Application Integration Guide

If you provide blockchain services to your customers and wish to add the Aptos blockchain to your platform, then this guide is for you. This system integrators guide will walk you through all you need to integrate the Aptos blockchain into your platform.

Overview

This document will guide you through the following tasks to integrate with Aptos:

1. Prepare an environment for testing.
2. Create an account on the blockchain.
3. Exchange account identifiers with another entity on the blockchain, for example, to perform swaps.
4. Create a transaction.
5. Obtain a gas estimate and validate the transaction for correctness.
6. Submit the transaction to the blockchain.
7. Wait for the outcome of the transaction.
8. Query historical transactions and interactions for a given account with a specific account, i.e., withdraws and deposits.

Getting Started

In order to get started you’ll need to select a network and pick your set of tools. There are also a handful of SDKs to help accelerate development.

SDKs and tools

Aptos has multiple SDKs across many different languages and platforms, please check out SDKs for more information.

Almost all developers will benefit from exploring the CLI. Using the CLI demonstrates how the CLI can be used to create accounts, transfer coins, publish Move modules, and more.

Accounts on Aptos

An account represents an entity on the Aptos blockchain that can send transactions. Each account is identified by a particular 32-byte account address and is a container for Move modules and resources. On Aptos, accounts must be created on-chain prior to any blockchain operations involving that account. The Aptos framework supports implicitly creating accounts when transferring Aptos coin via aptos_account::transfer or explicitly via aptos_account::create_account.

At creation, an Aptos account contains:

• A resource containing Aptos Coin and deposit and withdrawal of coins from that resource.
• An authentication key associated with their current public, private key(s).
• A strictly increasing sequence number that represents the account’s next transaction’s sequence number to prevent replay attacks.
• A strictly increasing number that represents the next distinct GUID creation number.
• An event handle for all new types of coins added to the account.
• An event handle for all key rotations for the account.

Read more about Accounts and set one up.

Transactions

Aptos transactions are encoded in Binary Canonical Serialization (BCS). Transactions contain information such as the sender’s account address, authentication from the sender, the desired operation to be performed on the Aptos blockchain, and the amount of gas the sender is willing to pay to execute the transaction.

Read more in Transactions and States.

Generating transactions

Aptos supports two methods for constructing transactions:

• Using the Aptos client libraries to generate native BCS transactions.
• Constructing JSON-encoded objects and interacting with the REST API to generate native transactions.

The preferred approach is to directly generate native BCS transactions. Generating them via the REST API enables rapid development at the cost of trusting the fullnode to generate the transaction correctly.

BCS-encoded transactions

BCS-encoded transactions can be submitted to the /transactions endpoint but must specify Content-Type: application/x.aptos.signed_transaction+bcs in the HTTP headers. This will return a transaction submission result that, if successful, contains a transaction hash in the hash field.

Types of transactions

Within a given transaction, the target of execution can be one of two types:

• An entry function
• A Move script

All official SDKs support the generation of transactions that target entry functions. This guide points out many of those entry functions, such as aptos_account::transfer and aptos_account::create_account.

Most basic operations on the Aptos blockchain should be available via entry point calls. While one could submit multiple transactions calling entry points in series, such operations benefit from being called atomically from a single transaction. A script payload transaction can call any public (entry) function defined within any module. Here’s an example Move script that uses a MultiAgent transaction to extract funds from two accounts and deposit them into two other accounts. This is a Python example that uses the bytecode generated by compiling that script.

Status of a transaction

Obtain transaction status by querying the API /transactions/by_hash/{hash} with the hash returned during the submission of the transaction.

A reasonable strategy for submitting transactions is to limit their lifetime to 30 to 60 seconds, and polling that API at regular intervals until success or several seconds after that time has elapsed. If there is no commitment on-chain, the transaction was likely discarded.

All SDKs support this automatically for waiting for transactions.

Testing transactions or transaction pre-execution

To facilitate evaluation of transactions as well as gas estimation, Aptos supports a simulation API that does not require and should not contain valid signatures on transactions.

The simulation API is a synchronous API that executes a transaction and returns the output inclusive of gas usage. The simulation API can be accessed by submitting a transaction to /transactions/simulate.

Both the Typescript SDK and Python SDK support the simulation API. Note the output and gas used may change based upon the state of the account. For gas estimations, we recommend that the maximum gas amount be larger than the amount quoted by this API.

