Clean up gRPC debug_error_string messages in Sentry

The upgrade of gRPC brought along a `debug_error_string` that makes it
harder for Sentry to group similar exceptions together. There doesn't
appear to be a way to turn this off, so we clean this up in a Sentry
field processsor. Now exceptions will have a field
`grpc_debug_error_string` field in the `extra` section.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/238465

lib/gitlab/error_tracking.rb

@@ -26,6 +26,8 @@ module Gitlab
           # Sanitize fields based on those sanitized from Rails.
           config.sanitize_fields = Rails.application.config.filter_parameters.map(&:to_s)
           config.processors << ::Gitlab::ErrorTracking::Processor::SidekiqProcessor
+          config.processors << ::Gitlab::ErrorTracking::Processor::GrpcErrorProcessor
+
           # Sanitize authentication headers
           config.sanitize_http_headers = %w[Authorization Private-Token]
           config.tags = extra_tags_from_env.merge(program: Gitlab.process_name)

lib/gitlab/error_tracking/processor/grpc_error_processor.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module ErrorTracking
+    module Processor
+      class GrpcErrorProcessor < ::Raven::Processor
+        DEBUG_ERROR_STRING_REGEX = RE2('(.*) debug_error_string:(.*)')
+
+        def process(value)
+          return value unless grpc_exception?(value)
+
+          process_message(value)
+          process_exception_values(value)
+          process_custom_fingerprint(value)
+
+          value
+        end
+
+        def grpc_exception?(value)
+          value[:exception] && value[:message].start_with?('GRPC::')
+        end
+
+        def process_message(value)
+          message, debug_str = split_debug_error_string(value[:message])
+
+          return unless message
+
+          value[:message] = message
+          extra = value[:extra] || {}
+          extra[:grpc_debug_error_string] = debug_str if debug_str
+        end
+
+        def process_exception_values(value)
+          exceptions = value.dig(:exception, :values)
+
+          return unless exceptions.is_a?(Array)
+
+          exceptions.each do |entry|
+            message, _ = split_debug_error_string(entry[:value])
+            entry[:value] = message if message
+          end
+        end
+
+        def process_custom_fingerprint(value)
+          fingerprint = value[:fingerprint]
+
+          return value unless custom_grpc_fingerprint?(fingerprint)
+
+          message, _ = split_debug_error_string(fingerprint[1])
+          fingerprint[1] = message if message
+        end
+
+        private
+
+        def custom_grpc_fingerprint?(fingerprint)
+          fingerprint.is_a?(Array) && fingerprint.length == 2 && fingerprint[0].start_with?('GRPC::')
+        end
+
+        def split_debug_error_string(message)
+          return unless message
+
+          match = DEBUG_ERROR_STRING_REGEX.match(message)
+
+          return unless match
+
+          [match[1], match[2]]
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/error_tracking/processor/grpc_error_processor_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::ErrorTracking::Processor::GrpcErrorProcessor do
+  describe '#process' do
+    subject { described_class.new }
+
+    context 'when there is no GRPC exception' do
+      let(:data) { { fingerprint: ['ArgumentError', 'Missing arguments'] } }
+
+      it 'leaves data unchanged' do
+        expect(subject.process(data)).to eq(data)
+      end
+    end
+
+    context 'when there is a GPRC exception with a debug string' do
+      let(:data) do
+        {
+          exception: {
+            values: [
+              {
+                value: "GRPC::DeadlineExceeded: 4:DeadlineExceeded. debug_error_string:{\"hello\":1}"
+              }
+            ]
+          },
+          extra: {
+            caller: 'test'
+          },
+          message: "GRPC::DeadlineExceeded: 4:DeadlineExceeded. debug_error_string:{\"hello\":1}",
+          fingerprint: [
+            "GRPC::DeadlineExceeded",
+            "4:Deadline Exceeded. debug_error_string:{\"created\":\"@1598938192.005782000\",\"description\":\"Error received from peer unix:/home/git/gitalypraefect.socket\",\"file\":\"src/core/lib/surface/call.cc\",\"file_line\":1055,\"grpc_message\":\"Deadline Exceeded\",\"grpc_status\":4}"
+          ]
+        }
+      end
+
+      let(:expected) do
+        {
+          message: "GRPC::DeadlineExceeded: 4:DeadlineExceeded.",
+          fingerprint: [
+            "GRPC::DeadlineExceeded",
+            "4:Deadline Exceeded."
+          ],
+          exception: {
+            values: [
+              {
+                value: "GRPC::DeadlineExceeded: 4:DeadlineExceeded."
+              }
+            ]
+          },
+          extra: {
+            caller: 'test',
+            grpc_debug_error_string: "{\"hello\":1}"
+         }
+        }
+      end
+
+      it 'removes the debug error string and stores it as an extra field' do
+        expect(subject.process(data)).to eq(expected)
+      end
+
+      context 'with no custom fingerprint' do
+        before do
+          data.delete(:fingerprint)
+          expected.delete(:fingerprint)
+        end
+
+        it 'removes the debug error string and stores it as an extra field' do
+          expect(subject.process(data)).to eq(expected)
+        end
+      end
+    end
+  end
+end