LogstashSocketAppender prefix example incorrect

[superfly72]

I have tried using the example given in the README with my SpringBoot (1.3.2) app

<configuration>
  <conversionRule conversionWord="syslogStart" converterClass="ch.qos.logback.classic.pattern.SyslogStartConverter"/>

  <appender name="stash" class="net.logstash.logback.appender.LogstashSocketAppender">
    <host>127.0.0.1</host>
    <port>514</port>
    <prefix class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
      <layout class="ch.qos.logback.classic.PatternLayout">
        <pattern>%syslogStart{LOCAL5}</pattern>
      </layout>
    </prefix>
  </appender>

  ...
</configuration>

but this results in an error

Application startup failed
java.lang.IllegalStateException: Logback configuration error detected: 
ERROR in ch.qos.logback.core.joran.util.PropertySetter@10d307f1 - A "ch.qos.logback.core.encoder.LayoutWrappingEncoder" object is not assignable to a "ch.qos.logback.core.Layout" variable.
ERROR in ch.qos.logback.core.joran.util.PropertySetter@10d307f1 - The class "ch.qos.logback.core.Layout" was loaded by 
ERROR in ch.qos.logback.core.joran.util.PropertySetter@10d307f1 - [sun.misc.Launcher$AppClassLoader@73d16e93] whereas object of type 
ERROR in ch.qos.logback.core.joran.util.PropertySetter@10d307f1 - "ch.qos.logback.core.encoder.LayoutWrappingEncoder" was loaded by [sun.misc.Launcher$AppClassLoader@73d16e93].

but if I remove the wrapping LayoutWrappingEncoder the code works.

  <appender name="JSON_SYSLOG" class="net.logstash.logback.appender.LogstashSocketAppender">
    <host>127.0.0.1</host>
    <port>514</port>
    <prefix class="ch.qos.logback.classic.PatternLayout">
       <pattern>%syslogStart{LOCAL5}</pattern>
    </prefix>
  </appender>

so I assume this example is incorrect.

[philsttr]

Thanks for reporting!

Fixed the documentation in commit 88b0c36

The LayoutWrappingEncoder is required when using a prefix within an encoder. But it's not required when using it within a layout or within the LogstashSocketAppender

[onema]

@philsttr, this works, but in your example of the documentation I get the following messages:

19:15:04,813 |-ERROR in ch.qos.logback.core.joran.util.PropertySetter@1f9d6c7b - A "net.logstash.logback.encoder.LogstashEncoder" object is not assignable to a "ch.qos.logback.core.Appender" variable.
19:15:04,813 |-ERROR in ch.qos.logback.core.joran.util.PropertySetter@1f9d6c7b - The class "ch.qos.logback.core.Appender" was loaded by 
19:15:04,813 |-ERROR in ch.qos.logback.core.joran.util.PropertySetter@1f9d6c7b - [sun.misc.Launcher$AppClassLoader@3d4eac69] whereas object of type 
19:15:04,813 |-ERROR in ch.qos.logback.core.joran.util.PropertySetter@1f9d6c7b - "net.logstash.logback.encoder.LogstashEncoder" was loaded by [sun.misc.Launcher$AppClassLoader@3d4eac69].

for the following config:

<configuration>
    <appender name="FOO" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="net.logstash.logback.encoder.LogstashEncoder">
            <customFields>{"stage":"${STAGE_NAME}","function":"${FUNCTION_NAME}"}</customFields>
            <prefix class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
                <layout class="ch.qos.logback.classic.PatternLayout">
                    <pattern>*** FOO:</pattern>
                </layout>
            </prefix>
        </encoder>
    </appender>
...
</configuration>

What can I do to fix this?

[philsttr]

Hi @onema,

Unfortunately, you're running into a backwards incompatibility introduced in logback (LOGBACK-1326), as mentioned in logstash-logback-encoder #232.

I have submitted logback PR#383 to address this problem, but it has not gotten any attention in over a year (ping @ceki).

Please help out by voting for LOGBACK-1326 and adding a thumbs up to PR#383 to try to get this addressed in logback.

In the meantime, the only solution to get this working would be to downgrade logback-classic and logback-core to 1.2.0 (before the backwards incompatibility was introduced)

[onema]

Thanks for your response @philsttr, I up-voted and added a comment. Hopefully, it helps!

[linzhou-zhong]

As @philsttr said, going to downgrade the version of logback-classic and logback-core to 1.2.0 is an excellent but unique solution at this moment. Trying to verify if these two dependencies have been added in the pom.xml is also important.
Anyway, thanks for @philsttr . 💪