Creating Transactions

Transaction structure

As described in section Signing Transactions, a ready-to-broadcast transaction is structured as follows:

{
    "nonce": 42,
    "value": "100000000000000000",
    "receiver": "erd1cux02zersde0l7hhklzhywcxk4u9n4py5tdxyx7vrvhnza2r4gmq4vw35r",
    "sender": "erd1ylzm22ngxl2tspgvwm0yth2myr6dx9avtx83zpxpu7rhxw4qltzs9tmjm9",
    "gasPrice": 1000000000,
    "gasLimit": 70000,
    "data": "Zm9vZCBmb3IgY2F0cw==",
    "chainID": "1",
    "version": 1,
    "signature": "5845301de8ca3a8576166fb3b7dd25124868ce54b07eec7022ae3ffd8d4629540dbb7d0ceed9455a259695e2665db614828728d0f9b0fb1cc46c07dd669d2f0e"
}

SDK and tools support for creating and signing transactions

There are SDKs or tools with support for interacting with the Elrond blockchain, so one can use one of the following SDKs to perform transactions creation and signing:

General network parameters

General network parameters, such as the chain ID, the minimum gas price, the minimum gas limit and the oldest acceptable transaction version are available at the API endpoint Get Network Configuration.

{
    "config": {
        "erd_chain_id": "1",
        "erd_gas_per_data_byte": 1500,
        "erd_min_gas_limit": 50000,
        "erd_min_gas_price": 1000000000,
        "erd_min_transaction_version": 1,
        ...
    }
}

Nonce management

Each transaction broadcasted to the Network must have the nonce field set consistently with the account nonce. In the Network, transactions of a given sender address are processed in order, with respect to the transaction nonce.

The account nonce can be fetched from the API: Get Address Nonce.

The nonce must be a strictly increasing number, scoped to a given sender. The sections below describe common issues and possible solutions when managing the nonce for transaction construction.

Issue: competing transactions

Broadcasted transactions that reach the mempool having the same sender address and the same nonce are competing transactions, and only one of them will be processed (the one providing a higher gas price or, if they have the same gas price, the one that arrived the second - but keep in mind that arrival time is less manageable).

tip

Avoid competing transactions by maintaining a strictly increasing nonce sequence when broadcasting transactions of the same sender address.

Although an explicit transaction cancellation trigger is not yet available in the Network, cancellation of a transaction T1 with nonce 42 could be possible if one broadcasts a second transaction T2 with same nonce 42, with higher gas price (and without a value to transfer) immediately (e.g. 1 second) after broadcasting T1.

Issue: nonce gaps

If broadcasted transactions have their nonces higher than the current account nonce of the sender, this is considered a nonce gap, and the transactions will remain in the mempool unprocessed, until new transactions from the same sender arrive to resolve the nonce gap - or until the transactions are swept from the mempool (sweeping takes place regularly).

tip

Avoid nonce gaps by regularly fetching the current account nonce, in order to populate the nonce field correctly before broadcasting the transactions. This technique is also known as periodically recalling the nonce.

Issue: fetching a stale account nonce

You should take care when fetching the current account nonce from the API immediately after broadcasting transactions.

Example:

  1. Time 12:00:01 - the sender's nonce is recalled, and its value is 42
  2. Time 12:00:02 - the sender broadcasts the transaction T1 with nonce 42
  3. Time 12:00:03 - the sender's nonce is recalled again, in order to broadcast a new transaction. The nonce is still 42. It is stale, not yet incremented on the Network (since T1 is still pending or being processed at this very moment).
  4. Time 12:00:04 - the sender broadcasts T2 with nonce 42, which will compete with T1, as they have the same nonce.
tip

Avoid fetching stale account nonces by periodically recalling the nonce.

Avoid recalling the nonce in between rapidly sequenced transactions from the same sender . For rapidly sequenced transactions, you have to programmatically manage, keep track of the account nonce using a local mirror (copy) of the account nonce and increment it appropriately.

Gas limit computation

Please follow Gas and Fees.

Signing transactions

Please follow Signing Transactions.

Simulate transaction execution

important

Documentation about transaction simulation is preliminary and subject to change.

← Accounts ManagementQuerying the Blockchain →