construction/preprocess - Cardano

Example code for the construction/preprocess JSON-RPC method. Complete guide on how to use construction/preprocess JSON-RPC in GetBlock Web3 documentation.

This endpoint creates a request to fetch the metadata needed to construct a transaction, from the intended operations. It is the first online-preparation step of the construction flow.

Parameters

The request body is a JSON object with the following fields.

Field	Type	Required	Description
network_identifier	object	Yes	The network to construct for
operations	array	Yes	The intended operations describing the transaction
metadata	object	No	Optional construction metadata, such as relative time to live

Request

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/construction/preprocess' \
--header 'Content-Type: application/json' \
--data-raw '{
    "network_identifier": {
        "blockchain": "cardano",
        "network": "mainnet"
    },
    "operations": [
        {
            "operation_identifier": {
                "index": 0
            },
            "type": "input",
            "account": {
                "address": "addr1qxy2lpan99fcnhhyzr8w8qk4dqz4mp7g6b8h3r2v5c9d0e1f2g3h4j5k6l7m8n9p0q"
            },
            "amount": {
                "value": "-9410563",
                "currency": {
                    "symbol": "ADA",
                    "decimals": 6
                }
            },
            "coin_change": {
                "coin_identifier": {
                    "identifier": "10b54fd708ab2e5703979b4ba27ca0339882abc2062e77fbe51e625203a49642:0"
                },
                "coin_action": "coin_spent"
            }
        }
    ],
    "metadata": {}
}'

JavaScript

example.js

const response = await fetch(
    'https://go.getblock.io/<ACCESS-TOKEN>/construction/preprocess',
    {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({"network_identifier": {"blockchain": "cardano", "network": "mainnet"}, "operations": [{"operation_identifier": {"index": 0}, "type": "input", "account": {"address": "addr1qxy2lpan99fcnhhyzr8w8qk4dqz4mp7g6b8h3r2v5c9d0e1f2g3h4j5k6l7m8n9p0q"}, "amount": {"value": "-9410563", "currency": {"symbol": "ADA", "decimals": 6}}, "coin_change": {"coin_identifier": {"identifier": "10b54fd708ab2e5703979b4ba27ca0339882abc2062e77fbe51e625203a49642:0"}, "coin_action": "coin_spent"}}], "metadata": {}})
    }
);
console.log(await response.json());

Python

example.py

import requests

response = requests.post(
    'https://go.getblock.io/<ACCESS-TOKEN>/construction/preprocess',
    headers={'Content-Type': 'application/json'},
    json={"network_identifier": {"blockchain": "cardano", "network": "mainnet"}, "operations": [{"operation_identifier": {"index": 0}, "type": "input", "account": {"address": "addr1qxy2lpan99fcnhhyzr8w8qk4dqz4mp7g6b8h3r2v5c9d0e1f2g3h4j5k6l7m8n9p0q"}, "amount": {"value": "-9410563", "currency": {"symbol": "ADA", "decimals": 6}}, "coin_change": {"coin_identifier": {"identifier": "10b54fd708ab2e5703979b4ba27ca0339882abc2062e77fbe51e625203a49642:0"}, "coin_action": "coin_spent"}}], "metadata": {}}
)

print(response.json())

Response

{
    "options": {
        "relative_ttl": 1000,
        "transaction_size": 246
    }
}

Response Parameters

Field	Type	Description
options	object	Options to pass to the metadata endpoint
required_public_keys	array	Accounts whose public keys are required, when applicable

Use Cases

• Construction Start: Begin building a transaction from operations

• Size Estimation: Read the estimated transaction size

• TTL Handling: Obtain the relative time to live for the transaction

• Offline Prep: Prepare metadata options before an online fetch

Error Handling

Error Code	Message	Description
1	Invalid request	A required construction field is missing or malformed
6	Transaction decode failed	The supplied transaction could not be decoded
14	Invalid signature	A supplied signature is malformed or does not match
5	Internal error	The node failed to process the construction step