Copyright © 2003 FhG FOKUS
| Revision History | |
|---|---|
| Revision $Revision: 1.4 $ | $Date: 2008/06/20 16:59:45 $ |
TM module enables stateful processing of SIP transactions. The main use of stateful logic, which is costly in terms of memory and CPU, is some services inherently need state. For example, transaction-based accounting (module acc) needs to process transaction state as opposed to individual messages, and any kinds of forking must be implemented statefully. Other use of stateful processing is it trading CPU caused by retransmission processing for memory. That makes however only sense if CPU consumption per request is huge. For example, if you want to avoid costly DNS resolution for every retransmission of a request to an unresolvable destination, use stateful mode. Then, only the initial message burdens server by DNS queries, subsequent retransmissions will be dropped and will not result in more processes blocked by DNS resolution. The price is more memory consumption and higher processing latency.
From user's perspective, there are these major functions : t_relay, t_relay_to_udp and t_relay_to_tcp. All of them setup transaction state, absorb retransmissions from upstream, generate downstream retransmissions and correlate replies to requests. t_relay forwards to current URI (be it original request's URI or a URI changed by some of URI-modifying functions, such as sethost). t_relay_to_udp and t_relay_to_tcp forward to a specific address over UDP or TCP respectively.
In general, if TM is used, it copies clones of received SIP messages in shared memory. That costs the memory and also CPU time (memcpys, lookups, shmem locks, etc.) Note that non-TM functions operate over the received message in private memory, that means that any core operations will have no effect on statefully processed messages after creating the transactional state. For example, calling record_route after t_relay is pretty useless, as the RR is added to privately held message whereas its TM clone is being forwarded.
TM is quite big and uneasy to program--lot of mutexes, shared memory access, malloc and free, timers--you really need to be careful when you do anything. To simplify TM programming, there is the instrument of callbacks. The callback mechanisms allow programmers to register their functions to specific event. See t_hooks.h for a list of possible events.
Other things programmers may want to know is UAC--it is a very simplistic code which allows you to generate your own transactions. Particularly useful for things like NOTIFYs or IM gateways. The UAC takes care of all the transaction machinery: retransmissions , FR timeouts, forking, etc. See t_uac prototype in uac.h for more details. Who wants to see the transaction result may register for a callback.
Possibly, performance could be improved by not parsing non-INVITEs, as they do not be replied with 100, and do not result in ACK/CANCELs, and other things which take parsing. However, we need to rethink whether we don't need parsed headers later for something else. Remember, when we now conserver a request in sh_mem, we can't apply any pkg_mem operations to it any more. (that might be redesigned too).
Another performance improvement may be achieved by not parsing CSeq in replies until reply branch matches branch of an INVITE/CANCEL in transaction table.
t_replicate should be done more cleanly--Vias, Routes, etc. should be removed from a message prior to replicating it (well, does not matter any longer so much as there is a new replication module).
Timer which hits if no final reply for a request or ACK for a negative INVITE reply arrives (in milliseconds).
Default value is 30000 ms (30 seconds).
See also: t_set_fr(), max_noninv_lifetime.
Timer which hits if no final reply for an INVITE arrives after a provisional message was received (in milliseconds).
Note: this timer can be restarted when a provisional response is received. For more details see restart_fr_on_each_reply.
Default value is 120000 ms (120 seconds).
See also: t_set_fr(), max_inv_lifetime.
Maximum time an INVITE transaction is allowed to be active (in milliseconds). After this interval has passed from the transaction creation, the transaction will be either moved into the wait state or in the final response retransmission state, irrespective of the transaction fr_inv_timer and fr_timer values.
An INVITE transaction will be kept in memory for maximum: max_inv_lifetime+fr_timer(from the ack to the final reply wait)+wt_timer.
The main difference between this timer and fr_inv_timer is that the fr_inv_timer is per branch, while max_inv_lifetime is per the whole transaction. Even on a per branch basis fr_inv_timer could be restarted. For example, by default if restart_fr_on_each_reply is not cleared, the fr_inv_timer will be restarted for each received provisional reply. Even if restart_fr_on_each_reply is not set the fr_inv_timer will still be restarted for each increasing reply (e.g. 180, 181, 182, ...). Another example when a transaction can live substantially more then its fr_inv_timer and where max_inv_lifetime will help is when dns failover is used (each failed dns destination can introduce a new branch).
