#include <stdlib.h>
Go to the source code of this file.
It should be noted that the simplified API, is sill not very simple. There are complexities invoved that cannot be avoided. However, this API does remove some issues with the full API such as multi-threading and advanced C++ concepts.
The other major feature of this API is the ability to be easily "late bound" using Windows LoadLibrary() or Unix dlopen() at run time. You may look at the sample code in opal/samples/c_api/main.c for an example of how to do late binding.
Late binding also allows for easier integration of OPAL fucntionality to interpreted languages such as Java, Perl etc. Systems like "swig" may be used to produce interface files for such languages.
To make the above easier, there are only four functions: OpalInitialise(), OpalShutDown(), OpalGetMessage() and OpalSendMessage(). All commands to OPAL and indications back from OPAL are done through the latter two functions.
This API also provides a basic C++ class OpalContext, which may be used for C++ programmers that do not wish to learn the large number of classes in the full API. At the cost of minimal extensibility and control.
| #define OPAL_C_API_VERSION 21 |
Current API version.
| #define OPAL_EXPORT |
| #define OPAL_FREE_MESSAGE_FUNCTION "OpalFreeMessage" |
String representation of the OpalFreeMessage() which may be used for late binding to the library.
| #define OPAL_GET_MESSAGE_FUNCTION "OpalGetMessage" |
String representation of the OpalGetMessage() which may be used for late binding to the library.
| #define OPAL_INITIALISE_FUNCTION "OpalInitialise" |
String representation of the OpalIntialise() which may be used for late binding to the library.
| #define OPAL_LINE_APPEARANCE_EVENT_PACKAGE "dialog;sla;ma" |
Name of SIP even package fo rmonitoring call status.
| #define OPAL_MWI_EVENT_PACKAGE "message-summary" |
Name of SIP event package for Message Waiting events.
| #define OPAL_PREFIX_ALL |
Value:
OPAL_PREFIX_H323 " " \ OPAL_PREFIX_SIP " " \ OPAL_PREFIX_IAX2 " " \ OPAL_PREFIX_PCSS " " \ OPAL_PREFIX_LOCAL " " \ OPAL_PREFIX_POTS " " \ OPAL_PREFIX_PSTN " " \ OPAL_PREFIX_IVR
| #define OPAL_PREFIX_H323 "h323" |
H.323 Protocol supported string for OpalInitialise().
| #define OPAL_PREFIX_IAX2 "iax2" |
IAX2 Protocol supported string for OpalInitialise().
| #define OPAL_PREFIX_IVR "ivr" |
Interactive Voice Response supported string for OpalInitialise().
| #define OPAL_PREFIX_LOCAL "local" |
Local endpoint supported string for OpalInitialise().
| #define OPAL_PREFIX_PCSS "pc" |
PC sound system supported string for OpalInitialise().
| #define OPAL_PREFIX_POTS "pots" |
Plain Old Telephone System supported string for OpalInitialise().
| #define OPAL_PREFIX_PSTN "pstn" |
Public Switched Network supported string for OpalInitialise().
| #define OPAL_PREFIX_SIP "sip" |
SIP Protocol supported string for OpalInitialise().
| #define OPAL_SEND_MESSAGE_FUNCTION "OpalSendMessage" |
Typedef representation of the pointer to the OpalSendMessage() function which may be used for late binding to the library.
| #define OPAL_SHUTDOWN_FUNCTION "OpalShutDown" |
String representation of the OpalShutDown() which may be used for late binding to the library.
| typedef void(OPAL_EXPORT *) OpalFreeMessageFunction(OpalMessage *message) |
Typedef representation of the pointer to the OpalFreeMessage() function which may be used for late binding to the library.
| typedef OpalMessage*(OPAL_EXPORT *) OpalGetMessageFunction(OpalHandle opal, unsigned timeout) |
Typedef representation of the pointer to the OpalGetMessage() function which may be used for late binding to the library.
| typedef struct OpalHandleStruct* OpalHandle |
Handle to initialised OPAL instance.
| typedef OpalHandle(OPAL_EXPORT *) OpalInitialiseFunction(unsigned *version, const char *options) |
Typedef representation of the pointer to the OpalIntialise() function which may be used for late binding to the library.
| typedef int(*) OpalMediaDataFunction(const char *token,const char *stream,const char *format,void *userData,void *data,int size) |
Function for reading/writing media data. Returns size of data actually read or written, or -1 if there is an error and the media stream should be shut down.
