📂 Developers

# Requesters and Sponsors

Table of Contents

As a developer it helps to understand what a requester is and what a sponsor does. They are both important parts of the Airnode ecosystem. This doc will further define them and walk you through the process of sponsoring a requester and deriving a sponsor wallet using the admin CLI commands.

# What is a Requester?

The term requester is important to remember. When requester is mentioned, the reference is to your smart contract that calls an Airnode.

As an example see the myContract.sol contract in the diagram within the Overview doc, it is a requester.

# What is a Sponsor?

Equally important is the term sponsor. A sponsor is an entity such as yourself, an organization, etc. Sponsors create relationships between requesters and Airnodes.

As a sponsor you will use the public address from an account within a mnemonic you own to "sponsor a requester" and then use the public address (known as a sponsorAddress) to "derive a sponsorWallet" for an Airnode. This action creates a relationship between a sponsor's requester and a particular Airnode. You do this because a sponsor is the entity that pays for the fulfillment of a request, the gas costs the Airnode will incur. These costs will be withdrawn from the sponsorWallet of the Airnode when the requester calls it.

sponsorAddress

A sponsorAddress is a public address of an account from a mnemonic, usually the default account. Rather than the default account another account from the mnemonic can be used. The sponsorAddress is used to uniquely identify a sponsor.

  1. In the diagram below a sponsor uses a sponsorAddress to sponsor a requester with the Admin CLI. The CLI will use the default address of the mnemonic passed as the sponsorAddress for the sponsorship unless another account is specified.

  2. Next the sponsor will derive a sponsorWallet for an Airnode using the sponsorAddress.

  3. The requester can now make requests of the Airnode.

image


In the above diagram it is possible to use the same sponsorAddress (0xF4...dDyu9) to derive other sponsor wallets for other Airnodes. And it is possible to sponsor more than one requester with the same sponsorAddress. However it is important to remember that all requesters can now access all the Airnodes regardless if they need to. There is no harm in this scenario.

# Advanced Scenarios

  • Two requesters, one Airnode, one sponsorWallet:

    Two requesters sponsored with the same sponsorAddress (e.g., 0xF4...dDyu9) would access the same Airnode using a single sponsorWallet derived by the sponsorAddress.

  • Two requesters, one Airnode, two sponsorWallets:

    Sponsor two different requesters each with a different sponsorAddress (e.g., 0xF4...dDyu9 and 0xG9...fFzc5). Using the separate sponsorAddresses you can derive two separate sponsorWallets for the same Airnode. Now each requester will deplete funds from a separate Airnode sponsorWallet when using the Airnode.

  • One requester, two Airnodes, two sponsorWallets:

    A requester can make requests from two different Airnodes. Sponsor the requester with a sponsorAddress. Derive two sponsorWallets, one for each of two the Airnodes, using the sponsorAddress. Despite the fact that the sponsorWallet for each Airnode was derived with the same sponsorAddress the sponsorWallets are different since they are derived using the airnode's xpub plus the sponsorAddress. The sponsor must fund both wallets separately using the unique sponsorWalletAddress of the two sponsorWallets.

# Things to Remember

When you sponsor a requester with a sponsorAddress you are giving it permission to use the sponsorWallet (associated with a Airnode) that was derived using the same sponsorAddress.

When the requester makes a request to the Airnode, the Airnode will use funds from the corresponding sponsorWallet to pay gas costs in response to the request. Therefore the sponsor pays for the fulfillment of the request.

Sponsors need to keep their sponsorWallets topped off if they want Airnodes to fulfill requests made by their requesters. However this does not cover the cost of API data that the Airnode serves, see API Provider Fees.

# Admin CLI Commands

There are several sponsor and requester related commands in the Admin CLI Commands package. You can also see a list of available commands using npx @api3/airnode-admin --help.

In the next two sections of this doc you will use two commands from the @api3/airnode-admin package to sponsor a requester and to derive a sponsor wallet.

  1. sponsor-requester sponsors a requester.
  2. derive-sponsor-wallet-addresscreates a sponsor wallet associated with an Airnode.

# How to Sponsor a Requester

To sponsor a requester execute the sponsor-requester command using the parameters detailed in the list below. Your requester should already be deployed on-chain. This command has transaction gas costs.

  • providerURL: A blockchain provider URL (such as Infura) with providerID for the desired network.
  • sponsor-mnemonic: Used for gas costs to fund the sponsorship and used to derive the sponsorAddress from the default address. The sponsorAddress will be needed to derive a sponsorWallet for an Airnode.
  • requester-address: Address of the requester contract.
  • derivation-path (optional) (not used in the example below): Selects an alternate account to use from the mnemonic rather than the default account.

Executing the command sponsor-requester will sponsor a requester and returns the requesterAddress and sponsorAddress.

# How to Derive a Sponsor Wallet

To use a particular Airnode you must derive a sponsorWallet. Once the sponsorWallet is created it must be funded using the public address (sponsorWalletAddress) returned by the command derive-sponsor-wallet-address. Each Airnode keeps a separate list of individual sponsorWallets that can access the Airnode. Learn more about a sponsorWallet.

To derive a sponsorWallet for an Airnode execute the derive-sponsor-wallet-address command using the parameters detailed in the list below. There are no transaction gas costs to do so.

  • airnode-xpub: The extended public address of the Airnode for path m/44'/60'/0'.
  • airnode-address: The public address of the desired Airnode.
  • sponsor-address: The sponsorAddress (an address of an Ethereum account) owned by a sponsor. Usually the sponsorAddress is the one returned when sponsoring a requester.

The command derive-sponsor-wallet-address will return the public address (sponsorWalletAddress) of the sponsorWallet to be funded by the sponsor.

Sponsors need to keep their sponsorWallets topped off if they want Airnodes to fulfill requests made by their requesters. However this does not cover the cost of API data that the Airnode serves, see API Provider Fees.

If you forget the public address (sponsorWalletAddress) of the sponsorWallet simply run derive-sponsor-wallet-address again. Since the wallet already exists for the airnodeAddress/sponsorAddress pair it will just return the address.

Designated Sponsor Wallets

Sponsors should not fund a sponsorWallet with more then they can trust the Airnode with, as the Airnode controls the private key to the sponsorWallet. The deployer of such Airnode undertakes no custody obligations, and the risk of loss or misuse of any excess funds sent to the sponsorWallet remains with the sponsor.

# Record Keeping

During and after sponsoring requesters and deriving a sponsorWallet there are a few things to keep track of.

Item Description
sponsor's mnemonic The mnemonic from which the sponsorAddress was extracted.
sponsor address The public address of an account derived from a sponsor's mnemonic when sponsoring a requester. Record which sponsorAddress was used to create a sponsorWallet for each Airnode.
sponsor wallet address Record the sponsorWalletAddress of the sponsorWallet derived for an Airnode. For each Airnode you have derived a sponsorWallet, the Airnode keeps the private key and returns the public address (sponsorWalletAddress) which is used to fund the sponsorWallet.

You can acquire the public address (sponsorWalletAddress) of a sponsorWallet later, if you lose it, by running the command derive-sponsor-wallet-address again. Since the sponsorWallet was already created for the sponsorAddress/airnodeAddress pair, the command will only return the public address for the wallet. However you must use the same sponsorAddress used when the wallet was first created or a new sponsorWallet will be created.

Last Updated: 8/16/2022, 12:50:05 PM