Ethereum Provider JavaScript API

Summary

A JavaScript Ethereum Provider API for consistency across clients and applications.

Abstract

A common convention in the Ethereum web application ("dapp") ecosystem is for key management software ("wallets") to expose their API via a JavaScript object in the web page. This object is called "the Provider".

Historically, Provider implementations have exhibited conflicting interfaces and behaviors between wallets. This EIP formalizes an Ethereum Provider API to promote wallet interoperability. The API is designed to be minimal, event-driven, and agnostic of transport and RPC protocols. Its functionality is easily extended by defining new RPC methods and message event types.

Historically, Providers have been made available as window.ethereum in web browsers, but this convention is not part of the specification.

Specification

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119.

Comments like this are non-normative.

Definitions

This section is non-normative.

• Provider
  • A JavaScript object made available to a consumer, that provides access to Ethereum by means of a Client.
• Client
  • An endpoint that receives Remote Procedure Call (RPC) requests from the Provider, and returns their results.
• Wallet
  • An end-user application that manages private keys, performs signing operations, and acts as a middleware between the Provider and the Client.
• Remote Procedure Call (RPC)
  • A Remote Procedure Call (RPC), is any request submitted to a Provider for some procedure that is to be processed by a Provider, its Wallet, or its Client.

Connectivity

The Provider is said to be "connected" when it can service RPC requests to at least one chain.

The Provider is said to be "disconnected" when it cannot service RPC requests to any chain at all.

To service an RPC request, the Provider must successfully submit the request to the remote location, and receive a response. In other words, if the Provider is unable to communicate with its Client, for example due to network issues, the Provider is disconnected.

API

The Provider API is specified using TypeScript. The authors encourage implementers to declare their own types and interfaces, using the ones in this section as a basis.

For consumer-facing API documentation, see Appendix I

The Provider MUST implement and expose the API defined in this section. All API entities MUST adhere to the types and interfaces defined in this section.

request

The request method is intended as a transport- and protocol-agnostic wrapper function for Remote Procedure Calls (RPCs).

interface RequestArguments {
  readonly method: string;
  readonly params?: readonly unknown[] | object;
}

Provider.request(args: RequestArguments): Promise<unknown>;

The Provider MUST identify the requested RPC method by the value of RequestArguments.method.

If the requested RPC method takes any parameters, the Provider MUST accept them as the value of RequestArguments.params.

RPC requests MUST be handled such that the returned Promise either resolves with a value per the requested RPC method's specification, or rejects with an error.

If resolved, the Promise MUST resolve with a result per the RPC method's specification. The Promise MUST NOT resolve with any RPC protocol-specific response objects, unless the RPC method's return type is so defined.

If the returned Promise rejects, it MUST reject with a ProviderRpcError as specified in the RPC Errors section below.

The returned Promise MUST reject if any of the following conditions are met:

• An error is returned for the RPC request.
  • If the returned error is compatible with the ProviderRpcError interface, the Promise MAY reject with that error directly.
• The Provider encounters an error or fails to process the request for any reason.

If the Provider implements any kind of authorization logic, the authors recommend rejecting with a 4100 error in case of authorization failures.

The returned Promise SHOULD reject if any of the following conditions are met:

• The Provider is disconnected.
  • If rejecting for this reason, the Promise rejection error code MUST be 4900.
• The RPC request is directed at a specific chain, and the Provider is not connected to that chain, but is connected to at least one other chain.
  • If rejecting for this reason, the Promise rejection error code MUST be 4901.

See the section Connectivity for the definitions of "connected" and "disconnected".

Supported RPC Methods

A "supported RPC method" is any RPC method that may be called via the Provider.

All supported RPC methods MUST be identified by unique strings.

Providers MAY support whatever RPC methods required to fulfill their purpose, standardized or otherwise.

If an RPC method defined in a finalized EIP is not supported, it SHOULD be rejected with a 4200 error per the Provider Errors section below, or an appropriate error per the RPC method's specification.

