no need for this.
 just remove the @return and merge it with the previous line. Also please use {@code -1} to highlight it. 
 When there are two cases for return values, I find `@return` useful.

```
Returns the length of the input.
@return the length of the input if the length of the input is known.
        a negative value if the length of the input is unknown.
```
 Shouldn't this be `endOffset - startOffset`?
 This also should be `endOffset - startOffset`.

Allow ChunkedInput to provide the progress information
Related issue: #2151 

There is no way for `ChunkedWriteHandler` to know the progress of the transfer of a `ChannelInput`.  Therefore, `ChannelProgressiveFutureListener` cannot get exact information about the progress of the transfer.

If you add a few methods that optionally provides the transfer progress to `ChannelInput`, it becomes possible for `ChunkedWriteHandler` to notify `ChannelProgressiveFutureListener`s.

If the input has no definite length, we can still use the progress so far, and consider the length of the input as 'undefined'.

codec-http/src/main/java/io/netty/handler/codec/http/HttpChunkedInput.java codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.java handler/src/main/java/io/netty/handler/stream/ChunkedFile.java handler/src/main/java/io/netty/handler/stream/ChunkedInput.java handler/src/main/java/io/netty/handler/stream/ChunkedNioFile.java handler/src/main/java/io/netty/handler/stream/ChunkedNioStream.java handler/src/main/java/io/netty/handler/stream/ChunkedStream.java handler/src/main/java/io/netty/handler/stream/ChunkedWriteHandler.java
codec-http/src/main/java/io/netty/handler/codec/http/HttpChunkedInput.java codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.java handler/src/main/java/io/netty/handler/stream/ChunkedFile.java handler/src/main/java/io/netty/handler/stream/ChunkedInput.java handler/src/main/java/io/netty/handler/stream/ChunkedNioFile.java handler/src/main/java/io/netty/handler/stream/ChunkedNioStream.java handler/src/main/java/io/netty/handler/stream/ChunkedStream.java handler/src/main/java/io/netty/handler/stream/ChunkedWriteHandler.java
handler/src/test/java/io/netty/handler/stream/ChunkedWriteHandlerTest.java
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/HttpChunkedInput.java b/codec-http/src/main/java/io/netty/handler/codec/http/HttpChunkedInput.java
index a6d317a1ff7..652ba6ae6fa 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/HttpChunkedInput.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/HttpChunkedInput.java
@@ -96,4 +96,14 @@ public HttpContent readChunk(ChannelHandlerContext ctx) throws Exception {
             return new DefaultHttpContent(buf);
         }
     }
+
+    @Override
+    public long length() {
+        return input.length();
+    }
+
+    @Override
+    public long progress() {
+        return input.progress();
+    }
 }
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.java b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.java
index e984b5f5979..044acf449d4 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostRequestEncoder.java
@@ -244,11 +244,14 @@ public void cleanFiles() {
      * While adding a FileUpload, is the multipart currently in Mixed Mode
      */
     private boolean duringMixedMode;
-
     /**
      * Global Body size
      */
     private long globalBodySize;
+    /**
+     * Global Transfer progress
+     */
+    private long globalProgress;
 
     /**
      * True if this request is a Multipart request
@@ -997,7 +1000,9 @@ public HttpContent readChunk(ChannelHandlerContext ctx) throws Exception {
         if (isLastChunkSent) {
             return null;
         } else {
-            return nextChunk();
+            HttpContent nextChunk = nextChunk();
+            globalProgress += nextChunk.content().readableBytes();
+            return nextChunk;
         }
     }
 
@@ -1083,6 +1088,16 @@ public boolean isEndOfInput() throws Exception {
         return isLastChunkSent;
     }
 
