chain-data

Use chain-data to retrieve the blockchain-specific public metadata for a transaction. This function returns an object with the following fields:

• chain-id: The chain identifier (0-19) for the blockchain where the transaction was executed.
• block-height: The height of the block that includes the transaction.
• block-time: The timestamp of the block that includes the transaction.
• prev-block-hash: The hash of the previous block.
• sender: The sender of the transaction.
• gas-limit: The gas limit for the transaction.
• gas-price: The gas price for the transaction.
• gas-fee: The gas fee for the transaction.

Basic syntax

To retrieve the public metadata for a transaction using chain-data, use the following syntax:

(chain-data)

Arguments

You can use the chain-data function without arguments in code that identifies the transaction that you want to return metadata for.

Return value

The chain-data function returns the public metadata for a transaction as an object with the following fields

Field	Type	Description
chain-id	string	The chain identifier (0-19) for the blockchain where the transaction was executed.
block-height	integer	The height of the block that includes the transaction.
block-time	time	The timestamp of the block that includes the transaction.
prev-block-hash	string	The hash of the previous block.
sender	string	The sender of the transaction.
gas-limit	integer	The gas limit for the transaction.
gas-price	decimal	The gas price for the transaction.
gas-fee	decimal	The gas fee for the transaction.

Examples

If you call the chain-data function in the Pact REPL without providing a transaction context in the surrounding code, the function returns the object with placeholder fields. For example:

{"block-height": 0
,"block-time": "1970-01-01T00:00:00Z"
,"chain-id": ""
,"gas-limit": 0
,"gas-price": 0.0
,"prev-block-hash": ""
,"sender": ""}

If you provide context for the call, the function returns an object with fields similar to the following:

pact> (chain-data)
{
  "chain-id": "3",
  "block-height": 4357306,
  "block-time": "2024-06-06 20:12:56 UTC",
  "prev-block-hash": "33caae279bd584b655283b7d692d7e7b408d6549869c5eb6dcf2dc60021c3916",
  "sender": "k:1d5a5e10eb15355422ad66b6c12167bdbb23b1e1ef674ea032175d220b242ed4,
  "gas-limit": 2320,
  "gas-price": 1.9981e-7,
  "gas-fee": 726
}

In most cases, you use chain-data in Pact modules or in combination with frontend libraries to return information in the context of a specific transaction. The following example illustrates using chain-data in a Pact module to get the block time from a transaction:

(let ((curr-time:time (at 'block-time (chain-data))))