RPC Errors

interface ProviderRpcError extends Error {
  code: number;
  data?: unknown;
}

• message
  • MUST be a human-readable string
  • SHOULD adhere to the specifications in the Error Standards section below
• code
  • MUST be an integer number
  • SHOULD adhere to the specifications in the Error Standards section below
• data
  • SHOULD contain any other useful information about the error

Error Standards

ProviderRpcError codes and messages SHOULD follow these conventions, in order of priority:

1. The errors in the Provider Errors section below

2. Any errors mandated by the erroring RPC method's specification

3. The CloseEvent status codes

Provider Errors

Status code	Name	Description
4001	User Rejected Request	The user rejected the request.
4100	Unauthorized	The requested method and/or account has not been authorized by the user.
4200	Unsupported Method	The Provider does not support the requested method.
4900	Disconnected	The Provider is disconnected from all chains.
4901	Chain Disconnected	The Provider is not connected to the requested chain.

4900 is intended to indicate that the Provider is disconnected from all chains, while 4901 is intended to indicate that the Provider is disconnected from a specific chain only. In other words, 4901 implies that the Provider is connected to other chains, just not the requested one.

Events

The Provider MUST implement the following event handling methods:

• on
• removeListener

These methods MUST be implemented per the Node.js EventEmitter API.

To satisfy these requirements, Provider implementers should consider simply extending the Node.js EventEmitter class and bundling it for the target environment.

message

The message event is intended for arbitrary notifications not covered by other events.

When emitted, the message event MUST be emitted with an object argument of the following form:

interface ProviderMessage {
  readonly type: string;
  readonly data: unknown;
}

Subscriptions

If the Provider supports Ethereum RPC subscriptions, e.g. eth_subscribe, the Provider MUST emit the message event when it receives a subscription notification.

If the Provider receives a subscription message from e.g. an eth_subscribe subscription, the Provider MUST emit a message event with a ProviderMessage object of the following form:

interface EthSubscription extends ProviderMessage {
  readonly type: 'eth_subscription';
  readonly data: {
    readonly subscription: string;
    readonly result: unknown;
  };
}

connect

See the section Connectivity for the definition of "connected".

If the Provider becomes connected, the Provider MUST emit the event named connect.

This includes when:

• The Provider first connects to a chain after initialization.
• The Provider connects to a chain after the disconnect event was emitted.

This event MUST be emitted with an object of the following form:

interface ProviderConnectInfo {
  readonly chainId: string;
}

chainId MUST specify the integer ID of the connected chain as a hexadecimal string, per the eth_chainId Ethereum RPC method.

disconnect

See the section Connectivity for the definition of "disconnected".

If the Provider becomes disconnected from all chains, the Provider MUST emit the event named disconnect with value error: ProviderRpcError, per the interfaced defined in the RPC Errors section. The value of the error's code property MUST follow the status codes for CloseEvent.

chainChanged

If the chain the Provider is connected to changes, the Provider MUST emit the event named chainChanged with value chainId: string, specifying the integer ID of the new chain as a hexadecimal string, per the eth_chainId Ethereum RPC method.

accountsChanged

If the accounts available to the Provider change, the Provider MUST emit the event named accountsChanged with value accounts: string[], containing the account addresses per the eth_accounts Ethereum RPC method.

The "accounts available to the Provider" change when the return value of eth_accounts changes.

Rationale

The purpose of a Provider is to provide a consumer with access to Ethereum. In general, a Provider must enable an Ethereum web application to do two things:

• Make Ethereum RPC requests
• Respond to state changes in the Provider's Ethereum chain, Client, and Wallet

The Provider API specification consists of a single method and five events. The request method and the message event alone, are sufficient to implement a complete Provider. They are designed to make arbitrary RPC requests and communicate arbitrary messages, respectively.

The remaining four events can be separated into two categories:

• Changes to the Provider's ability to make RPC requests
  • connect
  • disconnect
• Common Client and/or Wallet state changes that any non-trivial application must handle
  • chainChanged
  • accountsChanged

These events are included due to the widespread production usage of related patterns, at the time of writing.

Backwards Compatibility

Many Providers adopted a draft version of this specification before it was finalized. The current API is designed to be a strict superset of the legacy version, and this specification is in that sense fully backwards compatible. See Appendix III for the legacy API.

Providers that only implement this specification will not be compatible with Ethereum web applications that target the legacy API.

