Simple Message Queue

Functionalities

• client will connect to server
• the client is free to push (enqueue) or pull (dequeue) messages to the queue after it is connected
• when the client pulls (dequeue), they will get EMPTY_QUEUE response if the queue is empty and SUCCESS response if the queue is not empty.
• client can push (enqueue) anytime they want, the messages are kept in the server until the server is stopped

Request and Response

Each request and response have a 9 byte header and a body. The body can have a variable size. The first byte of the header denotes the type of action done to the server. The last 8 bytes denotes the body size.

There are 2 types of action that can be done when doing request to the server:

• push
• pull

Push

Request

• Header's first byte is 0.
• The body is the message (see Message Format).

Response

• Header's first byte is 0 if message is successfully pushed, else header is 1.
• Body is empty.

Pull

Request

• Header's first byte is 1.
• The body is empty.

Response

• The header's first byte can be of any value.
• The body is the message saved in the message queue (see Message Format).

Message Format

Metadata (when pull):

code: EMPTY_QUEUE, SUCCESS
type: I8, I16, I32, I64, U8, U16, U32, U64 , F32, F64, Str
count: unsigned int (4 bytes)

3 kinds of metadata are used to describe the data. code describes the kind of response and type describes the data type. count describes how many data is in it. If count > 1 then the data is treated as an array. For strings, each element will be seperated with a null-terminator character (\0), it is also added at the end of the data bytes.

The metadata is 5 bytes data. The first byte consists of the code and type metadata. code takes first 4 left bits and type takes the rest 4 bits. count is 4 bytes (which is an unsigned 4 bytes integer) which means the whole metadata takes 5 bytes. This means when sending an array, the maximum element limit is 4,294,967,295 elements.

With the metadata, the response will be 5 megabytes with additional bytes if the data exists.

Code and type to bits mapping

bits	code and type
0000	SUCCESS or U8
0001	U16
0010	EMPTY_QUEUE or U32
0011	U64
0100	I8
0101	I16
0110	I32
0111	I64
1000	F32
1001	F64
1010	Str