parametrized-message

parametrized-message

Parametrized messages are binary structures that provide unified way of handling known and unknown data at the cost of adding prefixes to each message and parameter.

Structure of messages

Message is a structure for storing parameters.

name	description
message-size	number of bytes message consists of (including this field)
message-id	if of the message
parameters	array of parameters

Structure of parameters

name	description
data-size	number of bytes in data filed
parameter-id	id of the parameter
data	data bytes

Documentation

Work in progress...

Message

This class...

Methods

• constructor(buffer, args)
• getParameter(id)
• getParameters(id)

Example

const Message = require('parametrized-message');

Message.Parameter

This class...

Methods

Example

const Message = require('parametrized-message');

Message.Builder

This class...

Methods

• constructor(id, args)
• generateBytes()
• addParameter(id, buffer)
• addInt8(id, val)
• addUInt8(id, val)
• addInt16LE(id, val)
• addInt16BE(id, val)
• addUInt16LE(id, val)
• addUInt16BE(id, val)
• addInt32LE(id, val)
• addInt32BE(id, val)
• addUInt32LE(id, val)
• addUInt32BE(id, val)
• addInt64LE(id, val)
• addInt64BE(id, val)
• addUInt64LE(id, val)
• addUInt64BE(id, val)
• addFloatLE(id, val)
• addFloatBE(id, val)
• addDoubleLE(id, val)
• addDoubleBE(id, val)

Example

const Message = require('parametrized-message');

Message.Defaults

This object is used to determine structure of messages and parameters, that is:

• type of message size field,
• type of message id field,
• type of parameter data size field,
• type of parameter id field.

All are by default set to Message.Types.Int32LE.

When no object describing structure is passed to constructors of Message, Message.Parameter and Message.Builder classes, values from Message.Defaults are used.

Available types are defined in Message.Types object.

Methods

• update(defaults)

• reset()

Example

const Message = require('parametrized-message');

const defaults = {
  messageSizeType   : Message.Types.Int8,
  messageIdType     : Message.Types.Int16LE,
  parameterSizeType : Message.Types.Int32LE,
  parameterIdType   : Message.Types.Int64LE,
};

Message.Defaults.update(defaults);

const messageId = 1;

const builder1 = new Message.Builder(messageId);
const builder2 = new Message.Builder(messageId, defaults);

Message.Types

This object stores objects containing properties describing size of the type and how to read and write values to the buffer object.

Members

• Message.Types.Int8
• Message.Types.Int16LE
• Message.Types.Int16BE
• Message.Types.Int32LE
• Message.Types.Int32BE
• Message.Types.Int64LE
• Message.Types.Int64BE
• Message.Types.UInt8
• Message.Types.UInt16LE
• Message.Types.UInt16BE
• Message.Types.UInt32LE
• Message.Types.UInt32BE
• Message.Types.UInt64LE
• Message.Types.UInt64BE

Custom types

To define custom type, an object with following structure must be created:

const MyType = {
	size: 12,
	read: (buffer, pos) => { return 0; }
	write: (buffer, val, pos) => {}
}

• size - number of bytes type takes
• read - method accepting an Buffer object (buffer) and buffer offset (pos), it needs to read data from the buffer and return numeric value
• write - method accepting an Buffer object (buffer), numeric value (val) and buffer offset (pos), it needs to write given value to the buffer at given offset

Example message

By default types all of the following fileds: message-size, message-id, data-size, parameter-id are int32_t. This can be changed using defaults or by passing desired properties to constructors of objects.

Example structure of message with id = 1 containing 2 parameters: { id: 1, data: 1.234f } and { id: 2, data: 4000000000u }:

byte #	type	name	value
0	int32_t	message-size	32
4	int32_t	message-id	1
8	int32_t	data-size	4
12	int32_t	parameter-id	1
16	float	data	1.234f
20	int32_t	data-size	4
24	int32_t	parameter-id	2
28	uint32_t	data	4000000000

Example code

const Message = require('parametrized-message');

// update default properties so they would not need to be passed as argument
// to every instance of Message, Parameter or MessageBuilder object
Message.Defaults.update({
  messageSizeType   : Message.Types.Int32LE,
  messageIdType     : Message.Types.Int32LE,
  parameterSizeType : Message.Types.Int32LE,
  parameterIdType   : Message.Types.Int32LE,
});

// use MessageBuilder to generate message bytes
const builder = new Message.Builder(1); // message-id = 1
builder.addInt32LE(0, 123); // parameter-id = 0, data = 123
builder.addInt32LE(0, 456);
builder.addInt32LE(1, 1);
builder.addInt32LE(2, 2);
const messageBytes = builder.generateBytes();

// extract the parameters from message bytes
const message = new Message(messageBytes);

// get all parameters
console.log('all:');
for (var param of message.getParameters()) {
  console.log(param.id + ' = ' + param.readInt32LE());
}

// get only parameters with id 0
console.log('zeroes:');
for (var param of message.getParameters(0)) {
  console.log(param.id + ' = ' + param.readInt32LE());
}

Tests

npm test