SOLR-18417: Remove PingRequestHandler and related code

changelog/unreleased/SOLR-18417-deprecate-pingrequesthandler.yml

@@ -0,0 +1,7 @@
+type: deprecated
+title: Deprecate PingRequestHandler (the "/admin/ping" endpoint), SolrPing, SolrPingResponse, and SolrClient.ping()/ping(String).
+authors:
+  - name: Jason Gerlowski
+links:
+  - name: SOLR-18417
+    url: https://issues.apache.org/jira/browse/SOLR-18417

changelog/unreleased/SOLR-18417-remove-pingrequesthandler.yml

@@ -0,0 +1,7 @@
+type: removed
+title: `PingRequestHandler` (the "/admin/ping" endpoint), `SolrPing`, `SolrPingResponse`, and `SolrClient.ping()` have been removed.  Users looking for a healthcheck API can use `/api/node/health` (v2) or `/solr/admin/info/health` (v1) instead.  SolrJ users looking to replace "ping" functionality can either use `QueryRequest` for true query submission, or `HealthCheckRequest` for making a node-level healthcheck request.
+authors:
+  - name: Jason Gerlowski
+links:
+  - name: SOLR-18417
+    url: https://issues.apache.org/jira/browse/SOLR-18417

solr/core/src/java/org/apache/solr/cloud/RecoveryStrategy.java

@@ -35,6 +35,7 @@
 import org.apache.solr.client.solrj.jetty.HttpJettySolrClient;
 import org.apache.solr.client.solrj.request.AbstractUpdateRequest;
 import org.apache.solr.client.solrj.request.CoreAdminRequest.WaitForState;
+import org.apache.solr.client.solrj.request.HealthCheckRequest;
 import org.apache.solr.client.solrj.request.UpdateRequest;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.SolrException.ErrorCode;
@@ -824,7 +825,7 @@ private Replica pingLeader(String ourUrl, CoreDescriptor coreDesc, boolean mayPu
       try (SolrClient httpSolrClient =
           recoverySolrClientBuilder(leaderReplica.getBaseUrl(), leaderReplica.getCoreName())
               .build()) {
-        httpSolrClient.ping();
+        new HealthCheckRequest().process(httpSolrClient);
         return leaderReplica;
       } catch (IOException e) {
         log.error("Failed to connect leader {} on recovery, try again", leaderReplica.getBaseUrl());

solr/core/src/java/org/apache/solr/metrics/SolrMetricInfo.java

@@ -29,7 +29,7 @@ public final class SolrMetricInfo {
    * Creates a new instance of {@link SolrMetricInfo}.
    *
    * @param category the category of the metric (e.g. `QUERY`)
-   * @param scope the scope of the metric (e.g. `/admin/ping`)
+   * @param scope the scope of the metric (e.g. `/admin/segments`)
    * @param name the name of the metric (e.g. `Requests`)
    */
   public SolrMetricInfo(SolrInfoBean.Category category, String scope, String name) {

solr/core/src/resources/ImplicitPlugins.json

@@ -57,14 +57,6 @@
         "omitHeader": true
       }
     },
-    "/admin/ping": {
-      "class": "solr.PingRequestHandler",
-      "useParams":"_ADMIN_PING",
-      "invariants": {
-        "echoParams": "all",
-        "q": "{!lucene}*:*"
-      }
-    },
     "/admin/segments": {
       "class": "solr.SegmentsInfoRequestHandler",
       "useParams":"_ADMIN_SEGMENTS"