Node Interaction

This page will guide you through some basic interactions with your node.

This page will guide you through some basic interactions with your node. Always refer to the proper documentation for the tool you are using. This guide should guide you to the proper tools, not be seen as canonical reference.

• Substrate RPC API

• Polkadot JS RPC Documentation

• Substrate API Sidecar

RPC

The Substrate Chain client exposes HTTP and WS endpoints for RPC connections. The default ports are 9933 for HTTP and 9944 for WS.

To get a list of all RPC methods, the node has an RPC endpoint called rpc_methods.

For example:

$ curl -H "Content-Type: application/json" -d '{"id":1, "jsonrpc":"2.0", "method": "rpc_methods"}' http://localhost:9933/

{"jsonrpc":"2.0","result":{"methods":["account_nextIndex","author_hasKey","author_hasSessionKeys","author_insertKey","author_pendingExtrinsics","author_removeExtrinsic","author_rotateKeys","author_submitAndWatchExtrinsic","author_submitExtrinsic","author_unwatchExtrinsic","chain_getBlock","chain_getBlockHash","chain_getFinalisedHead","chain_getFinalizedHead","chain_getHead","chain_getHeader","chain_getRuntimeVersion","chain_subscribeAllHeads","chain_subscribeFinalisedHeads","chain_subscribeFinalizedHeads","chain_subscribeNewHead","chain_subscribeNewHeads","chain_subscribeRuntimeVersion","chain_unsubscribeAllHeads","chain_unsubscribeFinalisedHeads","chain_unsubscribeFinalizedHeads","chain_unsubscribeNewHead","chain_unsubscribeNewHeads","chain_unsubscribeRuntimeVersion","offchain_localStorageGet","offchain_localStorageSet","payment_queryInfo","state_call","state_callAt","state_getChildKeys","state_getChildStorage","state_getChildStorageHash","state_getChildStorageSize","state_getKeys","state_getKeysPaged","state_getKeysPagedAt","state_getMetadata","state_getPairs","state_getRuntimeVersion","state_getStorage","state_getStorageAt","state_getStorageHash","state_getStorageHashAt","state_getStorageSize","state_getStorageSizeAt","state_queryStorage","state_subscribeRuntimeVersion","state_subscribeStorage","state_unsubscribeRuntimeVersion","state_unsubscribeStorage","subscribe_newHead","system_accountNextIndex","system_addReservedPeer","system_chain","system_health","system_name","system_networkState","system_nodeRoles","system_peers","system_properties","system_removeReservedPeer","system_version","unsubscribe_newHead"],"version":1},"id":1}

Add parameters in the call, for example get a block by its hash value:

$ curl -H "Content-Type: application/json" -d '{"id":1, "jsonrpc":"2.0", "method": "chain_getBlock", "params":["0x3fa6a530850324391fde50bdf0094bdc17ee17ec84aca389b4047ef54fea0037"]}' http://localhost:9933

{"jsonrpc":"2.0","result":{"block":{"extrinsics":["0x280402000b50055ee97001","0x1004140000"],"header":{"digest":{"logs":["0x06424142453402af000000937fbd0f00000000","0x054241424501011e38401b0aab22f4d72ebc95329c3798445786b92ca1ae69366aacb6e1584851f5fcdfcc0f518df121265c343059c62ab0a34e8e88fda8578810fbe508b6f583"]},"extrinsicsRoot":"0x0e354333c062892e774898e7ff5e23bf1cdd8314755fac15079e25c1a7765f06","number":"0x16c28c","parentHash":"0xe3bf2e8f0e901c292de24d07ebc412d67224ce52a3d1ffae76dc4bd78351e8ac","stateRoot":"0xd582f0dfeb6a7c73c47db735ae82d37fbeb5bada67ee8abcd43479df0f8fc8d8"}},"justification":null},"id":1}

Some return values may not appear meaningful at first glance. Substrate uses SCALE encoding as a format that is suitable for resource-constrained execution environments. You will need to decode the information and use the chain metadata (state_getMetadata) to obtain human-readable information.

Tracking the Chain Head

Use the RPC endpoint chain_subscribeFinalizedHeads to subscribe to a stream of hashes of finalized headers, or chain_FinalizedHeads to fetch the latest hash of the finalized header. Use chain_getBlock to get the block associated with a given hash. chain_getBlock only accepts block hashes, so if you need to query intermediate blocks, use chain_getBlockHash to get the block hash from a block number.

Substrate API Sidecar

Parity maintains an RPC client, written in TypeScript, that exposes a limited set of endpoints. It handles the metadata and codec logic so that you are always dealing with decoded information. It also aggregates information that an infrastructure business may need for accounting and auditing, e.g. transaction fees.

The sidecar can fetch blocks, get the balance of an address atomically (i.e., with a corresponding block number), get the chain's metadata, get a transaction fee prediction, and submit transactions to a node's transaction queue. If you have any feature/endpoint requests, log an issue in the repo.

The client runs on an HTTP host. The following examples use python3, but you can query any way you prefer at http://HOST:PORT/. The default is http://127.0.0.1:8080.

Fetching a Block

Fetch a block using the block/number endpoint. To get the chain tip, omit the block number.

import requests
import json

url = 'http://127.0.0.1:8080/block/2077200'
response = requests.get(url)
if response.ok:
    block_info = json.loads(response.text)
    print(block_info)

This returns a fully decoded block. In the balances.transfer extrinsic, the partialFee item is the transaction fee. It is called "partial fee" because the total fee would include the tip field. Notice that some extrinsics do not have a signature. These are inherents.

