bossam

bossam

Bossam is an object serialization library, with Rust-like domain-specific language.

Installation

Install bossam from NPM registry by running npm install bossam.

Usage

Bossam itself is a compiler that compiles bossam code into Javascript code. You can embed the compiler into your project, or compile the code using offline compiler.

Using bossam by embeding

import bossam from 'bossam';

const namespace = bossam(`
  struct Point {
    x: f32,
    y: f32,
  }
`);

namespace.Point.encode({x: 3, y: 3}); // Returns Uint8Array or Buffer (Node.js)
console.log(namespace.Point.decode(new Uint8Array([0, 0, 0, 0, 0, 0, 0, 0])));

// Expanding existing namespace is possible by using:
bossam(`
  struct Data(i32, i32);
  struct DataT<T>(T, T);
`, namespace);
// Create generics with the resolve function
const DataT = namespace.resolve('DataT<i8>');
console.log(DataT.encode([3, 3]));

NOTE: If you're not using Babel, you can import it using var bossam = require('bossam').default;

Using bossam by compiling

import compile from 'bossam/lib/offlineCompile';

console.log(compile(`
  struct Point {
    x: f32,
    y: f32,
  }
`)); // JavaScript code.

Compiled code requires CommonJS environment to be present - it uses require and module.exports.

Bossam language

Bossam uses Rust-like domain specific language for structing the data.

/*
  Block comments are supported too.
*/
// Tuple structs
struct Point(f64, f64, f64);
// Object structs
struct Entity {
  type: u32,
  position: Point,
  // Nullable types can be specified by prepending ?
  health: ?u8,
}
// Object enums. Resulting objects receive 'type' value by default, which is
// one of "Join" or "Kill" in this case.
enum Packet {
  Join { entity: Entity },
  Kill { entity: ?Entity, reason: String },
}

// A slightly complex example to showcase the features of bossam language.
struct User {
  createdAt: Date,
  favoritesCount: u32,
  following: ?bool,
  id: u64,
  name: String,
  description: ?String,
  // Fixed width arrays.
  position: [f64; 3],
  // Dynamic width arrays. Bossam supports template strings too.
  email: Array<String>,
  // Inline tuples.
  acl: (bool, bool, bool),
  // Inline objects.
  inventory: {
    gold: uvar,
    items: Array<Item>,
  },
  // This may look weird, but Javascript-side default value can be specified
  // using this - unit: "User", unitId: 3 will be set by default.
  // Only strings and numbers are supported.
  unit: "User",
  unitId: 3,
}

// Type name and encoded type can be specified.
// In this case, enum itself will be encoded using u8, and Item's type will be
// specified using type.
enum Item(u8, type) {
  // Type value can be overriden like this.
  Iron { type: "iron" },
  Pickaxe { strength: u8 },
  Axe { rarity: Rarity<u8> },
  // You can use aliases in the enum.
  BizCard = User,
  // You can also point to other types in enums like this.
  Shovel = Item.Axe,
}

// Tuple enums are supported too. 0th position of array will be the type and
// it can't be changed.
// Encoded type can be String too, and encode type specifier can be overriden.
// Templates are supported too.
enum Rarity<T>(String) {
  // It'll be encoded as "c" in binary
  "c" => Common(T),
  "r" => Rare(T),
  "e" => Epic(T),
  "l" => Legendary(T),
}

// Aliases are also possible.
struct Hello = Rarity<i32>;
struct There = Item.Axe;

// Expressions are possible too.
struct TestArray = [i8; 1 + 5 * (6 % 2) + floor(3 / 2)];
// ... It can also be used with generics.
struct TestArray<T> {
  a: [i16; sizeof(Entity) * T],
}
struct TestArray2 = TestArray<3>;

Expressions

// a + b
// a - b
// a * b
// a / b
// a % b
// floor(a)
// round(a)
// ceil(a)
// min(a, b)
// max(a, b)
// sizeof(T)

Primitive types

All types use big endian unless specified.

