_section: Interface @ @SRC The **Interface** Class abstracts the encoding and decoding required to interact with contracts on the Ethereum network. Many of the standards organically evolved along side the [[link-solidity]] language, which other languages have adopted to remain compatible with existing deployed contracts. The EVM itself does not understand what the ABI is. It is simply an agreed upon set of formats to encode various types of data which each contract can expect so they can interoperate with each other. _subsection: Creating Instances @ _property: new ethers.utils.Interface(abi) @SRC Create a new **Interface** from a JSON string or object representing //abi//. The //abi// may be a JSON string or the parsed Object (using JSON.parse) which is emitted by the [Solidity compiler](link-solc-output) (or compatible languages). The //abi// may also be a [Human-Readable Abi](link-ricmoo-humanreadableabi), which is a format the Ethers created to simplify manually typing the ABI into the source and so that a Contract ABI can also be referenced easily within the same source file. _code: Creating an Interface instance @lang //_hide: const Interface = ethers.utils.Interface; // This interface is used for the below examples const iface = new Interface([ // Constructor "constructor(string symbol, string name)", // State mutating method "function transferFrom(address from, address to, uint amount)", // State mutating method, which is payable "function mint(uint amount) payable", // Constant method (i.e. "view" or "pure") "function balanceOf(address owner) view returns (uint)", // An Event "event Transfer(address indexed from, address indexed to, uint256 amount)", // A Custom Solidity Error "error AccountLocked(address owner, uint256 balance)", // Examples with structured types "function addUser(tuple(string name, address addr) user) returns (uint id)", "function addUsers(tuple(string name, address addr)[] user) returns (uint[] id)", "function getUser(uint id) view returns (tuple(string name, address addr) user)" ]); //_hide: _page.iface = iface; _subsection: Properties @ _property: interface.fragments => Array<[[Fragment]]> All the [Fragments](Fragment) in the interface. _property: interface.errors => Array<[[ErrorFragment]]> All the [Error Fragments](ErrorFragment) in the interface. _property: interface.events => Array<[[EventFragment]]> All the [Event Fragments](EventFragment) in the interface. _property: interface.functions => Array<[[FunctionFragment]]> All the [Function Fragments](FunctionFragment) in the interface. _property: interface.deploy => [[ConstructorFragment]] The [Constructor Fragments](ConstructorFragment) for the interface. _subsection: Formatting @ _property: interface.format( [ format ]) => string | Array @SRC Return the formatted **Interface**. If the format type is ``json`` a single string is returned, otherwise an Array of the human-readable strings is returned. _code: @lang //_hide: const iface = _page.iface; const FormatTypes = ethers.utils.FormatTypes; //_result: iface.format(FormatTypes.json) //_log: //_result: iface.format(FormatTypes.full) //_log: //_result: iface.format(FormatTypes.minimal) //_log: _subsection: Fragment Access @ _property: interface.getFunction(fragment) => [[FunctionFragment]] @SRC Returns the [[FunctionFragment]] for //fragment// (see [[Interface--specifying-fragments]]). _code: @lang //_hide: const iface = _page.iface; // By method signature, which is normalized so whitespace // and superfluous attributes are ignored iface.getFunction("transferFrom(address, address, uint256)"); // By name; this ONLY works if the method is non-ambiguous iface.getFunction("transferFrom"); // By method selector iface.getFunction("0x23b872dd"); // Throws if the method does not exist //_throws: iface.getFunction("doesNotExist()"); //_log: _property: interface.getError(fragment) => [[ErrorFragment]] @SRC Returns the [[ErrorFragment]] for //fragment// (see [[Interface--specifying-fragments]]). _code: @lang //_hide: const iface = _page.iface; // By error signature, which is normalized so whitespace // and superfluous attributes are ignored iface.getError("AccountLocked(address, uint256)"); // By name; this ONLY works if the error is non-ambiguous iface.getError("AccountLocked"); // By error selector iface.getError("0xf7c3865a"); // Throws if the error does not exist //_throws: iface.getError("DoesNotExist()"); //_log: _property: interface.getEvent(fragment) => [[EventFragment]] @SRC Returns the [[EventFragment]] for //fragment// (see [[Interface--specifying-fragments]]). _code: @lang //_hide: const iface = _page.iface; // By event signature, which is normalized so whitespace // and superfluous attributes are ignored iface.getEvent("Transfer(address, address, uint256)"); // By name; this ONLY works if the event is non-ambiguous iface.getEvent("Transfer"); // By event topic hash iface.getEvent("0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"); // Throws if the event does not exist //_throws: iface.getEvent("DoesNotExist()"); //_log: _subsection: Signature and Topic Hashes @ _property: interface.getSighash(fragment) => string<[[DataHexString]]<4>> @SRC Return the sighash (or Function Selector) for //fragment// (see [[Interface--specifying-fragments]]). _code: @lang //_hide: const iface = _page.iface; //_result: