Unhelpful error message for duplicate xpath reference in xml filter

Elastic Stack Logstash
1

In 6.2 this config

input { generator { message => '<a>1</a>' count => 1 } }
output { stdout { codec => rubydebug } }
filter {
    xml {
      source => "message"
      xpath => {
        "/a" => "a"
        "/a" => "b"
      }
    }
}

get the extraordinarily unhelpful error message

[2018-04-09T17:16:16,509][ERROR][logstash.agent           ] Failed to execute action {:action=>LogStash::PipelineAction::Create/pipeline_id:main, :exception=>"NameError", :message=>"uninitialized constant LogStashCompilerLSCLGrammar::LogStash::Compiler::LSCL::AST::Hash::ConfigurationError", :backtrace=>["org/jruby/RubyModule.java:3343:in `const_missing'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:184:in `validate!'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:202:in `expr'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:134:in `expr'", "org/jruby/RubyArray.java:2486:in `map'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:98:in `expr_attributes'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:76:in `expr'", "org/jruby/RubyArray.java:2486:in `map'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:69:in `expr'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:48:in `block in compile'", "org/jruby/RubyArray.java:1734:in `each'", "/usr/share/logstash/logstash-core/lib/logstash/compiler/lscl.rb:46:in `compile'", "/usr/share/logstash/logstash-core/lib/logstash/compiler.rb:46:in `compile_imperative'", "/usr/share/logstash/logstash-core/lib/logstash/compiler.rb:50:in `compile_graph'", "/usr/share/logstash/logstash-core/lib/logstash/compiler.rb:12:in `block in compile_sources'", "org/jruby/RubyArray.java:2486:in `map'", "/usr/share/logstash/logstash-core/lib/logstash/compiler.rb:11:in `compile_sources'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:51:in `initialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:169:in `initialize'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline_action/create.rb:40:in `execute'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:315:in `block in converge_state'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:141:in `with_pipelines'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:312:in `block in converge_state'", "org/jruby/RubyArray.java:1734:in `each'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:299:in `converge_state'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:166:in `block in converge_state_and_update'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:141:in `with_pipelines'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:164:in `converge_state_and_update'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:90:in `execute'", "/usr/share/logstash/logstash-core/lib/logstash/runner.rb:348:in `block in execute'", "/usr/share/logstash/vendor/bundle/jruby/2.3.0/gems/stud-0.0.23/lib/stud/task.rb:24:in `block in initialize'"]}

If this is a bug, which component is it a bug in? I ask because I see no reference to the filter in the stacktrace.

2

Oy, that is definitely unhelpful.

I've filed a PR to fix: elastic/logstash#9343

In the mean-time, maps with multiple values for the same key don't typically work out well (last entry wins); what is it you're trying to accomplish?

3

It was not intentional.

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4

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