HDFS-16981. Support getFileLinkStatus API in WebHDFS (#5572). Contributed by Hualong Zhang.

Reviewed-by: Simbarashe Dzinamarira <sdzinamarira@linkedin.com>
Signed-off-by: Ayush Saxena <ayushsaxena@apache.org>

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/WebHdfsFileSystem.java

@@ -2160,6 +2160,24 @@ Path decodeResponse(Map<?, ?> json) {
     }.run();
   }
 
+  @Override
+  public FileStatus getFileLinkStatus(Path f) throws IOException {
+    statistics.incrementReadOps(1);
+    storageStatistics.incrementOpCounter(OpType.GET_FILE_LINK_STATUS);
+    final HttpOpParam.Op op = GetOpParam.Op.GETFILELINKSTATUS;
+    HdfsFileStatus status =
+        new FsPathResponseRunner<HdfsFileStatus>(op, f) {
+          @Override
+          HdfsFileStatus decodeResponse(Map<?, ?> json) {
+            return JsonUtilClient.toFileStatus(json, true);
+          }
+        }.run();
+    if (status == null) {
+      throw new FileNotFoundException("File does not exist: " + f);
+    }
+    return status.makeQualified(getUri(), f);
+  }
+
   @VisibleForTesting
   InetSocketAddress[] getResolvedNNAddr() {
     return nnAddrs;

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/resources/GetOpParam.java

@@ -65,6 +65,7 @@ public enum Op implements HttpOpParam.Op {
     GETSNAPSHOTDIFFLISTING(false, HttpURLConnection.HTTP_OK),
     GETSNAPSHOTTABLEDIRECTORYLIST(false, HttpURLConnection.HTTP_OK),
     GETLINKTARGET(false, HttpURLConnection.HTTP_OK),
+    GETFILELINKSTATUS(false, HttpURLConnection.HTTP_OK),
     GETSNAPSHOTLIST(false, HttpURLConnection.HTTP_OK);
 
     final boolean redirect;

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterWebHdfsMethods.java

@@ -386,6 +386,7 @@ protected Response get(
       case LISTXATTRS:
       case CHECKACCESS:
       case GETLINKTARGET:
+      case GETFILELINKSTATUS:
       {
         return super.get(ugi, delegation, username, doAsUser, fullpath, op,
             offset, length, renewer, bufferSize, xattrNames, xattrEncoding,

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/web/resources/NamenodeWebHdfsMethods.java

@@ -1388,6 +1388,14 @@ protected Response get(
       final String js = JsonUtil.toJsonString("Path", target);
       return Response.ok(js).type(MediaType.APPLICATION_JSON).build();
     }
+    case GETFILELINKSTATUS: {
+      HdfsFileStatus status = cp.getFileLinkInfo(fullpath);
+      if (status == null) {
+        throw new FileNotFoundException("File does not exist: " + fullpath);
+      }
+      final String js = JsonUtil.toJsonString(status, true);
+      return Response.ok(js).type(MediaType.APPLICATION_JSON).build();
+    }
     default:
       throw new UnsupportedOperationException(op + " is not supported");
     }

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/WebHDFS.md

@@ -59,6 +59,7 @@ The HTTP REST API supports the complete [FileSystem](../../api/org/apache/hadoop
     * [`GETECPOLICY`](#Get_EC_Policy) (see [HDFSErasureCoding](./HDFSErasureCoding.html#Administrative_commands).getErasureCodingPolicy)
     * [`GETSERVERDEFAULTS`](#Get_Server_Defaults) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getServerDefaults)
     * [`GETLINKTARGET`](#Get_Link_Target) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getLinkTarget)
+    * [`GETFILELINKSTATUS`](#Get_File_Link_Status) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getFileLinkStatus)
 *   HTTP PUT
     * [`CREATE`](#Create_and_Write_to_a_File) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).create)
     * [`MKDIRS`](#Make_a_Directory) (see [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).mkdirs)
@@ -1156,6 +1157,39 @@ See also: [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getServer
 
 See also: [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getLinkTarget
 
+### Get File Link Status
+
+* Submit a HTTP GET request.
+
+        curl -i "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=GETFILELINKSTATUS"
+
+  The client receives a response with a [`FileStatus` JSON object](#FileStatuses_JSON_Schema):
+
+        HTTP/1.1 200 OK
+        Content-Type: application/json
+        Transfer-Encoding: chunked
+
+        {
+            "FileStatus": {
+                "accessTime": 0,
+                "blockSize": 0,
+                "childrenNum":0,
+                "fileId": 16388,
+                "group": "supergroup",
+                "length": 0,
+                "modificationTime": 1681916788427,
+                "owner": "hadoop",
+                "pathSuffix": "",
+                "permission": "777",
+                "replication": 0,
+                "storagePolicy": 0,
+                "symlink": "/webHdfsTest/file",
+                "type": "SYMLINK"
+            }
+        }
+
+See also: [FileSystem](../../api/org/apache/hadoop/fs/FileSystem.html).getFileLinkInfo
+
 Storage Policy Operations
 -------------------------
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/web/TestWebHDFS.java

@@ -2230,6 +2230,31 @@ public void testLinkTarget() throws Exception {
     }
   }
 
+  @Test
+  public void testFileLinkStatus() throws Exception {
+    final Configuration conf = WebHdfsTestUtil.createConf();
+    try {
+      cluster = new MiniDFSCluster.Builder(conf).build();
+      cluster.waitActive();
+
+      final WebHdfsFileSystem webHdfs =
+          WebHdfsTestUtil.getWebHdfsFileSystem(conf,
+              WebHdfsConstants.WEBHDFS_SCHEME);
+      // Symbolic link
+      Path root = new Path("/webHdfsTest/");
+      Path file = new Path(root, "file");
+      FileSystemTestHelper.createFile(webHdfs, file);
+
+      Path linkToFile = new Path(root, "linkToFile");
+
+      webHdfs.createSymlink(file, linkToFile, false);
+      assertFalse(webHdfs.getFileLinkStatus(file).isSymlink());
+      assertTrue(webHdfs.getFileLinkStatus(linkToFile).isSymlink());
+    } finally {
+      cluster.shutdown();
+    }
+  }
+
   /**
    * Get FileStatus JSONObject from ListStatus response.
    */