The default value is 180000 ms (180 seconds - the rfc3261 timer C value).
See also: max_noninv_lifetime, t_set_max_lifetime() (allows changing max_inv_lifetime on a per transaction basis), t_reset_max_lifetime fr_timer, wt_timer, restart_fr_on_each_reply.
Maximum time a non-INVITE transaction is allowed to be active (in milliseconds). After this interval has passed from the transaction creation, the transaction will be either moved into the wait state or in the final response retransmission state, irrespective of the transaction fr_timer value. It's the same as max_inv_lifetime, but for non-INVITEs.
A non-INVITE transaction will be kept in memory for maximum: max_noninv_lifetime+wt_timer.
The main difference between this timer and fr_timer is that the fr_timer is per branch, while max_noninv_lifetime is per the whole transaction. An example when a transaction can live substantially more then its fr_timer and where max_noninv_lifetime will help is when dns failover is used (each failed dns destination can introduce a new branch).
The default value is 32000 ms (32 seconds - the rfc3261 timer F value).
See also: max_inv_lifetime, t_set_max_lifetime() (allows changing max_noninv_lifetime on a per transaction basis), t_reset_max_lifetime fr_timer, wt_timer.
Time for which a transaction stays in memory to absorb delayed messages after it completed (in milliseconds); also, when this timer hits, retransmission of local cancels is stopped (a puristic but complex behavior would be not to enter wait state until local branches are finished by a final reply or FR timer--we simplified).
Default value is 5000 ms (5 seconds).
Time after which a to-be-deleted transaction currently ref-ed by a process will be tried to be deleted again (in milliseconds).
Note: this parameter is obsolete for ser 2.1 (in 2.1 the transaction is deleted the moment it's not referenced anymore).
Default value is 200 milliseconds.
Initial retransmission period (in milliseconds).
Default value is 500 milliseconds.
Maximum retransmission period (in milliseconds). The retransmission interval starts with retr_timer1 and increases until it reaches this value. After this it stays constant at retr_timer2.
Default value is 4000 milliseconds.
If set, INVITE transactions that time-out (FR INV timer) will be always replied. If it's not set, the transaction has only one branch and no response was ever received on this branch, it will be silently dropped (no 408 reply will be generated) This behavior is overridden if a request is forked, the transaction has a failure route or callback, or some functionality explicitly turned it on for a transaction (like acc does to avoid unaccounted transactions due to expired timer). Turn this off only if you know the client UACs will timeout and their timeout interval for INVITEs is lower or equal than tm's fr_inv_timer.
Default value is 1 (on).
If set (default), the fr_inv_timer for an INVITE transaction will be restarted for each provisional reply received (rfc3261 mandated behaviour). If not set, the fr_inv_timer will be restarted only for the first provisional replies and for increasing replies greater or equal 180 (e.g. 180, 181, 182, 185, ...).
Setting it to 0 is especially useful when dealing with bad UAs that continuously retransmit 180s, not allowing the transaction to timeout (and thus making impossible the implementation of certain services, like automatic voicemail after x seconds).
Default value is 1 (on).
See also: fr_inv_timer, max_inv_lifetime.
If set (default) tm will automatically send and 100 reply to INVITEs.
Setting it to 0 one can be used to enable doing first some tests or pre-processing on the INVITE and only if some conditions are met manually send a 100 (using t_reply()). Note however that in this case all the 100s have to be sent "by hand". t_set_auto_inv_100() might help to selectively turn off this feature only for some specific transactions.
Default value is 1 (on).
See also: t_set_auto_inv_100().
Unix socket transmission timeout, in milliseconds.
If unix sockets are used (e.g.: to communicate with sems) and sending a message on a unix socket takes longer then unix_tx_timeout, the send will fail.
The default value is 500 milliseconds.
If set (default), the final reply is a 401 or a 407 and more then one branch received a 401 or 407, then all the WWW-Authenticate and Proxy-Authenticate headers from all the 401 and 407 replies will be aggregated in a new final reply. If only one branch received the winning 401 or 407 then this reply will be forwarded (no new one will be built). If 0 only the first 401, or if no 401 was received the first 407, will be forwarded (no header aggregation).
Default value is 1 (required by rfc3261).
