SQL: handle SQL not being available in a more graceful way

x-pack/plugin/sql/qa/no-sql/build.gradle

@@ -0,0 +1,5 @@
+testClusters.integTest {
+  setting 'xpack.security.enabled', 'false'
+  setting 'xpack.sql.enabled', 'false'
+  setting 'xpack.license.self_generated.type', 'trial'
+}

x-pack/plugin/sql/qa/no-sql/src/test/java/org/elasticsearch/xpack/sql/qa/no_sql/JdbcNoSqlIT.java

@@ -0,0 +1,13 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+package org.elasticsearch.xpack.sql.qa.no_sql;
+
+import org.elasticsearch.xpack.sql.qa.jdbc.JdbcNoSqlTestCase;
+
+public class JdbcNoSqlIT extends JdbcNoSqlTestCase {
+
+}

x-pack/plugin/sql/qa/src/main/java/org/elasticsearch/xpack/sql/qa/jdbc/JdbcNoSqlTestCase.java

@@ -0,0 +1,21 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+package org.elasticsearch.xpack.sql.qa.jdbc;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+
+public class JdbcNoSqlTestCase extends JdbcIntegrationTestCase {
+
+    public void testJdbcExceptionMessage() throws SQLException {
+        try (Connection c = esJdbc()) {
+            SQLException e = expectThrows(SQLException.class, () -> c.prepareStatement("SELECT * FROM bla").executeQuery());
+            assertTrue(e.getMessage().startsWith("X-Pack/SQL does not seem to be available on the Elasticsearch"
+                    + " node using the access path"));
+        }
+    }
+}

x-pack/plugin/sql/sql-client/src/main/java/org/elasticsearch/xpack/sql/client/JreHttpUrlConnection.java

@@ -48,8 +48,8 @@ public class JreHttpUrlConnection implements Closeable {
      * error.
      */
     public static final String SQL_STATE_BAD_SERVER = "bad_server";
-    private static final String SQL_NOT_AVAILABLE_ERROR_MESSAGE = "request [" + SQL_QUERY_REST_ENDPOINT
-            + "] contains unrecognized parameter: [mode]";
+    private static final String SQL_NOT_AVAILABLE_ERROR_MESSAGE = "Incorrect HTTP method for uri [" + SQL_QUERY_REST_ENDPOINT
+            + "?error_trace] and method [POST], allowed:";
 
     public static <R> R http(String path, String query, ConnectionConfiguration cfg, Function<JreHttpUrlConnection, R> handler) {
         final URI uriPath = cfg.baseUri().resolve(path);  // update path if needed
@@ -181,9 +181,8 @@ private <R> ResponseOrException<R> parserError() throws IOException {
         if (type == null) {
             // check if x-pack or sql are not available (x-pack not installed or sql not enabled)
             // by checking the error message the server is sending back 
-            if (con.getResponseCode() >= HttpURLConnection.HTTP_BAD_REQUEST
-                    && failure.reason().contains(SQL_NOT_AVAILABLE_ERROR_MESSAGE)) {
-                return new ResponseOrException<>(new SQLException("X-Pack/SQL do not seem to be available"
+            if (con.getResponseCode() >= HttpURLConnection.HTTP_BAD_REQUEST && failure.reason().contains(SQL_NOT_AVAILABLE_ERROR_MESSAGE)) {
+                return new ResponseOrException<>(new SQLException("X-Pack/SQL does not seem to be available"
                         + " on the Elasticsearch node using the access path '"
                         + con.getURL().getHost()
                         + (con.getURL().getPort() > 0 ? ":" + con.getURL().getPort() : "")

x-pack/plugin/sql/sql-client/src/main/java/org/elasticsearch/xpack/sql/client/RemoteFailure.java

@@ -155,10 +155,15 @@ private static RemoteFailure parseResponseTopLevel(JsonParser parser) throws IOE
             } else {
                 switch (fieldName) {
                 case "error":
-                    if (token != JsonToken.START_OBJECT) {
-                        throw new IOException("Expected [error] to be an object but was [" + token + "][" + parser.getText() + "]");
+                    if (token != JsonToken.START_OBJECT && token != JsonToken.VALUE_STRING) {
+                        throw new IOException("Expected [error] to be an object or string but was [" + token + "]["
+                                + parser.getText() + "]");
+                    }
+                    if (token == JsonToken.VALUE_STRING) {
+                        exception = new RemoteFailure(StringUtils.EMPTY, parser.getText(), null, null, null, null);
+                    } else {
+                        exception = parseFailure(parser);
                     }
-                    exception = parseFailure(parser);
                     continue;
                 case "status":
                     if (token != JsonToken.VALUE_NUMBER_INT) {

x-pack/plugin/sql/sql-client/src/test/java/org/elasticsearch/xpack/sql/client/RemoteFailureTests.java

@@ -70,9 +70,9 @@ public void testNoError() {
     public void testBogusError() {
         IOException e = expectThrows(IOException.class, () -> parse("bogus_error.json"));
         assertEquals(
-            "Can't parse error from Elasticsearch [Expected [error] to be an object but was [VALUE_STRING][bogus]] "
+            "Can't parse error from Elasticsearch [Expected [error] to be an object or string but was [START_ARRAY][[]] "
                 + "at [line 1 col 12]. Response:\n"
-                + "{ \"error\": \"bogus\" }",
+                + "{ \"error\": [\"bogus\"] }",
             e.getMessage());
     }
 

x-pack/plugin/sql/sql-client/src/test/resources/remote_failure/bogus_error.json

@@ -1 +1 @@
-{ "error": "bogus" }
+{ "error": ["bogus"] }