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/* -*- c -*- */
/**@MODULEPAGE "nta" - SIP Transactions Module
*
* @section nta_meta Module Meta Information
*
* Sofia SIP Transaction API (nta) provides simple interface to the SIP
* transaction, transport and message handling. The @b nta interface is
* intended for both network and user elements. The public interface for @b
* nta is mostly defined in <sofia-sip/nta.h>, but tag parameters are
* defined in <sofia-sip/nta_tag.h>.
*
* @CONTACT Pekka Pessi <Pekka.Pessi@nokia.com>
*
* @STATUS @SofiaSIP Core library
*
* @LICENSE LGPL
*
* @section nta_objects NTA Objects
*
* The NTA deals with a few kinds of objects: @e agent (#nta_agent_t), @e
* call @e legs (#nta_leg_t), @e outgoing @e client @e requests
* (#nta_outgoing_t), and @e incoming @e server @e requests
* (#nta_incoming_t).
*
* NTA also uses SIP message objects #msg_t and #sip_t for handling
* messages, as defined in <sofia-sip/msg.h> and <sofia-sip/sip.h>,
* respectively. The various SIP headers are also defined in
* <sofia-sip/sip.h>.
*
* @section nta_agent_t Creating an NTA Agent
*
* Most of the SIP entities, like @e user @e agent or @e proxy, consist of a
* SIP server and a SIP client working together. The NTA provides a simple
* interface to SIP server and client with the #nta_agent_t objects.
*
* The #nta_agent_t object is created by calling nta_agent_create(). The
* object listens for incoming connections, receives messages, parses them,
* and pass them to the application. It also takes care of resolving the
* domain names and sending the messages.
*
* The agent needs a #su_root_t object to schedule its execution. A root
* object is used to wait for the network events, schedule the timer
* routines, and pass messages asyncronously. A root object can be created
* by, e.g., the function su_root_create(). The root object can be have its
* own thread, or its main loop can be executed by an application thread by
* calling the function su_root_run(). The main loop can be terminated by
* calling the function su_root_break().
*
* A simple agent could be created as follows:
* @code
* registrar->reg_root = su_root_create(NULL);
*
* if (registrar->reg_root) {
* registrar->reg_agent = nta_agent_create(registrar->reg_root,
* (url_string_t*)argv[1],
* NULL,
* NULL,
* NULL);
*
* if (registrar->reg_agent) {
* su_root_run(registrar->reg_root);
* nta_agent_destroy(registrar->reg_agent);
* }
*
* su_root_destroy(registrar->reg_root);
* }
* @endcode
*
* @section nta_server SIP Server Action
*
* A SIP server responds to the transactions sent by a client. The SIP
* server can operate in two modes; it can be stateless or stateful. This
* section describes how a stateful SIP server uses NTA.
*
* @subsection nta_leg_t The NTA Legs
*
* A leg is required for stateful transaction processing. A default
* leg is created like this:
* @code
* default_leg = nta_leg_tcreate(agent, process_requests, context,
* URLTAG_URL(url),
* NTATAG_NO_DIALOG(1),
* TAG_END());
* @endcode
*
* The @a url parameter is used to specify which URLs match to the leg. If
* it is given, only requests with requestURI matching are processed by the
* leg. The nta_leg_tcreate() is a @ref tagarg "tagarg" function, taking a
* tagged argument list as its arguments.
*
* Other, ordinary legs can be used to match incoming requests with existing
* dialogs, calls or transaction contexts, or to provide outgoing requests
* with consistent headers. When a call leg is created, it is provided with
* @From and @To headers, and optionally with other headers like
* @CallID, @Route, or @CSeq.
*
* A new call leg can be created as follows:
* @code
* call_leg = nta_leg_tcreate(agent,
* process_call_requests, call_context,
* SIPTAG_CALL_ID(sip->sip_call_id),
* SIPTAG_TO(sip->sip_from),
* SIPTAG_FROM(sip->sip_to),
* TAG_END());
* @endcode
*
* @note In the example above, the @From and @To are reversed. This
* happens if the headers are taken from an incoming request; the @From
* and @To headers change direction when an outgoing request is initiated.
