Merge pull request #4 from caspiano/feat/log-backend

Add `OpenTelemetry::Instrumentation::LogBackend`

Author: wyhaines

spec/log_backend_spec.cr

@@ -0,0 +1,39 @@
+require "./spec_helper"
+require "../src/opentelemetry-instrumentation/log_backend"
+
+describe OpenTelemetry::Instrumentation::LogBackend do
+  it "should add the log to the existing span" do
+    memory = IO::Memory.new
+    OpenTelemetry.configure do |config|
+      config.service_name = "Crystal OTel Instrumentation - OpenTelemetry::Instrumentation::LogBackend"
+      config.service_version = "1.0.0"
+      config.exporter = OpenTelemetry::Exporter.new(variant: :io, io: memory)
+    end
+
+    random_source = Random::DEFAULT.base64
+    ::Log.setup(sources: random_source, level: Log::Severity::Trace, backend: OpenTelemetry::Instrumentation::LogBackend.new)
+
+    trace = OpenTelemetry.trace
+    trace.in_span("Fake Span") do |_span|
+      exception = Exception.new("Oh no!")
+      ::Log.with_context do
+        ::Log.context.set(context: 42)
+        ::Log.for(random_source).warn(exception: exception, &.emit("Oh no!", data: "stuff"))
+      end
+    end
+
+    memory.rewind
+    strings = memory.gets_to_end
+    json_finder = FindJson.new(strings)
+
+    traces = [] of JSON::Any
+    while json = json_finder.pull_json
+      traces << JSON.parse(json)
+    end
+
+    traces[0]["spans"][0]["kind"].should eq 1
+    traces[0]["spans"][0]["name"].should eq "Fake Span"
+    traces[0]["spans"][0]["events"][0]["attributes"]["data"].should eq "stuff"
+    traces[0]["spans"][0]["events"][0]["attributes"]["context"].should eq 42
+  end
+end

src/opentelemetry-instrumentation.cr

@@ -1,6 +1,7 @@
 require "opentelemetry-api"
 require "tracer"
 require "./ext/*"
+require "./opentelemetry-instrumentation/log_backend"
 
 macro finished
   require "./opentelemetry/instrumentation/**"

src/opentelemetry-instrumentation/log_backend.cr

@@ -0,0 +1,47 @@
+require "opentelemetry-api"
+require "log"
+require "log/backend"
+
+# # OpenTelemetry::Instrumentation::LogBackend
+#
+# Provides a simple implementation of `Log::Backend`.
+#
+# If a `Log` call takes place within a span, the log and its context are added as an event.
+#
+# ```
+# require "opentelemetry-instrumentation/log_backend"
+# Log.builder.bind("*", Log::Severity::Warn, OpenTelemetry::Instrumentation::LogBackend.new)
+# ```
+class OpenTelemetry::Instrumentation::LogBackend < ::Log::Backend
+  def self.apply_log_entry(entry, event)
+    entry.context.each do |key, value|
+      if (raw = value.raw).is_a?(ValueTypes)
+        event[key.to_s] = raw
+      end
+    end
+
+    entry.data.each do |key, value|
+      if (raw = value.raw).is_a?(ValueTypes)
+        event[key.to_s] = raw
+      end
+    end
+
+    event["message"] = String.build { |io| ::Log::ShortFormat.format(entry, io) }
+    if exception = entry.exception
+      event["exception"] = exception.to_s
+      if backtrace = exception.backtrace?.try(&.join('\n'))
+        event["backtrace"] = backtrace
+      end
+    end
+    event["source"] = entry.source if !entry.source.empty?
+    event["timestamp"] = entry.timestamp.to_s
+  end
+
+  def write(entry : ::Log::Entry)
+    if (span = OpenTelemetry::Trace.current_span)
+      span.add_event("Log.#{entry.severity.label}#{" - #{entry.source}" unless entry.source.empty?}") do |event|
+        self.class.apply_log_entry(entry, event)
+      end
+    end
+  end
+end

src/opentelemetry/instrumentation/crystal/log.cr

@@ -1,5 +1,5 @@
 require "../instrument"
-require "io/memory"
+require "../../../opentelemetry-instrumentation/log_backend"
 
 # # OpenTelemetry::Instrumentation::CrystalLog
 #
@@ -57,23 +57,15 @@ unless_enabled?("OTEL_CRYSTAL_DISABLE_INSTRUMENTATION_LOG") do
                 dsl.emit(result.to_s)
               end
             backend = @backend
-            io = IO::Memory.new
-            ShortFormat.format(entry, io)
-            span.add_event("Log.#{entry.severity.label}#{!entry.source.empty? ? " - #{entry.source}" : ""}") do |event|
-              event["message"] = io.rewind.gets_to_end
-              if exception = entry.exception
-                event["exception"] = exception.to_s
-                event["backtrace"] = exception.backtrace.join("\n")
-              end
-              event["source"] = entry.source if !entry.source.empty?
-              event["timestamp"] = entry.timestamp.to_s
+            span.add_event("Log.#{entry.severity.label}#{" - #{entry.source}" unless entry.source.empty?}") do |event|
+              OpenTelemetry::Instrumentation::LogBackend.apply_log_entry(entry, event)
             end
 
             return unless backend
 
             backend.dispatch entry
           else
-            previous_def {|e| yield e}
+            previous_def { |e| yield e }
           end
         end
         {% end %}