Support $ and / in ccr follow (#99892) (#100294)

Currently the renameReplacement variable in the restore snapshot request
is intended to be a string literal for ccr. However, when a string is passed
to replaceAll in java $ and / will be treated as special characters. This
means that following indices with $ in them breaks. This commit fixes the
issue by quoting the special characters before calling replaceAll.

Fixes #99078.

docs/changelog/99892.yaml

@@ -0,0 +1,6 @@
+pr: 99892
+summary: Support $ and / in restore rename replacements
+area: Snapshot/Restore
+type: bug
+issues:
+ - 99078

x-pack/plugin/ccr/src/internalClusterTest/java/org/elasticsearch/xpack/ccr/IndexFollowingIT.java

@@ -630,6 +630,13 @@ public void testFollowNonExistentIndex() throws Exception {
         );
     }
 
+    public void testFollowWith$InIndexName() throws Exception {
+        String indexSettings = getIndexSettings(1, 0);
+        assertAcked(leaderClient().admin().indices().prepareCreate("test-leader$").setSource(indexSettings, XContentType.JSON).get());
+        followerClient().execute(PutFollowAction.INSTANCE, putFollow("test-leader$", "test-follower$")).actionGet();
+        ensureFollowerGreen("test-follower$");
+    }
+
     public void testFollowIndexMaxOperationSizeInBytes() throws Exception {
         final String leaderIndexSettings = getIndexSettings(1, between(0, 1));
         assertAcked(leaderClient().admin().indices().prepareCreate("index1").setSource(leaderIndexSettings, XContentType.JSON));

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/TransportPutFollowAction.java

@@ -51,6 +51,7 @@
 import java.util.Objects;
 import java.util.concurrent.Executor;
 import java.util.function.BiConsumer;
+import java.util.regex.Matcher;
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.cluster.metadata.DataStream.BACKING_INDEX_PREFIX;
@@ -185,7 +186,7 @@ private void createFollowerIndex(
         )
             .indicesOptions(request.indicesOptions())
             .renamePattern("^(.*)$")
-            .renameReplacement(request.getFollowerIndex())
+            .renameReplacement(Matcher.quoteReplacement(request.getFollowerIndex()))
             .masterNodeTimeout(request.masterNodeTimeout())
             .indexSettings(overrideSettings)
             .quiet(true);