[HIVE-19700] Workaround for JLine issue with UnsupportedTerminal

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.1.0, 2.4.0, 4.0.0-alpha-1
• Assignee: Naveen Gangam
• Reporter: Naveen Gangam
• Created: 24/May/18 20:34
• Updated: 21/Oct/22 06:59
• Resolved: 04/Jun/18 14:59

Description

From the JLine's ConsoleReader, readLine(prompt, mask) calls the following beforeReadLine() method.

        try {
            // System.out.println("is terminal supported " + terminal.isSupported());
            if (!terminal.isSupported()) {
                beforeReadLine(prompt, mask);
            }

So specifically when using UnsupportedTerminal -Djline.terminal and prompt=null and mask!=null, a "null" string gets printed to the console before and after the query result. UnsupportedTerminal is required to be used when running beeline as a background process, hangs otherwise.

    private void beforeReadLine(final String prompt, final Character mask) {
        if (mask != null && maskThread == null) {
            final String fullPrompt = "\r" + prompt
                + "                 "
                + "                 "
                + "                 "
                + "\r" + prompt;

            maskThread = new Thread()
            {
                public void run() {
                    while (!interrupted()) {
                        try {
                            Writer out = getOutput();
                            out.write(fullPrompt);

So the prompt is null and mask is NOT in atleast 2 scenarios in beeline.
when beeline's silent=true, prompt is null

• https://github.com/apache/hive/blob/master/beeline/src/java/org/apache/hive/beeline/BeeLine.java#L1264
  when running multiline queries
• https://github.com/apache/hive/blob/master/beeline/src/java/org/apache/hive/beeline/Commands.java#L1093

When executing beeline in script mode (commands in a file), there should not be any masking while reading lines from the script file. aka, entire line should be a beeline command or part of a multiline hive query.

So it should be safe to use a null mask instead of ConsoleReader.NULL_MASK when using UnsupportedTerminal as jline terminal.