The "write" function, which is taking data from a remote and providing it to the "C" application for writing, should not be assumed to have a one to one correspondence with RTP packets. The OPAL jiter buffer may insert "silence" data for missing or too late packets. In this case the function is called with the size parameter equal to zero. It is up to the application what it does in that circumstance.
Note that this function will be called in the context of different threads so the user must take care of any mutex and synchonisation issues.
| typedef struct OpalMessage OpalMessage |
| typedef int(*) OpalMessageAvailableFunction(const OpalMessage *message) |
Function called when a message event becomes available. This function is called before the message is queued for the GetMessage() function.
A return value of zero indicates that the message is not to be passed on to the GetMessage(). A non-zero value will pass the message on.
Note that this function will be called in the context of different threads so the user must take care of any mutex and synchonisation issues. If the user subsequently uses the GetMessage() then the message will have been serialised so that there are no multi-threading issues.
A simple use case would be for this function to send a signal or message to the applications main thread and then return a non-zero value. The main thread would then wake up and get the message using GetMessage.
| typedef struct OpalStatusUserInput OpalParamUserInput |
User input information for the OpalIndUserInput/OpalCmdUserInput indication.
This is may be returned from the OpalGetMessage() function or provided to the OpalSendMessage() function.
| typedef OpalMessage*(OPAL_EXPORT *) OpalSendMessageFunction(OpalHandle opal, const OpalMessage *message) |
String representation of the OpalSendMessage() which may be used for late binding to the library.
| typedef void(OPAL_EXPORT *) OpalShutDownFunction(OpalHandle opal) |
Typedef representation of the pointer to the OpalShutDown() function which may be used for late binding to the library.
| enum OpalCallEndReason |
Type code for media stream status/control. This is used by the OpalIndMediaStream indication and OpalCmdMediaStream command in the OpalStatusMediaStream structure.
| enum OpalEchoCancelMode |
Type code the echo cancellation algorithm modes. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.
Type code for media stream status/control. This is used by the OpalIndMediaStream indication and OpalCmdMediaStream command in the OpalStatusMediaStream structure.
| enum OpalMediaDataType |
Type code the media data call back functions data type. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.
This controls if the whole RTP data frame or just the paylaod part is passed to the read/write function.
| enum OpalMediaStates |
Type code for media stream status/control. This is used by the OpalIndMediaStream indication and OpalCmdMediaStream command in the OpalStatusMediaStream structure.
| enum OpalMediaTiming |
Timing mode for the media data call back functions data type. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.
This controls if the read/write function is in control of the real time aspects of the media flow. If synchronous then the read/write function is expected to handle the real time "pacing" of the read or written data.
Note this is important both for reads and writes. For example in synchronous mode you cannot simply read from a file and send, or you will likely overrun the remotes buffers. Similarly for writing to a file, the correct operation of the OPAL jitter buffer is dependent on it not being drained too fast by the "write" function.
If marked as asynchroous then the OPAL stack itself will take care of the timing and things like read/write to a disk file will work correctly.
| enum OpalMessageType |
Type code for messages defined by OpalMessage.
| OpalIndCommandError | An error occurred during a command. This is only returned by OpalSendMessage(). The details of the error are shown in the OpalMessage::m_commandError field. |
| OpalCmdSetGeneralParameters | Set general parameters command. This configures global settings in OPAL. See the OpalParamGeneral structure for more information. |
| OpalCmdSetProtocolParameters | Set protocol parameters command. This configures settings in OPAL that may be different for each protocol, e.g. SIP & H.323. See the OpalParamProtocol structure for more information. |
| OpalCmdRegistration | Register/Unregister command. This initiates a registration or unregistration operation with a protocol dependent server. Currently only for H.323 and SIP. See the OpalParamRegistration structure for more information. |
| OpalIndRegistration | Status of registration indication. After the OpalCmdRegistration has initiated a registration, this indication will be returned by the OpalGetMessage() function when the status of the registration changes, e.g. successful registration or communications failure etc. See the OpalStatusRegistration structure for more information. |
| OpalCmdSetUpCall | Set up a call command. This starts the outgoing call process. The OpalIndAlerting, OpalIndEstablished and OpalIndCallCleared messages are returned by OpalGetMessage() to indicate the call progress. See the OpalParamSetUpCall structure for more information. |
