plugins: `bin` and `config` only plugins do not install correctly

When installing a bin only plugin, it is identified as a site plugin.

A current workaround would be to create in the zip file another empty dir. So if you have:

* `bin/myfile.sh`
* `empty/empty.txt`

the `bin` content will be extracted as expected.

Closes #7152.

src/main/java/org/elasticsearch/plugins/PluginManager.java

@@ -76,6 +76,13 @@ public class PluginManager {
                     "plugin.bat",
                     "service.bat").build();
 
+    // Valid directory names for plugin ZIP files when it has only one single dir
+    private static final ImmutableSet<Object> VALID_TOP_LEVEL_PLUGIN_DIRS = ImmutableSet.builder()
+            .add("_site",
+                    "bin",
+                    "config",
+                    "_dict").build();
+
     private final Environment environment;
 
     private String url;
@@ -218,6 +225,8 @@ public class PluginManager {
             throw new IllegalArgumentException("Plugin installation assumed to be site plugin, but contains source code, aborting installation.");
         }
 
+        // It could potentially be a non explicit _site plugin
+        boolean potentialSitePlugin = true;
         File binFile = new File(extractLocation, "bin");
         if (binFile.exists() && binFile.isDirectory()) {
             File toLocation = pluginHandle.binDir(environment);
@@ -227,6 +236,7 @@ public class PluginManager {
                 throw new IOException("Could not move ["+ binFile.getAbsolutePath() + "] to [" + toLocation.getAbsolutePath() + "]");
             }
             debug("Installed " + name + " into " + toLocation.getAbsolutePath());
+            potentialSitePlugin = false;
         }
 
         File configFile = new File(extractLocation, "config");
@@ -238,12 +248,13 @@ public class PluginManager {
                 throw new IOException("Could not move ["+ configFile.getAbsolutePath() + "] to [" + configFile.getAbsolutePath() + "]");
             }
             debug("Installed " + name + " into " + toLocation.getAbsolutePath());
+            potentialSitePlugin = false;
         }
 
         // try and identify the plugin type, see if it has no .class or .jar files in it
         // so its probably a _site, and it it does not have a _site in it, move everything to _site
         if (!new File(extractLocation, "_site").exists()) {
-            if (!FileSystemUtils.hasExtensions(extractLocation, ".class", ".jar")) {
+            if (potentialSitePlugin && !FileSystemUtils.hasExtensions(extractLocation, ".class", ".jar")) {
                 log("Identified as a _site plugin, moving to _site structure ...");
                 File site = new File(extractLocation, "_site");
                 File tmpLocation = new File(environment.pluginsFile(), extractLocation.getName() + ".tmp");
@@ -354,7 +365,12 @@ public class PluginManager {
                 return false;
             }
         }
-        return topLevelDirNames.size() == 1 && !"_site".equals(topLevelDirNames.iterator().next());
+
+        if (topLevelDirNames.size() == 1) {
+            return !VALID_TOP_LEVEL_PLUGIN_DIRS.contains(topLevelDirNames.iterator().next());
+        }
+
+        return false;
     }
 
     private static final int EXIT_CODE_OK = 0;

src/test/java/org/elasticsearch/plugin/PluginManagerTests.java

@@ -125,6 +125,30 @@ public class PluginManagerTests extends ElasticsearchIntegrationTest {
         }
     }
 
+    // For #7152
+    @Test
+    public void testLocalPluginInstallWithBinOnly_7152() throws Exception {
+        String pluginName = "plugin-test";
+        Tuple<Settings, Environment> initialSettings = InternalSettingsPreparer.prepareSettings(
+                ImmutableSettings.settingsBuilder().build(), false);
+        Environment env = initialSettings.v2();
+        File binDir = new File(env.homeFile(), "bin");
+        if (!binDir.exists() && !FileSystemUtils.mkdirs(binDir)) {
+            throw new IOException("Could not create bin directory [" + binDir.getAbsolutePath() + "]");
+        }
+        File pluginBinDir = new File(binDir, pluginName);
+        try {
+            PluginManager pluginManager = pluginManager(getPluginUrlForResource("plugin_with_bin_only.zip"), initialSettings);
+            pluginManager.downloadAndExtract(pluginName);
+            File[] plugins = pluginManager.getListInstalledPlugins();
+            assertThat(plugins.length, is(1));
+            assertTrue(pluginBinDir.exists());
+        } finally {
+            // we need to clean up the copied dirs
+            FileSystemUtils.deleteRecursively(pluginBinDir);
+        }
+    }
+
     @Test
     public void testLocalPluginInstallSiteFolder() throws Exception {
         //When we have only a folder in top-level (no files either) but it's called _site, we make it work