SIP-29: Snap Assets API

SIPS/sip-29.md

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+---
+sip: 29
+title: Snap Assets API
+status: Draft
+author: Daniel Rocha (@danroc), Guillaume Roux (@GuillaumeRx)
+created: 2024-12-05
+---
+
+## Abstract
+
+This SIP aims to define a new API that can be exposed by Snaps to allow clients
+to retrieve asset information in a chain-agnostic way.
+
+## Motivation
+
+To enable clients to be chain-agnostic, the logic for obtaining asset
+information should be abstracted away from the client. Additionally, this SIP
+defines the types that represent the asset information required by clients.
+
+## Specification
+
+> Indented sections like this are considered non-normative.
+
+### Language
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
+"SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" written
+in uppercase in this document are to be interpreted as described in [RFC
+2119](https://www.ietf.org/rfc/rfc2119.txt)
+
+### Definitions
+
+1. In this document, all definitions are written in TypeScript.
+
+2. Any time an asset needs to be identified, it MUST use the [CAIP-19][caip-19]
+   representation.
+
+### Snap Manifest
+
+This SIP introduces a new permission named `endowment:assets`.
+This permission grants a Snap the ability to provide asset information to the client.
+
+This permission is specified as follows in `snap.manifest.json` files:
+
+```json
+{
+  "initialPermissions": {
+    "endowment:assets": {
+      "scopes": [
+        "bip122:000000000019d6689c085ae165831e93"
+      ]
+    }
+  }
+}
+```
+
+`scopes` - A non-empty array of CAIP-2 chain IDs that the snap supports. This field is useful for a client in order to avoid unnecessary overhead.
+
+### Snap Implementation
+
+Two methods are defined in the Snap Assets API:
+
+Any Snap that wishes to provide asset information **MUST** implement the following API:
+
+#### Get Asset Metadata
+
+```typescript
+import { OnAssetLookupHandler } from "@metamask/snaps-sdk";
+
+export const onAssetLookup: OnAssetLookupHandler = async ({
+  assets
+}) => {
+  const assetsMetadata = /* Get metadata */;
+  return { assets: assetsMetadata };
+};
+```
+
+The type for an `onAssetLookup` handler function’s arguments is:
+
+```typescript
+interface OnAssetLookupArgs {
+  assets: Caip19AssetType[];
+}
+```
+
+The type for an `onAssetLookup` handler function’s return value is:
+
+```typescript
+type OnAssetLookupReturn = {
+  assets: Record<Caip19AssetType, AssetMetadata>;
+};
+```
+
+#### Get Asset Conversion Rate
+
+```typescript
+import { OnAssetConversionHandler } from "@metamask/snaps-sdk";
+
+export const onAssetConversion: OnAssetConversionHandler = async ({
+  conversions
+}) => {
+  const conversionRates = /* Get conversion rate */;
+  return { conversionRates };
+};
+```
+
+The type for an `onAssetConversion` handler function’s arguments is:
+
+```typescript
+type Conversion = {
+  from: Caip19AssetType;
+  to: Caip19AssetType;
+};
+
+type OnAssetConversionArgs = {
+  conversions: Conversion[];
+};
+```
+
+The type for an `onAssetConversion` handler function’s return value is:
+
+```typescript
+type AssetConversionRate = {
+  // The rate of conversion from the source asset to the target asset. It
+  // means that 1 unit of the `from` asset should be converted to this amount
+  // of the `to` asset.
+  rate: string;
+
+  // The UNIX timestamp of when the conversion rate was last updated.
+  conversionTime: number;
+
+  // The UNIX timestamp of when the conversion rate will expire.
+  expirationTime: number;
+};
+
+type FromAsset = Conversion["from"];
+
+type ToAsset = Conversion["to"];
+
+type OnAssetConversionReturn = {
+  conversionRates: Record<From, Record<To, AssetConversionRate>>;
+};
+```
+
+### Fiat currency representation
+
+We SHOULD use CAIP-19 to represent fiat currencies as well. This approach
+provides a consistent way to represent all assets, making the API more
+predictable. The proposed format is:
+
+```
+asset_type:        chain_id + "/" + asset_namespace + ":" + asset_reference
+chain_id:          namespace + ":" + reference
+namespace:         "fiat"
+reference:         country_code
+asset_namespace:   "currency"
+asset_reference:   currency_code
+```
+
+The country code is a two-letter lowercase code, as defined by ISO 3166-1
+alpha-2, representing the emitter country, with the exception of the European
+Union, which is represented by "eu".
+
+The currency code is a three-letter uppercase code as defined by ISO 4217.
+
+Examples:
+
+```
+# Euro
+fiat:eu/currency:eur
+
+# United States Dollar
+fiat:us/currency:usd
+
+# Brazilian Real
+fiat:br/currency:brl
+
+# Japanese Yen
+fiat:jp/currency:jpy
+```
+
+## Appendix I: Fungible Asset Metadata
+
+The following asset metadata fields for a fungible asset are defined.
+As of the time of creation of this SIP, they are the only possible assets requested by clients.
+
+```typescript
+// Represents an asset unit.
+type FungibleAssetUnit = {
+  // Human-friendly name of the asset unit.
+  name: string;
+
+  // Ticker symbol of the asset unit.
+  symbol: string;
+
+  // Number of decimals of the asset unit.
+  decimals: number;
+};
+
+// Fungible asset metadata.
+type FungibleAssetMetadata = {
+  // Human-friendly name of the asset.
+  name: string;
+
+  // Ticker symbol of the asset's main unit.
+  symbol: string;
+
+  // Whether the asset is native to the chain.
+  native: boolean;
+
+  // Represents a fungible asset
+  fungible: true;
+
+  // Base64 representation of the asset icon.
+  iconBase64: string;
+
+  // List of asset units.
+  units: FungibleAssetUnit[];
+};
+```
+
+## Backwards compatibility
+
+Any SIPs that break backwards compatibility MUST include a section describing
+those incompatibilities and their severity. The SIP SHOULD describe how the
+author plans on proposes to deal with such these incompatibilities.
+
+## Copyright
+
+Copyright and related rights waived via [CC0](../LICENSE).
+
+[caip-19]: https://github.com/ChainAgnostic/CAIPs/blob/main/CAIPs/caip-19.md