get_header_by_number - Nervos

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

Returns the information about a block header by block number. Same response shape as get_header.

Parameters

Parameter	Type	Required	Description
block_number	Uint64	Yes	Block number (hex string)
verbosity	Uint32	No	"0x1" for full object, "0x0" for serialized bytes

Request Example

cURL

curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "get_header_by_number",
    "params": [
        "0xe5a45f",
        "0x1"
    ],
    "id": "getblock.io"
}'

JavaScript (Axios)

import axios from 'axios';

const data = JSON.stringify({
    "jsonrpc": "2.0",
    "method": "get_header_by_number",
    "params": [
        "0xe5a45f",
        "0x1"
    ],
    "id": "getblock.io"
});

const config = {
    method: 'post',
    url: 'https://go.getblock.io/<ACCESS-TOKEN>/',
    headers: {
        'Content-Type': 'application/json'
    },
    data: data
};

axios(config)
    .then(response => console.log(JSON.stringify(response.data, null, 2)))
    .catch(error => console.log(error));

Python (Requests)

import requests
import json

url = "https://go.getblock.io/<ACCESS-TOKEN>/"

payload = json.dumps({
    "jsonrpc": "2.0",
    "method": "get_header_by_number",
    "params": [
        "0xe5a45f",
        "0x1"
    ],
    "id": "getblock.io"
})

headers = {
    'Content-Type': 'application/json'
}

response = requests.post(url, headers=headers, data=payload)
print(response.text)

Rust (Reqwest)

use reqwest::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();

    let payload = json!({
        "jsonrpc": "2.0",
        "method": "get_header_by_number",
        "params": [
                "0xe5a45f",
                "0x1"
        ],
        "id": "getblock.io"
});

    let response = client
        .post("https://go.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&payload)
        .send()
        .await?;

    let result: serde_json::Value = response.json().await?;
    println!("{:#?}", result);

    Ok(())
}

Response Example

{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": {
        "hash": "0x02530b25ad0ff677acc365cb73de3e8cc09c7ddd58272e879252e199d08df83b",
        "number": "0xe5a45f",
        "timestamp": "0x18f3b8d2a3c",
        "parent_hash": "0x77fdd22f6ae8a717de9ae2b128834e9b2a1bb7e7387f01ddc278c6ec37ebaa05",
        "epoch": "0x707080a000ca6"
    }
}

Response Parameters

Field	Type	Description
result	Header | null	Header object, or null if not found

Use Cases

• Light client walking the chain by number

• Header-chain-only synchronization

Error Handling

Status Code	Error Message	Cause
403	Forbidden	Missing or invalid <ACCESS-TOKEN>
-32602	Invalid params	Request parameters are missing or malformed
-32601	Method not found	Method does not exist or is not enabled on this node
-32603	Internal error	Server-side error while processing the request
429	Too Many Requests	Rate limit exceeded for your plan

SDK Integration

@ckb-lumos/lumos

import { RPC } from '@ckb-lumos/rpc';

const rpc = new RPC('https://go.getblock.io/<ACCESS-TOKEN>/');

// Lumos provides typed methods on `rpc` (e.g. rpc.getTipHeader(), rpc.getBlock(hash)).
// For raw access to any CKB RPC method:
const result = await rpc.send('get_header_by_number', ["0xe5a45f", "0x1"]);
console.log(result);

ckb-sdk-python / requests

# Using the official CKB SDK Python (ckb-sdk-python).
# For methods not yet wrapped, fall back to raw requests.
import requests

response = requests.post('https://go.getblock.io/<ACCESS-TOKEN>/', json={
    'jsonrpc': '2.0',
    'id': 'getblock.io',
    'method': 'get_header_by_number',
    'params': ["0xe5a45f", "0x1"]
})
print(response.json())