Communication with the codec layer

If a transport layer plug-in is to be able to receive messages and then pass them on to the codec layer it must be able to communicate with appropriate decoding codecs. A decoding codec is one that can accept messages from the transport layer and parse them (decode them) into the normalised event format accepted by the Semantic Mapper.

When a codec is loaded into the IAF its details are passed to all transport layer plug-ins by calling their addEventDecoder function. This tells the transport layer plug-in the name of the decoding codec and provides a reference to its AP_EventDecoder structure.

sendTransportEvent

/**
  * Called by the event transport to decode an event and send it on to the
  * Semantic Mapper. Ownership of the message is transferred to the
  * decoder when this function is called. It is assumed that the encoder
  * and transport share the same definition of the content of the event, so
  * that the transport can effectively interpret the event and free any
  * dynamically-allocated memory.
  *
  * @param decoder The event decoder instance
  * @param event The event to be decoded
  * @param timeStamp Timestamps associated with this event
  * @return Event codec error code. If this is not AP_EventCodec_OK, the
  * getLastError() function of the decoder should be called to get a more
  * detailed description of what went wrong.
  */
  AP_EventCodecError (*sendTransportEvent)(struct AP_EventDecoder* decoder,
     AP_TransportEvent event, AP_TimestampSet* timeStamp);

getLastError
/**
  * getLastError
  *
  * Return the decoder's stored error message, if any. The message string
  * is owned by the decoder so should not be modified or freed by the
  * caller.
  *
  * @param decoder The event decoder instance
  * @return The last error message generated by the decoder
  */
  const AP_char8* (*getLastError)(struct AP_EventDecoder* decoder);