Light Client for Exonum Blockchain
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A JavaScript library to work with Exonum blockchain from browser and Node.js.
Used to sign transactions before sending to blockchain and verify blockchain responses using cryptographic proofs.
Contains numerous helper functions. Find out more information about the [architecture and tasks][docs:clients] of light clients in Exonum.
If you are using Exonum in your project and want to be listed on our website & GitHub list — write
us a line to
Library compatibility with Exonum core:
| JavaScript light client | Exonum core |
|---|---|
| 0.18.4 | 1.0.* |
| 0.18.3 | 1.0.0-rc.1 |
| 0.17.1 | 0.12.* |
| 0.16.9 | 0.11.* |
| 0.16.9 | 0.10.* |
| 0.13.0 | 0.9.* |
| 0.10.2 | 0.8.* |
| 0.9.0 | 0.7.* |
| 0.6.1 | 0.6.* |
| 0.6.1 | 0.5.* |
| 0.3.0 | 0.4.0 |
| 0.3.0 | 0.3.0 |
| 0.2.0 | 0.2.0 |
| 0.1.1 | 0.1.* |
* Getting started
* Data types
* Hash
* Signature
* Sign data
* Verify signature
* Transactions
* Define transaction
* Sign transaction
* Send transaction
* Send multiple transactions
* Cryptographic proofs
* Merkle tree proof
* Map proof
* Integrity checks
* Verify block
* Verify table
* Built-in structures
* Helpers
* Generate key pair
* Get random number
* Converters
* Hexadecimal to Uint8Array
* Hexadecimal to String
* Uint8Array to Hexadecimal
* Binary String to Uint8Array
* Binary String to Hexadecimal
* String to Uint8Array
* Contributing
* Coding standards
* Test coverage
* Changelog
* License
There are several options to include light client library in the application:
The preferred way is to install Exonum Client as a [package][npmjs] from npm registry:
``sh`
npm install exonum-client
Otherwise you can download the source code from GitHub and compile it before use in browser.
Include in browser:
`html`
Usage in Node.js:
`javascript`
let Exonum = require('exonum-client')
Exonum uses [protobufjs][protobufjs] library to serialize structured data into [protobuf][protobuf] format.
Each transaction is signed before sending into blockchain.
Before the transaction is signed it is converted into byte array under the hood.
The data received from the blockchain should be converted into byte array under the hood
before it will be possible to verify proof of its existence using cryptographic algorithm.
Developer can both define data structures on the fly or use precompiled stubs with data structures.
To define Protobuf structures use [protobufjs][protobufjs] library.
Example:
`javascript`
const MessageSchema = new Type('CustomMessage')
.add(new Field('balance', 1, 'uint32'))
.add(new Field('name', 2, 'string'))
const Message = Exonum.newType(MessageSchema)
Exonum.newType function requires a single argument of protobuf.Type type.
Exonum uses [cryptographic hashes][docs:glossary:hash] of certain data for transactions and
proofs.
Different signatures of the hash function are possible:
`javascript`
Exonum.hash(data, type)
type.hash(data)
| Argument | Description | Type |
|---|---|---|
| data | Data to be processed using a hash function. | Object |
| type | Definition of the data type. | Custom data type or transaction. |
An example of hash calculation:
`javascript
// Define a data structure
const Message = new Type('User')
.add(new Field('balance', 1, 'uint32'))
.add(new Field('name', 2, 'string'))
// Define a data type
const User = Exonum.newType(Message)
// Data to hash
const data = {
balance: 100,
name: 'John Doe'
}
// Get a hash
const hash = User.hash(data)
`
It is also possible to get a hash from byte array:
`javascript`
Exonum.hash(buffer)
| Argument | Description | Type |
|---|---|---|
| buffer | Byte array. | Array or Uint8Array. |
An example of byte array hash calculation:
`javascript`
const arr = [8, 100, 18, 8, 74, 111, 104, 110, 32, 68, 111, 101]
const hash = Exonum.hash(arr)
The procedure for signing data using signing key pair
and verifying of obtained signature is commonly used
in the process of data exchange between the client and the service.
*Built-in Exonum.keyPair helper function can be used
to generate a new random signing key pair.*
The signature can be obtained using the secret key of the signing pair.