Viewing current and historical state

Most integrations into the Aptos blockchain benefit from a holistic and comprehensive overview of the current and historical state of the blockchain. Aptos provides historical transactions, state, and events, all the result of transaction execution.

• Historical transactions specify the execution status, output, and tie to related events. Each transaction has a unique version number associated with it that dictates its global sequential ordering in the history of the blockchain ledger.
• The state is the representation of all transaction outputs up to a specific version. In other words, a state version is the accumulation of all transactions inclusive of that transaction version.
• As transactions execute, they may emit events. Events are hints about changes in on-chain data.

The storage service on a node employs two forms of pruning that erase data from nodes:

• state
• events, transactions, and everything else

While either of these may be disabled, storing the state versions is not particularly sustainable.

Events and transactions pruning can be disabled via setting the enable_ledger_pruner to false. This is default behavior in Mainnet. In the near future, Aptos will provide indexers that mitigate the need to directly query from a node.

The REST API offers querying transactions and events in these ways:

• Transactions for an account
• Transaction by version
• Events by event handle

Exchanging and tracking fungible assets

Aptos has a standard Fungible Asset. Different types of fungible asset (FA) can be represented in this standard through the use of distinct metadata object.

A user’s FA is stored in FungibleStore objects owned by them. For each type of FA, every account has one primary store for that FA and optional multiple secondary stores. The difference between primary and secondary stores is the address of primary store is deterministic based on the addresses of user account and metadata object.

Transferring FAs between users

FAs, including APT, can be transferred between users’ primary stores via the primary_fungible_store::transfer function. For any FungibleStore s, fungible_asset::transfer would be invoked with FungibleStore object addresses.

Current balance for Fungible Asset

The current balance for an APT FA of FungibleStore is available at the account resources URL: https://{rest_api_server}/accounts/{fungible_store_object_address}/resource/0x1::fungible_asset::FungibleStore. The balance is stored as balance. The resource also contains a metadata object of the FA type and the frozen status. The address of the primary fungible store can be calculated as sha3_256(32-byte account address | 32-byte metadata object address | 0xFC). The metadata object address of APT FA is 0xA.

Aptos users have the option to upgrade to concurrent fungible balance to allow parallelization of balance updates, improving the performance of a single account. When a user has upgraded a fungible store balance to support concurrent update, the fungible store object will have another resource ConcurrentFungibleBalance that contains the balance of the store, and the balance field of FungibleStore will be set to 0. The current balance for an APT FA of ConcurrentFungibleBalance (if exists) is available at the account resources URL: https://{rest_api_server}/accounts/{fungible_store_object_address}/resource/0x1::fungible_asset::ConcurrentFungibleBalance.

Therefore, to get the total balance of a fungible asset, it is either the non-zero balance of FungibleStore or the balance field of ConcurrentFungibleBalance if it exists and the balance of FungibleStore is 0.

{
  "type": "0x1::fungible_asset::FungibleStore",
  "data": {
    "balance": "233910778869",
    "frozen": false,
    "metadata": {
      "inner": "0xedc2704f2cef417a06d1756a04a16a9fa6faaed13af469be9cdfcac5a21a8e2e"
    }
  }
}

{
    "type": "0x1::fungible_asset::ConcurrentFungibleBalance",
    "data": {
        "balance": "233910778869"
    }
}

Exchanging and tracking coins

Aptos has a standard Coin type. Different types of coins can be represented in this type through the use of distinct structs that represent the type parameter or generic for Coin<T>.

Coins are stored within an account under the resource CoinStore<T>. At account creation, each user has the resource CoinStore<0x1::aptos_coin::AptosCoin> or CoinStore<AptosCoin>, for short. Within this resource is the Aptos coin: Coin<AptosCoin>.

Transferring coins between users

Coins, including APT, can be transferred between users via the aptos_account::transfer_coins function for all coins and aptos_account::transfer for Aptos coins.

