10. Monitoring

Symbol nodes can monitor blockchain state changes via WebSocket communication.

10.1 Listener configuration

Generate a WebSocket and configure a listener.

nsRepo = repo.createNamespaceRepository();
wsEndpoint = NODE.replace("http", "ws") + "/ws";
listener = new sym.Listener(wsEndpoint, nsRepo, WebSocket);
listener.open();

The format of the endpoints is as follows.

• wss://{node url}:3001/ws

If there is no communication, the listener is disconnected after one minute.

10.2 Receiving transactions

Detects transactions received by the account.

listener.open().then(() => {
  //Detection of approval transactions
  listener.confirmed(alice.address).subscribe((tx) => {
    //Describes the process after reception
    console.log(tx);
  });
  //Detection of unconfirmed transactions
  listener.unconfirmedAdded(alice.address).subscribe((tx) => {
    //Describes the process after reception
    console.log(tx);
  });
});

After executing the above listener, announce the transaction to be sent to Alice.

Sample output

> Promise {<pending>}
> TransferTransaction {type: 16724, networkType: 152, version: 1, deadline: Deadline, maxFee: UInt64, …}
    deadline: Deadline {adjustedValue: 12449258375}
    maxFee: UInt64 {lower: 32000, higher: 0}
    message: RawMessage {type: -1, payload: ''}
    mosaics: []
    networkType: 152
    payloadSize: undefined
    recipientAddress: Address {address: 'TBXUTAX6O6EUVPB6X7OBNX6UUXBMPPAFX7KE5TQ', networkType: 152}
    signature: "914B625F3013635FA9C99B2F138C47CD75F6E1DF7BDDA291E449390178EB461AA389522FA126D506405163CC8BA51FA9019E0522E3FA9FED7C2F857F11FBCC09"
    signer: PublicAccount {publicKey: 'D4933FC1E4C56F9DF9314E9E0533173E1AB727BDB2A04B59F048124E93BEFBD2', address: Address}
    transactionInfo: TransactionInfo
        hash: "3B21D8842EB70A780A662CCA19B8B030E2D5C7FB4C54BDA8B3C3760F0B35FECE"
        height: UInt64 {lower: 316771, higher: 0}
        id: undefined
        index: undefined
        merkleComponentHash: "3B21D8842EB70A780A662CCA19B8B030E2D5C7FB4C54BDA8B3C3760F0B35FECE"
    type: 16724
    version: 1

Unconfirmed transactions are received with transactionInfo.height=0.

10.3 Block monitoring

Detects newly generated blocks.

listener.open().then(() => {
  //Detection of block generation
  listener.newBlock().subscribe((block) => console.log(block));
});

Sample output

> Promise {<pending>}
> NewBlock
    beneficiaryAddress: Address {address: 'TAKATV2VSYBH3RX4JVCCILITWANT6JRANZI2AUQ', networkType: 152}
    blockReceiptsHash: "ABDDB66A03A270E4815C256A8125B70FC3B7EFC4B95FF5ECAD517CB1AB5F5334"
    blockTransactionsHash: "0000000000000000000000000000000000000000000000000000000000000000"
    difficulty: UInt64 {lower: 1316134912, higher: 2328}
    feeMultiplier: 0
    generationHash: "5B4F32D3F2CDD17917D530A6A967927D93F73F2B52CC590A64E3E94408D8CE96"
    hash: "E8294BDDDAE32E17242DF655805EC0FCAB3B628A331824B87A3CA7578683B09C"
    height: UInt64 {lower: 316759, higher: 0}
    networkType: 152
    previousBlockHash: "38382D616772682321D58046511DD942F36A463155C5B7FB0A2CBEE8E29B253C"
    proofGamma: "37187F1C8BD8C87CB4F000F353ACE5717D988BC220EFBCC25E2F40B1FB9B7D7A"
    proofScalar: "AD91A572E5D81EA92FE313CA00915E5A497F60315C63023A52E292E55345F705"
    proofVerificationHash: "EF58228B3EB3C422289626935DADEF11"
    signature: "A9481E5976EDA86B74433E8BCC8495788BA2B9BE0A50F9435AD90A14D1E362D934BA26069182C373783F835E55D7F3681817716295EC1EFB5F2375B6DE302801"
    signer: PublicAccount {publicKey: 'F2195B3FAFBA3DF8C31CFBD9D5BE95BB3F3A04BDB877C59EFB9D1C54ED2DC50E', address: Address}
    stateHash: "4A1C828B34DE47759C2D717845830BA14287A4EC7220B75494BDC31E9539FCB5"
    timestamp: UInt64 {lower: 3851456497, higher: 2}
    type: 33091
    version: 1

