Fixes HDFS-17181 by routing all CREATE requests to the BlockManager (a…

…pache#6108)

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

@@ -36,6 +36,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.ExecutionException;
 
 import javax.servlet.ServletContext;
@@ -278,6 +279,9 @@ protected void queueExternalCall(ExternalCall call)
     namenode.queueExternalCall(call);
   }
 
+  /**
+   * Chooses a Datanode to redirect a request to.
+   */
   @VisibleForTesting
   static DatanodeInfo chooseDatanode(final NameNode namenode,
       final String path, final HttpOpParam.Op op, final long openOffset,
@@ -288,18 +292,18 @@ static DatanodeInfo chooseDatanode(final NameNode namenode,
       throw new IOException("Namesystem has not been initialized yet.");
     }
     final BlockManager bm = fsn.getBlockManager();
-    
-    HashSet<Node> excludes = new HashSet<Node>();
+
+    Set<Node> excludes = new HashSet<>();
     if (excludeDatanodes != null) {
       for (String host : StringUtils
           .getTrimmedStringCollection(excludeDatanodes)) {
-        int idx = host.indexOf(":");
+        int idx = host.indexOf(':');
         Node excludeNode = null;
-        if (idx != -1) {
-          excludeNode = bm.getDatanodeManager().getDatanodeByXferAddr(
-             host.substring(0, idx), Integer.parseInt(host.substring(idx + 1)));
-        } else {
+        if (idx == -1) {
           excludeNode = bm.getDatanodeManager().getDatanodeByHost(host);
+        } else {
+          excludeNode = bm.getDatanodeManager().getDatanodeByXferAddr(
+            host.substring(0, idx), Integer.parseInt(host.substring(idx + 1)));
         }
 
         if (excludeNode != null) {
@@ -311,25 +315,15 @@ static DatanodeInfo chooseDatanode(final NameNode namenode,
       }
     }
 
-    if (op == PutOpParam.Op.CREATE) {
-      //choose a datanode near to client 
-      final DatanodeDescriptor clientNode = bm.getDatanodeManager(
-          ).getDatanodeByHost(remoteAddr);
-      if (clientNode != null) {
-        final DatanodeStorageInfo[] storages = bm.chooseTarget4WebHDFS(
-            path, clientNode, excludes, blocksize);
-        if (storages.length > 0) {
-          return storages[0].getDatanodeDescriptor();
-        }
-      }
-    } else if (op == GetOpParam.Op.OPEN
+    // For these operations choose a datanode containing a replica
+    if (op == GetOpParam.Op.OPEN
         || op == GetOpParam.Op.GETFILECHECKSUM
         || op == PostOpParam.Op.APPEND) {
-      //choose a datanode containing a replica 
       final NamenodeProtocols np = getRPCServer(namenode);
       if (status == null) {
         throw new FileNotFoundException("File " + path + " not found.");
       }
+
       final long len = status.getLen();
       if (op == GetOpParam.Op.OPEN) {
         if (openOffset < 0L || (openOffset >= len && len > 0)) {
@@ -344,10 +338,22 @@ static DatanodeInfo chooseDatanode(final NameNode namenode,
         final int count = locations.locatedBlockCount();
         if (count > 0) {
           return bestNode(locations.get(0).getLocations(), excludes);
+        } else {
+          throw new IOException("Block could not be located. Path=" + path + ", offset=" + offset);
         }
       }
     }
 
+    // All other operations don't affect a specific node so let the BlockManager pick a target
+    DatanodeDescriptor clientNode = bm.getDatanodeManager(
+    ).getDatanodeByHost(remoteAddr);
+
+    DatanodeStorageInfo[] storages = bm.chooseTarget4WebHDFS(
+      path, clientNode, excludes, blocksize);
+    if (storages.length > 0) {
+      return storages[0].getDatanodeDescriptor();
+    }
+
     return (DatanodeDescriptor)bm.getDatanodeManager().getNetworkTopology(
         ).chooseRandom(NodeBase.ROOT, excludes);
   }
@@ -358,13 +364,13 @@ static DatanodeInfo chooseDatanode(final NameNode namenode,
    * to return the first element of the node here.
    */
   protected static DatanodeInfo bestNode(DatanodeInfo[] nodes,
-      HashSet<Node> excludes) throws IOException {
+      Set<Node> excludes) throws IOException {
     for (DatanodeInfo dn: nodes) {
-      if (false == dn.isDecommissioned() && false == excludes.contains(dn)) {
+      if (!dn.isDecommissioned() && !excludes.contains(dn)) {
         return dn;
       }
     }
-    throw new IOException("No active nodes contain this block");
+    throw new IOException("No active and not excluded nodes contain this block");
   }
 
   public long renewDelegationToken(Token<DelegationTokenIdentifier> token)