Merge pull request #1010 from appsignal/nested-errors

Add error causes tree as transaction metadata

.changesets/store-error-causes-as-transaction-sample-data.md

@@ -0,0 +1,6 @@
+---
+bump: "minor"
+type: "add"
+---
+
+Nested errors are now supported. The error causes are stored as sample data on the transaction so they can be displayed in the UI.

lib/appsignal/transaction.rb

@@ -12,6 +12,7 @@ class Transaction
     ALLOWED_TAG_KEY_TYPES = [Symbol, String].freeze
     ALLOWED_TAG_VALUE_TYPES = [Symbol, String, Integer].freeze
     BREADCRUMB_LIMIT = 20
+    ERROR_CAUSES_LIMIT = 10
 
     class << self
       def create(id, namespace, request, options = {})
@@ -374,6 +375,41 @@ def set_error(error)
         cleaned_error_message(error),
         backtrace ? Appsignal::Utils::Data.generate(backtrace) : Appsignal::Extension.data_array_new
       )
+
+      root_cause_missing = false
+
+      causes = []
+      while error
+        error = error.cause
+
+        break unless error
+
+        if causes.length >= ERROR_CAUSES_LIMIT
+          Appsignal.logger.debug "Appsignal::Transaction#set_error: Error has more " \
+            "than #{ERROR_CAUSES_LIMIT} error causes. Only the first #{ERROR_CAUSES_LIMIT} " \
+            "will be reported."
+          root_cause_missing = true
+          break
+        end
+
+        causes << error
+      end
+
+      return if causes.empty?
+
+      causes_sample_data = causes.map do |e|
+        {
+          :name => e.class.name,
+          :message => cleaned_error_message(e)
+        }
+      end
+
+      causes_sample_data.last[:is_root_cause] = false if root_cause_missing
+
+      set_sample_data(
+        "error_causes",
+        causes_sample_data
+      )
     end
     alias_method :add_exception, :set_error
 

spec/lib/appsignal/transaction_spec.rb

@@ -788,6 +788,99 @@ def to_s
         end
       end
 
+      context "when the error has no causes" do
+        it "should not send the causes information as sample data" do
+          expect(transaction.ext).to_not receive(:set_sample_data)
+
+          transaction.set_error(error)
+        end
+      end
+
+      context "when the error has multiple causes" do
+        let(:error) do
+          e = ExampleStandardError.new("test message")
+          e2 = RuntimeError.new("cause message")
+          e3 = StandardError.new("cause message 2")
+          allow(e).to receive(:backtrace).and_return(["line 1"])
+          allow(e).to receive(:cause).and_return(e2)
+          allow(e2).to receive(:cause).and_return(e3)
+          e
+        end
+
+        it "sends the causes information as sample data" do
+          expect(transaction.ext).to receive(:set_error).with(
+            "ExampleStandardError",
+            "test message",
+            Appsignal::Utils::Data.generate(["line 1"])
+          )
+
+          expect(transaction.ext).to receive(:set_sample_data).with(
+            "error_causes",
+            Appsignal::Utils::Data.generate(
+              [
+                {
+                  :name => "RuntimeError",
+                  :message => "cause message"
+                },
+                {
+                  :name => "StandardError",
+                  :message => "cause message 2"
+                }
+              ]
+            )
+          )
+
+          expect(Appsignal.logger).to_not receive(:debug)
+
+          transaction.set_error(error)
+        end
+      end
+
+      context "when the error has too many causes" do
+        let(:error) do
+          e = ExampleStandardError.new("root cause error")
+
+          11.times do |i|
+            next_e = ExampleStandardError.new("wrapper error #{i}")
+            allow(next_e).to receive(:cause).and_return(e)
+            e = next_e
+          end
+
+          allow(e).to receive(:backtrace).and_return(["line 1"])
+          e
+        end
+
+        it "sends only the first causes as sample data" do
+          expect(transaction.ext).to receive(:set_error).with(
+            "ExampleStandardError",
+            "wrapper error 10",
+            Appsignal::Utils::Data.generate(["line 1"])
+          )
+
+          expected_error_causes = Array.new(10) do |i|
+            {
+              :name => "ExampleStandardError",
+              :message => "wrapper error #{9 - i}"
+            }
+          end
+
+          expected_error_causes.last[:is_root_cause] = false
+
+          expect(transaction.ext).to receive(:set_sample_data).with(
+            "error_causes",
+            Appsignal::Utils::Data.generate(expected_error_causes)
+          )
+
+          expect(Appsignal.logger).to receive(:debug).with(
+            "Appsignal::Transaction#set_error: Error has more " \
+              "than 10 error causes. Only the first 10 " \
+              "will be reported."
+          )
+
+          transaction.set_error(error)
+        end
+      end
+
       context "when error message is nil" do
         let(:error) do
           e = ExampleStandardError.new