If set (default), the CANCEL and negative ACK requests are constructed from the INVITE message which was sent out instead of building them from the received request. The disadvantage is that the outgoing INVITE has to be partially re-parsed, the advantage is that the CANCEL/ACK is always RFC 3261-compliant, it always contains the same route-set as the INVITE message. Do not disable the INVITE re-parsing for example in the following cases:
- The INVITE contains a preloaded route-set, and SER forwards the message to the next hop according to the Route header. The Route header is not removed in the CANCEL without reparse_invite=1.
- SER record-routes, thus an in-dialog INVITE contains a Route header which is removed during loose routing. If the in-dialog INVITE is rejected, the negative ACK still contains the Route header without reparse_invite=1.
Default value is 1.
Header fields prefixed by this parameter value are included in the CANCEL and negative ACK messages if they were present in the outgoing INVITE.
Note, that the parameter value effects only those headers which are not covered by RFC-3261 (which are neither mandatory nor prohibited in CANCEL and ACK), and the parameter can be used only together with reparse_invite=1.
Default value is "".
If set and the blacklist support is enabled, every 503 reply source is added to the blacklist. The initial blacklist timeout (or ttl) depends on the presence of a Retry-After header in the reply and the values of the following tm parameters: blst_503_def_timeout, blst_503_min_timeout and blst_503_max_timeout.
WARNING:blindly allowing 503 blacklisting could be very easily exploited for DOS attacks in most network setups.
The default value is 0 (disabled due to the reasons above).
Blacklist interval in seconds for a 503 reply with no Retry-After header. See also blst_503, blst_503_min_timeout and blst_503_max_timeout.
The default value is 0, which means that if no Retry-After header is present, the 503 reply source will not be blacklisted (rfc conformant behaviour).
Minimum blacklist interval in seconds for a 503 reply with a Retry-After header. It will be used if the Retry-After value is smaller. See also blst_503, blst_503_def_timeout and blst_503_max_timeout.
The default value is 0
Maximum blacklist interval in seconds for a 503 reply with a Retry-After header. It will be used if the Retry-After value is greater. See also blst_503, blst_503_def_timeout and blst_503_min_timeout.
The default value is 3600
Bitmap of method types that trigger blacklisting on transaction timeouts. (This setting has no effect on blacklisting because of send failures.)
The following values are associated to the request methods: INVITE=1, CANCEL=2, ACK=4 (not retransmitted, thus, never times-out), BYE=8, INFO=16, REGISTER=32, SUBSCRIBE=64, NOTIFY=126, OTHER=256 (all the unknown types). Check parser/msg_parser.h for farther details.
Change the value carefully, because requests not having provisional response (everything but INVITE) can easily cause the next hop to be inserted into the blacklist by mistake. For exmaple the next hop is a proxy, it is alive, but waiting for the response of the UAS, and has higher fr_timer value.
The default value is 1, only INVITEs trigger blacklisting
Bitmap of method types that are looked-up in the blacklist before statefull forwarding. See also blst_methods_add
The default value is 4294967287, every method type except BYE. (We try to deliver BYEs no matter what)
Method used when attempting to CANCEL an unreplied transaction branch (a branch where no reply greater the 99 was received). The possible values are 0, 1, and 2.
0 will immediately stop the request (INVITE) retransmission on the branch and it will behave as if the branch was immediately replied with a 487 (a fake internal 487 reply). The advantage is the unreplied branches will be terminated immediately. However it introduces a race risk with a possible slightly delayed 2xx reply. In this case we could have an UA receiving a 2xx after a 487. Moreover this risk is greatly amplified by packet loss (e.g. if an 180 is lost the branch will look as unreplied and a CANCEL will silently drop the branch, but a 2xx can still come at a later time). This is the behaviour for ser versions older then 2.1.
1 will keep retransmitting the request on unreplied branches. If a provisional answer is later received a CANCEL will be immediately sent back (attempting to quickly trigger a 487). This approach is race free and avoids the 2xx after 487 problem, but it's more resource intensive: faced with a branch towards and UA that doesn't answer, a CANCEL attempt will keep the transaction alive for the whole timeout interval (fr_timer).
2 will send and retransmit CANCEL even on unreplied branches, stopping the request retransmissions. This has the same advantages as 1 and also avoids the extra roundtrip in the case of the provisional reply, but it's not RFC 3261 conforming (the RFC allows sending CANCELs only on pending branches).
