Nethereum.Contracts.EventExtensions.Sort() throws Value cannot be null. (Parameter 'source')

[moccajoghurt]

When you run Nethereums log processor for a few minutes, it sometimes crashes with the following exception: System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)

Here is a sample that you can run to reproduce the error:

using System;
using System.Numerics;
using System.Threading.Tasks;
using Nethereum.Signer;
using Nethereum.Web3;
using Nethereum.Web3.Accounts;

public class BugExample {
    public async Task RunProcessor() {
        BigInteger blockStart = 13436170; 
        BigInteger blockEnd = 13441170;
        var url = "https://mainnet.infura.io/v3/"; // insert your own infura-url here
        var privateKey = "b5b1f848776e3af46b02501cc53da9e37c8f4c522245c27eabb95b9bde91277d"; // just a random key
        var account = new Account(privateKey, Chain.MainNet);
        var web3 = new Web3(account, url);
        var processor = web3.Processing.Logs.CreateProcessor(
            async log => {
                Console.WriteLine("Block: " + log.BlockNumber);
                await Task.Delay(500);
            });
        await processor.ExecuteAsync(blockEnd, default, blockStart);
    }
}

The error is caused inside Nethereum/src/Nethereum.Contracts/Extensions/EventExtensions.cs:

Nethereum/src/Nethereum.Contracts/Extensions/EventExtensions.cs

Line 556 in 35ad7a7

var list = events.ToList();

Here is the stack trace:

Value cannot be null. (Parameter 'source')
at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument) 
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) 
at Nethereum.Contracts.EventExtensions.Sort(IEnumerable`1 logs) 
at Nethereum.BlockchainProcessing.LogProcessing.LogOrchestrator.ProcessAsync(BigInteger fromNumber, BigInteger toNumber, CancellationToken cancellationToken) 
at Nethereum.BlockchainProcessing.BlockchainProcessor.ExecuteAsync(BigInteger toBlockNumber, CancellationToken cancellationToken, Nullable`1 startAtBlockNumberIfNotProcessed) 

[juanfranblanco]

@moccajoghurt many thanks for this, do you know what specific block range you had the issue? If you use the blockchain progress storage, you should be able to identify the block, error and restart from there.

The log processor is designed to get a specific log, for example all the transfer events (for all contracts), so you may be encountering a range of blocks with no logs, and hence a null value, which is highly unlikely or you may have a bad response with infura. Also the processor has a retry process (in case of failure).

In anyway I am looking into it, as I had tested this crawling / logs for many blocks but this has never occurred.

[juanfranblanco]

@moccajoghurt Ok it seems that this is an intermittent issue with infura as I have reproduced the issue, in random blocks, in which we are not getting any logs as a response. This is an interesting scenario, as it is not expected, so the result is incorrect. As a side effect the logs when getting sorted, as there should be some are being rejected even if this is for 100 block range.