you must put AOR B in a branch,
            and if this flag enabled, the function will also
            expand AOR B to contacts, which will be put back into
            the branches. The AOR's that were in branches before
            the function call shall be removed.
            WARNING: if you want this flag activated, the
            'no-branches' flag must not be set, because by setting
            that flag you won't allow mid_registrar_lookup() to
            write in a branch.
          + 'method-filtering' - (old m flag) setting this flag
            will enable contact filtering based on the supported
            methods listed in the "Allow" header field during
            registration. Contacts which did not present an
            "Allow" header field during registration are assumed
            to support all standard SIP methods.
          + 'ua-filtering=[val]' (old u flag) (User-Agent
            filtering) - this flag enables regexp filtering by
            user-agent. It's useful with enabled append_branches
            parameter. The value must use the format '/regexp/'.
          + 'case-insensitive' (old i flag) - this flag enables
            case insensitive filtering for the 'ua-filtering'
            flag.
          + 'extended-regexp' - (old e flag) this flag enables
            using of extended regexp format for the 'ua-filtering'
            flag.
          + 'global' (old g flag) (Global lookup) - this flag is
            only relevant with federated user location clustering.
            If set, the mid_registrar_lookup() function will not
            only perform the classic in-memory
            "search-AoR-and-push-branches" operation, but will
            also perform a metadata lookup and append an
            additional branch for each returned result. The
            "in-memory branches" correspond to local contacts
            (current location), while the "metadata branches"
            correspond to contacts available on one or more of the
            remaining locations of the platform.
            The AoR metadata consists of the minimally required
            information in order for one of the VoIP platform's
            locations (data centers) to advertise the presence of
            a locally registered AoR for the global platform.
            Specifically, this consists of two pieces of
            information:
               o the AoR (e.g. "vladimir@federation-cluster")
               o the home IP (e.g. "10.0.0.223")
          + 'max-ping-latency=[int]' - (old y flag) maximally
            accepted contact pinging latency (microseconds).
            Contacts of an AoR with a higher latency will be
            discarded during mid_registrar_lookup().
          + 'sort-by-latency' - (old Y flag) contacts will be
            picked in ascending order of their last successful
            pinging latency (fastest ping -> slowest ping). This
            flag may work together with the "max-ping-latency"
            flag.
     * aor (string, optional) - a custom Address-of-Record. If not
       given, the AOR will be taken from the Request-URI

   Return codes:
     * 1 - contacts found and successfully pushed as branches.
       Contacts which required awakening prior to being reachable
       are being notified via async Push Notifications.
     * 2 - successfully started at least one async Push
       Notification for the found contacts, however no extra
       branches were populated (i.e. there is no need to call
       t_relay()).
     * -1 - no contact found.
     * -2 - contacts found, but neither of them supports the
       current SIP method.
     * -3 - internal error during processing.

   This function can only be used from the request route.

   Example 1.35. mid_registrar_lookup usage
...
        # initial invites from the main registrar - need to look them up
!
        if (is_method("INVITE") and $si == "10.0.0.3" and $sp == 5070) {
                if (!mid_registrar_lookup("location")) {
                        t_reply(404, "Not Found");
                        exit;
                }

                if (!t_relay())
                        send_reply(500, "Server Internal Error 3");

            exit;
        }
...

1.7. Exported Asynchronous Functions

1.7.1.  pn_process_purr(domain)

   Perform mid-dialog request processing, according to RFC 8599.
   For such requests, search the R-URI and topmost Route header
   field URI for a ";pn-purr" parameter value that both matches
   the OpenSIPS PURR format and corresponds to an usrloc
   registration. Once a usrloc contact is located, trigger an
   E_UL_CONTACT_REFRESH event and place the request on async hold
   for at most pn_refresh_timeout seconds, until a matching
   REGISTER request arrives.

   If processing ends before triggering the Push Notification, the
   request will no longer be put on async hold, with the resume
   route being immediately called.

   Meaning of the parameters is as follows:
     * domain (static string) - Logical domain within registrar.
       If a database is used, then this must be name of the table
       which stores the contacts.

   Return Codes
     * 1 - Success, PN was launched.
     * 2 - Success, but PN was not launched (due to missing PURR,
       foreign PURR or offline contact)
     * -1 - Internal Error

   Example 1.36. async pn_process_purr() usage
route {
        ...
        if (has_totag()) {
                if (is_method("ACK") && t_check_trans()) {
                        t_relay();
                        exit;
                }

                if (!loose_route()) {
                        send_reply(404, "Not Found");
                        exit;
                }

                if (!is_method("ACK"))
                        async (pn_process_purr("location"), resume_route
);

                route(relay);
                exit;
        }
}

route [resume_route] {
        $var(rc) = $rc;
        xlog("pn_process_purr() finished with $var(rc)\n");

        ...
}

Chapter 2. Contributors

2.1. By Commit Statistics

   Table 2.1. Top contributors by DevScore^(1), authored
   commits^(2) and lines added/removed^(3)
     Name DevScore Commits Lines ++ Lines --
   1. Liviu Chircu (@liviuchircu) 507 203 16332 10230
   2. Vlad Patrascu (@rvlad-patrascu) 14 7 127 248
   3. Bogdan-Andrei Iancu (@bogdan-iancu) 10 7 103 111
   4. Razvan Crainea (@razvancrainea) 9 7 23 18
   5. Chad Attermann (@attermann) 7 5 19 5
   6. Maksym Sobolyev (@sobomax) 5 3 14 14
   7. Dan Pascu (@danpascu) 4 2 4 4
   8. Alexey Vasilyev (@vasilevalex) 3 1 2 5
   9. Peter Lemenkov (@lemenkov) 3 1 1 1
   10. Italo Rossi (@italorossi) 2 1 6 0

   (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. Regarding imported patches/code, we do our best
   to count the work on behalf of the proper owner, as per the
   "fix_authors" and "mod_renames" arrays in
   opensips/doc/build-contrib.sh. If you identify any
   patches/commits which do not get properly attributed to you,
   please submit a pull request which extends "fix_authors" and/or
   "mod_renames".

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

2.2. By Commit Activity

   Table 2.2. Most recently active contributors^(1) to this module
                      Name                   Commit Activity
   1.  Liviu Chircu (@liviuchircu)         Jul 2016 - May 2024
   2.  Maksym Sobolyev (@sobomax)          Oct 2020 - Nov 2023
   3.  Vlad Patrascu (@rvlad-patrascu)     May 2017 - May 2023
   4.  Razvan Crainea (@razvancrainea)     Mar 2017 - Jan 2023
   5.  Bogdan-Andrei Iancu (@bogdan-iancu) Apr 2017 - Feb 2022
   6.  Alexey Vasilyev (@vasilevalex)      Jan 2022 - Jan 2022
   7.  Dan Pascu (@danpascu)               May 2019 - May 2019
   8.  Italo Rossi (@italorossi)           Jul 2018 - Jul 2018
   9.  Peter Lemenkov (@lemenkov)          Jun 2018 - Jun 2018
   10. Chad Attermann (@attermann)         Jun 2017 - Jul 2017

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

Chapter 3. Documentation

3.1. Contributors

   Last edited by: Liviu Chircu (@liviuchircu), Vlad Patrascu
   (@rvlad-patrascu), Bogdan-Andrei Iancu (@bogdan-iancu), Peter
   Lemenkov (@lemenkov).

   Documentation Copyrights:

   Copyright © 2016-2020 OpenSIPS Solutions
