pipeline logging: add cause chain when logging

logstash-core/lib/logstash/java_pipeline.rb

@@ -137,9 +137,7 @@ def start
 
     @thread = Thread.new do
       error_log_params = ->(e) {
-        default_logging_keys(
-          :exception => e,
-          :backtrace => e.backtrace,
+        exception_logging_keys(e,
           "pipeline.sources" => pipeline_source_details
         )
       }
@@ -312,7 +310,7 @@ def start_workers
             @crash_detected.make_true
             @logger.error(
               "Pipeline worker error, the pipeline will be stopped",
-              default_logging_keys(:error => e.cause.message, :exception => e.cause.class, :backtrace => e.cause.backtrace)
+              exception_logging_keys(e.cause)
             )
           end
         end
@@ -422,21 +420,14 @@ def inputworker(plugin)
       if plugin.stop?
         @logger.debug(
           "Input plugin raised exception during shutdown, ignoring it.",
-           default_logging_keys(
-             :plugin => plugin.class.config_name,
-             :exception => e.message,
-             :backtrace => e.backtrace))
+           exception_logging_keys(e, :plugin => plugin.class.config_name))
         return
       end
 
       # otherwise, report error and restart
       @logger.error(I18n.t(
         "logstash.pipeline.worker-error-debug",
-        **default_logging_keys(
-          :plugin => plugin.inspect,
-          :error => e.message,
-          :exception => e.class,
-          :stacktrace => e.backtrace.join("\n"))))
+        **exception_logging_keys(e, :plugin => plugin.inspect)))
 
       # Assuming the failure that caused this exception is transient,
       # let's sleep for a bit and execute #run again
@@ -580,10 +571,7 @@ def close_plugin_and_ignore(plugin)
     rescue => e
       @logger.warn(
         "plugin raised exception while closing, ignoring",
-        default_logging_keys(
-          :plugin => plugin.class.config_name,
-          :exception => e.message,
-          :backtrace => e.backtrace))
+        exception_logging_keys(e, :plugin => plugin.class.config_name))
     end
   end
 
@@ -607,12 +595,12 @@ def init_worker_loop
     rescue => e
       @logger.error(
         "Worker loop initialization error",
-        default_logging_keys(:error => e.message, :exception => e.class, :stacktrace => e.backtrace.join("\n")))
+        exception_logging_keys(e))
       nil
     rescue Java::java.lang.StackOverflowError => se
       @logger.error(
         "Stack overflow error while compiling Pipeline. Please increase thread stack size using -Xss",
-        default_logging_keys())
+        exception_logging_keys(se))
       nil
     end
   end
@@ -630,6 +618,42 @@ def default_logging_keys(other_keys = {})
     keys
   end
 
+  def exception_logging_keys(active_exception = $!, other_keys = {})
+    base = active_exception ? unwind_cause_chain(active_exception) : {}
+    default_logging_keys(base.merge(other_keys))
+  end
+
+  ##
+  # Yields once per exception in the provided exception's cause chain
+  # @param exception [Exception]
+  # @yield_param [Exception]
+  def cause_chain(exception, &block)
+    return enum_for(:cause_chain, exception) unless block_given?
+
+    current = exception
+    while !current.nil?
+      yield current
+      cause = current.cause
+      current = (cause == current ? nil : cause)
+    end
+  end
+
+  ##
+  # unwinds the provided exception to create a deeply-nested structure
+  # representing the exception and its cause chain
+  # @param [Exception] exception
+  # @return [Hash{Symbol=>[String|Hash]}]
+  def unwind_cause_chain(exception)
+    cause_chain(exception).reverse_each.reduce(nil) do |cause, exception|
+      {
+        :exception   => exception.class.name,
+        :error       => exception.message,
+        :stacktrace  => exception.backtrace.join("\n"),
+        :cause       => cause,
+      }.compact
+    end
+  end
+
   def preserve_event_order?(pipeline_workers)
     case settings.get("pipeline.ordered")
     when "auto"