If listener.newBlock() is used, communication occurs approximately every 30 seconds, making WebSocket disconnections less likely to occur.

In rare cases, block generation may exceed one minute, in which case the listener must be reconnected. (Other factors may also cause disconnection, so if you want to be sure, supplement with onclose as described below.)

10.4 Signature request

Detects when a transaction requiring a signature occurs.

listener.open().then(() => {
  //Detection of Aggregate Bonded Transaction occurrences requiring signatures
  listener
    .aggregateBondedAdded(alice.address)
    .subscribe(async (tx) => console.log(tx));
});

Sample output

> AggregateTransaction
    cosignatures: []
    deadline: Deadline {adjustedValue: 12450154608}
  > innerTransactions: Array(2)
        0: TransferTransaction {type: 16724, networkType: 152, version: 1, deadline: Deadline, maxFee: UInt64, …}
        1: TransferTransaction {type: 16724, networkType: 152, version: 1, deadline: Deadline, maxFee: UInt64, …}
    maxFee: UInt64 {lower: 94400, higher: 0}
    networkType: 152
    signature: "972968C5A2FB70C1D644BE206A190C4FCFDA98976F371DBB70D66A3AAEBCFC4B26E7833BCB86C407879C07927F6882C752C7012C265C2357CAA52C29834EFD0F"
    signer: PublicAccount {publicKey: '0E5C72B0D5946C1EFEE7E5317C5985F106B739BB0BC07E4F9A288417B3CD6D26', address: Address}
  > transactionInfo: TransactionInfo
        hash: "44B2CD891DA0B788F1DD5D5AB24866A9A172C80C1749DCB6EB62255A2497EA08"
        height: UInt64 {lower: 0, higher: 0}
        id: undefined
        index: undefined
        merkleComponentHash: "0000000000000000000000000000000000000000000000000000000000000000"
    type: 16961
    version: 1

All Aggregate Transactions involving the specified address are detected. Whether a cosignature is required is determined by a separate filter.

10.5 Tips for use

Continuous connection

Select randomly from the node list and try to connect.

Connection to node

//Node list
NODES = ["https://node.com:3001",...];
function connectNode(nodes) {
    const node = nodes[Math.floor(Math.random() * nodes.length)] ;
    console.log("try:" + node);
    return new Promise((resolve, reject) => {
        let req = new XMLHttpRequest();
        req.timeout = 2000; //timeout value:2sec(=2000ms)
        req.open('GET', node + "/node/health", true);
        req.onload = function() {
            if (req.status === 200) {
                const status = JSON.parse(req.responseText).status;
                if(status.apiNode == "up" && status.db == "up"){
                    return resolve(node);
                }else{
                    console.log("fail node status:" + status);
                    return connectNode(nodes).then(node => resolve(node));
                }
            } else {
                console.log("fail request status:" + req.status)
                return connectNode(nodes).then(node => resolve(node));
            }
        };
        req.onerror = function(e) {
            console.log("onerror:" + e)
            return connectNode(nodes).then(node => resolve(node));
        };
        req.ontimeout = function (e) {
            console.log("ontimeout")
            return connectNode(nodes).then(node => resolve(node));
        };
    req.send();
    });
}

Set a timeout value and re-select a node if connected node response is slow. Check the endpoint /node/health and reselect the node if the status is not normal.

