Merge branch 'fix-trace-seeking-readline' into 'master'

After Trace#limit, we seek to the next line in case

Closes #30796

See merge request !10681

changelogs/unreleased/fix-trace-seeking.yml

+---
+title: Fix invalid encoding when showing some traces
+merge_request: 10681
+author:

lib/gitlab/ci/trace/stream.rb

@@ -25,11 +25,10 @@ module Gitlab
         end
         def limit(last_bytes = LIMIT_SIZE)
-          stream_size = size
-          if stream_size < last_bytes
-            last_bytes = stream_size
+          if last_bytes < size
+            stream.seek(-last_bytes, IO::SEEK_END)
+            stream.readline
           end
-          stream.seek(-last_bytes, IO::SEEK_END)
         end
         def append(data, offset)

spec/fixtures/trace/ansi-sequence-and-unicode

+.
+..
+😺
+ヾ(´༎ຶД༎ຶ`)ﾉ
+許功蓋

spec/lib/gitlab/ci/trace/stream_spec.rb

@@ -17,12 +17,12 @@ describe Gitlab::Ci::Trace::Stream do
   describe '#limit' do
     let(:stream) do
       described_class.new do
-        StringIO.new("12345678")
+        StringIO.new((1..8).to_a.join("\n"))
       end
     end
-    it 'if size is larger we start from beggining' do
-      stream.limit(10)
+    it 'if size is larger we start from beginning' do
+      stream.limit(20)
       expect(stream.tell).to eq(0)
     end
@@ -30,7 +30,27 @@ describe Gitlab::Ci::Trace::Stream do
     it 'if size is smaller we start from the end' do
       stream.limit(2)
-      expect(stream.tell).to eq(6)
+      expect(stream.raw).to eq("8")
+    end
+
+    context 'when the trace contains ANSI sequence and Unicode' do
+      let(:stream) do
+        described_class.new do
+          File.open(expand_fixture_path('trace/ansi-sequence-and-unicode'))
+        end
+      end
+
+      it 'forwards to the next linefeed, case 1' do
+        stream.limit(7)
+
+        expect(stream.raw).to eq('')
+      end
+
+      it 'forwards to the next linefeed, case 2' do
+        stream.limit(29)
+
+        expect(stream.raw).to eq("\e[01;32m許功蓋\e[0m\n")
+      end
     end
   end

spec/support/fixture_helpers.rb

 module FixtureHelpers
   def fixture_file(filename)
     return '' if filename.blank?
-    file_path = File.expand_path(Rails.root.join('spec/fixtures/', filename))
-    File.read(file_path)
+    File.read(expand_fixture_path(filename))
+  end
+
+  def expand_fixture_path(filename)
+    File.expand_path(Rails.root.join('spec/fixtures/', filename))
   end
 end