Add support for Gitaly calls over TCP connection

Closes gitaly#166

config/gitlab.yml.example

@@ -461,7 +461,7 @@ production: &base
     storages: # You must have at least a `default` storage path.
       default:
         path: /home/git/repositories/
-        gitaly_address: unix:/home/git/gitlab/tmp/sockets/private/gitaly.socket
+        gitaly_address: unix:/home/git/gitlab/tmp/sockets/private/gitaly.socket # TCP connections are supported too (e.g. tcp://host:port)
   ## Backup settings
   backup:

config/initializers/8_gitaly.rb

@@ -9,7 +9,7 @@ if Gitlab.config.gitaly.enabled || Rails.env.test?
       raise "storage #{name.inspect} is missing a gitaly_address"
     end
-    unless URI(address).scheme == 'unix'
+    unless URI(address).scheme.in?(%w(tcp unix))
       raise "Unsupported Gitaly address: #{address.inspect}"
     end

lib/gitlab/gitaly_client.rb

@@ -12,9 +12,11 @@ module Gitlab
     end
     def self.new_channel(address)
-      # NOTE: Gitaly currently runs on a Unix socket, so permissions are
+      address = address.sub(%r{^tcp://}, '') if URI(address).scheme == 'tcp'
+      # NOTE: When Gitaly runs on a Unix socket, permissions are
       # handled using the file system and no additional authentication is
       # required (therefore the :this_channel_is_insecure flag)
+      # TODO: Add authentication support when Gitaly is running on a TCP socket.
       GRPC::Core::Channel.new(address, {}, :this_channel_is_insecure)
     end

spec/lib/gitlab/gitaly_client_spec.rb

+require 'spec_helper'
+
+describe Gitlab::GitalyClient, lib: true do
+  describe '.new_channel' do
+    context 'when passed a UNIX socket address' do
+      it 'passes the address as-is to GRPC::Core::Channel initializer' do
+        address = 'unix:/tmp/gitaly.sock'
+
+        expect(GRPC::Core::Channel).to receive(:new).with(address, any_args)
+
+        described_class.new_channel(address)
+      end
+    end
+
+    context 'when passed a TCP address' do
+      it 'strips tcp:// prefix before passing it to GRPC::Core::Channel initializer' do
+        address = 'localhost:9876'
+        prefixed_address = "tcp://#{address}"
+
+        expect(GRPC::Core::Channel).to receive(:new).with(address, any_args)
+
+        described_class.new_channel(prefixed_address)
+      end
+    end
+  end
+end