The default value is 1.
If set to 1, the SIP message after a DNS failover is constructed from the outgoing message buffer of the failed branch instead of from the received request.
It must be set if multiple branches are installed, the SIP message is modified differently in them, and at least one of them can result in DNS failover. If the parameter is not set the per-branch modifications are lost after the failover.
Note: If the parameter is set, branch route block and TMCB_REQUEST_FWDED callback are not called in case of the failover.
Disadvantage: only the via header is replaced in the message buffer, so the outgoing socket address is not corrected in any other part of the message. It is dangerous on multihomed hosts: when the new SIP request after the DNS failover is sent via different interface than the first request, the message can contain incorrect ip address in the Record-Route header for instance.
Default value is 1.
Sets reply route block, to which control is passed when a reply is received that has no associated transaction. The reply is passed to the core for stateless forwarding after the route block execution unless it returns 0.
Relay a message statefully using a fixed protocol either to the specified fixed destination or to a destination derived from the message uri (if the host address and port are not specified). These along with t_relay are the functions most users want to use--all other are mostly for programming. Programmers interested in writing TM logic should review how t_relay is implemented in tm.c and how TM callbacks work.
Meaning of the parameters is as follows:
ip - IP address where the message should be sent.
port - Port number.
If no parameters are specified the message is sent to a destination derived from the message uri (using sip sepcific DNS lookups), but with the protocol corresponding to the function name.
Relay a message statefully either to the destination indicated in the current URI (if called without any parameters) or to the specified host and port. In the later case (host and port specified) the protocol used is the same protocol on which the message was received.
t_relay() is the statefull version for forward(uri:host, uri:port) while t_relay(host, port) is similar to forward(host, port).
In the forward to uri case (t_relay()), if the original URI was rewritten (by UsrLoc, RR, strip/prefix, etc.) the new URI will be taken). The destination (including the protocol) is determined from the uri, using SIP specific DNS resolving if needed (NAPTR, SRV a.s.o depending also on the dns options).
Returns a negative value on failure--you may still want to send a negative reply upstream statelessly not to leave upstream UAC in lurch.
Sets failure routing block, to which control is passed after a transaction completed with a negative result but before sending a final reply. In the referred block, you can either start a new branch (good for services such as forward_on_no_reply) or send a final reply on your own (good for example for message silo, which received a negative reply from upstream and wants to tell upstream "202 I will take care of it"). Note that the set of commands which are usable within failure_routes is strictly limited to rewriting URI, initiating new branches, logging, and sending stateful replies (t_reply). Any other commands may result in unpredictable behavior and possible server failure. Note that whenever failure_route is entered, uri is reset to value which it had on relaying. If it temporarily changed during a reply_route processing, subsequent reply_route will ignore the changed value and use again the original one.
Meaning of the parameters is as follows:
failure_route - Failure route block to be called.
Example 27. t_on_failure usage
...
route {
t_on_failure("1");
t_relay();
}
failure_route[1] {
revert_uri();
setuser("voicemail");
append_branch();
}
...
See test/onr.cfg for a more complex example of combination of serial with parallel forking.
Sets the reply routing block, to which control is passed when a reply for the current transaction is received. Note that the set of commands which are usable within onreply_routes is limited.
Meaning of the parameters is as follows:
onreply_route - Onreply route block to be called.
Example 28. t_on_reply usage
...
loadmodule "/usr/local/lib/ser/modules/nathelper.so"
...
route {
/* if natted */
t_on_reply("1");
t_relay();
}
onreply_route[1] {
if (status=~ "(183)|2[0-9][0-9]"){
force_rtp_proxy();
search_append('^(Contact|m)[ \t]*:.*sip:[^>[:cntrl:]]*', ';nat=yes');
}
if (nat_uac_test("1")){
fix_nated_contact();
}
}
Sets the branch routing block, to which control is passed after forking (when a new branch is created). For now branch routes are intended only for last minute changes of the SIP messages (like adding new headers). Note that the set of commands which are usable within branch_routes is very limited. It is not possible to drop a message or generate a reply.
Meaning of the parameters is as follows:
branch_route - branch route block to be called.
Similarly to t_fork_to, it extends destination set by a new entry. The difference is that current URI is taken as new entry.