Creation of repositories

function createRepo(nodes) {
  return connectNode(nodes).then(async function onFulfilled(node) {
    const repo = new sym.RepositoryFactoryHttp(node);
    try {
      epochAdjustment = await repo.getEpochAdjustment().toPromise();
    } catch (error) {
      console.log("fail createRepo");
      return await createRepo(nodes);
    }
    return await repo;
  });
}

In rare cases, there are some nodes for which the /network/properties endpoint has not been freed, so the getEpochAdjustment() information is retrieved and checked. If it cannot be obtained, createRepo is read recursively.

Continuous connection listeners

async function listenerKeepOpening(nodes) {
  const repo = await createRepo(NODES);
  let wsEndpoint = repo.url.replace("http", "ws") + "/ws";
  const nsRepo = repo.createNamespaceRepository();
  const lner = new sym.Listener(wsEndpoint, nsRepo, WebSocket);
  try {
    await lner.open();
    lner.newBlock();
  } catch (e) {
    console.log("fail websocket");
    return await listenerKeepOpening(nodes);
  }
  lner.webSocket.onclose = async function () {
    console.log("listener onclose");
    return await listenerKeepOpening(nodes);
  };
  return lner;
}

If the listener closes, it reconnects.

Start of listener.

listener = await listenerKeepOpening(NODES);

Unsigned transaction auto-signature

Detect unsigned transactions, then sign and announce to the network.
Two patterns of detection are required: reception during initial screen display and during screen viewing.

//read rxjs.operators
op = require("/node_modules/rxjs/operators");
rxjs = require("/node_modules/rxjs");

//Aggregate Transaction detection
bondedListener = listener.aggregateBondedAdded(bob.address);
bondedHttp = txRepo
  .search({ address: bob.address, group: sym.TransactionGroup.Partial })
  .pipe(
    op.delay(2000),
    op.mergeMap((page) => page.data),
  );
//Completed transaction detection listeners for selected accounts
const statusChanged = function (address, hash) {
  const transactionObservable = listener.confirmed(address);
  const errorObservable = listener.status(address, hash);
  return rxjs.merge(transactionObservable, errorObservable).pipe(
    op.first(),
    op.map((errorOrTransaction) => {
      if (errorOrTransaction.constructor.name === "TransactionStatusError") {
        throw new Error(errorOrTransaction.code);
      } else {
        return errorOrTransaction;
      }
    }),
  );
};
//Cosignature execution
function exeAggregateBondedCosignature(tx) {
  txRepo
    .getTransactionsById(
      [tx.transactionInfo.hash],
      sym.TransactionGroup.Partial,
    )
    .pipe(
      //Only if the transaction is detected
      op.filter((aggTx) => aggTx.length > 0),
    )
    .subscribe(async (aggTx) => {
      //If my account is designated as the signatory of the inner transaction
      if (
        aggTx[0].innerTransactions.find((inTx) =>
          inTx.signer.equals(bob.publicAccount),
        ) != undefined
      ) {
        //Sign with Alice transaction
        const cosignatureTx = sym.CosignatureTransaction.create(aggTx[0]);
        const signedTx = bob.signCosignatureTransaction(cosignatureTx);
        const cosignedAggTx = await txRepo
          .announceAggregateBondedCosignature(signedTx)
          .toPromise();
        statusChanged(bob.address, signedTx.parentHash).subscribe((res) => {
          console.log(res);
        });
      }
    });
}
bondedSubscribe = function (observer) {
  observer
    .pipe(
      //If not already signed
      op.filter((tx) => {
        return !tx.signedByAccount(
          sym.PublicAccount.createFromPublicKey(bob.publicKey, networkType),
        );
      }),
    )
    .subscribe((tx) => {
      console.log(tx);
      exeAggregateBondedCosignature(tx);
    });
};
bondedSubscribe(bondedListener);
bondedSubscribe(bondedHttp);

Note

To avoid auto-signing scam transactions, make sure that you ensure a checking procedure is carried out, e.g. by checking the sender's account.