AppIds on Avail DA?

DON'T CARE ABOUT THEORY?
If you are just looking for the easiest way to create your own AppID on Avail to continue building, you can skip to this page.

LOOKING FOR PROGRAMMATIC INSTRUCTIONS?
You can check out our API reference for the same.

Introduction

As a general-purpose base layer, Avail is designed to support many modular chains at the same time, providing consensus and data availability to all of them simultaneously.

How does this work? Avail headers contain an index that allows a given modular chain (or "application" in Avail terminology) to determine and download only the sections of a block that have data for that particular application.

This has significant benefits, including:

Modular applications are mainly unaffected by other uses of the base layer at the same time.
Block sizes can increase without requiring applications to fetch more data because they don't need to fetch the whole block, only what's relevant to them.
This filtering is done using the "application id" (AppId).

Data availability sampling is still done on the entire block, however--this is the process where clients sample tiny parts of the block at random to verify availability.

Consider a random block on Avail DA

It might contain data blobs from a variety of different rollups pertaining to their different execution environments. Think of the EVM, the SVM, Stackr, ZKsync chains, OP stack, and many more.
If all of this data is randomnly strewn about in a block, it would be tedious for an a rollup to parse through all of it just to fetch the data it needs.

random block on Avail DA

Now think of the same data neatly arranged into its own sections

But what if all of that same data in the same block was organised into different sections, stored alongside it's peers. Each of these 'sections' would be identified by an AppID.
A developer now does not need to parse through the entire block to find the data they need, they can simply query data from the AppID they are interested in.

random data arranged neatly in Avail DA block

These 'sections' are flexible

All of the rollups running on Avail DA probably won't submit data in all of the blocks. Thus, it is likely some AppIDs will be empty in some blocks.
On the flipside, some rollups might need to submit more data than usual in a particular block.
None of this is an issue on Avail DA, the individual block builds as needed in the moment.

AppIDs on Avail DA are flexible

Tell me more

Let's learn more about AppIds by going through a real-life example.

We recommend you go through the whole page before trying to go through the same steps.
Although there are multiple ways to retrieve existing AppIds and generate new ones, using the Avail DA explorer (opens in a new tab) to do so is a good way to start.
The Avail DA explorer (opens in a new tab) is very powerful and can be used in a variety of ways. For now though, let's stick to AppIds.

Make sure you're on the chain state section of the explorer. You can access it by simply clicking this link (opens in a new tab), or by navigating to it through the developer tab near the top right.
Make sure you've selected the dataAvailability pallet and the appKeys method.

Uncheck the include option toggle, and click on the + button next to the method name. You will fetch a list of all registered AppIds on Avail DA.

Each appID consists of 3 fields:

key: This is a string that is the name of the appID. Each appID should have a unique name.
owner: This is the address of the account that created the appID. A single address can create multiple AppIds.
id: This is the unique integer index of the appID. It is incremented by 1 everytime a new appID is created. Whenever a new appID is created, it is automatically assigned the next available id.

Next, check the include option toggle, and enter based avail as the bytes input. Call the function. What do you see? You will be returned a pair of owner and id, which together with the key you entered, form a unique appID.

The appKeys method is essentially a mapping that returns the owner and id of an appID given its key (key => (owner, id)).
By checking the include option toggle, you are essentially filtering the output.

How to check the next available `appID`?

Anyone can create their own appID on Avail DA. The process is entirely democratic, and it's rather simple too.

Let us first check out the next available appID on the newtork.

Within the dataAvailability pallet, select the nextAppId method. No need to pass any params, just click the + button next to the method name.
You will be returned the next available index/id for a new appID.

How to register my own `appID`?

Make sure you have one or more Avail DA wallets connected to the explorer. If you don't know how to do so, you can follow our docs on setting up a new wallet.
Simply click this link (opens in a new tab) OR navigate to the extrinsics section of the explorer through the developer tab.

Please note that the Developer tab does not show the extrinsics section at all if you don't have a wallet set up on the explorer or an extension wallet connected to it. So make sure you have an Avail DA wallet set up before moving forward.

Select the dataAvailability pallet, and the createApplicationKey method.

Enter a key for your appID. It can be anything you like, really.
This is how it should look like in the end:

Click on Submit Transaction, and then click on Sign and Submit in the box that pops up.

DO NOT CHANGE THE appID FOR THIS TRANSACTION

Each and every single transaction on Avail DA has an appID associated with it, which is greater than or equal to 0.
A transaction or data submission with the appID of 0 is used for chain-level operations.
This is what we need to use for creating a new appID, since the act of creating a new appID has nothing to do with a specific 'app' on Avail DA.
This field would instead have been a positive integer if we, for example, were submitting data to a specific application on Avail DA.

Authorize the transaction through your wallet, and you're done! You've successfully created your own appID on Avail DA.
You can verify 7 by using the steps covered earlier to query the appKeys method :)

How to submit data to my `appID`?

You can submit data to your, or any other appID on Avail DA using the explorer by calling the submitData extrinsic from within the dataAvailability pallet.

Make sure you have one or more Avail DA wallets connected to the explorer. If you don't know how to do so, you can follow our docs on setting up a new wallet.
Simply click this link (opens in a new tab) OR navigate to the extrinsics section of the explorer through the developer tab.
Select the dataAvailability pallet, and the submitData method.

Enter a random data string that you want to submit to your appID, and then click on Submit Transaction.

Fill in the AppID that you want to submit the data to. Click on Sign and Submit to authorize the transaction through your wallet.

Wait for the transaction to be included in a block and then open the detailed view of the block.

Click on your specific transaction to see it's details. This is what it should look like:

A few more things of note

As stated earlier, the key and id fields of every appID are unique. This means if you try to create an appID with the same key as an existing one, the operation will fail. This is why it makes sense to use the appKeys method to check if your desired name is already taken.
If you're a developer and are looking for more programmatic instructions, you can check out our API reference.
Anyone can submit any sort of data to any appID regardless of whether or not they created it.
But what does this mean? And is this an attack vector?

This is where it is important to understand that Avail DA is a DA layer, not an execution environment. We are not concerned with the validity of the data being submitted, only with its availability, which means we can support a wide variety of applications across multiple tech stacks.
This does not constitute an attack vector since that any app or execution layer building on top of Avail DA can always set up certain rules to filter out unwanted data submissions.
They could for example make it so that only data submitted with a particular signature, i.e. from a particular address, is accepted. All other data submitted to the particular appID is treated as spam, and ignored.

Learn more about Avail Get started with the Avail Apps Explorer