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https://github.com/soramitsu/fearless-utils-Android

fearless-utils-Android
https://github.com/soramitsu/fearless-utils-Android

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# Fearless Wallet native Android (Kotlin/Java) library



Fearless Wallet utils Android is a native Android library to help developers build native mobile apps for Substrate-based networks, e.g. Polkadot, Kusama, and Westend.



# Table of contents



* [Bip39](#bip39)

* [JSON import/export](#json-import-export)

    + [Import](#import)

    + [Export](#export)

* [Extensions](#extensions)

    + [Hex](#hex)

    + [Hashing](#hashing)

* [Icon generation](#icon-generation)

* [Junction Decoder](#junction-decoder)

* [Runtime](#runtime)

* [Scale](#scale)

    + [Define a schema](#define-a-schema)

    + [Create and encode structs](#create-and-encode-structs)

    + [Decode and use structs](#decode-and-use-structs)

    + [Standart Data Types](#standart-data-types)

    + [Custom Data Types](#custom-data-types)

    + [Default values](#default-values)

    + [Nullable fields](#nullable-fields)

* [SS58](#ss58)

* [WSRPC](#wsrpc)



## Bip39



Bip39 is the algorithm which provides an opportunity to use a list of words, called mnemonic, instead of a raw 32 byte seed. Library provides `Bip39` class to work with mnemonics:



``` kotlin

val bip39 = Bip39()



val newMnemonic = bip39.generateMnemonic(length = MnemonicLength.TWELVE) // twelve words

val entropy = bip39.generateEntropy(newMnemonic)

val theSameMnemonic = bip39.generateMnemonic(entropy)



```

To generate a seed, a `passphrase` is needed. Technically, it is a decoded derivation path (see [Junction Decoder](#junction-decoder))



``` kotlin

val seed = bip39.generateSeed(entropy, passphrase)

```



## JSON import/export

Library provides support for decoding/encoding account information using JSON format, compatible with Polkadot.js



### Import

Using `JsonSeedDecoder` you can perform decoding of the imported JSON:



``` kotlin

val decoder = JsonSeedDecoder(..)



decoder.extractImportMetaData(myJson) // does not perform full decoding (skips secret decrypting). Faster

decoder.decode(myJson, password) // performs full decoding. Slower

```



### Export

Using `JsonSeedEncoder` you can generate JSON out of account information:



``` kotlin

val encoder = JsonSeedEncoder(..)



val json = encoder.generate(keypair, seed, password, name, encryptionType, genesis, addressByte)

```



## Extensions

Library provides several extensions, that implement most common operations.

### Hex



``` kotlin

fun ByteArray.toHexString(withPrefix: Boolean = false): String

fun String.fromHex(): ByteArray

fun String.requirePrefix(prefix: String): String

fun String.requireHexPrefix(): String

```



### Hashing



``` kotlin

fun ByteArray.xxHash128(): ByteArray

fun ByteArray.xxHash64(): ByteArray



fun ByteArray.blake2b512(): ByteArray

fun ByteArray.blake2b256(): ByteArray

fun ByteArray.blake2b128(): ByteArray



fun XXHash64.hash(bytes: ByteArray, seed: Long = 0): ByteArray

fun BCMessageDigest.hashConcat(bytes: ByteArray): ByteArray

fun XXHash64.hashConcat(bytes: ByteArray): ByteArray

```



## Icon generation



There's a support for default Polkadot.js icon generation using `IconGenerator`:



``` kotlin

val generator = IconGenerator()

val drawable =  generator.getSvgImage(accountId, sizeInPixels)

```



## Junction Decoder



`JunctionDecoder` provides support for derivation paths:



``` kotlin

val derivationPath: String = ...

val decoder = JunctionDecoder()



val passphrase = decoder.getPassword(derivationPath) // retrieve passphrase to use in entropy -> seed generation

val decodedPath = decoder.decodeDerivationPath(derivationPath)

```



## Runtime



You can create storage keys easily:



``` kotlin

val accountId: ByteArray = ..



val bondedKey = Module.Staking.Bonded.storageKey(bytes)

val accountInfoKey = Module.System.Account.storageKey(bytes)

```



If you're missing some specific service/module, you can define it by your own:



``` kotlin

 object Staking : Module("Staking") {



    object ActiveEra : Service(Staking, "ActiveEra") {



        override fun storageKey(storageArgs: Unit): String {

            return StorageUtils.createStorageKey(

                service = this,

                identifier = null

            )

        }

    }

}

```



## Scale



Library provides a convenient DSL to deal with scale encoding/decoding. Original codec reference: [Link](https://substrate.dev/docs/en/knowledgebase/advanced/codec).