Implementations

At the time of writing, the following projects have working implementations:

• buidler.dev
• ethers.js
• eth-provider
• MetaMask
• WalletConnect
• web3.js

Security Considerations

The Provider is intended to pass messages between an Ethereum Client and an Ethereum application. It is not responsible for private key or account management; it merely processes RPC messages and emits events. Consequently, account security and user privacy need to be implemented in middlewares between the Provider and its Ethereum Client. In practice, we call these middleware applications "Wallets," and they usually manage the user's private keys and accounts. The Provider can be thought of as an extension of the Wallet, exposed in an untrusted environment, under the control of some third party (e.g. a website).

Handling Adversarial Behavior

Since it is a JavaScript object, consumers can generally perform arbitrary operations on the Provider, and all its properties can be read or overwritten. Therefore, it is best to treat the Provider object as though it is controlled by an adversary. It is paramount that the Provider implementer protects the user, Wallet, and Client by ensuring that:

• The Provider does not contain any private user data.
• The Provider and Wallet programs are isolated from each other.
• The Wallet and/or Client rate-limit requests from the Provider.
• The Wallet and/or Client validate all data sent from the Provider.

Chain Changes

Since all Ethereum operations are directed at a particular chain, it's important that the Provider accurately reflects the Client's configured chain, per the eth_chainId Ethereum RPC method (see EIP-695).

This includes ensuring that eth_chainId has the correct return value, and that the chainChanged event is emitted whenever that value changes.

User Account Exposure and Account Changes

Many Ethereum write operations (e.g. eth_sendTransaction) require a user account to be specified. Provider consumers access these accounts via the eth_accounts RPC method, and by listening for the accountsChanged event.

As with eth_chainId, it is critical that eth_accounts has the correct return value, and that the accountsChanged event is emitted whenever that value changes.

The return value of eth_accounts is ultimately controlled by the Wallet or Client. In order to protect user privacy, the authors recommend not exposing any accounts by default. Instead, Providers should support RPC methods for explicitly requesting account access, such as eth_requestAccounts (see EIP-1102) or wallet_requestPermissions (see EIP-2255).

References

• Initial discussion in ethereum/interfaces
• Deprecated Ethereum Magicians thread
• Continuing discussion
• Related EIPs
  • EIP-1102: Opt-in Account Exposure
  • EIP-1474: Remote Procedure Call Specification
  • EIP-1767: GraphQL Interface to Ethereum Node Data
  • EIP-2255: Wallet Permissions

Copyright

Copyright and related rights waived via CC0.

Appendix I: Consumer-Facing API Documentation

request

Makes an Ethereum RPC method call.

interface RequestArguments {
  readonly method: string;
  readonly params?: readonly unknown[] | object;
}

Provider.request(args: RequestArguments): Promise<unknown>;

The returned Promise resolves with the method's result or rejects with a ProviderRpcError. For example:

Provider.request({ method: 'eth_accounts' })
  .then((accounts) => console.log(accounts))
  .catch((error) => console.error(error));

Consult each Ethereum RPC method's documentation for its params and return type. You can find a list of common methods here.

RPC Protocols

Multiple RPC protocols may be available. For examples, see:

• EIP-1474, the Ethereum JSON-RPC API
• EIP-1767, the Ethereum GraphQL schema

Events

Events follow the conventions of the Node.js EventEmitter API.

connect

The Provider emits connect when it:

• first connects to a chain after being initialized.
• first connects to a chain, after the disconnect event was emitted.

interface ProviderConnectInfo {
  readonly chainId: string;
}

Provider.on('connect', listener: (connectInfo: ProviderConnectInfo) => void): Provider;

The event emits an object with a hexadecimal string chainId per the eth_chainId Ethereum RPC method, and other properties as determined by the Provider.

disconnect

The Provider emits disconnect when it becomes disconnected from all chains.

Provider.on('disconnect', listener: (error: ProviderRpcError) => void): Provider;

This event emits a ProviderRpcError. The error code follows the table of CloseEvent status codes.

chainChanged

The Provider emits chainChanged when connecting to a new chain.

Provider.on('chainChanged', listener: (chainId: string) => void): Provider;

The event emits a hexadecimal string chainId per the eth_chainId Ethereum RPC method.

accountsChanged

The Provider emits accountsChanged if the accounts returned from the Provider (eth_accounts) change.

