bre

A Binary-Object Mapper for JavaScript.

const bre = require("bre")
 
// Define a Record Type.
const TcpHeader = bre.defineObjectRecord("TcpHeader", [
    {type: "uint16", name: "srcPort"},
    {type: "uint16", name: "dstPort"},
    {type: "uint32", name: "seqNo"},
    {type: "uint32", name: "ackNo"},
    {type: "bit4", name: "dataOffset"},
    {skip: 6},
    {type: "bit1", name: "urgCode"},
    {type: "bit1", name: "ackCode"},
    {type: "bit1", name: "pshCode"},
    {type: "bit1", name: "rstCode"},
    {type: "bit1", name: "synCode"},
    {type: "bit1", name: "finCode"},
    {type: "uint16", name: "windowSize"},
    {type: "uint16", name: "checksum"},
    {type: "uint16", name: "urgentPonter"},
])
 
// Connect to a Buffer
const header = TcpHeader.view(a_buffer, 0)
 
// Read and Write the Buffer
console.log(header.srcPort, "→", header.dstPort, "🚀")
header.seqNo += 1
header.ackNo += 1
header.ackCode = 1

bre's record object is just the wrapper of an ArrayBuffer object.

• The read of a record object's property is the read of the wrapped buffer.
• The write of a record object's property is the write of the wrapped buffer.

💿 Installation

$ npm install --save bre

• Requires Node.js >=4.0.0

📖 Usage

Like C struct, bre allows accessing binary data as a structure fastly.

The following steps are the basic usage of bre:

1. Defines structures (calls it records).
2. Creates mapping between the structure and a binary data.
3. Reads/Writes the binary data as the structure.

1. Defines structures (calls it records).

const bre = require("bre")
const ExampleRecord = bre.defineObjectRecord("ExampleRecord", [
    {type: "uint8", name: "a"},
    {type: "uint8", name: "b"},
])

At first, it defines classes of structures by bre.defineObjectRecord or bre.defineArrayRecord.

The code above defines a class ExampleRecord which has 2 properties (a and b).

2. Creates mapping between the structure and a binary data.

ExampleRecord can be instantiated with an ArrayBuffer object or a view of an ArrayBuffer object. E.g., Node.js Buffer objects are the view of ArrayBuffer objects.

const buffer = Buffer.from([0x01, 0x02, 0x03])
const record1 = ExampleRecord.view(buffer, 0)
const record2 = ExampleRecord.view(buffer, 1)  // offset 1

ExampleRecord.view factory method creates an instance of ExampleRecord.

• The 1st argument is the buffer to access.
• The 2nd argument is the offset in bytes to access.

3. Reads/Writes the binary data as the structure.

console.log(record1.a, record1.b)  // => 1 2
console.log(record2.a, record2.b)  // => 2 3

record1.b = 10

console.log(record1.b)  // => 10
console.log(record2.a)  // => 10
console.log(buffer[1])  // => 10

Those record instances are just wrappers. The record1.a getter will read the 1st byte of buffer directly. The record2.a getter will read the 2nd byte of buffer directly.

Also, The record1.a setter will write the 1st byte of buffer directly. This means that record2.a which is sharing the buffer will be changed.

This would be useful to read and write binary data.

The size of records.

Record classes have 2 properties to get the record size. Those are static getter properties (since records are fixed size).

const bytes = ExampleRecord.byteLength
const bits = ExampleRecord.bitLength

Also, BinaryRecord class provides 2 methods to get the record size of a record instance.

const bytes = bre.BinaryRecord.byteLength(record1)
const bits = bre.BinaryRecord.bitLength(record1)

📚 API Reference

const bre = require("bre")

• bre.defineObjectRecord(className, fields)
• bre.defineArrayRecord(type, length)
• bre.getTextEncoder()
• bre.setTextEncoder(value)
• bre.BinaryRecord
  • bre.BinaryRecord.bitLength(record)
  • bre.BinaryRecord.byteLength(record)
  • bre.BinaryRecord.keys(record)
  • bre.BinaryRecord.values(record)
  • bre.BinaryRecord.entries(record)

📰 Changelog

• https://github.com/mysticatea/bre/releases

💪 Contributing

Thank you for contributing!

• Getting code:

  $ git clone https://github.com/mysticatea/bre.git
  $ cd bre
  $ npm install

• Testing:

  $ npm run watch