# 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.

## 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 represended 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 . HDNode . fromMnemonic ( mnemonic )
  Create an HDNode from a mnemonic phrase.
ethers . HDNode . fromSeed ( seed )
  Create an HDNode from a seed.

### 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 th hierarchy of this node.
prototype . derivePath ( path )
  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 infact 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.

### Static Methods

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

### Examples

    var HDNode = require('ethers').HDNode;

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

    var masterNode = HDNode.fromMnemonic(mnemonic);

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

## 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 . 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 . functions
  An object of the functions available in the ABI, by name. (collissions are dropped)
prototype . events
  An object of the events available in the ABI, by name. (collisions are dropped)
prototype . deployFunction ( bytecode [ , params… ])
  The function to deploy the contract (compiled to bytecode) to the network, passing params into the ABI constructor. If the ABI does not have a constructor, a default one is generated.

### Examples

Creating an Interface Instance

    var Interface = require('ethers').Interface;

    var abi = [
        {
            constant: true,
            inputs:[],
            name: "getValue",
            outputs:[ { name: "value", type: "string"} ],
            type: "function"
        },
        {
            constant: false,
            inputs: [ { name: "value", type: "string" } ],
            name: "setValue",
            outputs: [],
            type: "function"
        },
        {
            anonymous: false,
            inputs:[
                { indexed:false, name: "oldValue", type: "string" },
                { indexed:false, name: "newValue", type: "string" }
            ],
            name: "valueChanged",
            type: "event"
        }
    ];

    // NOTE: "interface" is a reserved keyword in JavaScript

    var iface = new Interface(abi)

Call (Constant) Functions

    var getValueInfo = iface.functions.getValue();

    console.log(getValueInfo);
    // {
    //     name: "getValue",
    //     signature: "getValue()",
    //     data: "0x20965255",
    //     parse: function(result),
    //     type: "call"
    // }

    // Here is the result of:
    // provider.call({
    //    to: "0x954De93D9f1Cd1e2e3AE5964F614CDcc821Fac64",
    //    data: getValue.data,
    // }).then(function(result) {
    //    console.log(result);
    // });
    var getDataResult = "0x0000000000000000000000000000000000000000000000000000000000000020" +
                          "000000000000000000000000000000000000000000000000000000000000000b" +
                          "48656c6c6f20576f726c64000000000000000000000000000000000000000000"

     console.log(getValueInfo.parse(getDataResult));
     // {
     //    0: "Hello World",
     //    value: "Hello World",
     //    length: 1
     // }

Transaction (Non-Constant) Functions

    var setValueInfo = iface.functions.setValue("Foobar!");

    console.log(setValueInfo);
    // {
    //     name: "setValue",
    //     signature: "setValue(string)",
    //     data: "0x93a09352" +
    //             "0000000000000000000000000000000000000000000000000000000000000020" +
    //             "0000000000000000000000000000000000000000000000000000000000000007" +
    //             "466f6f6261722100000000000000000000000000000000000000000000000000"
    //     type: "transaction"
    // }

    // To send this to the network, you would sign and send the transaction:
    // {
    //     to: "0x954De93D9f1Cd1e2e3AE5964F614CDcc821Fac64",
    //     data: setValueInfo.data,
    //     gasLimit: someGasLimit,
    //     gasPrice: someGasPrice,
    //     nonce: yourTransactionCountForYourAddress
    // }

Events

    var ethers = require('ethers');
    var Interface = ethers.Interface;
    var abi = [
        {
            anonymous: false,
            inputs:[
                { indexed:true, name: "from", type: "address" },
                { indexed:true, name: "to", type: "address" },
                { indexed:false, name: "value", type: "uint256" }
            ],
            name: "Transfer",
            type: "event"
        }
    ];
    // NOTE: "interface" is a reserved keyword in JavaScript
    var iface = new Interface(abi)
    var transferInfo = iface.events.Transfer();
    console.log(transferInfo);
    // EventDescription {
    //    inputs:
    //      [ { indexed: true, name: 'from', type: 'address' },
    //        { indexed: true, name: 'to', type: 'address' },
    //        { indexed: false, name: 'value', type: 'uint256' } ],
    //    name: 'Transfer',
    //    signature: 'Transfer(address,address,uint256)',
    //    topics: [ '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef' ],
    //    parse: [Function] }

    // To listen for this event:
    var provider = ethers.providers.getDefaultProvider();
    provider.on(transferInfo.topics, function(log) {
        // Parse event data (only returns the non-indexed entries)
        var result = transferInfo.parse(log.data);
        console.log('non-indexed entries: ', result);