There are three possible signatures of the sign function:
`javascript`
Exonum.sign(secretKey, data, type)
type.sign(secretKey, data)
Exonum.sign(secretKey, buffer)
| Argument | Description | Type |
|---|---|---|
| secretKey | Secret key as hexadecimal string. | String |Object
| data | Data to be signed. | |Array
| type | Definition of the data type. | Custom data type. |
| buffer | Byte array. | or Uint8Array. |
The sign function returns value as hexadecimal String.
The signature can be verified using the author's public key.
There are two possible signatures of the verifySignature function:
`javascript`
Exonum.verifySignature(signature, publicKey, data, type)
type.verifySignature(signature, publicKey, data)
| Argument | Description | Type |
|---|---|---|
| signature | Signature as hexadecimal string. | String |String
| publicKey | Author's public key as hexadecimal string. | |Object
| data | Data that has been signed. | |
| type | Definition of the data type. | Custom data type. |
The verifySignature function returns value of Boolean type.
An example of signature creation and verification:
`javascript
// Define a data structure
const Message = new Type('User')
.add(new Field('balance', 1, 'uint32'))
.add(new Field('name', 2, 'string'))
const User = Exonum.newType(Message)
// Define a signing key pair
const keyPair = Exonum.keyPair()
// Data that has been hashed
const data = {
balance: 100,
name: 'John Doe'
}
// Signature obtained upon signing using secret key
const signature = Exonum.sign(keyPair.secretKey, data, User)
// Verify the signature
const result = Exonum.verifySignature(signature, keyPair.publicKey, data, User)
`
Transaction in Exonum is an operation to change the data stored in blockchain.
Transaction processing rules is a part of business logic implemented
in a [service][docs:architecture:services].
Sending data to the blockchain from a light client consist of 3 steps:
1. Describe the fields of transaction using custom data types
2. Sign data of transaction using signing key pair
3. Send transaction to the blockchain
Read more about [transactions][docs:architecture:transactions] in Exonum,
or see the example of their usage.
An example of a transaction definition:
`javascript
const Transaction = new Type('CustomMessage')
.add(new Field('to', 2, 'string'))
.add(new Field('amount', 3, 'uint32'))
const SendFunds = new Exonum.Transaction({
schema: Transaction,
service_id: 130,
method_id: 0
})
`
Exonum.Transaction constructor requires a single argument of Object type with
the next structure:
| Property | Description | Type |
|---|---|---|
| schema | Protobuf data structure. | Object |Number
| service_id | [Service ID][docs:architecture:serialization:service-id]. | |Number
| method_id | [Method ID][docs:architecture:serialization:message-id]. | |
schema structure is identical to that of custom data type.
An example of a transaction signing:
`javascript
// Signing key pair
const keyPair = Exonum.keyPair()
// Transaction data to be signed
const data = {
from: 'John',
to: 'Adam',
amount: 50
}
// Create a signed transaction
const signed = SendFunds.create(data, keyPair)
`
To submit transaction to the blockchain send function can be used.
`javascript`
Exonum.send(explorerBasePath, transaction, attempts, timeout)
| Property | Description | Type |
|---|---|---|
| explorerBasePath | API address of transaction explorer on a blockchain node. | String |String
| transaction | Signed transaction bytes. | , Uint8Array or Array-like |0
| attempts | Number of attempts to check transaction status. Pass in case you do not need to verify if the transaction is accepted to the block. Optional. Default value is 10. | Number |500
| timeout | Timeout between attempts to check transaction status. Optional. Default value is . | Number |
The send function returns a Promise with the transaction hash.
The promise resolves when the transaction is committed (accepted to a block).
An example of a transaction sending:
`javascript`
// Define transaction explorer address
const explorerBasePath = 'http://127.0.0.1:8200/api/explorer/v1/transactions'
const transactionHash = await Exonum.send(explorerBasePath, signed.serialize())
To submit multiple transactions to the blockchain sendQueue function can be used.
Transactions will be sent in the order specified by the caller.
Each transaction from the queue will be sent to the blockchain only after the previous transaction
is committed.
