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Binary Canonical Serialization (BCS) in Dart.

BCS - Binary Canonical Serialization #


This library implements Binary Canonical Serialization (BCS) in Dart.

Quickstart #

import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// registering types so we can use them
bcs.registerAlias('UID', BCS.ADDRESS);
bcs.registerEnumType('Option<T>', {
	'none': null,
	'some': 'T',
bcs.registerStructType('Coin', {
	'id': 'UID',
	'value': BCS.U64,

// deserialization: BCS bytes into Coin
final bcsBytes = bcs
	.ser('Coin', {
		'id': '0000000000000000000000000000000000000000000000000000000000000001',
		'value': BigInt.from(1000000),
final coin = bcs.de('Coin', bcsBytes, Encoding.hex);

// serialization: Object into bytes - an Option with <T = Coin>
final data = bcs.ser('Option<Coin>', { 'some': coin }).hex();

Description #

BCS defines the way the data is serialized, and the result contains no type information. To be able to serialize the data and later deserialize, a schema has to be created (based on the built-in primitives, such as address or u64). There's no tip in the serialized bytes on what they mean, so the receiving part needs to know how to treat it.

Configuration #

BCS constructor is configurable for the target. The following parameters are available for custom configuration:

parameter required description
vectorType + Defines the type of the vector (vector<T> in SuiMove, Vec<T> in Rust)
addressLength + Length of the built-in address type. 20 for SuiMove, 32 for Core Move
addressEncoding - Custom encoding for addresses - "hex" or "base64"
genericSeparators - Generic type parameters syntax, default is ('<', '>')
types - Define enums, structs and aliases at initialization stage
withPrimitives - Whether to register primitive types (true by default)
// Example: All options used
import 'package:bcs/bcs.dart';

final bcs = BCS(BcsConfig(
  vectorType: "vector<T>",
  addressLength: SUI_ADDRESS_LENGTH,
  addressEncoding: Encoding.hex,
  genericSeparators: ("<", ">"),
  types: BcsConfigTypes(
    // define schema in the initializer
    structs: {
      "User": {
        "name": BCS.STRING,
        "age": BCS.U8,
    enums: {},
    aliases: { "hex": BCS.HEX }
  withPrimitives: true

final bytes = bcs.ser("User", { "name": "Adam", "age": "30" }).base64();

For Sui Move there's already a pre-built configuration which can be used through the getSuiMoveConfig() call.

// Example: Sui Move Config
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// use bcs.ser() to serialize data
const val = [1, 2, 3, 4];
final ser = bcs.ser(["vector", BCS.U8], val).toBytes();

// use bcs.de() to deserialize data
final res = bcs.de(["vector", BCS.U8], ser);

assert(res.toString() == val.toString());

Similar configuration exists for Rust, the difference is the Vec<T> for vectors and address (being a special Move type) is not needed:

// Example: Rust Config
import 'package:bcs/bcs.dart';

final bcs = BCS(getRustConfig());
const val = [1, 2, 3, 4];
final ser = bcs.ser(["Vec", BCS.U8], val).toBytes();
final res = bcs.de(["Vec", BCS.U8], ser);

assert(res.toString() == val.toString());

Built-in types #

By default, BCS will have a set of built-in type definitions and handy abstractions; all of them are supported in Move.

Supported integer types are: u8, u16, u32, u64, u128 and u256. Constants BCS.U8 to BCS.U256 are provided by the library.

Type Constant Description
'bool' BCS.BOOL Boolean type (converts to true / false)
'u8'...'u256' BCS.U8 ... BCS.U256 Integer types
'address' BCS.ADDRESS Address type (also used for IDs in Sui Move)
'vector<T>' | 'Vec<T>' Only custom use, requires T Generic vector of any element
'string' BCS.STRING vector<u8> that (de)serializes to/from ASCII string
'hex-string' BCS.HEX vector<u8> that (de)serializes to/from HEX string
'base64-string' BCS.BASE64 vector<u8> that (de)serializes to/from Base64 string
'base58-string' BCS.BASE58 vector<u8> that (de)serializes to/from Base58 string

All of the type usage examples below can be used for bcs.de(<type>, ...) as well.