*
* @note An existing leg can be used in any direction, however. If the leg
* was created for an incoming INVITE transaction, it is also possible to
* use the leg for an outgoing BYE transaction.
*
* @subsection nta_leg_tag Tagging the Call Leg
*
* All the SIP UAS elements are required to tag the @To header in their
* final responses. The function nta_leg_tag() adds a tag to the leg's local
* address. Local address is used as the @To header in the reply messages,
* and as the @From header in the requests. The function nta_incoming_tag()
* adds a tag to a incoming transaction. They are usually used in together,
* using the tag from initial response to the dialog, too:
* e.g.,
* @code
* if (!nta_leg_tag(leg, nta_incoming_tag(irq, NULL)))
* nta_incoming_treply(irq, SIP_500_INTERNAL_SERVER_ERROR, TAG_END());
* @endcode
*
* @subsection nta_incoming_t Incoming Transactions
*
* An incoming transaction object (nta_incoming_t) is created by NTA for
* each unique incoming request message. When NTA has created the incoming
* transaction object, it invokes the callback function provided with
* nta_leg_tcreate().
*
* The simplest way to reply to the request is to return a valid status code
* from the callback function. Valid status codes are in range of 100 to
* 699, inclusive. If no automatic response is desired, the callback
* function should return 0.
*
* @note If the status code is final, the incoming transaction object will
* be destroyed immediately after the callback function returns. It can not
* be used afterwards.
*
* @note It is not possible to respond with a 2xx status code to an incoming
* INVITE transaction by returning the status code from the callback.
*
* Valid return values for callback function are as follows:
* @li 0, 100 .. 699 for requests other than INVITE, and
* @li 0, 100 .. 199, 300..699 for INVITE requests.
*
* All other return codes are interpreted as 500, that is, a @e 500 @e
* Internal @e Server @e Error reply message is sent back to the client and
* the request is immediately destroyed.
*
* The simple registrar/redirect server may have a incoming request callback
* as follows:
* @code
* int process_request(server_t *server,
* nta_leg_t *leg,
* nta_incoming_t *irq,
* sip_t const *sip)
* {
* sip_contact_t *m;
*
* switch (sip->sip_request->rq_method) {
* case sip_method_register:
* return registrar_add(server, leg, reply, sip);
*
* case sip_method_ack:
* return 500;
*
* case sip_method_cancel:
* return 200;
*
* default:
* if (registrar_find(server, sip->sip_request->rq_url, &m) {
* nta_incoming_treply(irq, SIP_302_MOVED_TEMPORARILY,
* SIPTAG_CONTACT(m), TAG_END());
* return 302;
* }
* else {
* nta_incoming_treply(irq, SIP_404_NOT_FOUND, TAG_END());
* return 404;
* }
* }
* }
* @endcode
*
* The default reply message will contain the status line with default
* phrase, then @Via, @To, @From, @CallID, @CSeq, and @ContentLength headers.
* If a more complex response message is required, the application should
* respond using the function nta_incoming_treply():
* @code
* nta_incoming_treply(reply, SIP_200_OK,
* SIPTAG_CONTACT(contact),
* SIPTAG_CONTENT_TYPE_STR("application/sdp"),
* SIPTAG_PAYLOAD(sdp),
* TAG_END());
* @endcode
*
* The nta_incoming_treply() is a @ref tagarg "tagarg" function, taking a
* tagged argument list as its argument.
*
* @note It is possible to send provisional replies (containing 1xx status
* codes) several times with nta_incoming_treply(), but only one final
* reply (containing status codes 2xx..6xx) can be sent. However, with
* INVITE requests, a proxy can send a final 2xx reply even after an error
* reply (3xx..6xx).
*
* @section nta_100rel Reliable Provisional Responses - "100rel"
*
* The <A href="../specs/rfc3262.txt"><B>100rel</B></A> SIP extension
* provides reliable provisional responses, provisional responses that are
* retransmitted until a special acknowledgement request, PRACK, is
* received. In addition the PRACK method, the extension defines two
* headers, @RSeq and @RAck, that are used to identify different
* response messages. PRACK method is usable on INVITE requests only.
