[UNDERTOW-2157] UndertowOutputStream: behaviour discrepancies, clarify contract, fix bug

core/src/main/java/io/undertow/io/BufferWritableOutputStream.java

@@ -34,6 +34,10 @@ public interface BufferWritableOutputStream {
 
     void write(ByteBuffer byteBuffer) throws IOException;
 
+    /**
+     * Transfer the remaining content of the input FileChannel (from its current position, to end of file).
+     */
+    @Deprecated
     void transferFrom(FileChannel source) throws IOException;
 
 }

core/src/main/java/io/undertow/io/UndertowOutputStream.java

@@ -309,6 +309,8 @@ private void writeBufferBlocking(final boolean writeFinal) throws IOException {
 
     @Override
     public void transferFrom(FileChannel source) throws IOException {
+        final long startPosition = source.position();
+        final long count = source.size() - source.position();
         if (anyAreSet(state, FLAG_CLOSED)) {
             throw UndertowMessages.MESSAGES.streamIsClosed();
         }
@@ -318,10 +320,8 @@ public void transferFrom(FileChannel source) throws IOException {
         if (channel == null) {
             channel = exchange.getResponseChannel();
         }
-        long position = source.position();
-        long size = source.size();
-        Channels.transferBlocking(channel, source, position, size);
-        updateWritten(size - position);
+        Channels.transferBlocking(channel, source, startPosition, count);
+        updateWritten(count);
     }
 
     /**

servlet/src/main/java/io/undertow/servlet/spec/ServletOutputStreamImpl.java

@@ -556,46 +556,44 @@ public void transferFrom(FileChannel source) throws IOException {
         if (anyAreSet(state, FLAG_CLOSED) || servletRequestContext.getOriginalResponse().isTreatAsCommitted()) {
             throw UndertowServletMessages.MESSAGES.streamIsClosed();
         }
+        final long startPosition = source.position();
+        long count = source.size() - source.position();
         final long remainingContentLength = remainingContentLength();
+        if (count > remainingContentLength) {
+            count = remainingContentLength;
+        }
         if (listener == null) {
             if (buffer != null && buffer.position() != 0) {
                 writeBufferBlocking(false);
             }
             if (channel == null) {
                 channel = servletRequestContext.getExchange().getResponseChannel();
             }
-            long position = source.position();
-            long count = source.size() - position;
-            if (count > remainingContentLength) {
-                count = remainingContentLength;
-            }
-            Channels.transferBlocking(channel, source, position, count);
+            Channels.transferBlocking(channel, source, startPosition, count);
             updateWritten(count);
         } else {
             setFlags(FLAG_WRITE_STARTED);
             createChannel();
 
             long pos = 0;
             try {
-                long size = Math.min (source.size(), remainingContentLength);
-                pos = source.position();
+                long end = pos + count;
+                pos = startPosition;
 
-                while (size - pos > 0) {
-                    long ret = channel.transferFrom(pendingFile, pos, size - pos);
+                while (end - pos > 0) {
+                    long ret = channel.transferFrom(pendingFile, pos, end - pos);
                     if (ret <= 0) {
                         clearFlags(FLAG_READY);
                         pendingFile = source;
-                        source.position(pos);
                         channel.resumeWrites();
                         return;
                     }
                     pos += ret;
                 }
             } finally {
-                updateWrittenAsync(pos - source.position());
+                updateWrittenAsync(pos - startPosition);
             }
         }
-
     }