        // non-indexed entries:  Result {
        //   '0': Indexed { indexed: true, hash: null },
        //   '1': Indexed { indexed: true, hash: null },
        //   '2': BigNumber { _bn: <BN: 1db3c5934d11e3c0000> },
        //   from: Indexed { indexed: true, hash: null },
        //   to: Indexed { indexed: true, hash: null },
        //   value: BigNumber { _bn: <BN: 1db3c5934d11e3c0000> },
        //   length: 3 }

        // Parse event topics and data (returns all entries)
        // Note: Any indexed entry which is not a 32 byte value is hashed.
        //       Dynamic arrays are hashed as a static sized array.
        result = transferInfo.parse(log.topics, log.data);
        console.log('all entries: ', result);

        // all entries:  Result {
        //   '0': '0x0000000000000000000000000000000000000000',
        //   '1': '0x92239D0512c313E1b001b3996707F822a76C0901',
        //   '2': BigNumber { _bn: <BN: 1db3c5934d11e3c0000> },
        //   from: '0x0000000000000000000000000000000000000000',
        //   to: '0x92239D0512c313E1b001b3996707F822a76C0901',
        //   value: BigNumber { _bn: <BN: 1db3c5934d11e3c0000> },
        //   length: 3 }
    });

## 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 ( [ names , ] types , values )
  Returns a hex string of the values encoded as the types. If names is provided, values may contain named keys for tuples, otherwise each tuple expects an Array. Throws if a value is invalid for the type.
prototype . decode ( [ names , ] types , data )
  Returns an Object by parsing data assuming types, with each parameter accessible as apositional parameters. If names is provided, each parameter is also accessible by its name. Throws if data is invalid for the types.

## Provider (Sub-Classing)

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

### Static Methods

Provider . inherits ( childProvider )
  Set up childProvider as an provider, inheriting the parent prototype and set up a prototype.inherits on the childProvider.
Provider . fetchJSON ( url , body , processFunc )
  Convenience method for returning a Promise with the result of fetching JSON from a url with an optional body. The optional processFunc is called on the parsed JSON before being passed to the Promise’s resolve. (throwing an error in the processFunc will cause the Promise to reject)

### Prototype

prototype . perform ( method , params )
  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.

### Examples

    var ethers = require('ethers');
    var utils = ethers.utils;
    var Provider = ethers.providers.Provider;

    // The new provider Object
    function DemoProvider(testnet, somethingElse) {
        Provide.call(this, testnet);

        utils.defineProperty(this, 'somethingElse', somethingElse);
    }

    // Inherit the Provider
    Provider.inherits(DemoProvider);

    // Override perform
    utils.defineProperty(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));
    });

## 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 . 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.

### Static Methods

SigningKey . recover ( digest, r, s, recoveryParam )
  Given a message digest and the signature parameters r, s and recoveryParam compute the the address that signed the message.
SigningKey . getPublicKey ( publicOrPrivateKey [, compressed] )

  Given a publicOrPrivateKey, return the public key, optionally compressed.

  default: compressed=false

SigningKey . publicKeyToAddress ( publicOrPrivateKey )
  Convert a publicOrPrivateKey to an Ethereum address.

### Prototype

prototype . privateKey
  The private key.
prototype . publicKey
  The compressed public key.
prototype . address
  The Ethereum address for this key pair.
prototype . signDigest ( messageDigest )
  The compressed public key

### Examples

    var ethers = require('ethers');
    var SigningKey = ethers._SigningKey;

    var privateKey = '0x0123456789012345678901234567890123456789012345678901234567890123';
    var signingKey = new SigningKey(privateKey);

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

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

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

    var signature = signingKey.signDigest(messageDigest);

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

    var recovered = SigningKey.recover(messageDigest, signature.r,
                        signature.s, signature.recoveryParam);

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

    var publicKey = signingKey.publicKey;

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

    var compressedPublicKey = SigningKey.getPublicKey(publicKey, true);
    var uncompressedPublicKey = SigningKey.getPublicKey(publicKey, false);

    console.log('Compressed: ' + compressedPublicKey);
    // "Compressed: 0x026655feed4d214c261e0a6b554395596f1f1476a77d999560e5a8df9b8a1a3515"

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

    var address = SigningKey.publicKeyToAddress(publicKey);

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

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

### Examples

    var rlp = require('ethers').utils.RLP;

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

    var encoded = rlp.encode(object);
    console.log(encoded);
    // 0xc8c142821234c2c0c0

    var decoded = rlp.decode(encoded);
    console.log(decoded);
    // [ [ '0x42' ], '0x1234', [ [], [] ] ]