*
* Using reliable responses is negotiated using the "100rel" option tag. The
* UAC (party sending the INVITE) can include the option tag to the
* @Supported or @Require header. In the first case, the UAC just
* announces support for reliable responses, in the second case, the UAC
* requires that the UAS (party responding to the call) always sends
* provisional responses in reliable manner.
*
* When reliable responses are enabled with NTATAG_REL100() tag, the @b nta
* engine automatically inserts the "100rel" option tag to the @Supported
* header in the INVITE requests.
*
* @subsection nta_reliable_t Responding Reliably
*
* When a UAS wants to respond reliably to a INVITE request, instead of
* familiar nta_incoming_treply() or nta_incoming_mreply() it uses the
* functions nta_reliable_treply() or nta_reliable_mreply(). These functions
* return a pointer to a special object, nta_reliable_t, that is used to
* keep track of unacknowledged responses and respond to the the PRACK
* acknowledgement request.
*
* Both the functions nta_reliable_treply () and nta_reliable_mreply() take
* a callback funtion pointer and an application context pointer as their
* arguments. The callback function is similar to the leg callback function.
* The callback is invoked when a corresponding PRACK request is received,
* or when there is a timeout.
*
* The @b nta takes care of assigning a serial number to each reliable
* response and resending them if no PRACK request is received. It also
* automatically adds the 100rel option tag to the @Require header.
*
* Also, if a request with 100rel in @Require header is responded with usual
* nta_incoming_treply()/nta_incoming_mreply() functions, the @b nta creates
* a reliable response object for each provisional response in behalf of
* application. As the application can not provide a PRACK callback function
* to @b nta, the PRACK requests are not delivered to the application.
*
* @subsection early_dialog UAC Receives a Reliable Response
*
* When a UAC receives a provisional response with a @RSeq header, it is
* required to acknowledge it. In order to do that, it must establish an @e
* early @e dialog with the UAS. In another view, a reliable response is
* used to establish the early dialog. UAC establishes a leg object for the
* early dialog by calling nta_leg_tcreate() with the parameters derived
* from the response message.
*
* @code
* int invite_callback(call_t *call,
* nta_outgoing_t *orq,
* sip_t const *sip)
* {
* int status = sip->sip_status->st_status;
*
* if (!call->has_dialog &&
* (status >= 200 || (status > 100 && sip->sip_rseq))) {
* nta_leg_t *early =
* nta_leg_tcreate(call->nta_agent, mid_dialog_request, call,
* SIPTAG_TO(sip->sip_to),
* SIPTAG_FROM(sip->sip_from),
* SIPTAG_CALL_ID(sip->sip_call_id),
* SIPTAG_CSEQ(sip->sip_cseq),
* TAG_END());
*
* nta_leg_client_route(early,
* sip->sip_record_route,
* sip->sip_contact);
*
* fork = call_fork(call, leg = early);
*
* if (!fork)<29>{
* handle error;
* }
* call = fork;
* }
* @endcode
*
* The original dialog object and client transaction object are used to
* process other call forks. For instance, if the early dialog is
* established with an announcement server it will never lead to an fully
* established call, but an another dialog will be used when the call is
* completed.
*
* @subsection nta_prack Acknowledging Reliable Response
*
* After an early dialog has been established, acknowledging the reliable
* response is trivial. The application can create a PRACK client
* transaction object by calling nta_outgoing_prack()
*
* @section nta_client SIP Client Action
*
* A SIP client initiates the transactions. In some cases, a SIP client is
* also required to invoke additional transactions, like @b ACK or @b
* CANCEL, to finalize the original transaction. This section describes how
* a SIP client uses NTA to make transactions.
*
* @subsection client_nta_leg_t Creating the Call Leg
*
* If the client does not have a suitable call leg, it must create it by
* calling the function nta_leg_tcreate():
* @code
* context->leg = nta_leg_tcreate(agent,
* callback, context,
* SIPTAG_CALL_ID(call_id),
* SIPTAG_FROM(from),
* SIPTAG_TO(to),
* TAG_END());
* @endcode
*
* The @p callback function and @p context pointer are used for incoming
* transactions, and they may be @c NULL if no such transactions are
* expected. If the callback is @c NULL, NTA responds to incoming
* transactions with status @e 403 @e Forbidden.