| OpalIndIncomingCall | Incoming call indication. This is returned by the OpalGetMessage() function at any time after listeners are set up via the OpalCmdSetProtocolParameters command. See the OpalStatusIncomingCall structure for more information. |
| OpalCmdAnswerCall | Answer call command. After a OpalIndIncomingCall is returned by the OpalGetMessage() function, an application maye indicate that the call is to be answered with this message. The OpalMessage m_callToken field is set to the token returned in OpalIndIncomingCall. |
| OpalCmdClearCall | Hang Up call command. After a OpalCmdSetUpCall command is executed or a OpalIndIncomingCall indication is received then this may be used to "hang up" the call. The OpalIndCallCleared is subsequently returned in the OpalGetMessage() when the call has completed its hang up operation. See OpalParamCallCleared structure for more information. |
| OpalIndAlerting | Remote is alerting indication. This message is returned in the OpalGetMessage() function when the underlying protocol states the remote telephone is "ringing". See the OpalParamSetUpCall structure for more information. |
| OpalIndEstablished | Call is established indication. This message is returned in the OpalGetMessage() function when the remote or local endpont has "answered" the call and there is media flowing. See the OpalParamSetUpCall structure for more information. |
| OpalIndUserInput | User input indication. This message is returned in the OpalGetMessage() function when, during a call, user indications (aka DTMF tones) are received. See the OpalStatusUserInput structure for more information. |
| OpalIndCallCleared | Call is cleared indication. This message is returned in the OpalGetMessage() function when the call has completed. The OpalMessage m_callToken field indicates which call cleared. |
| OpalCmdHoldCall | Place call in a hold state. The OpalMessage m_callToken field is set to the token returned in OpalIndIncomingCall. |
| OpalCmdRetrieveCall | Retrieve call from hold state. The OpalMessage m_callToken field is set to the token returned in OpalIndIncomingCall. |
| OpalCmdTransferCall | Transfer a call to another party. This starts the outgoing call process for the other party. See the OpalParamSetUpCall structure for more information. |
| OpalCmdUserInput | User input command. This sends specified user input to the remote connection. See the OpalStatusUserInput structure for more information. |
| OpalIndMessageWaiting | Message Waiting indication. This message is returned in the OpalGetMessage() function when an MWI is received on any of the supported protocols. |
| OpalIndMediaStream | A media stream has started/stopped. This message is returned in the OpalGetMessage() function when a media stream is started or stopped. See the OpalStatusMediaStream structure for more information. |
| OpalCmdMediaStream | Execute control on a media stream. See the OpalStatusMediaStream structure for more information. |
| OpalCmdSetUserData | Set the user data field associated with a call |
| OpalIndLineAppearance | Line Appearance indication. This message is returned in the OpalGetMessage() function when any of the supported protocols indicate that the state of a "line" has changed, e.g. free, busy, on hold etc. |
| OpalCmdStartRecording | Start recording an active call. See the OpalParamRecording structure for more information. |
| OpalCmdStopRecording | Stop recording an active call. Only the m_callToken field of the OpalMessage union is used. |
| OpalIndProceeding | Call has been accepted by remote. This message is returned in the OpalGetMessage() function when the underlying protocol states the remote endpoint acknowledged that it will route the call. This is distinct from OpalIndAlerting in that it is not known at this time if anything is ringing. This indication may be used to distinguish between "transport" level error, in which case another host may be tried, and that the responsibility for finalising the call has moved "upstream". See the OpalParamSetUpCall structure for more information. |
| OpalCmdAlerting | Send an indication to the remote that we are "ringing". The OpalMessage m_callToken field indicates which call is alerting. |
| OpalMessageTypeCount |
Type code for media stream status/control. This is used by the OpalIndRegistration indication in the OpalStatusRegistration structure.
| OpalRegisterSuccessful | Successfully registered. |
| OpalRegisterRemoved | Successfully unregistered. Note that the m_error field may be non-null if an error occurred during unregistration, however the unregistration will "complete" as far as the local endpoint is concerned and no more registration retries are made. |
| OpalRegisterFailed | Registration has failed. The m_error field of the OpalStatusRegistration structure will contain more details. |
| OpalRegisterRetrying | Registrar/Gatekeeper has gone offline and a failed retry has been executed. |
| OpalRegisterRestored | Registration has been restored after a succesfull retry. |
Type code the silence detect algorithm modes. This is used by the OpalCmdSetGeneralParameters command in the OpalParamGeneral structure.
