Maven custom wagon Could not validate integrity of download Troubleshooting

I have implemented a custom maven wagon interacting with cloud based storage. The files are uploaded successfully to the cloud storage and the checksums are correct.

md5 of maven-metadata.xml matches with the contents of maven-metadata.xml.md5

The same happens with the jar and pom files

1. md5 of jar matches the contents of *.jar.md5
2. md5 of maven-metadata.xml matches the contents of maven-metadata.xml.md5
3. md5 of pom matches the contents of *.pom.md5

When I retrieve the files through http instead of using the custom wagon they are downloaded without any checksum validation exceptions.

However when I retrieve the files using the custom wagon the I get the integrity of download warnings.

[WARNING] Could not validate integrity of download from gs://mavenbucket/snapshot/com/gkatzioura/storage/CloudStorageTest/1.0-SNAPSHOT/maven-metadata.xml
 org.eclipse.aether.transfer.ChecksumFailureException: Checksum validation failed, expected 7e0c3c33db781362483c0baed3ba175352945028 but is da39a3ee5e6b4b0d3255bfef95601890afd80709
at org.eclipse.aether.connector.basic.ChecksumValidator.validateExternalChecksums (ChecksumValidator.java:174)
at org.eclipse.aether.connector.basic.ChecksumValidator.validate (ChecksumValidator.java:103)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$GetTaskRunner.runTask (BasicRepositoryConnector.java:456)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$TaskRunner.run (BasicRepositoryConnector.java:360)
at org.eclipse.aether.util.concurrency.RunnableErrorForwarder$1.run (RunnableErrorForwarder.java:75)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector$DirectExecutor.execute (BasicRepositoryConnector.java:583)
at org.eclipse.aether.connector.basic.BasicRepositoryConnector.get (BasicRepositoryConnector.java:232)

Once the artifact is downloaded through the custom wagon successfully i check the md5 of the files downloaded from the cloud storage and they match with the *.md5 file in the cloud storage.

What is the process of troubleshooting this issue and how can I debug it?

The reason why this was happening had to do with not calling the transferProgress method of the TransferListeners.

In order to do so you have to provide a mechanism so that when your OutputStream (while downloading) and your InputStream (while uploading) get copied are also going to call the transferProgress method.

For example

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import org.apache.maven.wagon.events.TransferEvent;
import org.apache.maven.wagon.events.TransferListener;

public class WrappedOutputStreamExample extends FileOutputStream {

    private TransferListener transferListener;

    public WrappedOutputStreamExample(File file,TransferListener transferListener) throws FileNotFoundException {
        super(file);
        this.transferListener = transferListener;
    }

    @Override
    public void write(int b) throws IOException {
        super.write(b);
        TransferEvent transferEvent = null; //provide corrent transfer event
        this.transferListener.transferProgress(transferEvent,new byte[]{(byte) b}, 1);
    }

    @Override
    public void write(byte b[]) throws IOException {
        super.write(b);
        TransferEvent transferEvent = null; //provide corrent transfer event
        this.transferListener.transferProgress(transferEvent,b, b.length);
    }

    @Override
    public void write(byte b[], int off, int len) throws IOException {
        TransferEvent transferEvent = null; //provide corrent transfer event

        super.write(b, off, len);
        if (off == 0) {
            this.transferListener.transferProgress(transferEvent,b, len);
        } else {
            byte[] bytes = new byte[len];
            System.arraycopy(b, off, bytes, 0, len);
            this.transferListener.transferProgress(transferEvent,bytes, len);
        }
    }

}