feat(storage): Adding CumulativeHasher wrapper class for Full object …

[Dhriti07]

Adding CumulativeHasher wrapper class for Full object checksum

Refer to: go/full_checksum_java

[gemini-code-assist]

Code Review

This pull request introduces the CumulativeHasher class, which wraps a Hasher to track and validate cumulative CRC32C checksums for full object reads. It also updates the visibility of existing checksum exception constructors in Hasher.java. The review feedback highlights a logic gap where direct calls to hash methods were not being accumulated, potentially leading to incorrect cumulative totals. Additionally, suggestions were made to mark the new exception class as final and to use Locale.US in string formatting for consistency with existing patterns in the codebase.

[gemini-code-assist]

The CumulativeHasher should accumulate checksums for all data processed, including calls to the hash methods. Currently, hash(ByteBuffer) and hash(ByteString) only delegate without updating cumulativeHash. Updating these methods to accumulate and then having the validate methods leverage them ensures consistency and reduces duplication.

  @Override
  public Crc32cLengthKnown hash(ByteBuffer b) {
    Crc32cLengthKnown actual = delegate.hash(b);
    if (actual != null) {
      accumulate(actual);
    }
    return actual;
  }

  @Override
  public Crc32cLengthKnown hash(ByteString byteString) {
    Crc32cLengthKnown actual = delegate.hash(byteString);
    if (actual != null) {
      accumulate(actual);
    }
    return actual;
  }

  @Override
  public void validate(Crc32cValue<?> expected, Supplier<ByteBuffer> b) throws ChecksumMismatchException {
    Crc32cLengthKnown actual = hash(b.get());
    if (actual != null && expected != null && !actual.eqValue(expected)) {
      throw new ChecksumMismatchException(expected, actual);
    }
  }

  @Override
  public void validate(Crc32cValue<?> expected, ByteString byteString) throws ChecksumMismatchException {
    Crc32cLengthKnown actual = hash(byteString);
    if (actual != null && expected != null && !actual.eqValue(expected)) {
      throw new ChecksumMismatchException(expected, actual);
    }
  }

  @Override
  public void validateUnchecked(Crc32cValue<?> expected, ByteString byteString)
      throws UncheckedChecksumMismatchException {
    Crc32cLengthKnown actual = hash(byteString);
    if (actual != null && expected != null && !actual.eqValue(expected)) {
      throw new UncheckedChecksumMismatchException(expected, actual);
    }
  }

[gemini-code-assist]

Mark the exception class as final for consistency with other exception classes in the com.google.cloud.storage package.

Suggested change

	class UncheckedCumulativeChecksumMismatchException extends com.google.api.gax.rpc.DataLossException {
	final class UncheckedCumulativeChecksumMismatchException extends DataLossException {

[gemini-code-assist]

Use Locale.US with String.format to ensure consistent message formatting across different environments, matching the pattern used in ChecksumMismatchException.

Suggested change

	String.format(
	"Mismatch cumulative checksum value. Expected %s actual %s",
	expected.debugString(), actual.debugString()),
	String.format(
	Locale.US,
	"Mismatch cumulative checksum value. Expected %s actual %s",
	expected.debugString(), actual.debugString()),