*
* The @a call_id may be @c NULL or left out. In that case, NTA generates a
* new call ID.
*
* The @a from and @a to are used in outgoing transactions. They are also
* used to select which incoming messages belong to this leg.
*
* The initial sequence number can be supplied with SIPTAG_CSEQ() (taking a
* @CSeq structure as parameter).
*
* The additional parameters (after @a to) are included in outgoing messages
* using this leg. Currently, only @c SIPTAG_ROUTE() is supported.
*
* @note Additional tagged parameters are ignored.
*
* @subsection nta_outgoing_t Outgoing requests
*
* The outgoing request is created and sent by nta_outgoing_tcreate(). It
* can be used as follows:
* @code
* oreq = nta_outgoing_tcreate(leg, response_to_register, reg,
* proxy_url,
* SIP_METHOD_REGISTER,
* registrar_url,
* SIPTAG_CONTACT(my_contact),
* TAG_END());
* @endcode
*
* NTA invokes the callback function response_to_register() each time a
* provisional answer is received, and when a final answer is received.
*
* @note There may be multiple final answers to the INVITE request.
*
* If NTA does not receive answer in timely manner, it will generate a
* @e 408 @e Timeout response and hand that back to the application.
*
* @note After a provisional answer to the INVITE request, no timeout will
* occur inside NTA. Application must itself timeout the INVITE
* transactions if any answer has been received.
*
* The request can be destroyed with NTA function nta_outgoing_destroy().
* If no final answer has been received, the request is cancelled when it is
* destroyed, too. The application can also cancel the outgoing request by
* calling nta_outgoing_cancel().
*
* @subsection nta_ack Acknowledging Answers to INVITE
*
* The final answers to the INVITE request must be acknowledged. NTA takes
* care of acknowledging automatically the 3xx..6xx answers; the appliction
* must explicitly create a separate acknowledge transaction to final 2xx
* answers.
*
* The final answer can be acknowledged like this:
* @code
* url = sip->sip_contact ? sip->sip_contact->m_url : original_url;
* ack = nta_outgoing_tcreate(leg, NULL, NULL,
* SIP_METHOD_ACK,
* (url_string_t*)url,
* SIPTAG_CSEQ(sip->sip_cseq),
* SIPTAG_PAYLOAD(sdp),
* TAG_END());
* @endcode
*
* @note The ACK transaction should be sent to the @Contact specified in the
* 2xx reply.
*
* <a name="nta_register_f"></a>
* @section nta_stateless_callback Stateless Processing of SIP Messages
*
* When an NTA agent is created, it is possible to provide it with a
* stateless callback function. The callback function will be called when an
* incoming SIP request or response message does not match with an existing
* transaction.
*
* Before invoking the stateless callback the agent will try to match the
* incoming request message with an existing dialog or dialog-less leg (or
* default leg). So, if you have created a default leg, all request messages
* are processed statefully by it instead of being passed to the stateless
* callback function.
*
* If you want to process request messages with stateless callback and still
* use dialog-less legs (for instance, in order to look up domains with
* nta_leg_by_uri()), you have to switch over to @em stateless @em mode by
* including NTATAG_STATELESS(1) in nta_agent_create() or
* nta_agent_set_params() arguments.
*
* Also, if a response message does not match with an existing client
* transaction, the agent will try to use the default outgoing (client)
* transaction. If you have created an default outgoing transaction, all
* stray response messages are passed to it instead of the stateless
* processing function.
*
* @section nta_message_f_example Stateless Callback Function
*
* In addition to the message (@a msg) and its
* parsed contents (@a sip) the callback function gets the
* application-specific context pointer (in this case, @a registrar) and a
* pointer to the NTA agent (@a agent) as its arguments:
*
* @code
* int process_message(nta_agent_context_t *registrar,
* nta_agent_t *agent,
* msg_t *msg,
* sip_t *sip);
* @endcode
*
* The application has three functions that can be used to process the
* messages in stateless manner:
* @li nta_msg_discard() ignores and destroys the message,
* @li nta_msg_tsend() forwards a request or response message, and
* @li nta_msg_treply() replies to a request message in a stateless way.