// Example: Primitive types
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// Integers
final _u8 = bcs.ser(BCS.U8, 100).toBytes();
final _u64 = bcs.ser(BCS.U64, BigInt.from(1000000)).hex();
final _u128 = bcs.ser(BCS.U128, "100000010000001000000").base64();

// Other types
final _bool = bcs.ser(BCS.BOOL, true).hex();
final _addr = bcs
  .ser(BCS.ADDRESS, "0000000000000000000000000000000000000001")
final _str = bcs.ser(BCS.STRING, "this is an ascii string").toBytes();

// Vectors (vector<T>)
final _u8_vec = bcs.ser(["vector", BCS.U8], [1, 2, 3, 4, 5, 6, 7]).toBytes();
final _bool_vec = bcs.ser(["vector", BCS.BOOL], [true, true, false]).toBytes();
final _str_vec = bcs
  .ser("vector<bool>", ["string1", "string2", "string3"])

// Even vector of vector (...of vector) is an option
final _matrix = bcs
  .ser("vector<vector<u8>>", [
    [0, 0, 0],
    [1, 1, 1],
    [2, 2, 2],

Ser/de and formatting #

To serialize and deserialize data to and from BCS there are two methods: bcs.ser() and bcs.de().

// Example: Ser/de and Encoding
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// bcs.ser() returns an instance of BcsWriter which can be converted to bytes or a string
BcsWriter bcsWriter = bcs.ser(BCS.STRING, "this is a string");

// writer.toBytes() returns a Uint8List
Uint8List bytes = bcsWriter.toBytes();

// custom encodings can be chosen when needed (just like Buffer)
String hex = bcsWriter.hex();
String base64 = bcsWriter.base64();
String base58 = bcsWriter.base58();

// bcs.de() reads BCS data and returns the value
// by default it expects data to be `Uint8List`
final str1 = bcs.de(BCS.STRING, bytes);

// alternatively, an encoding of input can be specified
final str2 = bcs.de(BCS.STRING, hex, Encoding.hex);
final str3 = bcs.de(BCS.STRING, base64, Encoding.base64);
final str4 = bcs.de(BCS.STRING, base58, Encoding.base58);

assert((str1 == str2) == (str3 == str4), "Result is the same");

Registering new types #

Tip: all registering methods start with bcs.register* (eg bcs.registerStructType).

Alias #

Alias is a way to create custom name for a registered type. It is helpful for fine-tuning a predefined schema without making changes deep in the tree.

// Example: Alias
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

bcs.registerAlias("ObjectDigest", BCS.BASE58);

// ObjectDigest is now treated as base58 string
final _b58 = bcs.ser("ObjectDigest", "Ldp").toBytes();

// we can override already existing definition to make it a HEX string
bcs.registerAlias("ObjectDigest", BCS.HEX);

final _hex = bcs.ser("ObjectDigest", "C0FFEE").toBytes();

Struct #

Structs are the most common way of working with data; in BCS, a struct is simply a sequence of base types.

// Example: Struct
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// register a custom type (it becomes available for using)
bcs.registerStructType("Balance", {
  "value": BCS.U64,

bcs.registerStructType("Coin", {
  "id": BCS.ADDRESS,
  // reference another registered type
  "balance": "Balance",

// value passed into ser function has to have the same
// structure as the definition
final _bytes = bcs
  .ser("Coin", {
    "id": "0x0000000000000000000000000000000000000000000000000000000000000005",
    "balance": {
      "value": BigInt.from(100000000),

Using Generics #

To define a generic struct or an enum, pass the type parameters. It can either be done as a part of a string or as an Array. See below:

// Example: Generics
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// Container -> the name of the type
// T -> type parameter which has to be passed in `ser()` or `de()` methods
// If you're not familiar with generics, treat them as type Templates
bcs.registerStructType(["Container", "T"], {
  "contents": "T"

