[GitHub] [hadoop] openinx commented on a change in pull request #597: HDFS-3246: pRead equivalent for direct read path

[GitBox <gi...@apache.org>]

openinx commented on a change in pull request #597: HDFS-3246: pRead equivalent for direct read path
URL: https://github.com/apache/hadoop/pull/597#discussion_r267674071
 
 

 ##########
 File path: hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/CryptoInputStream.java
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 @@ -341,6 +343,26 @@ public int read(long position, byte[] buffer, int offset, int length)
           "positioned read.");
     }
   }
+
+   /** Positioned read using ByteBuffers. It is thread-safe */
+  @Override
+  public int read(long position, final ByteBuffer buf)
+      throws IOException {
+    checkStream();
+    try {
+      int pos = buf.position();
+      final int n = ((ByteBufferPositionedReadable) in).read(position, buf);
+      if (n > 0) {
+        // This operation does not change the current offset of the file
+        decrypt(position, buf, n, pos);
+      }
+
+      return n;
+    } catch (ClassCastException e) {
 
 Review comment:
   Here we catch the ClassCastException to check whether the inpustream has implemented an ByteBufferPositionedReadable interface ?  I don't think it's a good way, because the catch{...} block need an full stack and not so efficient .  
   How about use the following : 
   
   ```java
   if(in instanceof ByteBufferPositionedReadable){
       //...
   }else{
       throw new UnsupportedOperationException(...)
   }
   ```
    

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