Provider.on('accountsChanged', listener: (accounts: string[]) => void): Provider;

The event emits with accounts, an array of account addresses, per the eth_accounts Ethereum RPC method.

message

The Provider emits message to communicate arbitrary messages to the consumer. Messages may include JSON-RPC notifications, GraphQL subscriptions, and/or any other event as defined by the Provider.

interface ProviderMessage {
  readonly type: string;
  readonly data: unknown;
}

Provider.on('message', listener: (message: ProviderMessage) => void): Provider;

Subscriptions

eth_ subscription methods and shh_ subscription methods rely on this event to emit subscription updates.

For e.g. eth_subscribe subscription updates, ProviderMessage.type will equal the string 'eth_subscription', and the subscription data will be the value of ProviderMessage.data.

Errors

interface ProviderRpcError extends Error {
  message: string;
  code: number;
  data?: unknown;
}

Appendix II: Examples

These examples assume a web browser environment.

// Most Providers are available as window.ethereum on page load.
// This is only a convention, not a standard, and may not be the case in practice.
// Please consult the Provider implementation's documentation.
const ethereum = window.ethereum;

// Example 1: Log chainId
ethereum
  .request({ method: 'eth_chainId' })
  .then((chainId) => {
    console.log(`hexadecimal string: ${chainId}`);
    console.log(`decimal number: ${parseInt(chainId, 16)}`);
  })
  .catch((error) => {
    console.error(`Error fetching chainId: ${error.code}: ${error.message}`);
  });

// Example 2: Log last block
ethereum
  .request({
    method: 'eth_getBlockByNumber',
    params: ['latest', true],
  })
  .then((block) => {
    console.log(`Block ${block.number}:`, block);
  })
  .catch((error) => {
    console.error(
      `Error fetching last block: ${error.message}.
       Code: ${error.code}. Data: ${error.data}`
    );
  });

// Example 3: Log available accounts
ethereum
  .request({ method: 'eth_accounts' })
  .then((accounts) => {
    console.log(`Accounts:\n${accounts.join('\n')}`);
  })
  .catch((error) => {
    console.error(
      `Error fetching accounts: ${error.message}.
       Code: ${error.code}. Data: ${error.data}`
    );
  });

// Example 4: Log new blocks
ethereum
  .request({
    method: 'eth_subscribe',
    params: ['newHeads'],
  })
  .then((subscriptionId) => {
    ethereum.on('message', (message) => {
      if (message.type === 'eth_subscription') {
        const { data } = message;
        if (data.subscription === subscriptionId) {
          if ('result' in data && typeof data.result === 'object') {
            const block = data.result;
            console.log(`New block ${block.number}:`, block);
          } else {
            console.error(`Something went wrong: ${data.result}`);
          }
        }
      }
    });
  })
  .catch((error) => {
    console.error(
      `Error making newHeads subscription: ${error.message}.
       Code: ${error.code}. Data: ${error.data}`
    );
  });

// Example 5: Log when accounts change
const logAccounts = (accounts) => {
  console.log(`Accounts:\n${accounts.join('\n')}`);
};
ethereum.on('accountsChanged', logAccounts);
// to unsubscribe
ethereum.removeListener('accountsChanged', logAccounts);

// Example 6: Log if connection ends
ethereum.on('disconnect', (code, reason) => {
  console.log(`Ethereum Provider connection closed: ${reason}. Code: ${code}`);
});

Appendix III: Legacy Provider API

This section documents the legacy Provider API, which is extensively used in production at the time of writing. As it was never fully standardized, significant deviations occur in practice. The authors recommend against implementing it except to support legacy Ethereum applications.

sendAsync (DEPRECATED)

This method is superseded by request.

sendAsync is like request, but with JSON-RPC objects and a callback.

Provider.sendAsync(request: Object, callback: Function): void;

Historically, the request and response object interfaces have followed the Ethereum JSON-RPC specification.

send (DEPRECATED)

This method is superseded by request.

Provider.send(...args: unknown[]): unknown;

Legacy Events

close (DEPRECATED)

This event is superseded by disconnect.

networkChanged (DEPRECATED)

The event networkChanged is superseded by chainChanged.

For details, see EIP-155: Simple replay attack protection and EIP-695: Create eth_chainId method for JSON-RPC.

notification (DEPRECATED)

This event is superseded by message.

Historically, this event has been emitted with e.g. eth_subscribe subscription updates of the form { subscription: string, result: unknown }.