Creates a new transaction, returns a negative value on error. This is the only way a script can add a new transaction in an atomic way. Typically, it is used to deploy a UAS.
Example 31. t_newtran usage
...
if (t_newtran()) {
log("UAS logic");
t_reply("999","hello");
} else sl_reply_error();
...
See test/uas.cfg for more examples.
Sends a stateful reply after a transaction has been established. See t_newtran for usage.
Meaning of the parameters is as follows:
code - Reply code number.
reason_phrase - Reason string.
Checks if a transaction exists. Returns a positive value if so, negative otherwise. Most likely you will not want to use it, as a typical application of a looku-up is to introduce a new transaction if none was found. However this is safely (atomically) done using t_newtran.
Retransmits a reply sent previously by UAS transaction.
Remove transaction from memory (it will be first put on a wait timer to absorb delayed messages).
mainly for internal usage--forward a non-ACK request statefully.
Meaning of the parameters is as follows:
ip - IP address where the message should be sent.
port - Port number.
Sets the fr_inv_timeout and optionally fr_timeout for the current transaction or for transactions created during the same script invocation, after calling this function. If the transaction is already created (e.g called after t_relay() or in an onreply_route) all the branches will have their final response timeout updated on-the-fly. If one of the parameters is 0, its value won't be changed.
Meaning of the parameters is as follows:
fr_inv_timeout - new final response timeout (in milliseconds) for INVITEs. See also fr_inv_timer.
fr_timeout - new final response timeout (in milliseconds) for non-INVITE transaction, or INVITEs which haven't received yet a provisional response. See also fr_timer.
See also: fr_timer, fr_inv_timer, t_reset_fr().
Example 37. t_set_fr usage
...
route {
t_set_fr(10000); # set only fr invite timeout to 10s
t_on_branch("1");
t_relay();
}
branch_route[1] {
# if we are calling the pstn, extend the invite timeout to 50s
# for all the branches, and set the no-reply-received timeout to 2s
if (uri=~"sip:[0-9]+"){
t_set_fr(50000, 2000);
}
}
Resets the fr_inv_timer and fr_timer for the current transaction to the default values (set using the tm module parameters fr_inv_timer and fr_timer).
It will effectively cancel any previous calls to t_set_fr for the same transaction.
See also: fr_timer, fr_inv_timer, t_set_fr.
Sets the maximum lifetime for the current INVITE or non-INVITE transaction, or for transactions created during the same script invocation, after calling this function (that's why it takes values for both INVITE and non-INVITE). If one of the parameters is 0, its value won't be changed.
It works as a per transaction max_inv_lifetime or max_noninv_lifetime.
Meaning of the parameters is as follows:
inv_lifetime - maximum INVITE transaction lifetime (in milliseconds). See also max_inv_lifetime.
noninv_lifetime - maximum non-INVITE transaction lifetime (in milliseconds). See also max_noninv_lifetime.
See also: max_inv_lifetime, max_noninv_lifetime, t_reset_max_lifetime.
Resets the the maximum lifetime for the current INVITE or non-INVITE transaction to the default value (set using the tm module parameter max_inv_lifetime or max_noninv_lifetime).
It will effectively cancel any previous calls to t_set_max_lifetime for the same transaction.
See also: max_inv_lifetime, max_noninv_lifetime, t_set_max_lifetime.
Sets the retr_t1_interval and retr_t2_interval for the current transaction or for transactions created during the same script invocation, after calling this function. If one of the parameters is 0, it's value won't be changed. If the transaction is already created (e.g called after t_relay() or in an onreply_route) all the existing branches will have their retransmissions intervals updated on-the-fly: if the retransmission interval for the branch has not yet reached T2 the interval will be reset to retr_t1_interval, else to retr_t2_interval. Note that the change will happen after the current interval expires (after the next retransmission, the next-next retransmission will take place at retr_t1_interval or retr_t2_interval). All new branches of the same transaction will start with the new values. This function will work even if it's called in the script before a transaction creating function (e.g.: t_set_retr(500, 4000); t_relay()). All new transaction created after this function call, during the same script invocation will use the new values. Note that this function will work only if tm is compile with -DTM_DIFF_RT_TIMEOUT (which increases every transaction size with 4 bytes).
