HDFS-14949. Add getServerDefaults() support to HttpFS. Contributed by hemanthboyina.

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/client/HttpFSFileSystem.java

@@ -34,6 +34,7 @@ import org.apache.hadoop.fs.FSDataOutputStream;
 import org.apache.hadoop.fs.FileChecksum;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.PositionedReadable;
 import org.apache.hadoop.fs.QuotaUsage;
@@ -253,7 +254,7 @@ public class HttpFSFileSystem extends FileSystem
     ALLOWSNAPSHOT(HTTP_PUT), DISALLOWSNAPSHOT(HTTP_PUT),
     CREATESNAPSHOT(HTTP_PUT), DELETESNAPSHOT(HTTP_DELETE),
     RENAMESNAPSHOT(HTTP_PUT), GETSNAPSHOTDIFF(HTTP_GET),
-    GETSNAPSHOTTABLEDIRECTORYLIST(HTTP_GET);
+    GETSNAPSHOTTABLEDIRECTORYLIST(HTTP_GET), GETSERVERDEFAULTS(HTTP_GET);
 
     private String httpMethod;
 
@@ -1591,4 +1592,21 @@ public class HttpFSFileSystem extends FileSystem
       return super.hasPathCapability(p, capability);
     }
   }
+
+  @Override
+  public FsServerDefaults getServerDefaults() throws IOException {
+    Map<String, String> params = new HashMap<String, String>();
+    params.put(OP_PARAM, Operation.GETSERVERDEFAULTS.toString());
+    HttpURLConnection conn =
+        getConnection(Operation.GETSERVERDEFAULTS.getMethod(), params,
+            new Path(getUri().toString(), "/"), true);
+    HttpExceptionUtils.validateResponse(conn, HttpURLConnection.HTTP_OK);
+    JSONObject json = (JSONObject) HttpFSUtils.jsonParse(conn);
+    return JsonUtilClient.toFsServerDefaults(json);
+  }
+
+  @Override
+  public FsServerDefaults getServerDefaults(Path p) throws IOException {
+    return getServerDefaults();
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/FSOperations.java

@@ -24,6 +24,7 @@ import org.apache.hadoop.fs.FileChecksum;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.FilterFileSystem;
+import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.GlobFilter;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.PathFilter;
@@ -1821,4 +1822,38 @@ public class FSOperations {
       return JsonUtil.toJsonString(sds);
     }
   }
+
+  /**
+   * Executor that performs a getServerDefaults operation.
+   */
+  @InterfaceAudience.Private
+  public static class FSGetServerDefaults
+      implements FileSystemAccess.FileSystemExecutor<String> {
+
+    /**
+     * Creates a getServerDefaults executor.
+     */
+    public FSGetServerDefaults() {
+    }
+
+    /**
+     * Executes the filesystem operation.
+     * @param fs filesystem instance to use.
+     * @return A JSON string.
+     * @throws IOException thrown if an IO error occurred.
+     */
+    @Override
+    public String execute(FileSystem fs) throws IOException {
+      FsServerDefaults sds = null;
+      if (fs instanceof DistributedFileSystem) {
+        DistributedFileSystem dfs = (DistributedFileSystem) fs;
+        sds = dfs.getServerDefaults();
+      } else {
+        throw new UnsupportedOperationException("getServerDefaults is "
+            + "not supported for HttpFs on " + fs.getClass()
+            + ". Please check your fs.defaultFS configuration");
+      }
+      return JsonUtil.toJsonString(sds);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSParametersProvider.java

@@ -117,6 +117,7 @@ public class HttpFSParametersProvider extends ParametersProvider {
         new Class[] {OldSnapshotNameParam.class,
             SnapshotNameParam.class});
     PARAMS_DEF.put(Operation.GETSNAPSHOTTABLEDIRECTORYLIST, new Class[] {});
+    PARAMS_DEF.put(Operation.GETSERVERDEFAULTS, new Class[] {});
   }
 
   public HttpFSParametersProvider() {

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSServer.java

@@ -418,6 +418,14 @@ public class HttpFSServer {
       response = Response.ok(js).type(MediaType.APPLICATION_JSON).build();
       break;
     }
+    case GETSERVERDEFAULTS: {
+      FSOperations.FSGetServerDefaults command =
+          new FSOperations.FSGetServerDefaults();
+      String js = fsExecute(user, command);
+      AUDIT_LOG.info("[{}]", "/");
+      response = Response.ok(js).type(MediaType.APPLICATION_JSON).build();
+      break;
+    }
     default: {
       throw new IOException(
           MessageFormat.format("Invalid HTTP GET operation [{0}]", op.value()));

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/client/BaseTestHttpFSWith.java