// When serializing, we have to pass the type to use for `T`
bcs.ser(["Container", BCS.U8], {
  "contents": 100

// Reusing the same Container type with different contents.
// Mind that generics need to be passed as Array after the main type.
bcs.ser(["Container", [ "vector", BCS.BOOL ]], {
  "contents": [ true, false, true ]

// Using multiple generics - you can use any string for convenience and
// readability. See how we also use array notation for a field definition.
bcs.registerStructType(["VecMap", "Key", "Val"], {
  "keys": ["vector", "Key"],
  "values": ["vector", "Val"]

// To serialize VecMap, we can use:
bcs.ser(["VecMap", BCS.STRING, BCS.STRING], {
  "keys": [ "key1", "key2", "key3" ],
  "values": [ "value1", "value2", "value3" ]

Enum #

In BCS enums are encoded in a special way - first byte marks the order and then the value. Enum is an object, only one property of which is used; if an invariant is empty, null should be used to mark it (see Option<T> below).

// Example: Enum
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

bcs.registerEnumType("Option<T>", {
  "none": null,
  "some": "T",

bcs.registerEnumType("TransactionType", {
  "single": "vector<u8>",
  "batch": "vector<vector<u8>>",

// any truthy value marks empty in struct value
final _optionNone = bcs.ser("Option<TransactionType>", {
  "none": true,

// some now contains a value of type TransactionType
final _optionTx = bcs.ser("Option<TransactionType>", {
  "some": {
    "single": [1, 2, 3, 4, 5, 6],

// same type signature but a different enum invariant - batch
final _optionTxBatch = bcs.ser("Option<TransactionType>", {
  "some": {
    "batch": [
      [1, 2, 3, 4, 5, 6],
      [1, 2, 3, 4, 5, 6],

Inline (de)serialization #

Sometimes it is useful to get a value without registering a new struct. For that inline struct definition can be used.

Nested struct definitions are not yet supported, only first level properties can be used (but they can reference any type, including other struct types).

// Example: Inline Struct
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// Some value we want to serialize
final coin = {
  "id": "0000000000000000000000000000000000000000000000000000000000000005",
  "value": BigInt.from(1111333333222),

// Instead of defining a type we pass struct schema as the first argument
final coin_bytes = bcs.ser({ "id": BCS.ADDRESS, "value": BCS.U64 }, coin).toBytes();

// Same with deserialization
final coin_restored = bcs.de({ "id": BCS.ADDRESS, "value": BCS.U64 }, coin_bytes);

assert(coin["id"] == coin_restored["id"], "`id` must match");
assert(coin["value"].toString() == coin_restored["value"], "`value` must match");

Aligning schema with Move #

Currently, main applications of this library are:

  1. Serializing transactions and data passed into a transaction
  2. Deserializing onchain data for performance and formatting reasons
  3. Deserializing events

In this library, all of the primitive Move types are present as built-ins, however, there's a set of special types in Sui which can be simplified to a primitive.

// Definition in Move which we want to read in JS
module me::example {
    struct Metadata has store {
        name: std::ascii::String,

    struct ChainObject has key {
        id: sui::object::UID,
        owner: address,
        meta: Metadata
    // ...

Definition for the above should be the following:

// Example: Simplifying UID
import 'package:bcs/bcs.dart';

final bcs = BCS(getSuiMoveConfig());

// If there's a deep nested struct we can ignore Move type
// structure and use only the value.
bcs.registerAlias("UID", BCS.ADDRESS);

// Simply follow the definition onchain
bcs.registerStructType("Metadata", {
  "name": BCS.STRING,

// Same for the main object that we intend to read
bcs.registerStructType("ChainObject", {
  "id": "UID",
  "owner": BCS.ADDRESS,
  "meta": "Metadata",
See definition of the UID here
struct UID has store {
    id: ID

struct ID has store, copy, drop { bytes: address }

// { id: { bytes: '0x.....' } }

pub points


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Binary Canonical Serialization (BCS) in Dart.

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