Meaning of the parameters is as follows:
retr_t1_interval - new T1 retransmission interval (in milliseconds). See also retr_t1_timeout.
retr_t2_interval - new T2 (or maximum) retransmission interval (in milliseconds). See also retr_t2_timeout.
See also: retr_timer1, retr_timer2, t_reset_retr().
Resets the retr_timer1 and retr_timer2 for the current transaction to the default values (set using the tm module parameters retr_timer1 and retr_timer2).
It will effectively cancel any previous calls to t_set_retr for the same transaction.
See also: retr_timer1, retr_timer2, t_set_retr.
Switch automatically sending 100 replies to INVITEs on/off on a per transaction basis. It overrides the auto_inv_100 value for the current transaction.
See also: auto_inv_100.
Returns true if the failure route is executed for a branch that did timeout. It can be used only from the failure_route.
Returns true if the failure route is executed for a branch that did receive at least one reply in the past (the "current" reply is not taken into account). It can be used only from the failure_route.
Returns true if at least one of the current transactions branches did timeout.
Returns true if at least one of the current transactions branches did receive some reply in the past. If called from a failure or onreply route, the "current" reply is not taken into account.
Returns true if "code" is the final reply received (or locally generated) in at least one of the current transactions branches.
Returns true if the current transaction was canceled.
Returns true if the current transaction has already been expired, i.e. the max_inv_lifetime/max_noninv_lifetime interval has already elapsed.
Forwards the CANCEL if the corresponding INVITE transaction exists. The function is supposed to be used at the very beginning of the script, because the CANCELs can be caught and the rest of the script can be bypassed this way. Do not disable reparse_invite module parameter, and call t_relay_cancel() right after the sanity tests.
Return value is 0 (drop) if the corresponding INVITE was found and the CANCELs were successfully sent to the pending branches, true if the INVITE was not found, and false in case of any error.
Example 51. t_relay_cancel usage
if (method == CANCEL) {
if (!t_relay_cancel()) { # implicit drop if relaying was successful,
# nothing to do
# corresponding INVITE transaction found but error occurred
sl_reply("500", "Internal Server Error");
drop;
}
# bad luck, corresponding INVITE transaction is missing,
# do the same as for INVITEs
}
Returns true if the corresponding INVITE transaction exists for a CANCEL request. The function can be called at the beginning of the script to check whether or not the CANCEL can be immediately forwarded bypassing the rest of the script. Note however that t_relay_cancel includes t_lookup_cancel as well, therefore it is not needed to explicitly call this function unless something has to be logged for example.
If the function parameter (optional) is set to 1, the message flags are overwritten with the flags of the INVITE. isflagset() can be used to check the flags of the previously forwarded INVITE in this case.
Example 52. t_lookup_cancel usage
if (method == CANCEL) {
if (t_lookup_cancel()) {
log("INVITE transaction exists");
if (!t_relay_cancel()) { # implicit drop if
# relaying was successful,
# nothing to do
# corresponding INVITE transaction found
# but error occurred
sl_reply("500", "Internal Server Error");
drop;
}
}
# bad luck, corresponding INVITE transaction is missing,
# do the same as for INVITEs
}
Drops all the previously received replies in failure_route block to make sure that none of them is picked up again. Works only if a new branch is added to the transaction, or it is explicitly replied in the script!
Example 53. t_drop_replies() usage
...
failure_route[0]{
if (t_check_status("5[0-9][0-9]")){
# I do not like the 5xx responses,
# so I give another chance to "foobar.com",
# and I drop all the replies to make sure that
# they are not forwarded to the caller.
t_drop_replies();
rewritehostport("foobar.com");
append_branch();
t_relay();
}
}
Forces the modifications of the processed SIP message to be saved in shared memory before t_relay() is called. The new branches which are created in failure_route will contain the same modifications, and any other modification after t_save_lumps() will be lost.
Note that t_relay() automatically saves the modifications when it is called the first time, there is no need for t_save_lumps() unless message changes between t_save_lumps() and t_relay() must not be propagated to failure_route.
The transaction must be created by t_newtran() before calling t_save_lumps().
