Is batch.execute() asynchronous?

[ilyador]

I cannot figure out from the docs how to correctly use the data returned from the batch requests.

At first, I tried a naive implementation

async function getLatestBlocks (n) {
  const latest = await eth.getBlockNumber()
  const blockNumbers = getBlockNumbers(latest, n)
  const batch = new eth.BatchRequest()
  let blocks = []

  blockNumbers.forEach(blockNumber => {
    batch.add(
      eth.getBlock.request(blockNumber, (error, data) => {
        blocks.push(data)
      })
    )
  })

  batch.execute()
  return blocks
}

But blocks was returning empty.

I tried using execute() as a promise, but it is not (I got execute has no method "then").

Since I am using React, I tried to populate the state in the request callback, but in that case, I have no indication of when the batch call is actually finished.

async function getLatestBlocks (n) {
  const latest = await eth.getBlockNumber()
  const blockNumbers = getBlockNumbers(latest, n)
  const batch = new eth.BatchRequest()

  blockNumbers.forEach(blockNumber => {
    batch.add(
      eth.getBlock.request(blockNumber, (error, data) => {
        setBlocksInfo(blocksArray => ([...blocksArray, data]))
      })
    )
  })

  batch.execute()
  setLoading(false) // not in sync with batch.execute()
}

So how do I know when batch.execute() has finished executing all the callbacks?

[cgewecke]

@ilyador You can manage the promise yourself, for example

async function getLatestBlocks (n) {
  const latest = await eth.getBlockNumber()
  const blockNumbers = getBlockNumbers(latest, n)
  const batch = new eth.BatchRequest()

  const total = blockNumbers.length;
  let counter = 0;
  let blocks = [];

  await new Promise(function(resolve, reject){
    blockNumbers.forEach(blockNumber => {
      batch.add(
        eth.getBlock.request(blockNumber, (error, data) => {
          if (error) return reject(error);

          counter++;
          blocks.push(data);

          if (counter === total) resolve();
        })
      )
    });

    batch.execute()
  });

  return blocks
}

^^^ Haven't actually tried the above, may have syntax error or other problems

[ilyador]

@cgewecke thanx

This issue #1446 says it was already made into a promise, or am I confusing something?

[cgewecke]

@ilyador Yes, it looks like the change was made to what is now the 2.x branch in #2000. 1.x requires that you manage the async aspect yourself.

There are some nice solutions in #1446 for this though, thanks for linking to that.

[ilyador]

Got it, thanx

[cameronprestera]

@ilyador I am actually trying to implement this exact thing, when I give a callback function with the batch request add, I am getting undefined for the callback for some strange reason. Would you mine sharing how you were able to get each block from multiple batch requests?

[aymantaybi]

For anyone wondering how to make the batch.execute asynchronous and get an Array of responses instead of calling requests callbacks individually, here's a function :

const Jsonrpc = require('web3-core-requestmanager/src/jsonrpc');

var { errors } = require('web3-core-helpers');

function executeAsync(batch) {

    return new Promise((resolve, reject) => {

        var requests = batch.requests;

        batch.requestManager.sendBatch(requests, (err, results) => {

            results = results || [];

            var response = requests.map((request, index) => {

                return results[index] || {};

            }).map((result, index) => {

                if (result && result.error) {
                    return errors.ErrorResponse(result);
                }

                if (!Jsonrpc.isValidResponse(result)) {
                    return errors.InvalidResponse(result);
                }

                return requests[index].format ? requests[index].format(result.result) : result.result;

            });

            resolve(response);

        });
    })

}

To use it :

var batch = new web3.BatchRequest();

batch.add(web3.eth.getBlock.request("latest"));
  
var batchResponse = await executeAsync(batch);

console.log(batchResponse);

[alison84r]

I am getting following error
An error occurred: TypeError: web3.eth.getBlock.request is not a function