ResponseWriter.println(char) does not print newline

[mperktold]

Jetty version(s)
10.0.7

Java version/vendor (use: java -version)
openjdk version "11.0.9" 2020-10-20
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.9+11)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.9+11, mixed mode)

OS type/version
Windows 10, 64 bit

Description
When a single character is passed to response.getWriter().println, the newline after the character is not printed. In other words, for characters, print and println have the same effect.

Other overloads for other parameter types do not seem to have this problem, just character.

How to reproduce?

Call a servlet that writes single characters using response.getWriter().println(char) and verify the output.

[joakime]

This is quite the surprising issue.

For many reasons ...

• We don't have a test case for this.
• Nor do any of the other dozen open source projects that use Jetty that we build/test releases against.
• Nor does the actual Servlet TCK have a test for this.

[joakime]

So ...

The response.getWriter().println() and response.getWriter().println(char) are both implemented by javax.servlet.ServletOutputStream.
Both wind up calling javax.servlet.ServletOutputStream.println(String) with appropriate parameters. (this is the behaviour in Jakarta EE 8 / Jakarta Servlet 4.x, unknown if Java EE 7 / Servlet 4.x does the same, need to investigate)

The implementation of javax.servlet.ServletOutputStream.println(String) in Jetty is org.eclipse.jetty.server.HttpOutput.println(String).

I cannot see a bug there, as even the various small test of response.getWriter().println("X") (String vs char) would fail the same way.

[mperktold]

I'm talking about this one in ResponseWriter:

    @Override
    public void println(char c)
    {
        try
        {
            synchronized (lock)
            {
                isOpen();
                out.write(c);
            }
        }
        catch (InterruptedIOException ex)
        {
            if (LOG.isDebugEnabled())
                LOG.debug("Write interrupted", ex);
            Thread.currentThread().interrupt();
        }
        catch (IOException ex)
        {
            setError(ex);
        }
    }

It only calls out.write(c) without writing a newline, whereas e.g. println(String) calls out.write(__lineSeparator); after writing the string.

I actually saw this behavior in a custom org.eclipse.jetty.server.Handler, not a servlet. Since both receive a HttpServletRequest, I assumed that the behavior would be the same for servlets, but perhaps I was wrong.

[joakime]

I'm in the process of improving code coverage for both response.getServletOutputStream() and response.getWriter() based actions.
This has already revealed more issues in other places.
Stay tuned for PR.

[joakime]

Opened PR #7032

[joakime]

Two bugs were found and fixed in PR #7032

1. response.getWriter().println((char)c) would not include the System.lineSeparator().
2. response.getWriter().println((boolean)b) would include System.lineSeparator() twice.

[joakime]

Some history, this bug was introduced in the Unchecked Print Writer commit 0dc3948 (introduced in Jetty 9.3.0)

This has been fixed in all active branches.