Implement GitRevisionFilter

When the airbrake-ruby config doesn't specify `app_version` (99% of Rails apps),
then `GitRevisionFilter` tries to find current revision of the app and attach it
as `context/version`.

CHANGELOG.md

@@ -3,6 +3,9 @@ Airbrake Ruby Changelog
 
 ### master
 
+* Added `GitRevisionFilter`
+  ([#333](https://github.com/airbrake/airbrake-ruby/pull/333))
+
 ### [v2.10.0][v2.10.0] (May 3, 2018)
 
 * Added the `versions` option

lib/airbrake-ruby.rb

@@ -26,6 +26,7 @@
 require 'airbrake-ruby/filters/context_filter'
 require 'airbrake-ruby/filters/exception_attributes_filter'
 require 'airbrake-ruby/filters/dependency_filter'
+require 'airbrake-ruby/filters/git_revision_filter'
 require 'airbrake-ruby/filter_chain'
 require 'airbrake-ruby/notifier'
 require 'airbrake-ruby/code_hunk'

lib/airbrake-ruby/filters/git_revision_filter.rb

@@ -0,0 +1,57 @@
+module Airbrake
+  module Filters
+    # Attaches current git revision to `context`.
+    # @api private
+    # @since v2.11.0
+    class GitRevisionFilter
+      # @return [Integer]
+      attr_reader :weight
+
+      # @return [String]
+      PREFIX = 'ref: '.freeze
+
+      def initialize(root_directory)
+        @git_path = File.join(root_directory, '.git')
+        @weight = 120
+      end
+
+      # @macro call_filter
+      def call(notice)
+        return if notice[:context].key?(:version)
+        return unless File.exist?(@git_path)
+
+        revision = find_revision
+        notice[:context][:version] = revision if revision
+      end
+
+      private
+
+      def find_revision
+        head_path = File.join(@git_path, 'HEAD')
+        return unless File.exist?(head_path)
+
+        head = File.read(head_path)
+        return head unless head.start_with?(PREFIX)
+        head = head.chomp[PREFIX.size..-1]
+
+        ref_path = File.join(@git_path, head)
+        return File.read(ref_path).chomp if File.exist?(ref_path)
+
+        find_from_packed_refs(head)
+      end
+
+      def find_from_packed_refs(head)
+        packed_refs_path = File.join(@git_path, 'packed-refs')
+        return head unless File.exist?(packed_refs_path)
+
+        File.readlines(packed_refs_path).each do |line|
+          next if %w[# ^].include?(line[0])
+          next unless (parts = line.split(' ')).size == 2
+          return parts.first if parts.last == head
+        end
+
+        nil
+      end
+    end
+  end
+end

lib/airbrake-ruby/notifier.rb

@@ -143,6 +143,7 @@ def clean_backtrace
       clean_bt
     end
 
+    # rubocop:disable Metrics/AbcSize
     def add_default_filters
       if (whitelist_keys = @config.whitelist_keys).any?
         @filter_chain.add_filter(
@@ -165,6 +166,11 @@ def add_default_filters
       @filter_chain.add_filter(
         Airbrake::Filters::RootDirectoryFilter.new(root_directory)
       )
+
+      @filter_chain.add_filter(
+        Airbrake::Filters::GitRevisionFilter.new(root_directory)
+      )
     end
+    # rubocop:enable Metrics/AbcSize
   end
 end

spec/filters/git_revision_filter_spec.rb

@@ -0,0 +1,128 @@
+require 'spec_helper'
+
+RSpec.describe Airbrake::Filters::GitRevisionFilter do
+  subject { described_class.new('root/dir') }
+
+  let(:notice) do
+    Airbrake::Notice.new(Airbrake::Config.new, AirbrakeTestError.new)
+  end
+
+  context "when context/version is defined" do
+    it "doesn't attach anything to context/version" do
+      notice[:context][:version] = '1.2.3'
+      subject.call(notice)
+      expect(notice[:context][:version]).to eq('1.2.3')
+    end
+  end
+
+  context "when .git directory doesn't exist" do
+    it "doesn't attach anything to context/version" do
+      subject.call(notice)
+      expect(notice[:context][:version]).to be_nil
+    end
+  end
+
+  context "when .git directory exists" do
+    before do
+      expect(File).to receive(:exist?).with('root/dir/.git').and_return(true)
+    end
+
+    context "and when HEAD doesn't exist" do
+      before do
+        expect(File).to receive(:exist?).with('root/dir/.git/HEAD').and_return(false)
+      end
+
+      it "doesn't attach anything to context/version" do
+        subject.call(notice)
+        expect(notice[:context][:version]).to be_nil
+      end
+    end
+
+    context "and when HEAD exists" do
+      before do
+        expect(File).to receive(:exist?).with('root/dir/.git/HEAD').and_return(true)
+      end
+
+      context "and also when HEAD doesn't start with 'ref: '" do
+        before do
+          expect(File).to(
+            receive(:read).with('root/dir/.git/HEAD').and_return('refs/foo')
+          )
+        end
+
+        it "attaches the content of HEAD to context/version" do
+          subject.call(notice)
+          expect(notice[:context][:version]).to eq('refs/foo')
+        end
+      end
+
+      context "and also when HEAD starts with 'ref: " do
+        before do
+          expect(File).to(
+            receive(:read).with('root/dir/.git/HEAD').and_return("ref: refs/foo\n")
+          )
+        end
+
+        context "when the ref exists" do
+          before do
+            expect(File).to(
+              receive(:exist?).with('root/dir/.git/refs/foo').and_return(true)
+            )
+            expect(File).to(
+              receive(:read).with('root/dir/.git/refs/foo').and_return("d34db33f\n")
+            )
+          end
+
+          it "attaches the revision from the ref to context/version" do
+            subject.call(notice)
+            expect(notice[:context][:version]).to eq('d34db33f')
+          end
+        end
+
+        context "when the ref doesn't exist" do
+          before do
+            expect(File).to(
+              receive(:exist?).with('root/dir/.git/refs/foo').and_return(false)
+            )
+          end
+
+          context "and when '.git/packed-refs' exists" do
+            before do
+              expect(File).to(
+                receive(:exist?).with('root/dir/.git/packed-refs').and_return(true)
+              )
+              expect(File).to(
+                receive(:readlines).with('root/dir/.git/packed-refs').and_return(
+                  [
+                    "# pack-refs with: peeled fully-peeled\n",
+                    "ccb316eecff79c7528d1ad43e5fa165f7a44d52e refs/tags/v3.0.30\n",
+                    "^d358900f73ee5bfd6ca3a592cf23ac6e82df83c1",
+                    "d34db33f refs/foo\n"
+                  ]
+                )
+              )
+            end
+
+            it "attaches the revision from 'packed-refs' to context/version" do
+              subject.call(notice)
+              expect(notice[:context][:version]).to eq('d34db33f')
+            end
+          end
+
+          context "and when '.git/packed-refs' doesn't exist" do
+            before do
+              expect(File).to(
+                receive(:exist?).with('root/dir/.git/packed-refs').and_return(false)
+              )
+            end
+
+            it "attaches the content of HEAD to context/version" do
+              subject.call(notice)
+              expect(notice[:context][:version]).to eq('refs/foo')
+            end
+          end
+        end
+      end
+    end
+  end
+end