74 lines
3.7 KiB
Markdown
74 lines
3.7 KiB
Markdown
---
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eip: 926
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title: Address metadata registry
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author: Nick Johnson <nick@ethereum.org>
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type: Standards Track
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category: ERC
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status: Stagnant
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created: 2018-03-12
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requires: 165
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---
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## Abstract
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This EIP specifies a registry for address metadata, permitting both contracts and external accounts to supply metadata about themselves to onchain and offchain callers. This permits use-cases such as generalised authorisations, providing token acceptance settings, and claims registries.
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## Motivation
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An increasing set of use cases require storage of metadata associated with an address; see for instance EIP 777 and EIP 780, and the ENS reverse registry in EIP 181. Presently each use-case defines its own specialised registry. To prevent a proliferation of special-purpose registry contracts, we instead propose a single standardised registry using an extendable architecture that allows future standards to implement their own metadata standards.
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## Specification
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The metadata registry has the following interface:
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```solidity
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interface AddressMetadataRegistry {
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function provider(address target) view returns(address);
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function setProvider(address _provider);
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}
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```
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`setProvider` specifies the metadata registry to be associated with the caller's address, while `provider` returns the address of the metadata registry for the supplied address.
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The metadata registry will be compiled with an agreed-upon version of Solidity and deployed using the trustless deployment mechanism to a fixed address that can be replicated across all chains.
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## Provider specification
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Providers may implement any subset of the metadata record types specified here. Where a record types specification requires a provider to provide multiple functions, the provider MUST implement either all or none of them. Providers MUST throw if called with an unsupported function ID.
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Providers have one mandatory function:
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```solidity
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function supportsInterface(bytes4 interfaceID) constant returns (bool)
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```
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The `supportsInterface` function is documented in [EIP-165](./eip-165.md), and returns true if the provider implements the interface specified by the provided 4 byte identifier. An interface identifier consists of the XOR of the function signature hashes of the functions provided by that interface; in the degenerate case of single-function interfaces, it is simply equal to the signature hash of that function. If a provider returns `true` for `supportsInterface()`, it must implement the functions specified in that interface.
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`supportsInterface` must always return true for `0x01ffc9a7`, which is the interface ID of `supportsInterface` itself.
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The first argument to all provider functions MUST be the address being queried; this facilitates the creation of multi-user provider contracts.
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Currently standardised provider interfaces are specified in the table below.
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| Interface name | Interface hash | Specification |
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| --- | --- | --- |
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EIPs may define new interfaces to be added to this registry.
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## Rationale
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There are two obvious approaches for a generic metadata registry: the indirection approach employed here, or a generalised key/value store. While indirection incurs the cost of an additional contract call, and requires providers to change over time, it also provides for significantly enhanced flexibility over a key/value store; for that reason we selected this approach.
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## Backwards Compatibility
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There are no backwards compatibility concerns.
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## Implementation
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The canonical implementation of the metadata registry is as follows:
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```solidity
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contract AddressMetadataRegistry {
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mapping(address=>address) public provider;
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function setProvider(address _provider) {
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provider[msg.sender] = _provider;
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}
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}
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```
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## Copyright
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Copyright and related rights waived via [CC0](../LICENSE.md).
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