Type of mixing for video when recording. This is used by the OpalCmdStartRecording command in the OpalParamRecording structure.
| void OPAL_EXPORT OpalFreeMessage | ( | OpalMessage * | message | ) |
Free memeory in message the OPAL system has sent. The parameter must be the message returned by OpalGetMessage() or OpalSendMessage().
| OpalMessage* OPAL_EXPORT OpalGetMessage | ( | OpalHandle | opal, | |
| unsigned | timeout | |||
| ) |
Get a message from the OPAL system. The first parameter must be the handle returned by OpalInitialise(). The second parameter is a timeout in milliseconds. NULL is returned if a timeout occurs. A value of UINT_MAX will wait forever for a message.
The returned message must be disposed of by a call to OpalFreeMessage().
The OPAL system will serialise all messages returned from this function to avoid any multi-threading issues. If the application wishes to avoid even this small delay, there is a callback function that may be configured that is not thread safe but may be used to get the messages as soon as they are generated. See OpalCmdSetGeneralParameters.
Note if OpalShutDown() is called from a different thread then this function will break from its block and return NULL.
Example: OpalMessage * message;
while ((message = OpalGetMessage(hOPAL, timeout)) != NULL) { switch (message->m_type) { case OpalIndRegistration : HandleRegistration(message); break; case OpalIndIncomingCall : Ring(message); break; case OpalIndCallCleared : HandleHangUp(message); break; } FreeMessageFunction(message); }
| OpalHandle OPAL_EXPORT OpalInitialise | ( | unsigned * | version, | |
| const char * | options | |||
| ) |
Initialise the OPAL system, returning a "handle" to the system that must be used in other calls to OPAL.
The version parameter indicates the version of the API being used by the caller. It should always be set to the constant OPAL_C_API_VERSION. On return the library will indicate the API version it supports, if it is lower than that provided by the application.
The C string options are space separated tokens indicating various options to be enabled, for example the protocols to be available. NULL or an empty string will load all available protocols. The current protocol tokens are: sip sips h323 h323s iax2 pc local pots pstn ivr The above protocols are in priority order, so if a protocol is not explicitly in the address, then the first one of the opposite "category" s used. There are two categories, network protocols (sip, h323, iax & pstn) and non-network protocols (pc, local, pots & ivr).
Additional options are:
| TraceLevel=1 | Level for tracing. |
| TraceAppend | Append to the trace file. |
| TraceFile="name" | Set the filename for trace output. Note quotes are required if spaces are in filename. |
If NULL is returned then an initialisation error occurred. This can only really occur if the user specifies prefixes which are not supported by the library.
Example: OpalHandle hOPAL; unsigned version;
version = OPAL_C_API_VERSION; if ((hOPAL = OpalInitialise(&version, OPAL_PREFIX_H323 " " OPAL_PREFIX_SIP " " OPAL_PREFIX_IAX2 " " OPAL_PREFIX_PCSS " TraceLevel=4")) == NULL) { fputs("Could not initialise OPAL\n", stderr); return false; }
| OpalMessage* OPAL_EXPORT OpalSendMessage | ( | OpalHandle | opal, | |
| const OpalMessage * | message | |||
| ) |
Send a message to the OPAL system. The first parameter must be the handle returned by OpalInitialise(). The second parameter is a constructed message which is a command to the OPAL system.
Within the command message, generally a NULL or empty string, or zero value for integral types, indicates the particular parameter is to be ignored. Documentation on individiual messages will indicate which are mandatory.
The return value is another message which will have a type of OpalIndCommandError if an error occurs. The OpalMessage::m_commandError field will contain a string indicating the error that occurred.
If successful, the the type of the message is the same as the command type. The message fields in the return will generally be set to the previous value for the field, where relevant. For example in the OpalCmdSetGeneralParameters command the OpalParamGeneral::m_stunServer would contain the STUN server name prior to the command.
A NULL is only returned if the either OpalHandle or OpalMessage parameters is NULL.
The returned message must be disposed of by a call to OpalFreeMessage().
Example: void SendCommand(OpalMessage * command) { OpalMessage * response; if ((response = OpalSendMessage(hOPAL, command)) == NULL) { puts("OPAL not initialised."); else if (response->m_type != OpalIndCommandError) HandleResponse(response); else if (response->m_param.m_commandError == NULL || *response->m_param.m_commandError == '\0') puts("OPAL error."); else printf("OPAL error: %s\n", response->m_param.m_commandError);
FreeMessageFunction(response); }
| void OPAL_EXPORT OpalShutDown | ( | OpalHandle | opal | ) |
Shut down and clean up all resource used by the OPAL system. The parameter must be the handle returned by OpalInitialise().
Example: OpalShutDown(hOPAL);
1.4.7