# Low-Level API

These are advanced, low-level API features that should, for most people not be necessary to worry about.

They are lightly documented here, and in the future will have more documentation, but the emphasis at this point is documenting the more common methods.

## ABI Coder

### Creating Instances

new ethers . utils . AbiCoder ( [ coerceFunc ] )
  Create a new ABI Coder object, which calls coerceFunc for each parsed value during decoding. The coerceFunc should have the signature: `function(type, value)`.

### Static Properties

ethers . utils . defaultAbiCoder
  A default instance of the coder which can be used, which has a coerceFunc which will call `toNumber()` on BigNumbers whose type is less than 53 bits and is safe for JavaScript Number instances.

### Prototype

prototype . encode ( types , values ) => hex
  Returns a hex string of the values encoded as the types. Throws if a value is invalid for the type.
prototype . decode ( types , data ) => Result
  Returns an Object by parsing data assuming types, with each parameter accessible as a positional parameters. Throws if data is invalid for the types.

## HDNode

A Hierarchical Deterministic Wallet represents a large tree of private keys which can reliably be reproduced from an initial seed. Each node in the tree is represented by an HDNode which can be descended into.

A mnemonic phrase represents a simple way to generate the initial seed.

See the BIP 32 Specification to learn more about HD Wallets and hardened vs non-hardened nodes.

See the BIP 39 Specification to learn more about Mnemonic Phrases.

### Creating Instances

ethers . utils . HDNode . fromMnemonic ( mnemonic ) => HDNode
  Create an HDNode from a mnemonic phrase.
ethers . utils . HDNode . fromSeed ( seed ) => HDNode
  Create an HDNode from a seed.
ethers . utils . HDNode . fromExtendedKey ( extendedKey ) => HDNode
  Create an HDNode from an extended private key (xpriv) or extended public key (xpub).

### Prototype

prototype . privateKey
  The hex string private key for this node.
prototype . publicKey
  The (compressed) public key for this node.
prototype . chainCode
  The chain code for this node.
prototype . index
  The index (from the parent) of this node (0 for the master node).
prototype . depth
  The depth within the hierarchy of this node.
prototype . fingerprint
  The fingerprint of this node. This can be used to identify a node, but wallets should handle collisions.
prototype . parentFingerprint
  The fingerprint of this node’s parent (or 0x00000000 for the master node).
prototype . extendedKey
  The extended private key (xpriv) of the node, or the extended public key (xpub) if the node has been neutered.

### Deriving Child and Neutered Nodes

prototype . derivePath ( path ) => HDNode
  Derive the path from this node. Path is slash (/) delimited path components. The first component may be “m” for master (which enforces the starting node is in fact a master node) and each subsequent path component should be a positive integer (up to 31 bits), which can optionally include an apostrophe (‘) to indicate hardened derivation for that path components. See below for some examples.
prototype . neuter ( ) => HDNode
  Returns a new instance of the node without a private key. This can be used to derive an extended public key. See the BIP32 standard for more details.

### Static Methods

ethers . utils . HDNode . mnemonicToEntropy ( mnemonic ) => hex
  Convert a mnemonic to its binary entropy. (throws an error if the checksum is invalid)
ethers . utils . HDNode . entropyToMnemonic ( entropy ) => string
  Convert the binary entropy to the mnemonic phrase.
ethers . utils . HDNode . mnemonicToSeed ( mnemonic ) => hex
  Compute the BIP39 seed from mnemonic.
ethers . utils . HDNode . isValidMnemonic ( string ) => boolean
  Returns true if and only if the string is a valid mnemonic (including the checksum)

HDNode derivation

    let HDNode = require('ethers').utils.HDNode;

    let mnemonic = "radar blur cabbage chef fix engine embark joy scheme fiction master release";

    let masterNode = HDNode.fromMnemonic(mnemonic);

    let standardEthereum = masterNode.derivePath("m/44'/60'/0'/0/0");

    // Get the extended private key
    let xpriv = node.extendedKey;

    // Get the extended public key
    let xpub = node.neuter().extnededKey;

## Interface

The Interface Object is a meta-class that accepts a Solidity (or compatible) Application Binary Interface (ABI) and populates functions to deal with encoding and decoding the parameters to pass in and results returned.

### Creating an Instance

new ethers . utils . Interface ( abi )
  Returns a new instance and populates the properties with the ABI constructor, methods and events. The abi may be either a JSON string or the parsed JSON Object.

### Prototype

prototype . abi
  A copy of the ABI is returned, modifying this object will not alter the ABI.
prototype . deployFunction
  A DeployDesciption for the constructor defined in the ABI, or the default constructor if omitted.
prototype . events
  An object of all the events available in the ABI, by name and signature, which map to a EventDescription.
prototype . functions
  An object of all the functions available in the ABI, by name and signature, which map to a FunctionDescription.