### Define a schema



``` kotlin

object AccountData : Schema() {

    val free by uint128()

    val reserved by uint128()

    val miscFrozen by uint128()

    val feeFrozen by uint128()

}

```

### Create and encode structs



``` kotlin

val struct = AccountData { data ->

    data[AccountData.free] = BigDecimal("1")

    data[AccountData.reserved] = BigInteger("0")

    data[AccountData.miscFrozen] = BigInteger("0")

    data[AccountData.feeFrozen] = BigInteger("0")

}



val inHex = struct.toHexString() // encode

val asBytes = struct.toByteArray() // or as byte array

```

###  Decode and use structs



``` kotlin

val inHex = ...

val struct = AccountData.read(inHex)

val free = struct[AccountData.free]

```



### Standart Data Types

Library provides the support for the following data types:

* Numbers: `uint8`, `uint16`, `uint32`, `uint64`, `uint128`, `uint(nBytes)`, `compactInt`, `byte`, `long`

* Primitives: `bool`, `string`

* Arrays:

    * `sizedByteArray(n)` - only content is encoded/decoded), size is thus known in advance

    * `byteArray` - size can vary, so the size is also encoded/decoded alongside with the content

* Compound types:

    * `vector` - List of objects of the some data type

    * `optional` - Nullable container for other data type

    * `pair`

    * `enum(D1, D2, D3...)` - like union in C, stores only one value at once, but this value can have different data type

    * `enum` - for classical Kotlin enum



### Custom Data Types

If the decoding/encoding cannot be done using standart data types, you can create your own by extending `DataType`:

``` kotlin

object Delimiter : DataType() {

    override fun conformsType(value: Any?): Boolean {

        return value is Byte && value == 0

    }



    override fun read(reader: ScaleCodecReader): Byte {

        val read = reader.readByte()



        if (read != 0.toByte()) throw java.lang.IllegalArgumentException("Delimiter is not 0")



        return 0

    }



    override fun write(writer: ScaleCodecWriter, ignored: Byte) {

        writer.writeByte(0)

    }

}

```

And use it in your schema using `custom()` keyword:

``` kotlin

object CustomTypeTest : Schema() {

    val delimiter by custom(Delimiter)

}

````



### Default values

You can supply and default values for each field in the schema:

``` kotlin

object DefaultValues : Schema() {

    val bytes by sizedByteArray(length = 10, default = ByteArray(10))

    val text by string(default = "Default")

    val bigInteger by uint128(default = BigInteger.TEN)

}

```



### Nullable fields



By default, all fields are non null. However, you can use `optional()` to change the default behavior:

``` kotlin

object Person : Schema() {

    val friendName by string().optional() // friendName now is Field

}

```



## SS58



SS58 is an address format using in substate ecosystem. You can encode/decode address using `SS58Encoder`:



``` kotlin

val encoder = SS58Encoder()

val address = encoder.encode(publicKey, addressByte)

val accountId = encoder.decode(address)

```



## WSRPC



Library provides an implementation of `SocketService`, which simplifies communication with the node: it provides a seamless error recovery, subscription mechanism.



### Initialize socket

To create a socket service, you need to provide several parameters:



``` kotlin

val reconnector = Reconnector(..) // to configure reconnect strategy and scheduling executor

val requestExecutor = RequestExecutor(..) // to configure sending executor

val socketService = SocketService(gson, logger, websocketFactory, reconnector, requestExecutor)

```



### Use socket



``` kotlin

socketService.start(url) // async connect

socketService.stop() // all subscriptions/pending requests are cancelled

socketService.switchUrl(newUrl) // stops current connection and start a new one



// execute single request

socketService.executeRequest(runtimeRequest, deliveryType, object : SocketService.ResponseListener {

            override fun onNext(response: RpcResponse) {

                // success

            }



            override fun onError(throwable: Throwable) {

                // unrecoverable error happened

            }

        })



// subscribe to changes

socketService.subscribe(runtimeRequest, object : SocketService.ResponseListener {

                override fun onNext(response: SubscriptionChange) {

                   // change arrived

                }



                override fun onError(throwable: Throwable) {

                   // unrecoverable error happened

                }

            })

```



### Reconnect strategy



During setup of `Reconnector`, you can specify a `ReconnectStrategy`. There are several of them bundled with library:

* `ConstantReconnectStrategy`

* `LinearReconnectStrategy`

* `ExponentialReconnectStrategy`. This is a default reconnect strategy.



You can create your own strategy by implementing `ReconnectStrategy` interface.



### Delivery type



While sending a request, you can specify a `DeliveryType`. Currently, there are 3 of them:

* `AT_LEAST_ONCE` - attempts to send request until succeeded. This is a default delivery type.

* `AT_MOST_ONCE` - send request once, reports error if attempt failed.

* `ON_RECONNECT` - similar to `AT_LEAST_ONCE`, but remembers request and sends it on each reconnect. Currently used for subscription initiation.



### Using with coroutines



Library has a out-of-box support for coroutines:



``` kotlin

scope.launch {

    val response = socketService.executeAsync(request, deliveryType) // suspend function

}



socketService.subscriptionFlow(request).onEach { change ->

        // do stuff here

}.launchIn(scope)

```



### Mappers



The mappers for most common types are provided:

* `scale` - For scale-encoded values

* `scaleCollection` - For list of scale-encoded values

* `pojo` - for json values

* `pojoList` - for list of json values



All mappers return a `nullable` result by default. You can add `nonNull()` modifier to change this behavior. In case of null result, the `RpcException` will be thrown.



#### Usage



``` kotlin

scale().nonNull().map(response, gson)



// or with coroutines adapter

socketService.executeAsync(request, deliveryType, mapper = scale().nonNull())

```