Method QueryInterface

proxyAudioDevice/ProxyAudioDevice.cpp:415–459

#pragma mark Inheritence

HRESULT ProxyAudioDevice::QueryInterface(void *inDriver, REFIID inUUID, LPVOID *outInterface) {
    //    This function is called by the HAL to get the interface to talk to the plug-in through.
    //    AudioServerPlugIns are required to support the IUnknown interface and the
    //    AudioServerPlugInDriverInterface. As it happens, all interfaces must also provide the
    //    IUnknown interface, so we can always just return the single interface we made with
    //    gAudioServerPlugInDriverInterfacePtr regardless of which one is asked for.

    //    declare the local variables
    HRESULT theAnswer = 0;
    CFUUIDRef theRequestedUUID = NULL;

    //    validate the arguments
    FailWithAction(inDriver != gAudioServerPlugInDriverRef,
                   theAnswer = kAudioHardwareBadObjectError,
                   Done,
                   "ProxyAudio_QueryInterface: bad driver reference");
    FailWithAction(outInterface == NULL,
                   theAnswer = kAudioHardwareIllegalOperationError,
                   Done,
                   "ProxyAudio_QueryInterface: no place to store the returned interface");

    //    make a CFUUIDRef from inUUID
    theRequestedUUID = CFUUIDCreateFromUUIDBytes(NULL, inUUID);
    FailWithAction(theRequestedUUID == NULL,
                   theAnswer = kAudioHardwareIllegalOperationError,
                   Done,
                   "ProxyAudio_QueryInterface: failed to create the CFUUIDRef");

    //    AudioServerPlugIns only support two interfaces, IUnknown (which has to be supported by all
    //    CFPlugIns and AudioServerPlugInDriverInterface (which is the actual interface the HAL will
    //    use).
    if (CFEqual(theRequestedUUID, IUnknownUUID) || CFEqual(theRequestedUUID, kAudioServerPlugInDriverInterfaceUUID)) {
        CAMutex::Locker locker(stateMutex);
        ++gPlugIn_RefCount;
        *outInterface = gAudioServerPlugInDriverRef;
    } else {
        theAnswer = E_NOINTERFACE;
    }

    //    make sure to release the UUID we created
    CFRelease(theRequestedUUID);

Done:
    return theAnswer;
}

ULONG ProxyAudioDevice::AddRef(void *inDriver) {
    //    This call returns the resulting reference count after the increment.