`javascript`
Exonum.sendQueue(explorerBasePath, transactions, attempts, timeout)
| Property | Description | Type |
|---|---|---|
| explorerBasePath | API address of transaction explorer on a blockchain node. | String |Array
| transactions | List of transactions. | |0
| attempts | Number of attempts to check each transaction status. Pass in case you do not need to verify if the transactions are accepted to the block. Optional. Default value is 10. | Number |500
| timeout | Timeout between attempts to check each transaction status. Optional. Default value is . | Number |
The sendQueue function returns a Promise with an array of transaction hashes.
The promise resolves when all transactions are committed.
A cryptographic proof is a format in which a Exonum node can provide sensitive data from a blockchain.
These proofs are based on [Merkle trees][docs:glossary:merkle-tree] and their variants.
Light client library validates the cryptographic proof and can prove the integrity and reliability
of the received data.
Read more about design of [cryptographic proofs][docs:advanced:merkelized-list] in Exonum.
`javascript`
const proof = new Exonum.ListProof(json, ValueType)
console.log(proof.entries)
The ListProof class is used to validate proofs for Merkelized lists.
| Argument | Description | Type |
|---|---|---|
| json | The JSON presentation of the proof obtained from a full node. | Object |
| ValueType | Data type for values in the Merkelized list. | Custom data type |
The returned object has the following fields:
| Field | Description | Type |
|---|---|---|
| merkleRoot | Hexadecimal hash of the root of the underlying Merkelized list | String |Array<{ index: number, value: V }>
| entries | Elements that are proven to exist in the list, together with their indexes | |Number
| length | List length | |
See an example of using a ListProof.
`javascript`
const proof = new Exonum.MapProof(json, KeyType, ValueType)
console.log(proof.entries)
The MapProof class is used to validate proofs for Merkelized maps.
| Argument | Description | Type |
|---|---|---|
| json | The JSON presentation of the proof obtained from a full node. | Object |
| KeyType | Data type for keys in the Merkelized map. | Custom or built-in data type |
| ValueType | Data type for values in the Merkelized map. | Custom data type |
Keys in a map proof can either be hashed (which is the default option)
or raw. To obtain a raw version for KeyType, use MapProof.rawKey(KeyType).
The key type is determined by the service developer when the service schema
is created. Raw keys minimize the amount of hashing, but require that the underlying type
has fixed-width binary serialization.
The returned object has the following fields:
| Field | Description | Type |
|---|---|---|
| merkleRoot | Hexadecimal hash of the root of the underlying Merkelized map | String |Set
| missingKeys | Set of keys which the proof asserts as missing from the map | |Map
| entries | Map of key-value pairs that the are proven to exist in the map | |
See an example of using a MapProof.
`javascript`
Exonum.verifyBlock(data, validators)
Each new block in Exonum blockchain is signed by [validators][docs:glossary:validator].
To prove the integrity and reliability of the block, it is necessary to verify their signatures.
The signature of each validator are stored in the precommits.
The verifyBlock function throws an error if a block is invalid.
| Argument | Description | Type |
|---|---|---|
| data | Structure with block and precommits. | Object |Array
| validators | An array of validators public keys as a hexadecimal strings. | |
`javascript`
Exonum.verifyTable(proof, stateHash, fullTableName)
Verify table existence in the root tree.
Returns root hash for the table as hexadecimal String.
| Argument | Description | Type |
|---|---|---|
| proof | The JSON presentation of the proof obtained from a full node. | Object |String
| stateHash | Hash of current blockchain state stored in each block. | |token.wallets
| fullTableName | Name of the table, such as . | String |
The library exports Protobuf declarations from the core crate.
Consult Protobuf files included into the library for more details.
`javascript`
const pair = Exonum.keyPair()
`javascript`
{
publicKey: "...", // 32-byte public key
secretKey: "..." // 64-byte secret key
}
Exonum.keyPair function generates a new random [Ed25519][docs:glossary:digital-signature]
signing key pair using the [TweetNaCl][tweetnacl:key-pair] cryptographic library.
`javascript`
const rand = Exonum.randomUint64()
Exonum.randomUint64 function generates a new random Uint64 number of cryptographic quality
using the [TweetNaCl][tweetnacl:random-bytes] cryptographic library.
