JSON-RPC getBlockHash Request

Question

I am trying to request a block hash for a specific block using the Polkadot JSON-RPC but no matter how I construct the request (with Python), it always returns the latest block and not the one I want. How can I solve that?

import requests

import json

def get_block_hash(block_number):

  url = "https://dot.getblock.io/mainnet/"

  payload = json.dumps({

    "jsonrpc": "2.0",

    "method": "chain_getBlockHash",

    "id": 1

  })

  headers = {
    'x-api-key': 'enter-api-key',
    'blockNumber': block_number,
    'Content-Type': 'application/json'
  }

  response = requests.request("POST", url, headers=headers, data=payload)

  print(response.text)

  return response

Answer 1

The JSON-RPC 2.0 parameters doesn't go in the header, they are part of the body. Here is a correctly-formatted body for a getBlockHash query -

{
  "id":1,
  "jsonrpc":"2.0",
  "method":"chain_getBlockHash",
  "params":[123456]
}

The params above contain the blocknumber, 123456 in this case.

Answer 2

import json
# pip3 install websocket-client
import websocket

uri = 'wss://rpc.polkadot.io'
ws = websocket.create_connection(uri)

for block_number in range(11627380, 0, -1):
    print(block_number)

    data = f'{{\
        "jsonrpc": "2.0",\
        "id": 1,\
        "method": "chain_getBlockHash",\
        "params": [{block_number}]\
    }}'

    ws.send(data)

    block_hash = json.loads(ws.recv())['result']

    print(block_hash)

11627380
0x6d4d9db750b8b25c3a8b924c7a9987f4dfebc4f64d981d27f5ebfbcc36dc2acc
11627379
0x83f433b3cb100e41f4028849e1299632d8d3a9eb92c0429de68cd3345c22544f
11627378
0x98feb884664c370090bbabf8d43f6cf1d580cf99bed392b3b45173456e93e237
11627377
0x01810c5483943974e1c00fed4f49bf0ac057d131f2842566289b0f417d6e8bfd
11627376
0xd1ccb8a533a37db43947aa6bf3c854eded35558309d0e888356819bac6a6fcab
11627375
0xa9ded33c03d0f7ba435ed7ddc528fb3a4bbb1486ac7fdad41f3adb9c68cc656c
11627374
0x41d2512fcdd9fec34e97a5d931dbdff3144cd900fd5ef94b9f070b5abcd947a6

Answer 3

You can also have a look at https://github.com/polkascan/py-substrate-interface if you want more complex interaction with the RPC