When tracking transaction fees, the extrinsics.paysFee value is not sufficient for determining if the extrinsic had a fee. This field only means that it would require a fee if submitted as a transaction. In order to charge a fee, a transaction also needs to be signed. So in the following example, the timestamp.set extrinsic does not pay a fee because it is an inherent, put in the block by the block author.

{'number': '2077200',
 'hash': '0x00e4e8bd8ec39e54aa26f01f5af7484d771f810fd7f1f4685a204dbc8fbfe80b',
 'parentHash': '0xf4065df1171047819592013770a98fff4b9058a96c4499676b72b1b93f5589e9',
 'stateRoot': '0xf1258925262058ef5d9eaaed49bd878e82584356f42aade40b68cdbd219be46c',
 'extrinsicsRoot': '0xbd4ea887b1a3cb3068db0524b938a0fb13093584b4e6664b3f121448a871cd3d',
 'logs': [{'type': 'PreRuntime',
   'index': '6',
   'value': ['BABE', '0x02b300000087b5c60f00000000']},
  {'type': 'Seal',
   'index': '5',
   'value': ['BABE',
    '0x689eddf91f1551f74de96ab0e2e52f41522bd82920cbe595148f873aa6d0541f48cfbb9b281181f2e52141b1c401dde7259634485fdab02cc7b63febe51ff78a']}],
 'onInitialize': {'events': []},
 'extrinsics': [{'method': 'timestamp.set',
   'signature': None,
   'nonce': '0',
   'args': ['1588085034000'],
   'tip': '0',
   'hash': '0x3cb46207ef8fadf3def3400ae2cb2a09b780431a6daf0b9bde15d91aeaf8faa3',
   'info': {},
   'events': [{'method': 'system.ExtrinsicSuccess',
     'data': [{'weight': '10000000', 'class': 'Mandatory', 'paysFee': True}]}],
   'success': True,
   'paysFee': True},
  {'method': 'finalityTracker.finalHint',
   'signature': None,
   'nonce': '0',
   'args': ['2077197'],
   'tip': '0',
   'hash': '0x2214831b2a13c75288d2267ebd089fffef82ba99d41f6c319ca06e24facc4d51',
   'info': {},
   'events': [{'method': 'system.ExtrinsicSuccess',
     'data': [{'weight': '10000000', 'class': 'Mandatory', 'paysFee': True}]}],
   'success': True,
   'paysFee': True},
  {'method': 'parachains.setHeads',
   'signature': None,
   'nonce': '0',
   'args': [[]],
   'tip': '0',
   'hash': '0xcf52705d1ade64fc0b05859ac28358c0770a217dd76b75e586ae848c56ae810d',
   'info': {},
   'events': [{'method': 'system.ExtrinsicSuccess',
     'data': [{'weight': '1000000000',
       'class': 'Mandatory',
       'paysFee': True}]}],
   'success': True,
   'paysFee': True},
  {'method': 'balances.transfer',
   'signature': {'signature': '0xf4cd36691d6ceb0a913e9d8409bde34e83761829f2fb25db15052de7ba9a6f7c4c54949f884d59005248c2c8b2951575ad0ae8f3c5d866e147a1771f47d91385',
    'signer': 'HUewJvzVuEeyaxH2vx9XiyAPKrpu1Zj5r5Pi9VrGiBVty7q'},
   'nonce': '155',
   'args': ['GoJ89MXptpNt1dH4NaZ73YtzknhrYeZcBJ33mifX5BMqoFz',
    '5000000000000'],
   'tip': '0',
   'hash': '0xc7b57537e2e63f866083ea22265cb65c846528d76378a3b3490eeada97f83d1d',
   'info': {'weight': '200000000', 'class': 'Normal', 'partialFee': '10000000000'},
   'events': [{'method': 'system.NewAccount',
     'data': ['GoJ89MXptpNt1dH4NaZ73YtzknhrYeZcBJ33mifX5BMqoFz']},
    {'method': 'balances.Endowed',
     'data': ['GoJ89MXptpNt1dH4NaZ73YtzknhrYeZcBJ33mifX5BMqoFz',
      '5000000000000']},
    {'method': 'balances.Transfer',
     'data': ['HUewJvzVuEeyaxH2vx9XiyAPKrpu1Zj5r5Pi9VrGiBVty7q',
      'GoJ89MXptpNt1dH4NaZ73YtzknhrYeZcBJ33mifX5BMqoFz',
      '5000000000000']},
    {'method': 'treasury.Deposit', 'data': ['8000000000']},
    {'method': 'balances.Deposit',
     'data': ['E58yuhUAwWzhn2V4thF3VciAJU75eePPipMhxWZe9JKVVfq',
      '2000000000']},
    {'method': 'system.ExtrinsicSuccess',
     'data': [{'weight': '200000000', 'class': 'Normal', 'paysFee': True}]}],
   'success': True,
   'paysFee': True}],
 'onFinalize': {'events': []}}

The JS number type is a 53 bit precision float. There is no guarantee that the numerical values in the response will have a numerical type. Any numbers larger than 2**53-1 will have a string type.

Submitting a Transaction

Submit a serialized transaction using the tx endpoint with an HTTP POST request.

import requests
import json

url = 'http://127.0.0.1:8080/tx/'
tx_headers = {'Content-type' : 'application/json', 'Accept' : 'text/plain'}
response = requests.post(
    url,
    data='{"tx": "0xed0...000"}', # A serialized tx.
    headers=tx_headers
)
tx_response = json.loads(response.text)

If successful, this endpoint returns a JSON with the transaction hash. In case of error, it will return an error report, e.g.:

{
    "error": "Failed to parse a tx" | "Failed to submit a tx",
    "cause": "Upstream error description"
}