Example 54. t_save_lumps() usage
route {
...
t_newtran();
append_hf("hf1: my first header\r\n");
...
t_save_lumps();
append_hf("hf2: my second header\r\n");
...
t_on_failure("1");
t_relay();
}
failure_route[1] {
append_branch();
append_hf("hf3: my third header\r\n");
#
# This branch contains hf1 and hf3, but does
# not contain hf2 header.
# hf2 would be also present here without
# t_save_lumps().
...
t_relay();
}
There are applications which would like to generate SIP transactions without too big involvement in SIP stack, transaction management, etc. An example of such an application is sending instant messages from a website. To address needs of such apps, SER accepts requests for new transactions via fifo pipes too. If you want to enable this feature, start FIFO server with configuration option.
fifo="/tmp/ser_fifo"
Then, an application can easily launch a new transaction by writing a transaction request to this named pipe. The request must follow very simple format, which is
:t_uac_from:[<file_name>]\n <method>\n <sender's uri>\n <dst uri>\n <CR_separated_headers>\n <body>\n .\n \n
(Filename is to where a report will be dumped. ser assumes /tmp as file's directory.)
Note the request write must be atomic, otherwise it might get intermixed with writes from other writers. You can easily use it via Unix command-line tools, see the following example:
[jiri@bat jiri]$ cat > /tmp/ser_fifo
:t_uac_from:xxx
MESSAGE
sip:sender@iptel.org
sip:mrx@iptel.org
header:value
foo:bar
bznk:hjhjk
p_header: p_value
body body body
yet body
end of body
.
or cat test/transaction.fifo > /tmp/ser_fifo
ACK_TAG enables stricter matching of acknowledgments including to-tags. Without it, to-tags are ignored. It is disabled by default for two reasons:
It eliminates an unlikely race condition in which transaction's to-tag is being rewritten by a 200 OK whereas an ACK is being looked up by to-tag.
It makes UACs happy who set wrong to-tags.
It should not make a difference, as there may be only one negative reply sent upstream and 200/ACKs are not matched as they constitute another transaction. It will make no difference at all when the new magic cookie matching is enabled anyway.
CANCEL_TAG similarly enables strict matching of CANCELs including to-tags--act of mercy to UACs, who screw up the to-tags (however, it still depends on how forgiving the downstream UAS is). Like with ACK_TAG, all this complex transactions matching goes with RFC3261's magic cookie away anyway.
For programmatic use only--register a function to be called back on an event. See t_hooks.h for more details.
Meaning of the parameters is as follows:
cb_type - Callback type.
cb_func - Callback function.
For programmatic use only--import exported TM functions. See the acc module for an example of use.
Meaning of the parameters is as follows:
import_structure - Pointer to the import structure.
For programmatic use only. This function together with t_continue() can be used to implement asynchronous actions: t_suspend() saves the transaction, returns its identifiers, and t_continue() continues the SIP request processing. (The request processing does not continue from the same point in the script, a separate route block defined by the parameter of t_continue() is executed instead. The reply lock is held during the route block execution.) FR timer is ticking while the transaction is suspended, and the transaction's failure route is executed if t_continue() is not called in time.
Missing: message lumps are saved by t_suspend() and are not updated by the subsequent t_relay(). This means that the modifications made between them are lost.
Meaning of the parameters is as follows:
msg - SIP message pointer.
hash_index - transaction identifier.
label - transaction identifier.
Return value: 0 - success, <0 - error.
Usage: Allocate a memory block for storing the transaction identifiers (hash_index and label), and for storing also any variable related to the async query. Before calling t_suspend(), register for the following callbacks, and pass the pointer to the allocated shared memory as a parameter: TMCB_ON_FAILURE, TMCB_DESTROY, and TMCB_E2ECANCEL_IN (in case of INVITE transaction). The async operation can be cancelled, if it is still pending, when TMCB_ON_FAILURE or TMCB_E2ECANCEL_IN is called. TMCB_DESTROY is suitable to free the shared memory allocated for the async and SIP transaction identifiers. Once the async query result is available call t_continue(), see below. The SIP transaction must exist before calling t_suspend(), and the module function calling t_suspend() should return 0 to make sure that the script processing does not continue.
For programmatic use only. This function is the pair of t_suspend(), and is supposed to be called when the asynchronous query result is available. The function executes a route block with the saved SIP message. It is possible to add more branches to the transaction, or send a reply from the route block.
Meaning of the parameters is as follows:
hash_index - transaction identifier.
label - transaction identifier.
route - route block to execute.
Return value: 0 - success, <0 - error.