MTOM attachment not transferred properly (empty stream)

[grodrigues]

I was implementing a web service to upload files (from 120 Kb to 1 Mb). Most
of the time everything worked fine, but sometimes (randomly) the uploaded
file appeared to be empty (size == 0) in the target platform.

I’ve tested CXF 2.5 and 2.6 – same behavior.

I created the following Jira issue :
https://issues.apache.org/jira/browse/CXF-4356

After some debugging I found that the problem came from the temp file
created by the CachedOutputStream that was sometimes deleted during the
process of getting the cached stream. 

By digging a bit more, I also found that the problem occurred when the
created FileInputStream was collected by the GC before the last call to
CachedOutputStream#getInputStream()  for getting the stream. As the #close()
method of the created FileInputStream was overridden to call
CachedOutputStream#maybeDeleteTempFile() to delete the temp file and that
the #close() method is called within the FileInputStream#finalize() method I
understood why I got the empty stream.

What I didn’t understand is why the created FileInputStream is sometimes (!)
garbage collected prematurely? Has anyone else experienced the same problem?

I found a workaround by keeping an instance of the created FileInputStream
in CachedOutputStream#getInputStream() within the CachedOutputStream to
prevent the GC to collect it too early and therefore to delete the need temp
file. However the temp file is still deleted properly.

Here is the code I changed in CachedOutputStream class :

private FileInputStream fileInputStream; // <-- The instance we keep

public InputStream getInputStream() throws IOException {
    flush();
    if (inmem) {
        if (currentStream instanceof LoadingByteArrayOutputStream) {
            return ((LoadingByteArrayOutputStream)
currentStream).createInputStream();
        } else if (currentStream instanceof ByteArrayOutputStream) {
            return new ByteArrayInputStream(((ByteArrayOutputStream)
currentStream).toByteArray());
        } else if (currentStream instanceof PipedOutputStream) {
            return new PipedInputStream((PipedOutputStream) currentStream);
        } else {
            return null;
        }
    } else {
        try {
            fileInputStream = new FileInputStream(tempFile) { // <-- The
instance we keep
                public void close() throws IOException {
                    super.close();
                    maybeDeleteTempFile(this);
                }
            };
            streamList.add(fileInputStream);
            return fileInputStream;
        } catch (FileNotFoundException e) {
            throw new IOException("Cached file was deleted, " +
e.toString());
        }
    }
}



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