+    @Override
+    public long length() {
+        return isMultipart? globalBodySize : globalBodySize - 1;
+    }
+
+    @Override
+    public long progress() {
+        return globalProgress;
+    }
+
     /**
      * Exception when an error occurs while encoding
      */
diff --git a/handler/src/main/java/io/netty/handler/stream/ChunkedFile.java b/handler/src/main/java/io/netty/handler/stream/ChunkedFile.java
index aaa7c7bf960..69d1efb1419 100644
--- a/handler/src/main/java/io/netty/handler/stream/ChunkedFile.java
+++ b/handler/src/main/java/io/netty/handler/stream/ChunkedFile.java
@@ -161,4 +161,14 @@ public ByteBuf readChunk(ChannelHandlerContext ctx) throws Exception {
             }
         }
     }
+
+    @Override
+    public long length() {
+        return endOffset - startOffset;
+    }
+
+    @Override
+    public long progress() {
+        return offset - startOffset;
+    }
 }
diff --git a/handler/src/main/java/io/netty/handler/stream/ChunkedInput.java b/handler/src/main/java/io/netty/handler/stream/ChunkedInput.java
index fa6fd85322c..4c44bf9efc5 100644
--- a/handler/src/main/java/io/netty/handler/stream/ChunkedInput.java
+++ b/handler/src/main/java/io/netty/handler/stream/ChunkedInput.java
@@ -47,4 +47,16 @@ public interface ChunkedInput<B> {
      */
     B readChunk(ChannelHandlerContext ctx) throws Exception;
 
+    /**
+     * Returns the length of the input.
+     * @return  the length of the input if the length of the input is known.
+     *          a negative value if the length of the input is unknown.
+     */
+    long length();
+
+    /**
+     * Returns current transfer progress.
+     */
+    long progress();
+
 }
diff --git a/handler/src/main/java/io/netty/handler/stream/ChunkedNioFile.java b/handler/src/main/java/io/netty/handler/stream/ChunkedNioFile.java
index 6032644c090..dbb0521d4dc 100644
--- a/handler/src/main/java/io/netty/handler/stream/ChunkedNioFile.java
+++ b/handler/src/main/java/io/netty/handler/stream/ChunkedNioFile.java
@@ -172,4 +172,14 @@ public ByteBuf readChunk(ChannelHandlerContext ctx) throws Exception {
             }
         }
     }
+
+    @Override
+    public long length() {
+        return endOffset - startOffset;
+    }
+
+    @Override
+    public long progress() {
+        return offset - startOffset;
+    }
 }
diff --git a/handler/src/main/java/io/netty/handler/stream/ChunkedNioStream.java b/handler/src/main/java/io/netty/handler/stream/ChunkedNioStream.java
index f6dcc754baf..fd59e74477b 100644
--- a/handler/src/main/java/io/netty/handler/stream/ChunkedNioStream.java
+++ b/handler/src/main/java/io/netty/handler/stream/ChunkedNioStream.java
@@ -128,4 +128,14 @@ public ByteBuf readChunk(ChannelHandlerContext ctx) throws Exception {
             }
         }
     }
+
+    @Override
+    public long length() {
+        return -1;
+    }
+
+    @Override
+    public long progress() {
+        return offset;
+    }
 }
diff --git a/handler/src/main/java/io/netty/handler/stream/ChunkedStream.java b/handler/src/main/java/io/netty/handler/stream/ChunkedStream.java
index e50d4fbc575..bcaa6334537 100644
--- a/handler/src/main/java/io/netty/handler/stream/ChunkedStream.java
+++ b/handler/src/main/java/io/netty/handler/stream/ChunkedStream.java
@@ -120,4 +120,14 @@ public ByteBuf readChunk(ChannelHandlerContext ctx) throws Exception {
             }
         }
     }
+
+    @Override
+    public long length() {
+        return -1;
+    }
+
+    @Override
+    public long progress() {
+        return offset;
+    }
 }
diff --git a/handler/src/main/java/io/netty/handler/stream/ChunkedWriteHandler.java b/handler/src/main/java/io/netty/handler/stream/ChunkedWriteHandler.java
index 9f8ba6b1768..39bd22b109c 100644
--- a/handler/src/main/java/io/netty/handler/stream/ChunkedWriteHandler.java
+++ b/handler/src/main/java/io/netty/handler/stream/ChunkedWriteHandler.java
@@ -179,7 +179,7 @@ private void discard(Throwable cause) {
                         }
                         currentWrite.fail(cause);
                     } else {
-                        currentWrite.success();
+                        currentWrite.success(in.length());
                     }
                     closeInput(in);
                 } catch (Exception e) {
@@ -253,7 +253,6 @@ private void doFlush(final ChannelHandlerContext ctx) throws Exception {
                     message = Unpooled.EMPTY_BUFFER;
                 }
 