iface.getSighash("balanceOf"); //_log: //_result: iface.getSighash("balanceOf(address)"); //_log: const fragment = iface.getFunction("balanceOf") //_result: iface.getSighash(fragment); //_log: _property: interface.getEventTopic(fragment) => string<[[DataHexString]]<32>> @SRC Return the topic hash for //fragment// (see [[Interface--specifying-fragments]]). _code: @lang //_hide: const iface = _page.iface; //_result: iface.getEventTopic("Transfer"); //_log: //_result: iface.getEventTopic("Transfer(address, address, uint)"); //_log: const fragment = iface.getEvent("Transfer") //_result: iface.getEventTopic(fragment); //_log: _subsection: Encoding Data @ _property: interface.encodeDeploy([ values ]) => string<[[DataHexString]]> @SRC Return the encoded deployment data, which can be concatenated to the deployment bytecode of a contract to pass //values// into the contract constructor. _code: @lang //_hide: const iface = _page.iface; //_hide: const parseEther = ethers.utils.parseEther; // The data that should be appended to the bytecode to pass // parameters to the constructor during deployment //_result: iface.encodeDeploy([ "SYM", "Some Name" ]) //_log: _property: interface.encodeFilterTopics(fragment, values) => Array> @SRC Returns the encoded topic filter, which can be passed to getLogs for //fragment// (see [[Interface--specifying-fragments]]) for the given //values//. Each //topic// is a 32 byte (64 nibble) [[DataHexString]]. _code: @lang //_hide: const iface = _page.iface; //_hide: const parseEther = ethers.utils.parseEther; // Filter that matches all Transfer events //_result: iface.encodeFilterTopics("Transfer", []) //_log: // Filter that matches the sender //_result: iface.encodeFilterTopics("Transfer", [ "0x8ba1f109551bD432803012645Ac136ddd64DBA72" ]) //_log: // Filter that matches the receiver //_result: iface.encodeFilterTopics("Transfer", [ null, "0x8ba1f109551bD432803012645Ac136ddd64DBA72" ]) //_log: _property: interface.encodeFunctionData(fragment [ , values ]) => string<[[DataHexString]]> @SRC Returns the encoded data, which can be used as the data for a transaction for //fragment// (see [[Interface--specifying-fragments]]) for the given //values//. _code: @lang //_hide: const iface = _page.iface; //_hide: const parseEther = ethers.utils.parseEther; // Encoding data for the tx.data of a call or transaction //_result: iface.encodeFunctionData("transferFrom", [ "0x8ba1f109551bD432803012645Ac136ddd64DBA72", "0xaB7C8803962c0f2F5BBBe3FA8bf41cd82AA1923C", parseEther("1.0") ]) //_log: // Encoding structured data (using positional Array) user = [ "Richard Moore", "0x8ba1f109551bD432803012645Ac136ddd64DBA72" ]; //_result: iface.encodeFunctionData("addUser", [ user ]); //_log: // Encoding structured data, using objects. Only available // if paramters are named. user = { name: "Richard Moore", addr: "0x8ba1f109551bD432803012645Ac136ddd64DBA72" }; //_result: iface.encodeFunctionData("addUser", [ user ]); //_log: _property: interface.encodeFunctionResult(fragment [ , values ]) => string<[[DataHexString]]> @SRC Returns the encoded result, which would normally be the response from a call for //fragment// (see [[Interface--specifying-fragments]]) for the given //values//. Most developers will not need this method, but may be useful for authors of a mock blockchain. _code: @lang //_hide: const iface = _page.iface; //_hide: const parseEther = ethers.utils.parseEther; // Encoding result data (like is returned by eth_call) //_result: iface.encodeFunctionResult("balanceOf", [ "0x8ba1f109551bD432803012645Ac136ddd64DBA72" ]) //_log: _subsection: Decoding Data @ _property: interface.decodeEventLog(fragment, data [ , topics ]) => [[Result]] @SRC Returns the decoded event values from an event log for //fragment// (see [[Interface--specifying-fragments]]) for the given //data// with the optional //topics//. If //topics// is not specified, placeholders will be inserted into the result. Most develoeprs will find the [parsing methods](Interface--parsing) more convenient for decoding event data, as they will automatically detect the matching event. _code: @lang //_hide: const iface = _page.iface; // Decoding log data and topics (the entries in a receipt) const data = "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000"; const topics = [ "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef", "0x0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72", "0x000000000000000000000000ab7c8803962c0f2f5bbbe3fa8bf41cd82aa1923c" ]; //_result: iface.decodeEventLog("Transfer", data, topics); //_log: _property: interface.decodeFunctionData(fragment, data) => [[Result]] @SRC Returns the decoded values from transaction data for //fragment// (see [[Interface--specifying-fragments]]) for the given //data//. Most developers will not need this method, but may be useful for debugging or inspecting transactions. Most develoeprs will also find the [parsing methods](Interface--parsing) more convenient for decoding transation data, as they will automatically detect the matching function. _code: @lang //_hide: const iface = _page.iface; // Decoding function data (the value of tx.data) const txData = "0x23b872dd0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72000000000000000000000000ab7c8803962c0f2f5bbbe3fa8bf41cd82aa1923c0000000000000000000000000000000000000000000000000de0b6b3a7640000"; //_result: