Enhances get snapshots API to allow retrieving repository index only (#24477)

Currently, the get snapshots API (e.g. /_snapshot/{repositoryName}/_all)
provides information about snapshots in the repository, including the
snapshot state, number of shards snapshotted, failures, etc.  In order
to provide information about each snapshot in the repository, the call
must read the snapshot metadata blob (`snap-{snapshot_uuid}.dat`) for
every snapshot.  In cloud-based repositories, this can be expensive,
both from a cost and performance perspective.  Sometimes, all the user
wants is to retrieve all the names/uuids of each snapshot, and the
indices that went into each snapshot, without any of the other status
information about the snapshot.  This minimal information can be
retrieved from the repository index blob (`index-N`) without needing to
read each snapshot metadata blob.

This commit enhances the get snapshots API with an optional `verbose`
parameter.  If `verbose` is set to false on the request, then the get
snapshots API will only retrieve the minimal information about each
snapshot (the name, uuid, and indices in the snapshot), and only read
this information from the repository index blob, thereby giving users
the option to retrieve the snapshots in a repository in a more
cost-effective and efficient manner.

Closes #24288

2 files changed, 45 insertions, 0 deletions

diff --git a/rest-api-spec/src/main/resources/rest-api-spec/api/snapshot.get.json b/rest-api-spec/src/main/resources/rest-api-spec/api/snapshot.get.json
index 760809cdf9..02f5259bc2 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/api/snapshot.get.json
+++ b/rest-api-spec/src/main/resources/rest-api-spec/api/snapshot.get.json
@@ -25,6 +25,10 @@
         "ignore_unavailable": {
           "type": "boolean",
           "description": "Whether to ignore unavailable snapshots, defaults to false which means a SnapshotMissingException is thrown"
+        },
+        "verbose": {
+          "type": "boolean",
+          "description": "Whether to show verbose snapshot info or only show the basic info found in the repository index blob"
         }
       }
     },
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/snapshot.get/10_basic.yaml b/rest-api-spec/src/main/resources/rest-api-spec/test/snapshot.get/10_basic.yaml
index 24a7ac6adc..515662355d 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/test/snapshot.get/10_basic.yaml
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/snapshot.get/10_basic.yaml
@@ -33,6 +33,11 @@ setup:
 
   - is_true: snapshots
 
+  - do:
+      snapshot.delete:
+        repository: test_repo_get_1
+        snapshot: test_snapshot
+
 ---
 "Get missing snapshot info throws an exception":
 
@@ -52,3 +57,39 @@ setup:
         ignore_unavailable: true
 
   - is_true: snapshots
+
+---
+"Get snapshot info when verbose is false":
+  - skip:
+      version: " - 5.99.99"
+      reason: verbose mode was introduced in 6.0
+
+  - do:
+      indices.create:
+        index: test_index
+        body:
+          settings:
+            number_of_shards:   1
+            number_of_replicas: 0
+
+  - do:
+      snapshot.create:
+        repository: test_repo_get_1
+        snapshot: test_snapshot
+        wait_for_completion: true
+
+  - do:
+      snapshot.get:
+        repository: test_repo_get_1
+        snapshot: test_snapshot
+        verbose: false
+
+  - is_true: snapshots
+  - match: { snapshots.0.snapshot: test_snapshot }
+  - match: { snapshots.0.state: SUCCESS }
+  - is_false: snapshots.0.version
+
+  - do:
+      snapshot.delete:
+        repository: test_repo_get_1
+        snapshot: test_snapshot