forked from DecentralizedClimateFoundation/DCIPs
117 lines
4.6 KiB
Markdown
117 lines
4.6 KiB
Markdown
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---
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eip: 1577
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title: contenthash field for ENS
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author: Dean Eigenmann <dean@ens.domains>, Nick Johnson <nick@ens.domains>
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type: Standards Track
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category: ERC
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status: Stagnant
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created: 2018-11-13
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---
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## Abstract
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This EIP introduces the new `contenthash` field for ENS resolvers, allowing for a better defined system of mapping names to network and content addresses. Additionally the `content` and `multihash` fields are deprecated.
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## Motivation
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Multiple applications including [Metamask](https://metamask.io/) and mobile clients such as [Status](https://status.im) have begun resolving ENS names to content hosted on distributed systems such as [IPFS](https://ipfs.io/) and [Swarm](https://swarm-guide.readthedocs.io). Due to the various ways content can be stored and addressed, a standard is required so these applications know how to resolve names and that domain owners know how their content will be resolved.
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The `contenthash` field allows for easy specification of network and content addresses in ENS.
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## Specification
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The field `contenthash` is introduced, which permits a wide range of protocols to be supported by ENS names. Resolvers supporting this field MUST return `true` when the `supportsInterface` function is called with argument `0xbc1c58d1`.
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The fields `content` and `multihash` are deprecated.
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The value returned by `contenthash` MUST be represented as a machine-readable [multicodec](https://github.com/multiformats/multicodec). The format is specified as follows:
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```
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<protoCode uvarint><value []byte>
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```
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protoCodes and their meanings are specified in the [multiformats/multicodec](https://github.com/multiformats/multicodec) repository.
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The encoding of the value depends on the content type specified by the protoCode. Values with protocodes of 0xe3 and 0xe4 represent IPFS and Swarm content; these values are encoded as v1 [CIDs](https://github.com/multiformats/cid) without a base prefix, meaning their value is formatted as follows:
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```
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<protoCode uvarint><cid-version><multicodec-content-type><multihash-content-address>
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```
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When resolving a `contenthash`, applications MUST use the protocol code to determine what type of address is encoded, and resolve the address appropriately for that protocol, if supported.
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### Example
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#### IPFS
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Input data:
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```
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storage system: IPFS (0xe3)
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CID version: 1 (0x01)
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content type: dag-pb (0x70)
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hash function: sha2-256 (0x12)
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hash length: 32 bytes (0x20)
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hash: 29f2d17be6139079dc48696d1f582a8530eb9805b561eda517e22a892c7e3f1f
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```
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Binary format:
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```
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0xe3010170122029f2d17be6139079dc48696d1f582a8530eb9805b561eda517e22a892c7e3f1f
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```
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Text format:
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```
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ipfs://QmRAQB6YaCyidP37UdDnjFY5vQuiBrcqdyoW1CuDgwxkD4
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```
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### Swarm
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Input data:
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```
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storage system: Swarm (0xe4)
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CID version: 1 (0x01)
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content type: swarm-manifest (0xfa)
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hash function: keccak256 (0x1b)
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hash length: 32 bytes (0x20)
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hash: d1de9994b4d039f6548d191eb26786769f580809256b4685ef316805265ea162
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```
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Binary format:
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```
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0xe40101fa011b20d1de9994b4d039f6548d191eb26786769f580809256b4685ef316805265ea162
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```
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Text format:
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```
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bzz://d1de9994b4d039f6548d191eb26786769f580809256b4685ef316805265ea162
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```
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Example usage with swarm hash:
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```
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$ swarm hash ens contenthash d1de9994b4d039f6548d191eb26786769f580809256b4685ef316805265ea162
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> e40101fa011b20d1de9994b4d039f6548d191eb26786769f580809256b4685ef316805265ea162
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```
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### Fallback
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In order to support names that have an IPFS or Swarm hash in their `content` field, a grace period MUST be implemented offering those name holders time to update their names. If a resolver does not support the `multihash` interface, it MUST be checked whether they support the `content` interface. If they do, the value of that field SHOULD be treated in a context dependent fashion and resolved. This condition MUST be enforced until at least March 31st, 2019.
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### Implementation
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To support `contenthash`, a new resolver has been developed and can be found [here](https://github.com/ensdomains/resolvers/blob/master/contracts/PublicResolver.sol), you can also find this smart contract deployed on:
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* Mainnet : [0xd3ddccdd3b25a8a7423b5bee360a42146eb4baf3](https://etherscan.io/address/0xd3ddccdd3b25a8a7423b5bee360a42146eb4baf3)
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* Ropsten : [0xde469c7106a9fbc3fb98912bb00be983a89bddca](https://ropsten.etherscan.io/address/0xde469c7106a9fbc3fb98912bb00be983a89bddca)
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There are also implementations in multiple languages to encode and decode `contenthash`:
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* [JavaScript](https://github.com/pldespaigne/content-hash)
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* [Python](https://github.com/filips123/ContentHashPy)
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## Copyright
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Copyright and related rights waived via [CC0](../LICENSE.md).
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