Keep completed flag for retained/duplicated HttpData

[pderop]

Motivation:

When you retain and duplicate a multipart HttpData, then the "isCompleted" flag is not preserved.

Example:
Using the following code:

        HttpData data = new MemoryAttribute("test", 0),
        data.addContent(Unpooled.wrappedBuffer("foo".getBytes(CharsetUtil.UTF_8)), false);
        HttpData duplicate = httpDatadata.retainedDuplicate();

then data.isCompleted() returns false, but duplicate.isCompleted() will return true

Modification:

retainDuplicate actually calls replace method, and when the various replace methods are calling setContent(), then after the call to setContent, the isCompleted flag will be reset to true.

The propose patch adds a new setCompleted(boolean) method in AbstractHttpData class, and then all the replace methods ensure that the setCompleted method is called after having called setContent.

Example for the replace method implemented by the MemoryFileUpload class:

    @Override
    public FileUpload replace(ByteBuf content) {
        MemoryFileUpload upload = new MemoryFileUpload(
                getName(), getFilename(), getContentType(), getContentTransferEncoding(), getCharset(), size);
        if (content != null) {
            try {
                upload.setContent(content);
            } catch (IOException e) {
                throw new ChannelException(e);
            }
        }
        upload.setCompleted(isCompleted());
        return upload;
    }

Result:

The isCompleted flag is preserved in the HttpData returned by the retainedDuplicate() method, so users can check if the HttpData is partial or not.

thanks.

[pderop]

@chrisvest , @normanmaurer , can you please take a look ? thanks !

[normanmaurer]

Thanks a lot!

[pderop]

Thanks for the merge 👍 , I will now apply this fix to the netty-contrib/netty5 multipart porting PR.