Use with CosmJs

How to detect Fin

Fin API may be undefined right after the webpage shown. Please check the How to detect Fin first before reading this section.

Connecting with CosmJS

CosmJS link: https://www.npmjs.com/package/@cosmjs/launchpad (opens new window), https://www.npmjs.com/package/@cosmjs/stargate(opens new window)

You can connect Fin to CosmJS using the OfflineSigner.

// Enabling before using the Fin is recommended.
// This method will ask the user whether or not to allow access if they haven't visited this website.
// Also, it will request user to unlock the wallet if the wallet is locked.
await window.keplr.enable(chainId);

const offlineSigner = window.getOfflineSigner(chainId);

// You can get the address/public keys by `getAccounts` method.
// It can return the array of address/public key.
// But, currently, Fin extension manages only one address/public key pair.
// XXX: This line is needed to set the sender address for SigningCosmosClient.
const accounts = await offlineSigner.getAccounts();

// Initialize the gaia api with the offline signer that is injected by Fin extension.
const cosmJS = new SigningCosmosClient(
    "https://lcd-cosmoshub.keplr.app/rest",
    accounts[0].address,
    offlineSigner,
);

To get the OfflineSigner, you may use keplr.getOfflineSigner(chainId) or window.getOfflineSigner(chainId). (window.getOfflineSigner is an alias that runs keplr.getOfflineSigner and returns the value)

The window.keplr.enable(chainId) method will request the user to unlock their Fin extension if it's locked. If the user has not given permission to connect their extension to the website, it will first ask to connect the website.

If the user cancels the unlock or rejects the permission to connect, an error will be thrown.

If the extension is already unlocked and the website has permission to connect, no action will happen and resolve.

window.keplr.enable(chainId) is not mandatory. Even if the method wasn't called, if an API that requests access to Fin is called the flow above will automatically run. However, it is recommended that window.keplr.enable(chainId) is first run.

Types of Offline Signers

In CosmJS, there are two types of Signers: OfflineSigner and OfflineDirectSigner. OfflineSigner is used to sign SignDoc serialized with Amino in Cosmos SDK Launchpad (Cosmos SDK v0.39.x or below). OfflineDirectSigner is used to sign Protobuf encoded SignDoc.

Fin supports both types of Signers. Fin’s keplr.getOfflineSigner(chainId) or window.getOfflineSigner(chainId) returns a Signer that satisfies both the OfflineSigner and OfflineDirectSigner. Therefore, when using CosmJS with this Signer, Amino is used for Launchpad chains and Protobuf is used for Stargate chains.

However, if the msg to be sent is able to be serialized/deserialized using Amino codec you can use a signer for Amino. Also, as there are some limitations to protobuf type sign doc, there may be cases when Amino is necessary. For example, Protobuf formatted sign doc is currently not supported by Ledger Nano’s Cosmos app. Also, because protobuf sign doc is binary formatted, msgs not natively supported by Fin may not be human-readable.

If you’d like to enforce the use of Amino, you can use the following APIs: keplr.getOfflineSignerOnlyAmino(chainId) or window.getOfflineSignerOnlyAmino(chainId: string). Because this will always return an Amino compatible signer, any CosmJS requested msg that is Amino compatible will request an Amino SignDoc to Fin.

Also, window.getOfflineSignerAuto(chainId: string): Promise<OfflineSigner | OfflineDirectSigner> or window.getOfflineSignerAuto(chainId: string): Promise<OfflineSigner | OfflineDirectSigner> API is supported. Please note that the value returned is async. This API automatically returns a signer that only supports Amino if the account is a Ledger-based account, and returns a signer that is compatible for both Amino and Protobuf if the account is a mnemonic/private key-based account. Because this API is affected by the type of the connected Fin account, if keplr_keystorechange event is used to detect account changes the signer must be changed using the API when this event has been triggered.

Use with Stargate

Fin's OfflineSigner implements the OfflineDirectSigner interface. Use SigningStargateClient with Fin's OfflineSigner, and Fin will sign the transaction in Proto sign doc format.

Example

Refer to the keplr-example (opens new window)repository for example code on how to integrate Fin with CosmJS.

Interaction Options

You can use Fin native API’s to set interaction options even when using CosmJS. Please refer to this section.

Adding a custom blockchain to Fin

If Fin doesn't natively support your blockchain within the extension, please refer to the Suggest chain section.