How to make log messages display in remote REPL?

[tobyloxy]

I have web app that uses logback + clojure.tools.logging for logging.

In development, if I run (log/warn "foo") then foo would display in the REPL as well as getting appended to the log file. However, if I connect to the production app with a remote REPL, then when I run (log/warn "foo) I see foo is appended to the log file but not displayed in the REPL.

Is there a way to make it so that log messages are displayed in my REPL window when I connect to the production app with a remote REPL?

At first I thought the problem was with my logback.xml configuration, but I’m experiencing this even when I use the exact same logback.xml for dev and prod.

Thanks in advance for any advice!

Here’s my logback.xml in case it’s relevant.

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <statusListener class="ch.qos.logback.core.status.NopStatusListener" />
    <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>log/web-app.log</file>
        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <fileNamePattern>log/web-app.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
            <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
                <maxFileSize>100MB</maxFileSize>
            </timeBasedFileNamingAndTriggeringPolicy>
            <!-- keep 30 days of history -->
            <maxHistory>30</maxHistory>
        </rollingPolicy>
        <encoder>
            <charset>UTF-8</charset>
            <pattern>%date{ISO8601} [%thread] %-5level %logger{36} - %msg %n</pattern>
        </encoder>
    </appender>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <charset>UTF-8</charset>
            <pattern>%date{ISO8601} [%thread] %-5level %logger{36} - %msg %n</pattern>
        </encoder>
    </appender>
    <logger name="org.apache.http" level="warn" />
    <logger name="org.xnio.nio" level="warn" />
    <logger name="io.undertow.websockets.core.request" level="warn" />
    <logger name="io.undertow.request" level="warn" />
    <logger name="io.undertow.session" level="warn" />
    <logger name="io.undertow.request" level="warn" />
    <root level="DEBUG">
        <appender-ref ref="STDOUT" />
        <appender-ref ref="FILE" />
    </root>
</configuration>

[nbardiuk]

As I understand REPL overrides *out* in order to grab output from remote application.
But logback writes to System.out which REPL does not touch.

I would try to override System.out with a buffer, capture some logs and print them to the REPL, which should be displayed locally

(let [original-out System/out
      baos (java.io.ByteArrayOutputStream.)]
  (System/setOut (java.io.PrintStream. baos true "UTF-8"))
  (try

    ;; call some code that prints logs
    (log/warn "foo")

    (finally
      (System/setOut original-out)
      (print (str baos)))))

[tobyloxy]

@nbardiuk

REPL overrides *out* in order to grab output from remote application.
But logback writes to System.out which REPL does not touch

Thank you! This is what I didn’t understand.

My ideal situation would be that I can use the same logging functions in local development and production, and that when I REPL into the production machine I can see the log messages in my REPL.

I think what I’ll do is wrap the clojure.tools.logging warn etc functions with versions that println as well as the usual log.