DCIPs/eip-695.md at 58b766a9239b34a0ac2934744f6d5124a1ba7c54

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eip	title	author	discussions-to	type	category	status	created	requires
695	Create `eth_chainId` method for JSON-RPC	Isaac Ardis <isaac.ardis@gmail.com>, Wei Tang (@sorpaas), Fan Torchz (@tcz001), Erik Marks (@rekmarks)	https://ethereum-magicians.org/t/eip-695-create-eth-chainid-method-for-json-rpc/1845	Standards Track	Interface	Final	2017-08-21	155

Simple Summary

Include eth_chainId method in eth_-namespaced JSON-RPC methods.

Abstract

The eth_chainId method should return a single STRING result for an integer value in hexadecimal format, describing the currently configured CHAIN_ID value used for signing replay-protected transactions, introduced by EIP-155.

Motivation

Currently although we can use net_version RPC call to get the current network ID, there's no RPC for querying the chain ID. This makes it impossible to determine the current actual blockchain using the RPC.

Specification

`eth_chainId`

Returns the currently configured chain ID, a value used in replay-protected transaction signing as introduced by EIP-155.

The chain ID returned should always correspond to the information in the current known head block. This ensures that caller of this RPC method can always use the retrieved information to sign transactions built on top of the head.

If the current known head block does not specify a chain ID, the client should treat any calls to eth_chainId as though the method were not supported, and return a suitable error.

Parameters

None.

Returns

QUANTITY - integer of the current chain ID.

Example

curl -X POST --data '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":83}'

// Result
{
  "id": 83,
  "jsonrpc": "2.0",
  "result": "0x3d" // 61
}

Rationale

An ETH/ETC client can accidentally connect to an ETC/ETH RPC endpoint without knowing it unless it tries to sign a transaction or it fetch a transaction that is known to have signed with a chain ID. This has since caused trouble for application developers, such as MetaMask, to add multi-chain support.

Backwards Compatibility

Not relevant.

Security Considerations

Consumers should prefer eth_chainId over net_version, so that they can reliably identify chain they are communicating with.

Implementers should take care to implement eth_chainId correctly and promote its use, since the chain ID is critical in replay attack prevention as described in EIP-155, and consumers will rely on it to identify the chain they are communicating with.

Implementation

Reference

Return value QUANTITY adheres to standard JSON RPC hex value encoding, as documented in the Ethereum Wiki.

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