Current balance for a coin

To retrieve the balance of a coin, or a coin that was migrated to a fungible asset, you can use the 0x1::coin::balance<CoinType>(account address) view function. This will combine the coin and coin migrated to fungible asset balances.

import { Aptos, AptosConfig, Network } from "@aptos-labs/ts-sdk";
 
const config = new AptosConfig({ network: Network.DEVNET });
const aptos = new Aptos(config);
 
const coinType = "0x1::aptos_coin::AptosCoin";
const account = "0x00000000000000000000000000000001";
const [balanceStr] = await aptos.view<[string]>({
  payload: {
    function: "0x1::coin::balance",
    typeArguments: [coinType],
    functionArguments: [account]
  }
});
const balance = parseInt(balanceStr, 10);

Querying transactions

In Aptos, each transaction is committed as a distinct version to the blockchain. This allows for the convenience of sharing committed transactions by their version number; to do so, query: https://{rest_server_api}/transactions/by_version/{version}

Transactions submitted by an account can also be queried via the following URL where the sequence_number matches the sequence number of the transaction: https://{rest_server_api}/account/{address}/transactions?start={sequence_number}&limit=1

A transfer transaction would appear as follows:

{
  "version": "13629679",
  "gas_used": "4",
  "success": true,
  "vm_status": "Executed successfully",
  "changes": [
    {
      "address": "0xb258b91eee04111039320a85b0c24a2dd433909e14a6b5c32ee722e0fdecfddc",
      "data": {
        "type": "0x1::coin::CoinStore<0x1::aptos_coin::AptosCoin>",
        "data": {
          "coin": {
            "value": "1000"
          },
          "deposit_events": {
            "counter": "1",
             "guid": {
               "id": {
                 "addr": "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
                 "creation_num": "2"
               }
             }
          },
          ...
        }
      },
      "type": "write_resource"
    },
    ...
  ],
  "sender": "0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
  "sequence_number": "0",
  "max_gas_amount": "2000",
  "gas_unit_price": "1",
  "expiration_timestamp_secs": "1660616127",
  "payload": {
    "function": "0x1::aptos_account::transfer",
    "arguments": [
      "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
      "1000"
    ],
    "type": "entry_function_payload"
  },
  "events": [
    {
      "key": "0x0300000000000000810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
      "guid": {
        "id": {
          "addr": "0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
          "creation_num": "3"
        }
      },
      "sequence_number": "0",
      "type": "0x1::coin::WithdrawEvent",
      "data": {
        "amount": "1000"
      }
    },
    {
      "key": "0x02000000000000005098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
      "guid": {
        "id": {
          "addr": "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
          "creation_num": "2"
        }
      },
      "sequence_number": "0",
      "type": "0x1::coin::DepositEvent",
      "data": {
        "amount": "1000"
      }
    }
  ],
  "timestamp": "1660615531147935",
  "type": "user_transaction"
}

Here is a breakdown of the information in a transaction:

• version indicates the globally unique identifier for this transaction, its ordered position in all the committed transactions on the blockchain
• sender is the account address of the entity that submitted the transaction
• gas_used is the units paid for executing the transaction
• success and vm_status indicate whether the transaction successfully executed and any reasons why it might not have
• changes include the final values for any state resources that have been modified during the execution of the transaction
• events contain all the events emitted during the transaction execution
• timestamp is the near real-time timestamp of the transaction’s execution

If success is false, then vm_status will contain an error code or message that resulted in the transaction failing to succeed. When success is false, changes will be limited to gas deducted from the account and the sequence number incrementing. There will be no events.

Each event in events is differentiated by a key. The key is derived from the guid in changes. Specifically, the key is a 40-byte hex string where the first eight bytes (or 16 characters) are the little-endian representation of the creation_num in the guid of the changes event, and the remaining characters are the account address.

As events do not dictate what emitted them, it is imperative to track the path in changes to determine the source of an event. In particular, each CoinStore<T> has both a WithdrawEvent and a DepositEvent, based upon the type of coin. In order to determine which coin type is used in a transaction, an indexer can compare the guid::creation_num in a changes event combined with the address to the key for events in events.

Using the above example, events[1].guid is equivalent to changes[0].data.data.deposit_events.guid, which is

{"addr": "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e", "creation_num": "2"}

Querying events

Aptos provides clear and canonical events for all withdraw and deposit of coins. This can be used in coordination with the associated transactions to present to a user the change of their account balance over time, when that happened, and what caused it. With some amount of additional parsing, metadata such as the transaction type and the other parties involved can also be shared.