• u8 - 8bit unsigned integer.
• i8 - 8bit signed integer.
• u16 - 16bit unsigned integer.
• i16 - 16bit signed integer.
• u32 - 32bit unsigned integer.
• i32 - 32bit signed integer.
• u48 - 48bit unsigned integer.
• u64 - 64bit unsigned integer. Since Javascript doesn't support 64bit integers, Bossam forcefully converts them to double. This means that numbers are usable up to 53 bits.
• i64 - 64bit signed integer. Same constraint for u64 affects this too.
• ivar - varying signed integer. Description is in the below.
• uvar - varying unsigned integer. Description is in the below.
• f32 - 32bit IEEE 754 floating number.
• f64 - 64bit IEEE 754 floating number.
• bool - Equivalent to u8, automatically converts from / to Boolean.
• Array<T> - dynamic array of type T.
• Vec<T> - Equivalent to Array<T>.
• String - UTF-8 encoded string.
• String<T> - String with encoding T. T should be one of: "utf-8", "utf-16", "utf-16le", "utf-16be". Other encodings are not supported because TextEncoder spec doesn't allow it.
• Date - Equivalent to u64, but automatically converts from / to Date.
• JSON - Equivalent to UTF-8 encoded string, but automatically converts from / to JSON. This stores JSON as a string!
• Padded<T, S> - Type T padded to size S. If the type is larger than the provided size, it'll throw an error.

Little endian types

Bossam supports little endian for the sake of optimization - it's not preferred endian for exchanging data. However, some may need to quickly read huge array of floats, ints, etc. Since most systems use little endian, little endian would be used for this purpose. Bossam automatically uses raw ArrayBuffer access to read arrays if they're aligned and the system uses same endian format, instead of DataView.

• u8le - 8bit unsigned integer.
• i8le - 8bit signed integer.
• u16le - 16bit unsigned integer.
• i16le - 16bit signed integer.
• u32le - 32bit unsigned integer.
• i32le - 32bit signed integer.
• u48le - 48bit unsigned integer.
• u64le - 64bit unsigned integer. Since Javascript doesn't support 64bit integers, Bossam forcefully converts them to double. This means that numbers are usable up to 53 bits.
• i64le - 64bit signed integer. Same constraint for u64 affects this too.
• f32le - 32bit IEEE 754 floating number.
• f64le - 64bit IEEE 754 floating number.

Note that ivarle, uvarle is not available because it depends on the big endian order.

Resulting byte sizes

Bossam encodes the data without any metadata or specifier. If you specify 4 u16s, then it'll be encoded to 8 bytes.

However, arrays, strings, nullable types, varying integers have dynamic byte sizes.

Varying integers

Varying unsigned integers are encoded like utf-8 - the first byte decides the size of varying unsigned integer.

• If the byte starts with 0 - it means the size is 1.
• If the byte starts with 10 - it means the size is 2.
• If the byte starts with 110 - it means the size is 3.
• ...

Remaining bits of first byte is used to encode numbers.

Since Javascript supports up to 32bit integers, varying integers are limited to 32 bits.

• 7 bits encodes to 1 byte.
• 14 bits encodes to 2 bytes.
• 21 bits encodes to 3 bytes.
• 28 bits encodes to 4 bytes.
• 32 bits encodes to 5 bytes.

Varying signed integers encodes the MSB (sign) value at the LSB, then encodes it as varying unsigned integers.

Nullable types

Each nullable type takes 1/8 bytes - 8 nullable types are bundled to make the size smaller.

First nullable type uses the lowest bit, so the order is quite weird.

Order         01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16
Bit position   0  1  2  3  4  5  6  7  0  1  2  3  4  5  6  7
Byte position  0  0  0  0  0  0  0  0  1  1  1  1  1  1  1  1

Object structs and tuples put the nullable data in the front, however, arrays and tuples put the nullable data 'on-demand', which means that a byte appears every 8 types.

Strings and arrays

Strings and arrays encode the size info using uvar.

Adapters

Bossam includes 'adapter' code to use certain serialization format libraries with Bossam. By default, they're not included in the default namespace - you have to include them manually.

MessagePack

import compileFromCode, { createNamespace } from 'bossam';
import createMsgPackEncoder from 'bossam/lib/adapter/msgpack';
import msgpack from 'msgpack-lite';

const namespace = createNamespace();
namespace.MsgPack = createMsgPackEncoder(msgpack);
compileFromCode('struct Test = MsgPack', namespace);