From 97c08939798bd9ee1a637732d90811cc057d89bd Mon Sep 17 00:00:00 2001
From: Monu Singh <msnghgw@amazon.com>
Date: Thu, 25 Sep 2025 15:08:34 +0530
Subject: [PATCH] Fix validation exception on shrink

---
 .../rest-api-spec/test/indices.shrink/10_basic.yml | 14 ++++++++++++++
 .../metadata/MetadataCreateIndexService.java       |  2 +-
 .../metadata/MetadataCreateIndexServiceTests.java  |  6 +++---
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/10_basic.yml b/rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/10_basic.yml
index 67b5be7eb0fd5..eaf3da27a1a45 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/10_basic.yml
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/indices.shrink/10_basic.yml
@@ -72,6 +72,20 @@ setup:
   - match: { _id:      "1"     }
   - match: { _source:  { foo: "hello world" } }
 
+  - do:
+      catch: /action_request_validation_exception/
+      indices.shrink:
+        index: "source"
+        target: "new_shrunken_index"
+        wait_for_active_shards: 1
+        cluster_manager_timeout: 10s
+        body:
+          settings:
+            index.number_of_replicas: 0
+            index.number_of_shards: 1
+            index.blocks.read_only: true
+
+
 # Related issue: https://github.com/opensearch-project/OpenSearch/issues/4845
 ---
 "Returns error if target index's metadata write is blocked":
diff --git a/server/src/main/java/org/opensearch/cluster/metadata/MetadataCreateIndexService.java b/server/src/main/java/org/opensearch/cluster/metadata/MetadataCreateIndexService.java
index a889091140d12..ad427a4b2e777 100644
--- a/server/src/main/java/org/opensearch/cluster/metadata/MetadataCreateIndexService.java
+++ b/server/src/main/java/org/opensearch/cluster/metadata/MetadataCreateIndexService.java
@@ -1652,7 +1652,7 @@ static IndexMetadata validateResize(ClusterState state, String sourceIndex, Stri
 
         // ensure write operations on the source index is blocked
         if (state.blocks().indexBlocked(ClusterBlockLevel.WRITE, sourceIndex) == false) {
-            throw new IllegalStateException(
+            throw new IllegalArgumentException(
                 "index " + sourceIndex + " must block write operations to resize index. use \"index.blocks.write=true\""
             );
         }
diff --git a/server/src/test/java/org/opensearch/cluster/metadata/MetadataCreateIndexServiceTests.java b/server/src/test/java/org/opensearch/cluster/metadata/MetadataCreateIndexServiceTests.java
index 785ba35afaf4d..a642c5a71faef 100644
--- a/server/src/test/java/org/opensearch/cluster/metadata/MetadataCreateIndexServiceTests.java
+++ b/server/src/test/java/org/opensearch/cluster/metadata/MetadataCreateIndexServiceTests.java
@@ -341,7 +341,7 @@ public void testValidateShrinkIndex() {
         assertEquals(
             "index source must block write operations to resize index. use \"index.blocks.write=true\"",
             expectThrows(
-                IllegalStateException.class,
+                IllegalArgumentException.class,
                 () -> MetadataCreateIndexService.validateShrinkIndex(
                     createClusterState("source", randomIntBetween(2, 100), randomIntBetween(0, 10), Settings.EMPTY),
                     "source",
@@ -443,7 +443,7 @@ public void testValidateSplitIndex() {
         assertEquals(
             "index source must block write operations to resize index. use \"index.blocks.write=true\"",
             expectThrows(
-                IllegalStateException.class,
+                IllegalArgumentException.class,
                 () -> MetadataCreateIndexService.validateSplitIndex(
                     createClusterState("source", randomIntBetween(2, 100), randomIntBetween(0, 10), Settings.EMPTY),
                     "source",
@@ -529,7 +529,7 @@ public void testValidateCloneIndex() {
         assertEquals(
             "index source must block write operations to resize index. use \"index.blocks.write=true\"",
             expectThrows(
-                IllegalStateException.class,
+                IllegalArgumentException.class,
                 () -> MetadataCreateIndexService.validateCloneIndex(
                     createClusterState("source", randomIntBetween(2, 100), randomIntBetween(0, 10), Settings.EMPTY),
                     "source",