### Parsing Objects

prototype . parseTransaction ( transaction ) => TransactionDescription
  Parse transaction and return a description of the call it represents.
prototype . parseLog ( log ) => LogDescription
  Parse log and return a description of the event logs it represents.

### Object Test Functions

prototype . isInterface ( value ) => boolean
  Returns true if value is an Interface.
prototype . isIndexed ( value ) => boolean
  Returns true if value is a dynamic Indexed value, which means the actual value of value is the hash of the actual value.

### Descriptions

Deploy Description

> name | description
> --- | ---
> inputs | The description of the constructor input parameters
> payable | Whether the constructor can accept Ether
> encode(params) | A function which encodes params

Event Description

> name | description
> --- | ---
> name | The event name (e.g. “Transfer”)
> signature | The event signature (e.g. “Transfer(address indexed,address indexed,uint256)”)
> inputs | The event input parameters
> anonymous | Whether the event is an anonymous event
> topic | The topic for this event signature
> encodeTopics(params) | A function which computes filter topics for given params
> decode(data, topics) | A function to parse the log result data and topics

Function Description

> name | description
> --- | ---
> name | The method name (e.g. “transfer”)
> type | The method type (i.e. “call” or “transaction”)
> signature | The method signature (e.g. “transfer(address to, uint256 amount)”)
> sighash | The signature hash of the signature (4 bytes)
> inputs | The description of the method input parameters
> outputs | The description of the method output parameters
> payable | Whether the method can accept Ether
> gas | The maximum gas this method will consume (null if unknown)
> encode(params) | A function which encodes params
> decode(data) | A function which decodes the result data

Log Description

> name | description
> --- | ---
> name | The event name (e.g. “Transfer”)
> signature | The event signature (e.g. “Transfer(address indexed,address indexed,uint256)”)
> topics | The event topics
> decode(data, topics) | A function to parse the logs
> values | The decoded values of the event

Transaction Description

> name | description
> --- | ---
> name | The method name (e.g. “transfer”)
> args | The arguments passed to the method
> signature | The method signature (e.g. “transfer(address to, uint256 amount)”)
> sighash | The signature hash of the signature (4 bytes)
> decode(data) | A function to parse the result data
> value | The value (in wei) of the transaction

## Provider (Sub-Classing)

See the Provider API for more common usage. This documentation is designed for developers that are sub-classing BaseProvider.

### Static Methods

BaseProvider . inherits ( childProvider ) => void
  Set up childProvider as an provider, inheriting the parent prototype and set up a prototype.inherits on the childProvider.

### Prototype

prototype . perform ( method , params ) => Promise<any>
  The only method needed to override in a subclass. All values are sanitized and defaults populated in params and the result is sanitized before returning. Returns a Promise, see the example below for overview of method and params.

BaseProvider Sub-Class Stub

    const ethers = require('ethers');

    // The new provider Object
    function DemoProvider(something) {

        let network = getNetworkSomehow()

        // The super must be called with either a Network or a Promise
        // that resolves to a Network
        ethers.providers.BaseProvider.call(this, network);

        ethers.utils.defineReadOnly(this, 'somethingElse', somethingElse);
    }

    // Inherit the Provider
    ethers.providers.BaseProvider.inherits(DemoProvider);

    // Override perform
    DemoProvider.prototype.perform = function(method, params) {
        switch (method) {
            case 'getBlockNumber':
                // Params:
                // { }

            case 'getGasPrice':
                // Params:
                // { }

            case 'getBalance':
                // Params:
                // {
                //     address: address,
                //     blockTag: blockTag
                // }

            case 'getTransactionCount':
                // Params:
                // {
                //     address: address,
                //     blockTag: blockTag
                // }

            case 'getCode':
                // Params:
                // {
                //     address: address,
                //     blockTag: blockTag
                // }

            case 'getStorageAt':
                // Params:
                // {
                //     address: address,
                //     position: hexString,
                //     blockTag: blockTag
                // }

            case 'sendTransaction':
                // Params:
                // {
                //     signedTransaction: hexString
                // }

            case 'getBlock':
                // Params:
                // Exactly one of the following will be specified, the other will be absent
                // {
                //     blockHash: blockHash,
                //     blockTag: blockTag
                // }

            case 'getTransaction':
                // Params:
                // {
                //     transactionHash: hexString
                // }

            case 'getTransactionReceipt':
                // Params:
                // {
                //     transactionHash: hexString
                // }

            case 'call':
                // Params:
                // {
                //     transaction: See Transaction Requests (on Providers API)
                // }

            case 'estimateGas':
                // Params:
                // {
                //     transaction: See Transaction Requests (on Providers API)
                // }

            case 'getLogs':
                // Params:
                // {
                //    address: address,
                //    fromBlock: blockTag,
                //    toBlock: blockTag,
                //    topics: array (possibly nested) of topics
                // }

            default:
                break;
        }

        return Promise.reject(new Error('not implemented - ' + method));
    };

## Recursive-Length Prefixed Encoding (RLP)

This encoding method is used internally for several aspects of Ethereum, such as encoding transactions and determining contract addresses. For most developers this should not be necessary to use.