iface.decodeFunctionData("transferFrom", txData); //_log: _property: interface.decodeFunctionResult(fragment, data) => [[Result]] @SRC Returns the decoded values from the result of a call for //fragment// (see [[Interface--specifying-fragments]]) for the given //data//. _code: @lang //_hide: const iface = _page.iface; // Decoding result data (e.g. from an eth_call) resultData = "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000"; //_result: iface.decodeFunctionResult("balanceOf", resultData) //_log: // Decoding result data which was caused by a revert // Throws a CALL_EXCEPTION, with extra details errorData = "0xf7c3865a0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba720000000000000000000000000000000000000000000000000de0b6b3a7640000"; //_throws: iface.decodeFunctionResult("balanceOf", errorData) //_log: // Decoding structured data returns a Result object, which // will include all values positionally and if the ABI // included names, values will additionally be available // by their name. resultData = "0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000400000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72000000000000000000000000000000000000000000000000000000000000000d52696368617264204d6f6f726500000000000000000000000000000000000000"; //_result: result = iface.decodeFunctionResult("getUser", resultData); //_log: // Access positionally: // The 0th output parameter, the 0th proerty of the structure //_result: result[0][0]; //_log: // Access by name: (only avilable because parameters were named) //_result: result.user.name //_log: _subsection: Parsing @ The functions are generally the most useful for most developers. They will automatically search the ABI for a matching Event or Function and decode the components as a fully specified description. _property: interface.parseLog(log) => [[LogDescription]] @SRC Search the event that matches the //log// topic hash and parse the values the log represents. _code: @lang //_hide: const iface = _page.iface; const data = "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000"; const topics = [ "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef", "0x0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72", "0x000000000000000000000000ab7c8803962c0f2f5bbbe3fa8bf41cd82aa1923c" ]; //_result: iface.parseLog({ data, topics }); //_hide: _.eventFragment = createClass("EventFragment"); //_log: _property: interface.parseTransaction(transaction) => [[TransactionDescription]] @SRC Search for the function that matches the //transaction// data sighash and parse the transaction properties. _code: @lang //_hide: const iface = _page.iface; //_hide: const parseEther = ethers.utils.parseEther; const data = "0x23b872dd0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72000000000000000000000000ab7c8803962c0f2f5bbbe3fa8bf41cd82aa1923c0000000000000000000000000000000000000000000000000de0b6b3a7640000"; const value = parseEther("1.0"); //_result: iface.parseTransaction({ data, value }); //_hide: _.functionFragment = createClass("FunctionFragment"); //_log: _subsection: Types @ _heading: Result @ @INHERIT> A **Result** is an array, so each value can be accessed as a positional argument. Additionally, if values are named, the identical object as its positional value can be accessed by its name. The name ``length`` is however reserved as it is part of the Array, so any named value for this key is renamed to ``_length``. If there is a name collision, only the first is available by its key. _heading: LogDescription @ _property: logDescription.args => [[Result]] The values of the input parameters of the event. _property: logDescription.eventFragment => [[EventFragment]] The [[EventFragment]] which matches the topic in the Log. _property: logDescription.name => string The event name. (e.g. ``Transfer``) _property: logDescription.signature => string The event signature. (e.g. ``Transfer(address,address,uint256)``) _property: logDescription.topic => string The topic hash. _heading: TransactionDescription @ _property: transactionDescription.args => [[Result]] The decoded values from the transaction data which were passed as the input parameters. _property: transactionDescription.functionFragment => [[FunctionFragment]] The [[FunctionFragment]] which matches the sighash in the transaction data. _property: transactionDescription.name => string The name of the function. (e.g. ``transfer``) _property: transactionDescription.sighash => string The sighash (or function selector) that matched the transaction data. _property: transactionDescription.signature => string The signature of the function. (e.g. ``transfer(address,uint256)``) _property: transactionDescription.value => [[BigNumber]] The value from the transaction. _subsection: Specifying Fragments @ When specifying a fragment to any of the functions in an **Interface**, any of the following may be used: - The **name** of the event or function, if it is unique and non-ambiguous within the ABI (e.g. ``transfer``) - The **signature** of the event or function. The signature is normalized, so, for example, ``uint`` and ``uint256`` are equivalent (e.g. ``transfer(address, uint)``) - The **sighash** or **topichash** of the function. The sighash is often referred to the function selector in Solidity (e.g. ``0xa9059cbb``) - A [[Fragment]]