org.eclipse.paho.client.mqttv3
Interface MqttPersistable

public interface MqttPersistable

Represents an object used to pass data to be persisted across the MqttClientPersistence interface.

When data is passed across the interface the header and payload are separated, so that unnecessary message copies may be avoided. For example, if a 10 MB payload was published it would be inefficient to create a byte array a few bytes larger than 10 MB and copy the MQTT message header and payload into a contiguous byte array.

When the request to persist data is made a separate byte array and offset is passed for the header and payload. Only the data between offset and length need be persisted. So for example, a message to be persisted consists of a header byte array starting at offset 1 and length 4, plus a payload byte array starting at offset 30 and length 40000. There are three ways in which the persistence implementation may return data to the client on recovery:

• It could return the data as it was passed in originally, with the same byte arrays and offsets.
• It could safely just persist and return the bytes from the offset for the specified length. For example, return a header byte array with offset 0 and length 4, plus a payload byte array with offset 0 and length 40000
• It could return the header and payload as a contiguous byte array with the header bytes preceeding the payload. The contiguous byte array should be set as the header byte array, with the payload byte array being null. For example, return a single byte array with offset 0 and length 40004. This is useful when recovering from a file where the header and payload could be written as a contiguous stream of bytes.

Method Summary

byte[]	getHeaderBytes() Returns the header bytes in an array.
int	getHeaderLength() Returns the length of the header.
int	getHeaderOffset() Returns the offset of the header within the byte array returned by getHeaderBytes().
byte[]	getPayloadBytes() Returns the payload bytes in an array.
int	getPayloadLength() Returns the length of the payload.
int	getPayloadOffset() Returns the offset of the payload within the byte array returned by getPayloadBytes().

Method Detail

getHeaderBytes

public byte[] getHeaderBytes()
                      throws MqttPersistenceException

Returns the header bytes in an array. The bytes start at getHeaderOffset() and continue for getHeaderLength().

Returns:

the header bytes.

Throws:

MqttPersistenceException

getHeaderLength

public int getHeaderLength()
                    throws MqttPersistenceException

Returns the length of the header.

Returns:

the header length

Throws:

MqttPersistenceException

getHeaderOffset

public int getHeaderOffset()
                    throws MqttPersistenceException

Returns the offset of the header within the byte array returned by getHeaderBytes().

Returns:

the header offset.

Throws:

MqttPersistenceException

getPayloadBytes

public byte[] getPayloadBytes()
                       throws MqttPersistenceException

Returns the payload bytes in an array. The bytes start at getPayloadOffset() and continue for getPayloadLength().

Returns:

the payload bytes.

Throws:

MqttPersistenceException

getPayloadLength

public int getPayloadLength()
                     throws MqttPersistenceException

Returns the length of the payload.

Returns:

the payload length.

Throws:

MqttPersistenceException

getPayloadOffset

public int getPayloadOffset()
                     throws MqttPersistenceException

Returns the offset of the payload within the byte array returned by getPayloadBytes().

Returns:

the payload offset.

Throws:

MqttPersistenceException