Add a helper method to append path to a base URL

In Ruby 2.4, `URI.join("http://test//", "a").to_s` will
remove the double slash, however it's not the case in
Ruby 2.5. Using chomp should work better for the intention,
as we're not trying to allow things like ../ or / paths
resolution.

This helper method append path to host, making sure
there's one single slash as path separator.

lib/gitlab/utils.rb

@@ -16,6 +16,11 @@ module Gitlab
       str.force_encoding(Encoding::UTF_8)
     end
 
+    # Append path to host, making sure there's one single / in between
+    def append_path(host, path)
+      "#{host.to_s.sub(%r{\/+$}, '')}/#{path.to_s.sub(%r{^\/+}, '')}"
+    end
+
     # A slugified version of the string, suitable for inclusion in URLs and
     # domain names. Rules:
     #

spec/lib/gitlab/utils_spec.rb

@@ -2,7 +2,7 @@ require 'spec_helper'
 
 describe Gitlab::Utils do
   delegate :to_boolean, :boolean_to_yes_no, :slugify, :random_string, :which, :ensure_array_from_string,
-   :bytes_to_megabytes, to: :described_class
+   :bytes_to_megabytes, :append_path, to: :described_class
 
   describe '.slugify' do
     {
@@ -106,4 +106,25 @@ describe Gitlab::Utils do
       expect(bytes_to_megabytes(bytes)).to eq(1)
     end
   end
+
+  describe '.append_path' do
+    using RSpec::Parameterized::TableSyntax
+
+    where(:host, :path, :result) do
+      'http://test/'  | '/foo/bar'  |  'http://test/foo/bar'
+      'http://test/'  | '//foo/bar' |  'http://test/foo/bar'
+      'http://test//' | '/foo/bar'  |  'http://test/foo/bar'
+      'http://test'   | 'foo/bar'   |  'http://test/foo/bar'
+      'http://test//' | ''          |  'http://test/'
+      'http://test//' | nil         |  'http://test/'
+      ''              | '/foo/bar'  |  '/foo/bar'
+      nil             | '/foo/bar'  |  '/foo/bar'
+    end
+
+    with_them do
+      it 'makes sure there is only one slash as path separator' do
+        expect(append_path(host, path)).to eq(result)
+      end
+    end
+  end
 end