class Message

Header File: <libkafka_asio/message.h>

Namespace: libkafka_asio

A message communication object as described on the Kafka wiki. Messages consist of a key-value pair and some metadata, like CRC for checking the message integrity and some attributes for handling compression.

Kafka handles compression by marshalling a complete set of messages, compressing it using one of the supported compression algorithms and finally putting it as the value of a single message, which has it's attributes set to the corresponding compression algorithm flag. Therefore, the Message class of libkafka-asio defines a pointer to a possibly nested message set. When consuming compressed data from Kafka, the nested message set will hold the actual uncompressed messages.

Constructor

Message

Message()

Creates a message with an empty key and empty value.

Message (Copy Constructor)

Message(const Message& orig, bool deep = false)

Creates a message by copying the given original message. If the optional deep parameter is set to true, the byte arrays for key and value as well as the nested message set, will be copied, too. Otherwise, the new message object will point to the same key, value and nested message set on the heap.

Message (Assignment Operator)

Message& operator= (const Message& rhs)

Flat-copy the given message.

Member functions

magic_byte

Int8 magic_byte() const;

Always returns zero.

attributes

Int8 attributes() const;

Returns the attribute bitset. The lowest 2 bits indicate the compression algorithm.

set_attributes

void set_attributes(Int8 attributes);

Sets the attributes byte of this message object.

key

const Bytes& key() const;
Bytes& mutable_key();

Optional message key. Can be NULL (default).

value

const Bytes& value() const;
Bytes& mutable_value();

Actual message data as byte array

nested_message_set

const MessageSet& nested_message_set() const;
MessageSet& mutable_nested_message_set();

Compressed messages contain a nested message set (see description above).

compression

constants::Compression compression() const;

Returns the compression algorithm, used for compressing the message value. The function only evaluates the lowest 2 bits of the attributes field.