RLP can encode nested arrays, with data as hex strings and Uint8Array (or other non-Array arrayish objects). A decoded object will always have data represented as hex strings and Arrays.

See: https://github.com/ethereum/wiki/wiki/RLP

### Static Methods

ethers . utils . RLP . encode( object ) => hex
  Encodes an object as an RLP hex string. (throws an Error if the object contains invalid items)
ethers . utils . RLP . decode( hexStringOrArrayish ) => any
  Decode hexStringOrArrayish into the encoded object. (throws an Error if invalid RLP-coded data)

RLP coder

    let object = [ ["0x42"], "0x1234", [ [], [] ] ];

    let encoded = ethers.utils.RLP.encode(object);
    console.log(encoded);
    // 0xc8c142821234c2c0c0

    let decoded = ethers.utils.RLP.decode(encoded);
    console.log(decoded);
    // [ [ '0x42' ], '0x1234', [ [], [] ] ]

## Signing Key

The SigningKey interface provides an abstraction around the secp256k1 elliptic curve cryptography library, which signs digests, computes public keys from private keys and performs ecrecover which computes a public key from a digest and a signature.

### Creating Instances

new ethers . utils . SigningKey ( privateKey )
  Create a new SigningKey and compute the corresponding public key and address. A private key may be a any hex string or an Arrayish representing 32 bytes.

### Prototype

prototype . address
  The Ethereum checksum address for this key pair.
prototype . privateKey
  The private key for the key pair.
prototype . publicKey
  The uncompressed public key for the key pair.

### Cryptographic Operations

prototype . signDigest ( messageDigest ) => Signature
  The expanded-format Signature for the digests, signed by this key pair.
prototype . computeSharedSecret ( publicOrPrivateKey ) => hex
  Compute the ECDH shared secret from this keys private key and the publicOrPrivateKey. In is generally considered good practice to further hash this value before using it as a key.

Signing Key

    const ethers = require('ethers');

    let privateKey = '0x0123456789012345678901234567890123456789012345678901234567890123';
    let signingKey = new ethers.utils.SigningKey(privateKey);

    console.log('Address: ' + signingKey.address);
    // "Address: 0x14791697260E4c9A71f18484C9f997B308e59325"

    let message = "Hello World";
    let messageBytes = ethers.utils.toUtf8Bytes(message);
    let messageDigest = ethers.utils.keccak256(messageBytes);

    console.log("Digest: " + messageDigest);
    // "Digest: 0x592fa743889fc7f92ac2a37bb1f5ba1daf2a5c84741ca0e0061d243a2e6707ba"

    let signature = signingKey.signDigest(messageDigest);

    console.log(signature);
    // {
    //    recoveryParam: 0,
    //    r: "0x79f56f3422dc67f57b2aeeb0b20295a99ec90420b203177f83d419c98beda7fe",
    //    s: "0x1a9d05433883bdc7e6d882740f4ea7921ef458a61b2cfe6197c2bb1bc47236fd"
    // }

    let recovered = ethers.utils.recoverAddress(messageDigest, signature);

    console.log("Recovered: " + recovered);
    // "Recovered: 0x14791697260E4c9A71f18484C9f997B308e59325"

    let publicKey = signingKey.publicKey;

    console.log('Public Key: ' + publicKey);
    // "Public Key: 0x026655feed4d214c261e0a6b554395596f1f1476a77d999560e5a8df9b8a1a3515"

    let compressedPublicKey = ethers.utlis.computePublicKey(publicKey, true);
    let uncompressedPublicKey = ethers.utils.computePublicKey(publicKey, false);

    console.log(compressedPublicKey);
    // "0x026655feed4d214c261e0a6b554395596f1f1476a77d999560e5a8df9b8a1a3515"

    console.log(uncompressedPublicKey);
    // "0x046655feed4d214c261e0a6b554395596f1f1476a77d999560e5a8df9b8a1a35" +
    //   "15217e88dd05e938efdd71b2cce322bf01da96cd42087b236e8f5043157a9c068e"

    let address = ethers.utils.computeAddress(publicKey);

    console.log('Address: ' + address);
    // "Address: 0x14791697260E4c9A71f18484C9f997B308e59325"