Add length() API call to OutMessage

Author: cstlee

include/Homa/Homa.h

@@ -163,6 +163,11 @@ class OutMessage {
      */
     virtual Status getStatus() const = 0;
 
+    /**
+     * Return the number of bytes this Message contains.
+     */
+    virtual size_t length() const = 0;
+
     /**
      * Copy an array of bytes to the beginning of the Message.
      *

src/Sender.cc

@@ -585,6 +585,15 @@ Sender::Message::getStatus() const
     return state.load();
 }
 
+/**
+ * @copydoc Homa::OutMessage::length()
+ */
+size_t
+Sender::Message::length() const
+{
+    return Util::downCast<size_t>(messageLength - start);
+}
+
 /**
  * @copydoc Homa::OutMessage::prepend()
  */

src/Sender.h

@@ -156,6 +156,7 @@ class Sender {
         virtual void append(const void* source, size_t count);
         virtual void cancel();
         virtual Status getStatus() const;
+        virtual size_t length() const;
         virtual void prepend(const void* source, size_t count);
         virtual void release();
         virtual void reserve(size_t count);

src/SenderTest.cc

@@ -1127,6 +1127,15 @@ TEST_F(SenderTest, Message_getStatus)
     // Nothing to test
 }
 
+TEST_F(SenderTest, Message_length)
+{
+    ON_CALL(mockDriver, getMaxPayloadSize).WillByDefault(Return(2048));
+    Sender::Message msg(sender, &mockDriver);
+    msg.messageLength = 200;
+    msg.start = 20;
+    EXPECT_EQ(180U, msg.length());
+}
+
 TEST_F(SenderTest, Message_prepend)
 {
     ON_CALL(mockDriver, getMaxPayloadSize).WillByDefault(Return(2048));