Fix read/write bugs in DatagramChannel and SocketChannel.

Also improve some exception detail messages for ease of debugging.

These bugs were found by external/apache-harmony tests.

Change-Id: I37a58c1d1f1c2150eb9171967f47ef9644e8ae15

4 files changed, 23 insertions, 7 deletions

diff --git a/luni/src/main/java/java/nio/Buffer.java b/luni/src/main/java/java/nio/Buffer.java
index c0ba368..bc152ef 100644
--- a/luni/src/main/java/java/nio/Buffer.java
+++ b/luni/src/main/java/java/nio/Buffer.java
@@ -303,7 +303,7 @@ public abstract class Buffer {
      */
     void limitImpl(int newLimit) {
         if (newLimit < 0 || newLimit > capacity) {
-            throw new IllegalArgumentException();
+            throw new IllegalArgumentException("Bad limit (capacity " + capacity + "): " + newLimit);
         }
 
         limit = newLimit;
@@ -355,7 +355,7 @@ public abstract class Buffer {
 
     void positionImpl(int newPosition) {
         if (newPosition < 0 || newPosition > limit) {
-            throw new IllegalArgumentException();
+            throw new IllegalArgumentException("Bad position (limit " + limit + "): " + newPosition);
         }
 
         position = newPosition;
@@ -383,7 +383,7 @@ public abstract class Buffer {
      */
     public final Buffer reset() {
         if (mark == UNSET_MARK) {
-            throw new InvalidMarkException();
+            throw new InvalidMarkException("Mark not set");
         }
         position = mark;
         return this;
diff --git a/luni/src/main/java/java/nio/DatagramChannelImpl.java b/luni/src/main/java/java/nio/DatagramChannelImpl.java
index 7874af6..a626857 100644
--- a/luni/src/main/java/java/nio/DatagramChannelImpl.java
+++ b/luni/src/main/java/java/nio/DatagramChannelImpl.java
@@ -262,7 +262,9 @@ class DatagramChannelImpl extends DatagramChannel implements FileDescriptorChann
                 begin();
                 int oldPosition = source.position();
                 sendCount = IoBridge.sendto(fd, source, 0, isa.getAddress(), isa.getPort());
-                source.position(oldPosition + sendCount);
+                if (sendCount > 0) {
+                    source.position(oldPosition + sendCount);
+                }
             } finally {
                 end(sendCount >= 0);
             }
@@ -353,7 +355,9 @@ class DatagramChannelImpl extends DatagramChannel implements FileDescriptorChann
         }
 
         int writeCount = writeImpl(src);
-        src.position(src.position() + writeCount);
+        if (writeCount > 0) {
+            src.position(src.position() + writeCount);
+        }
         return writeCount;
     }
 
diff --git a/luni/src/main/java/java/nio/InvalidMarkException.java b/luni/src/main/java/java/nio/InvalidMarkException.java
index cb1050e..349cf3a 100644
--- a/luni/src/main/java/java/nio/InvalidMarkException.java
+++ b/luni/src/main/java/java/nio/InvalidMarkException.java
@@ -29,4 +29,12 @@ public class InvalidMarkException extends IllegalStateException {
      */
     public InvalidMarkException() {
     }
+
+    /**
+     * Constructs an {@code InvalidMarkException} with the given detail message.
+     * @hide
+     */
+    public InvalidMarkException(String detailMessage) {
+        super(detailMessage);
+    }
 }
diff --git a/luni/src/main/java/java/nio/SocketChannelImpl.java b/luni/src/main/java/java/nio/SocketChannelImpl.java
index c659299..9f8c690 100644
--- a/luni/src/main/java/java/nio/SocketChannelImpl.java
+++ b/luni/src/main/java/java/nio/SocketChannelImpl.java
@@ -298,7 +298,9 @@ class SocketChannelImpl extends SocketChannel implements FileDescriptorChannel {
                     begin();
                 }
                 readCount = IoBridge.recvfrom(true, fd, dst, 0, null, false);
-                dst.position(dst.position() + readCount);
+                if (readCount > 0) {
+                    dst.position(dst.position() + readCount);
+                }
             } finally {
                 if (isBlocking()) {
                     end(readCount > 0);
@@ -360,7 +362,9 @@ class SocketChannelImpl extends SocketChannel implements FileDescriptorChannel {
                     begin();
                 }
                 writeCount = IoBridge.sendto(fd, src, 0, null, 0);
-                src.position(src.position() + writeCount);
+                if (writeCount > 0) {
+                    src.position(src.position() + writeCount);
+                }
             } finally {
                 if (isBlocking()) {
                     end(writeCount >= 0);