Flush log file after every write

CHANGELOG

+v7.1.1
+  - Flush log file after every write (!199)
+
 v7.1.0
   - Migrate `git-upload-archive` to gitaly
 

VERSION

-7.1.0
+7.1.1

bin/test-logger

+#!/usr/bin/env ruby
+
+# The purpose of this executable is to test that gitlab-shell logging
+# works correctly in combination with Kernel.exec.
+
+require_relative '../lib/gitlab_init'
+require_relative '../lib/gitlab_logger'
+
+$logger.info(ARGV.first)
+Kernel.exec('true')

lib/gitlab_logger.rb

@@ -25,7 +25,13 @@ class GitlabLogger
 
   def initialize(level, path, log_format)
     @level = level
+
     @log_file = File.open(path, 'ab')
+    # By default Ruby will buffer writes. This is a problem when we exec
+    # into a new command before Ruby flushed its buffers. Setting 'sync' to
+    # true disables Ruby's buffering.
+    @log_file.sync = true
+
     @log_format = log_format
   end
 

spec/gitlab_logger_spec.rb

 require_relative 'spec_helper'
 require_relative '../lib/gitlab_logger'
+require 'securerandom'
 
 describe :convert_log_level do
   subject { convert_log_level :extreme }
@@ -112,4 +113,15 @@ describe GitlabLogger do
       expect(JSON.parse(first_line)).to include('msg' => '"hello\x80world"')
     end
   end
+
+  describe 'log flushing' do
+    it 'logs get written even when calling Kernel.exec' do
+      msg = SecureRandom.hex(12)
+      test_logger_status = system('bin/test-logger', msg)
+      expect(test_logger_status).to eq(true)
+
+      grep_status = system('grep', '-q', '-e', msg, GitlabConfig.new.log_file)
+      expect(grep_status).to eq(true)
+    end
+  end
 end