*
* Additionally, it is possible to process a request message statefully with
* nta_incoming_create().
*
* The functionality of the stateless callback function can vary greatly,
* depending the purpose of the application. An user-agent, a proxy or a
* registrar/redirect server each have very different callback functions.
*
* A simple redirect server could have a message callback function as
* follows.
*
* @code
* int process_message(redirect_t *r,
* nta_agent_t *agent,
* msg_t *msg,
* sip_t *sip)
* {
* sip_contact_t *m;
* sip_unsupported_t *u;
*
* @endcode
*
* The incoming response messages are simply ignored. The @b ACK requests can
* safely be discarded, too, because the redirect server keeps no state.
*
* @code
* if (!sip->sip_request || sip->sip_request->rq_method == sip_method_ack) {
* nta_msg_discard(agent, msg);
* return 0;
* }
* @endcode
*
* Next, the redirect server first checks if processing the request requires
* a feature that is not supported by it:
* @code
* u = sip_unsupported(msg_home(msg), sip->sip_require, r->r_supported);
* if (u) {
* nta_msg_treply(agent, msg, SIP_420_BAD_EXTENSION,
* SIPTAG_SUPPORTED(r->r_supported),
* SIPTAG_UNSUPPORTED(u),
* TAG_END());
* return 0;
* }
* @endcode
*
* The @b CANCEL requests terminate a transacton. A stateless redirect
* server does not have transactions, so it redirect replies with a @e 481
* @e Call @e Leg/Transaction @e Does @e Not @e Exist message:
* @code
* if (sip->sip_request->rq_method == sip_method_cancel) {
* nta_msg_treply(agent, msg, SIP_481_NO_TRANSACTION, TAG_END());
* return 0;
* }
* @endcode
*
* All other requests are answered normally with a 302 response.
* The location service is
* searched for the request uri, and if a matching address was found, a
* list of active bindings is returned to the client.
* @code
* m = location_find(redirect, sip->sip_request->rq_url);
* if (m) {
* nta_msg_treply(agent, msg, SIP_302_MOVED_TEMPORARILY,
* SIPTAG_CONTACT(m),
* TAG_END());
* }
* @endcode
*
* Otherwise, @e 404 @e Not @e Found is sent:
* @code
* else {
* nta_msg_treply(agent, msg, SIP_404_NOT_FOUND, TAG_END());
* }
*
* return 0;
* }
* @endcode
*
*/
/**@page internal NTA Semantics and Internal Data Flows
*
* NTA implements simple state machines at transaction level. The figure
* below illustrates how a message is processed by NTA.
*
* @image html nta-receiving-message.gif "NTA processing incoming messages."
* @image latex nta-receiving-message.eps "NTA processing incoming messages."
*
*
*/
int invite_callback(call_t *call,
nta_outgoing_t *orq,
sip_t const *sip)
{
int status = sip->sip_status->st_status;
nta_leg_t *leg = call->leg;
if (!call->has_dialog &&
(status >= 200 || (status > 100 && sip->sip_rseq))) {
nta_leg_t *early =
nta_leg_tcreate(call->nta_agent, mid_dialog_request, call,
SIPTAG_TO(sip->sip_to),
SIPTAG_FROM(sip->sip_from),
SIPTAG_CALL_ID(sip->sip_call_id),
SIPTAG_CSEQ(sip->sip_cseq),
TAG_END());
nta_leg_client_route(early,
sip->sip_record_route,
sip->sip_contact);
fork = call_fork(call, leg = early);
if (!fork)<EFBFBD>{
handle error;
}
call = fork;
}
if (status > 100 && status < 200 && sip->sip_rseq) {
nta_outgoing_t *prack =
nta_outgoing_prack(leg, orq, NULL, NULL, NULL,
sip,
TAG_END());
nta_outgoing_destroy(prack);
return 0;
}
...
}
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