From 7b743ac87f174593f4cf3a9504b9d712cccec5f0 Mon Sep 17 00:00:00 2001
From: Todd Lipcon <todd@apache.org>
Date: Fri, 8 Jun 2012 19:54:42 +0000
Subject: [PATCH] HADOOP-8244. Improve comments on ByteBufferReadable.read.
 Contributed by Henry Robinson.

(svn merge -c 1309625 from trunk)


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1348209 13f79535-47bb-0310-9956-ffa450edef68
---
 .../hadoop-common/CHANGES.txt                 |  3 +++
 .../apache/hadoop/fs/ByteBufferReadable.java  | 22 ++++++++++++++-----
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index fa46641f0b6..b8959479d8f 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -34,6 +34,9 @@ Release 2.0.1-alpha - UNRELEASED
 
     HADOOP-8358. Config-related WARN for dfs.web.ugi can be avoided. (harsh)
 
+    HADOOP-8244. Improve comments on ByteBufferReadable.read. (Henry Robinson
+    via atm)
+
   BUG FIXES
 
     HADOOP-8372. NetUtils.normalizeHostName() incorrectly handles hostname
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ByteBufferReadable.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ByteBufferReadable.java
index f47269c9c97..e18a1151499 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ByteBufferReadable.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/ByteBufferReadable.java
@@ -28,18 +28,28 @@ public interface ByteBufferReadable {
   /**
    * Reads up to buf.remaining() bytes into buf. Callers should use
    * buf.limit(..) to control the size of the desired read.
-   *
-   * After the call, buf.position() should be unchanged, and therefore any data
-   * can be immediately read from buf.
-   *
+   * <p/>
+   * After a successful call, buf.position() and buf.limit() should be
+   * unchanged, and therefore any data can be immediately read from buf.
+   * buf.mark() may be cleared or updated.
+   * <p/>
+   * In the case of an exception, the values of buf.position() and buf.limit()
+   * are undefined, and callers should be prepared to recover from this
+   * eventuality.
+   * <p/>
    * Many implementations will throw {@link UnsupportedOperationException}, so
    * callers that are not confident in support for this method from the
    * underlying filesystem should be prepared to handle that exception.
+   * <p/>
+   * Implementations should treat 0-length requests as legitimate, and must not
+   * signal an error upon their receipt.
    *
    * @param buf
-   *          the ByteBuffer to receive the results of the read operation
+   *          the ByteBuffer to receive the results of the read operation. Up to
+   *          buf.limit() - buf.position() bytes may be read.
    * @return the number of bytes available to read from buf
-   * @throws IOException if there is some error performing the read
+   * @throws IOException
+   *           if there is some error performing the read
    */
   public int read(ByteBuffer buf) throws IOException;
 }