[logback-dev] [JIRA] (LOGBACK-1392) Improve support for the JANSI library in ConsoleAppender

QOS.CH (JIRA) noreply-jira at qos.ch
Sat Mar 24 13:00:00 CET 2018

Alexandre Dutra created LOGBACK-1392:

             Summary: Improve support for the JANSI library in ConsoleAppender
                 Key: LOGBACK-1392
                 URL: https://jira.qos.ch/browse/LOGBACK-1392
             Project: logback
          Issue Type: Improvement
          Components: logback-core
    Affects Versions: 1.2.3
            Reporter: Alexandre Dutra
            Assignee: Logback dev list
            Priority: Minor

The JANSI library provides an {{AnsiPrintStream}} that intercepts ANSI sequences and allows the application to react to them accordingly. Jansi is compatible with a variety of terminals, including xterm-like terminals for Windows like Mintty and MinGW.

Jansi has a good algorithm to detect whether or not ANSI sequences will be correctly interpreted or not, and if not, its default behavior is to filter out such sequences.

Logback's {{ConsoleAppender}} has a {{withJansi}} option. Unfortunately, Logback bypasses Jansi's detection algorithm and boldly assumes that if the OS is Windows, then the terminal is a DOS prompt. So while DOS prompts get colored, terminals like Mintty or MinGW not only lose their coloring but are sent DOS escape sequences that they can't interpret.

We could improve support for JANSI with the following ideas:
 * Amend {{ConsoleAppender}} so that when {{withJansi}} is {{true}}, then all {{OutputStream}}s are wrapped in an {{AnsiPrintStream}}, effectively delegating to the JANSI library the decision to filter out ANSI escape sequences or not, depending on the terminal capability. This also allows users to disable or customize the coloring behavior by using system properties recognized by JANSI, such as {{jansi.skip}}.
 * Amend the documentation and stress that the JANSI library is the recommended solution for Windows systems, as well as for cross-platform deployments that include a mix of Windows and non-Windows systems.

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