Query events by handle URL: https://{rest_api_server}/accounts/{address}/events/0x1::coin::CoinStore<0x1::aptos_coin::AptosCoin>/withdraw_events

[
  {
    "version":"13629679",
    "key": "0x0300000000000000cb2f940705c44ba110cd3b4f6540c96f2634938bd5f2aabd6946abf12ed88457",
    "guid": {
      "id": {
        "addr": "0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
        "creation_num": "3"
      }
    },
    "sequence_number": "0",
    "type": "0x1::coin::WithdrawEvent",
    "data": {
      "amount": "1000"
    }
  }
]

Gather more information from the transaction that generated the event by querying https://{rest_server_api}/transactions/by_version/{version} where {version} is the same value as the {version} in the event query.

Tracking coin balance changes

Consider the transaction from the earlier section, but now with an arbitrary coin 0x1337::my_coin::MyCoin and some gas parameters changed:

{
  "version": "13629679",
  "gas_used": "20",
  "success": true,
  "vm_status": "Executed successfully",
  "changes": [
    {
      "address": "0xb258b91eee04111039320a85b0c24a2dd433909e14a6b5c32ee722e0fdecfddc",
      "data": {
        "type": "0x1::coin::CoinStore<0x1337::my_coin::MyCoin>",
        "data": {
          "coin": {
            "value": "1000"
          },
          "deposit_events": {
            "counter": "1",
            "guid": {
              "id": {
                "addr": "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
                  "creation_num": "2"
              }
            }
          },
        ...
        }
      },
      "type": "write_resource"
    },
    ...
  ],
  "sender": "0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
  "sequence_number": "0",
  "max_gas_amount": "2000",
  "gas_unit_price": "110",
  "expiration_timestamp_secs": "1660616127",
  "payload": {
    "function": "0x1::aptos_account::transfer_coins",
    "type_arguments": [
      "0x1337::my_coin::MyCoin"
    ],
    "arguments": [
      "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
      "1000"
    ],
    "type": "entry_function_payload"
  },
  "events": [
    {
      "key": "0x0300000000000000810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
      "guid": {
        "id": {
          "addr": "0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b",
          "creation_num": "3"
        }
      },
      "sequence_number": "0",
      "type": "0x1::coin::WithdrawEvent",
      "data": {
        "amount": "1000"
      }
    },
    {
      "key": "0x02000000000000005098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
      "guid": {
        "id": {
          "addr": "0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e",
          "creation_num": "2"
        }
      },
      "sequence_number": "0",
      "type": "0x1::coin::DepositEvent",
      "data": {
        "amount": "1000"
      }
    }
  ],
  "timestamp": "1660615531147935",
  "type": "user_transaction"
}

There are three balance changes in this transaction:

1. A withdrawal of 1000 of 0x1337::my_coin::MyCoin from the transaction sending account 0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b
2. A deposit of 1000 of 0x1337::my_coin::MyCoin to receiving account 0x5098df8e7969b58ab3bd2d440c6203f64c60a1fd5c08b9d4abe6ae4216246c3e
3. A gas fee 2200 of 0x1::aptos_coin::AptosCoin from the sending account 0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b

To retrieve the withdrawal information:

1. Scan the changes for 0x1::coin::CoinStore<CoinType>. Note the CoinType is a generic signifying which coin is stored in the store. In this example, the CoinType is 0x1337::my_coin::MyCoin.
2. Retrieve the guid for withdraw_events. In this example, the guid contains addr 0x810026ca8291dd88b5b30a1d3ca2edd683d33d06c4a7f7c451d96f6d47bc5e8b and creation_num 3.
3. Scan for events with this guid and extract the event associated with it. In this example, it is the 0x1::coin::WithdrawEvent.
4. Note the amount field will be the number of CoinType removed from the account in the guid. In this example, it is 1000.

To retrieve the deposit information, it’s the same as withdrawal except:

1. The guid used is under deposit_events
2. The amount will be a positive increase on the account’s balance.
3. The event’s name will be: 0x1::coin::DepositEvent

To retrieve the gas fee:

1. The gas_used field must be multiplied times the gas_unit_price. In this example, gas_used=20 and gas_unit_price=110 so the total gas coins withdrawn is 2200.
2. Gas is always: 0x1::aptos_coin::AptosCoin

To retrieve information about the number of decimals of the coin:

1. You can retrieve the number of decimals for a coin via its: 0x1::coin::CoinInfo<CoinType>
2. This will be located at the address of the coin type. In this example, you would need to look up 0x1::coin::CoinInfo<0x1337::my_coin::MyCoin> at address 0x1337.

To create some sample data to explore, conduct “Your first transaction”. To learn more about coin creation, make “Your First Coin”.