fileDownload: "Response already committed" warning printed on WebSphere

[wtlucy]

1) Environment

• PrimeFaces version: 6.2
• Does it work on the newest released PrimeFaces version? Version?
• Does it work on the newest sources in GitHub? no
• Application server + version: Open Liberty 18.0.0.2 with jsf-2.2 (MyFaces 2.2)
• Affected browsers: all

2) Expected behavior

No warning messages are printed when using p:fileDownload to download a file.

3) Actual behavior

Downloading files that are larger than the servlet response buffer size results in a WebSphere warning message:
[WARNING ] WARNING: Cannot set status. Response already committed.

4) Steps to reproduce

Use a p:fileDownload button to attempt to download a large file; a warning message will be printed to the output log for every (download) request.

5) Sample XHTML

    <p:commandButton id="download" value="Download"
        ajax="false"
        onclick="PrimeFaces.monitorDownload(startMessage, finishMessage);">
        <p:fileDownload value="#{uploadController.XLSExport}"/>
    </p:commandButton>

6) Sample bean

public class UploadController implements java.io.Serializable {
	
	public UploadController() {
	}

	public StreamedContent getXLSExport() {
		byte[] bytes = new byte[33000]; // larger than 32K
		for (int i = 0; i < 33000; i++) {
			bytes[i] = 'f';
		}
		byte[] content = bytes;
	    return new DefaultStreamedContent(new ByteArrayInputStream(content), "application/csv", "something.xlsx", "UTF-8");
	}
}

The problem here looks to be that FileDownloadActionListener.processAction() makes a call to update the response status code after writing the entire contents of the downloaded file to the response output stream. If the downloaded file length is larger than the response output stream buffer size, then on WebSphere the response will be committed - and then the status code cannot be updated.

A fix for this would be to check externalContext.isResponseCommitted() before trying to call externalContext.setResponseStatus(200)

[tandraschko]

a PR would be great!

[tandraschko]

THanks!

[wtlucy]

Thanks for the quick review/merge!