@@ -27,6 +27,7 @@ import org.apache.hadoop.fs.FileChecksum;
 import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.FileSystemTestHelper;
+import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.QuotaUsage;
 import org.apache.hadoop.fs.RemoteIterator;
@@ -1141,7 +1142,8 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
     LIST_STATUS_BATCH, GETTRASHROOT, STORAGEPOLICY, ERASURE_CODING,
     CREATE_SNAPSHOT, RENAME_SNAPSHOT, DELETE_SNAPSHOT,
     ALLOW_SNAPSHOT, DISALLOW_SNAPSHOT, DISALLOW_SNAPSHOT_EXCEPTION,
-    FILE_STATUS_ATTR, GET_SNAPSHOT_DIFF, GET_SNAPSHOTTABLE_DIRECTORY_LIST
+    FILE_STATUS_ATTR, GET_SNAPSHOT_DIFF, GET_SNAPSHOTTABLE_DIRECTORY_LIST,
+    GET_SERVERDEFAULTS
   }
 
   private void operation(Operation op) throws Exception {
@@ -1262,7 +1264,11 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
     case GET_SNAPSHOTTABLE_DIRECTORY_LIST:
       testGetSnapshottableDirListing();
       break;
+    case GET_SERVERDEFAULTS:
+      testGetServerDefaults();
+      break;
     }
+
   }
 
   @Parameterized.Parameters
@@ -1702,4 +1708,33 @@ public abstract class BaseTestHttpFSWith extends HFSTestCase {
     // Clean up
     proxyFs.delete(new Path(dir), true);
   }
+
+  private void verifyGetServerDefaults(FileSystem fs, DistributedFileSystem dfs)
+      throws Exception {
+    FsServerDefaults sds = null;
+    if (fs instanceof HttpFSFileSystem) {
+      HttpFSFileSystem httpFS = (HttpFSFileSystem) fs;
+      sds = httpFS.getServerDefaults();
+    } else if (fs instanceof WebHdfsFileSystem) {
+      WebHdfsFileSystem webHdfsFileSystem = (WebHdfsFileSystem) fs;
+      sds = webHdfsFileSystem.getServerDefaults();
+    } else {
+      Assert.fail(
+          fs.getClass().getSimpleName() + " doesn't support getServerDefaults");
+    }
+    // Verify result with DFS
+    FsServerDefaults dfssds = dfs.getServerDefaults();
+    Assert.assertEquals(JsonUtil.toJsonString(sds),
+        JsonUtil.toJsonString(dfssds));
+  }
+
+  private void testGetServerDefaults() throws Exception {
+    if (!this.isLocalFS()) {
+      FileSystem fs = this.getHttpFSFileSystem();
+      Path path1 = new Path("/");
+      DistributedFileSystem dfs = (DistributedFileSystem) FileSystem
+          .get(path1.toUri(), this.getProxiedFSConf());
+      verifyGetServerDefaults(fs, dfs);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/server/TestHttpFSServer.java

@@ -54,6 +54,7 @@ import java.util.Map;
 import org.apache.commons.io.IOUtils;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.FsServerDefaults;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.XAttrCodec;
 import org.apache.hadoop.fs.http.server.HttpFSParametersProvider.DataParam;
@@ -1636,4 +1637,34 @@ public class TestHttpFSServer extends HFSTestCase {
     Assert.assertEquals(28L, checksum.get("length"));
     Assert.assertEquals("MD5-of-0MD5-of-512CRC32C", checksum.get("algorithm"));
   }
+
+  private void verifyGetServerDefaults(DistributedFileSystem dfs)
+      throws Exception {
+    // Send a request
+    HttpURLConnection conn =
+        sendRequestToHttpFSServer("/", "GETSERVERDEFAULTS", "");
+    // Should return HTTP_OK
+    Assert.assertEquals(conn.getResponseCode(), HttpURLConnection.HTTP_OK);
+    // Verify the response
+    BufferedReader reader =
+        new BufferedReader(new InputStreamReader(conn.getInputStream()));
+    // The response should be a one-line JSON string.
+    String dirLst = reader.readLine();
+    FsServerDefaults dfsDirLst = dfs.getServerDefaults();
+    Assert.assertNotNull(dfsDirLst);
+    Assert.assertEquals(dirLst, JsonUtil.toJsonString(dfsDirLst));
+  }
+
+  @Test
+  @TestDir
+  @TestJetty
+  @TestHdfs
+  public void testGetServerDefaults() throws Exception {
+    createHttpFSServer(false, false);
+    String pathStr1 = "/";
+    Path path1 = new Path(pathStr1);
+    DistributedFileSystem dfs = (DistributedFileSystem) FileSystem
+        .get(path1.toUri(), TestHdfsHelper.getHdfsConf());
+    verifyGetServerDefaults(dfs);
+  }
 }