HDDS-16389. Add command to display snapshot counts per bucket.

[sadanand48]

What changes were proposed in this pull request?

This PR is to add a command to understand snapshot counts per bucket as currently there is no direct way to fetch this info

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16389

How was this patch tested?

Unit tests

[Copilot]

🟡 Changes recommended

Unresolved OM aggregation, ACL, filtering, and empty-bucket issues block approval.

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Pull request overview

Adds ozone sh snapshot count to report active, deleted, and total snapshots per bucket.

Changes:

• Adds protobuf, OM, client, and RPC support.
• Implements filtering and ACL-aware aggregation.
• Registers the shell command and adds CLI tests.

File summaries

File	Summary
hadoop-ozone/s3gateway/src/test/java/org/apache/hadoop/ozone/client/ClientProtocolStub.java	Updates the protocol test stub.
hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/protocolPB/OzoneManagerRequestHandler.java	Handles and serializes count requests.
hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java	Aggregates counts, filtering, and ACL checks. Findings remain: cache-unaware reads (critical, 1 vote); ACL result-code mismatch (moderate, 2 votes); missing empty buckets (moderate, 3 votes); unbounded filtered scans (moderate, 1 vote); invalid extra separators accepted (moderate, 1 vote); insufficient server-side coverage (nit, 1 vote).
hadoop-ozone/interface-client/src/main/proto/OmClientProtocol.proto	Defines the new protocol messages and command.
hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/snapshot/SnapshotCountResponse.java	Adds the aggregate response model.
hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/snapshot/SnapshotBucketCount.java	Adds the per-bucket count model.
hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/OmUtils.java	Classifies the operation as read-only.
hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/protocolPB/OzoneManagerProtocolClientSideTranslatorPB.java	Translates the new RPC.
hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/protocol/OzoneManagerProtocol.java	Exposes the protocol method.
hadoop-ozone/client/src/main/java/org/apache/hadoop/ozone/client/rpc/RpcClient.java	Forwards the client call.
hadoop-ozone/client/src/main/java/org/apache/hadoop/ozone/client/protocol/ClientProtocol.java	Extends the client contract.
hadoop-ozone/client/src/main/java/org/apache/hadoop/ozone/client/ObjectStore.java	Exposes the object-store method.
hadoop-ozone/cli-shell/src/test/java/org/apache/hadoop/ozone/shell/snapshot/TestCountSnapshotHandler.java	Tests shell output and filtering.
hadoop-ozone/cli-shell/src/main/java/org/apache/hadoop/ozone/shell/snapshot/SnapshotCommands.java	Registers the command.
hadoop-ozone/cli-shell/src/main/java/org/apache/hadoop/ozone/shell/snapshot/CountSnapshotHandler.java	Implements the shell handler.

Review details

Suppressed comments (3)

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java:3285

• For an exact volume/bucket filter this still opens an unbounded iterator and examines every snapshot in the cluster before applying parsedFilter. SnapshotInfo keys are prefixed by /volume/bucket/, so using a prefix iterator/seek for exact filters would avoid making one-bucket queries O(total snapshots) and occupying an OM read thread unnecessarily.

      try (TableIterator<String, ? extends Table.KeyValue<String, SnapshotInfo>> keyIter =
               metadataManager.getSnapshotInfoTable().iterator()) {

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java:3363

• indexOf('/') only checks the first separator, so a value such as vol/bucket/extra is accepted and treated as a bucket name containing /; it silently returns zero counts even though the option accepts only <bucket> or <volume>/<bucket>. Reject a second separator before constructing the filter.

      int slashIndex = normalized.indexOf('/');
      if (slashIndex < 0) {
        return new BucketFilter(null, normalized);
      }

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java:3301

• The added tests mock ObjectStore.snapshotCount and never populate snapshotInfoTable or invoke OzoneManager.snapshotCount. As a result, the new aggregation, filter parsing, and ACL paths have no server-side coverage, allowing regressions such as the denial-status mismatch and missing empty-bucket result to pass; add an OM/metadata-level test covering active/deleted rows and filtered access.

      try (TableIterator<String, ? extends Table.KeyValue<String, SnapshotInfo>> keyIter =
               metadataManager.getSnapshotInfoTable().iterator()) {
        while (keyIter.hasNext()) {
          SnapshotInfo snapshotInfo = keyIter.next().getValue();
          String volumeName = snapshotInfo.getVolumeName();
          String bucketName = snapshotInfo.getBucketName();
          if (!parsedFilter.matches(volumeName, bucketName)) {
            continue;
          }

          if (getAclsEnabled() && !hasListAccess(volumeName, bucketName, bucketAclCache)) {
            continue;
          }

          String bucketKey = volumeName + "/" + bucketName;
          BucketSnapshotCount bucketCount =
              bucketCounts.computeIfAbsent(bucketKey, unused -> new BucketSnapshotCount(volumeName, bucketName));
          bucketCount.increment(snapshotInfo.getSnapshotStatus());

• Files reviewed: 15/15 changed files
• Comments generated: 3
• Review effort level: Lite

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