-                final int amount = amount(message);
                 ChannelFuture f = ctx.write(message);
                 if (endOfInput) {
                     this.currentWrite = null;
@@ -266,8 +265,8 @@ private void doFlush(final ChannelHandlerContext ctx) throws Exception {
                     f.addListener(new ChannelFutureListener() {
                         @Override
                         public void operationComplete(ChannelFuture future) throws Exception {
-                            currentWrite.progress(amount);
-                            currentWrite.success();
+                            currentWrite.progress(chunks.progress(), chunks.length());
+                            currentWrite.success(chunks.length());
                             closeInput(chunks);
                         }
                     });
@@ -279,7 +278,7 @@ public void operationComplete(ChannelFuture future) throws Exception {
                                 closeInput((ChunkedInput<?>) pendingMessage);
                                 currentWrite.fail(future.cause());
                             } else {
-                                currentWrite.progress(amount);
+                                currentWrite.progress(chunks.progress(), chunks.length());
                             }
                         }
                     });
@@ -291,7 +290,7 @@ public void operationComplete(ChannelFuture future) throws Exception {
                                 closeInput((ChunkedInput<?>) pendingMessage);
                                 currentWrite.fail(future.cause());
                             } else {
-                                currentWrite.progress(amount);
+                                currentWrite.progress(chunks.progress(), chunks.length());
                                 if (channel.isWritable()) {
                                     resumeTransfer();
                                 }
@@ -327,7 +326,6 @@ static void closeInput(ChunkedInput<?> chunks) {
     private static final class PendingWrite {
         final Object msg;
         final ChannelPromise promise;
-        private long progress;
 
         PendingWrite(Object msg, ChannelPromise promise) {
             this.msg = msg;
@@ -339,7 +337,7 @@ void fail(Throwable cause) {
             promise.tryFailure(cause);
         }
 
-        void success() {
+        void success(long total) {
             if (promise.isDone()) {
                 // No need to notify the progress or fulfill the promise because it's done already.
                 return;
@@ -347,27 +345,16 @@ void success() {
 
             if (promise instanceof ChannelProgressivePromise) {
                 // Now we know what the total is.
-                ((ChannelProgressivePromise) promise).tryProgress(progress, progress);
+                ((ChannelProgressivePromise) promise).tryProgress(total, total);
             }
 
             promise.trySuccess();
         }
 
-        void progress(int amount) {
-            progress += amount;
+        void progress(long progress, long total) {
             if (promise instanceof ChannelProgressivePromise) {
-                ((ChannelProgressivePromise) promise).tryProgress(progress, -1);
+                ((ChannelProgressivePromise) promise).tryProgress(progress, total);
             }
         }
     }
-
-    private static int amount(Object msg) {
-        if (msg instanceof ByteBuf) {
-            return ((ByteBuf) msg).readableBytes();
-        }
-        if (msg instanceof ByteBufHolder) {
-            return ((ByteBufHolder) msg).content().readableBytes();
-        }
-        return 1;
-    }
 }

diff --git a/handler/src/test/java/io/netty/handler/stream/ChunkedWriteHandlerTest.java b/handler/src/test/java/io/netty/handler/stream/ChunkedWriteHandlerTest.java
index 54879929384..204e140f4b5 100644
--- a/handler/src/test/java/io/netty/handler/stream/ChunkedWriteHandlerTest.java
+++ b/handler/src/test/java/io/netty/handler/stream/ChunkedWriteHandlerTest.java
@@ -124,6 +124,16 @@ public ByteBuf readChunk(ChannelHandlerContext ctx) throws Exception {
                 done = true;
                 return buffer.duplicate().retain();
             }
+
+            @Override
+            public long length() {
+                return -1;
+            }
+
+            @Override
+            public long progress() {
+                return 1;
+            }
         };
 
         final AtomicBoolean listenerNotified = new AtomicBoolean(false);
@@ -171,6 +181,16 @@ public Object readChunk(ChannelHandlerContext ctx) throws Exception {
                 done = true;
                 return 0;
             }
+
+            @Override
+            public long length() {
+                return -1;
+            }
+
+            @Override
+            public long progress() {
+                return 1;
+            }
         };
 
         EmbeddedChannel ch = new EmbeddedChannel(new ChunkedWriteHandler());
