Fix the calls to pre- and post-receive custom hooks

- Reset G_ID if the custom pre-receive hook fails
- Use a pipe to feed stdin to the custom pre- and post-receive
  hooks, in the same way that the standalone git works

lib/gitlab_custom_hook.rb

+require 'open3'
+
 class GitlabCustomHook
-  def pre_receive(refs, repo_path)
-    if receive('pre-receive', refs, repo_path)
+  def pre_receive(changes, repo_path)
+    hook = hook_file('pre-receive', repo_path)
+    return true if hook.nil?
+    if call_receive_hook(hook, changes)
       return true
     else
       # reset GL_ID env since we stop git push here
@@ -9,29 +13,52 @@ class GitlabCustomHook
     end
   end
 
-  def post_receive(refs, repo_path)
-    receive('post-receive', refs, repo_path)
+  def post_receive(changes, repo_path)
+    hook = hook_file('post-receive', repo_path)
+    return true if hook.nil?
+    call_receive_hook(hook, changes) ? true : false
   end
 
   def update(ref_name, old_value, new_value, repo_path)
     hook = hook_file('update', repo_path)
     return true if hook.nil?
-    system(*hook, ref_name, old_value, new_value) ? true : false
+    system(hook, ref_name, old_value, new_value) ? true : false
   end
 
   private
 
-  def receive(type, refs, repo_path)
-    unless type == 'pre-receive' || type == 'post-receive'
-      puts 'GitLab: An unexpected error occurred ' \
-           '(invalid pre/post-receive hook type)'
-      return false
+  def call_receive_hook(hook, changes)
+    # function  will return true if succesful
+    exit_status = false
+
+    # we combine both stdout and stderr as we don't know what stream
+    # will be used by the custom hook
+    Open3.popen2e (hook) do |stdin, stdout_stderr, wait_thr|
+      exit_status = true
+      stdin.sync = true
+
+      # in git, pre- and post- receive hooks may just exit without
+      # reading stdin. We catch the exception to avoid a broken pipe
+      # warning
+      begin
+        # inject all the changes as stdin to the hook
+        changes.lines do |line|
+          stdin.puts (line)
+        end
+      rescue Errno::EPIPE
       end
 
-    hook = hook_file(type, repo_path)
-    return true if hook.nil?
-    cmd = "#{hook} #{refs}"
-    system(*cmd) ? true : false
+      # need to close stdin before reading stdout
+      stdin.close
+
+      # only output stdut_stderr if scripts doesn't return 0
+      unless wait_thr.value == 0
+        exit_status = false
+        stdout_stderr.each_line { |line| puts line }
+      end
+    end
+
+    exit_status
   end
 
   def hook_file(hook_type, repo_path)