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Building a Resolver

Because of the open-ended nature of resolvers, it can be daunting to begin writing one. Below are some hints to get you started.

Enforcing isResolver

While not strictly necessary, resolvers are strongly recommended to enforce that calling EINs have set your Resolver via code that looks something like the following:

  require(identityRegistry.isResolverFor(ein, address(this)), "The EIN has not set this resolver.");

While Resolvers are of course free to let anyone they wish interact with their smart contract, they should, in most cases, restrict use to Identities who currently have their address set as a Resolver. This is helpful so that front-ends can know which Resolvers a given entity has set, and can also facilitate inter-Resolver logic.

Permissioning

There are several routes a Resolver could take when choosing how to let Identities interact with their smart contracts. Resolvers are recommended to implement one or more of the best practices outlined below.

Before diving in, let's first sketch out an updateInformation function that we want to call. Say it modifies data associated with an Identity.

// perform the desired operations on the EIN's Identity
function updateInformation(...) ... {
  ...
}

Obviously, we have to be careful about who can call this function, and how calls are permissioned to affect the data of Identities.

1. Allow Identities to call functions directly

The first and simplest option is to allow any associatedAddress of an identity to call updateInformation by simply looking up their EIN from the 1484 registry via getEIN. All further operations can now use that EIN.

function updateInformation(...) public {
  uint ein = identityRegistry.getEIN(msg.sender);
  ...
}

2. Allow Providers to call functions on behalf of Identities

Some users, though, might not want to interact with our Resolver directly. They might instead prefer to do so through a Provider. In this case, we want to allow a Provider to call updateInformation on behalf of an EIN. For this not to be an anti-pattern, we must:

  • Ensure that any time we receive a call from a Provider on behalf of an EIN, the EIN in question has actually set this Provider. This is easily achieved by code that looks something like the following:
function updateInformation(uint ein, ...) public {
  require(identityRegistry.isProviderFor(ein, msg.sender));
  ...;
}
  • Be convinced that Providers have appropriately permissioned their smart contracts so that we can trust that the calls we receive actually represent the intent of the EIN. (For example, a public function that triggers EIN-specific logic on your Resolver will probably be abused!) To this point, it is often enough to trust that Providers are treating permissions appropriately (see BuildingProviders.md for Provider best practices around this issue). Cases where Providers may not be operating as securely as possibly can be chalked up to user error, and plausibly don't have to be handled by individual Resolvers. However, if a Resolver wishes to use only a trusted subset of Providers, or utilize the functionality of one particular Provider, they are of course free to do so with code that looks something like the following:
function updateInformation(uint ein, ...) public {
  require(msg.sender == 0x...); // ensure that the calling address is e.g. a pre-determined whitelisted Provider
  require(identityRegistry.isProviderFor(ein, msg.sender));
  ...;
}

3. (Not Recommended) Allow third parties to submit permission signatures on behalf of Identities

This is an anti-pattern for a Resolver, and is not recommended. For cases in which it's absolutely necessary, refer to the BuildingProviders.md best practices.

4. (Not Recommended) Allow Resolver owners to call onlyOwner functions on behalf of Identities

This is an anti-pattern for a Resolver. For cases in which it's absolutely necessary, onlyOwner calls may be made like so:

function updateInformation(uint ein, ...) public onlyOwner() {
  ...;
}
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