#### Hexadecimal to Uint8Array
`javascript`
const hex = '674718178bd97d3ac5953d0d8e5649ea373c4d98b3b61befd5699800eaa8513b'
Exonum.hexadecimalToUint8Array(hex)
#### Hexadecimal to String
`javascript`
const hex = '674718178bd97d3ac5953d0d8e5649ea373c4d98b3b61befd5699800eaa8513b'
Exonum.hexadecimalToBinaryString(hex)
#### Uint8Array to Hexadecimal
`javascript`
const arr = new Uint8Array([103, 71, 24, 23, 139, 217, 125, 58, 197, 149, 61])
Exonum.uint8ArrayToHexadecimal(arr)
#### Uint8Array to Binary String
`javascript`
const arr = new Uint8Array([103, 71, 24, 23, 139, 217, 125, 58, 197, 149, 61])
Exonum.uint8ArrayToBinaryString(arr)
#### Binary String to Uint8Array
`javascript`
const str = '0110011101000111000110000001011110001011110110010111110100111010'
Exonum.binaryStringToUint8Array(str)
#### Binary String to Hexadecimal
`javascript`
const str = '0110011101000111000110000001011110001011110110010111110100111010'
Exonum.binaryStringToHexadecimal(str)
#### String to Uint8Array
`javascript`
const str = 'Hello world'
Exonum.stringToUint8Array(str)
The contributing to the Exonum Client is based on the same principles and rules as
[the contributing to exonum-core][contributing].
The coding standards are described in the .eslintrc file.
To help developers define and maintain consistent coding styles between different editors and IDEs
we used .editorconfig` configuration file.
All functions must include relevant unit tests.
This applies to both of adding new features and fixing existed bugs.
Detailed changes for each release are documented in the CHANGELOG file.
Light Clients for [Java][lc-java] and [Python][lc-python]
Exonum Client is licensed under the Apache License (Version 2.0). See LICENSE for details.
[docs:clients]: https://exonum.com/doc/version/latest/architecture/clients
[docs:architecture:services]: https://exonum.com/doc/version/latest/architecture/services
[docs:architecture:serialization]: https://exonum.com/doc/version/latest/architecture/serialization
[docs:architecture:serialization:network-id]: https://exonum.com/doc/version/latest/architecture/serialization/#etwork-id
[docs:architecture:serialization:protocol-version]: https://exonum.com/doc/version/latest/architecture/serialization/#protocol-version
[docs:architecture:serialization:service-id]: https://exonum.com/doc/version/latest/architecture/serialization/#service-id
[docs:architecture:serialization:message-id]: https://exonum.com/doc/version/latest/architecture/serialization/#message-id
[docs:architecture:transactions]: https://exonum.com/doc/version/latest/architecture/transactions
[docs:advanced:merkelized-list]: https://exonum.com/doc/version/latest/advanced/merkelized-list
[docs:glossary:digital-signature]: https://exonum.com/doc/version/latest/glossary/#digital-signature
[docs:glossary:hash]: https://exonum.com/doc/version/latest/glossary/#hash
[docs:glossary:blockchain-state]: https://exonum.com/doc/version/latest/glossary/#blockchain-state
[docs:glossary:merkle-tree]: https://exonum.com/doc/version/latest/glossary/#merkle-tree
[docs:glossary:validator]: https://exonum.com/doc/version/latest/glossary/#validator
[npmjs]: https://www.npmjs.com/package/exonum-client
[gitter]: https://gitter.im/exonum/exonum
[twitter]: https://twitter.com/ExonumPlatform
[newsletter]: https://exonum.com/#newsletter
[contributing]: https://exonum.com/doc/version/latest/contributing/
[is-safe-integer]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isSafeInteger
[vector-structure]: https://doc.rust-lang.org/std/vec/struct.Vec.html
[tweetnacl:key-pair]: https://github.com/dchest/tweetnacl-js#naclsignkeypair
[tweetnacl:random-bytes]: https://github.com/dchest/tweetnacl-js#random-bytes-generation
[protobuf]: https://developers.google.com/protocol-buffers/
[protobufjs]: https://www.npmjs.com/package/protobufjs
[lc-java]: https://github.com/exonum/exonum-java-binding/tree/master/exonum-light-client
[lc-python]: https://github.com/exonum/exonum-python-client