Add kamal app open command to open app in a web browser

lib/kamal/cli/app.rb

@@ -227,6 +227,24 @@ def logs
     end
   end
 
+  desc "open", "open app in a web browser"
+  def open
+    host = KAMAL.primary_role.proxy.hosts.first || KAMAL.primary_host
+    protocol = KAMAL.primary_role.ssl? ? "https" : "http"
+    cmd =
+      case RbConfig::CONFIG["host_os"]
+      when /mswin|mingw|cygwin/ then "start"
+      when /darwin/ then "open"
+      when /linux|bsd/ then "xdg-open"
+      end
+
+    if cmd
+      system(cmd, "#{protocol}://#{host}")
+    else
+      say "Could not detect OS browser"
+    end
+  end
+
   desc "remove", "Remove app containers and images from servers"
   def remove
     with_lock do

test/cli/app_test.rb

@@ -235,6 +235,20 @@ class CliAppTest < CliTestCase
     end
   end
 
+  test "open with proxy host domain" do
+    RbConfig::CONFIG.stubs(:[]).with("host_os").returns("linux")
+    Object.any_instance.expects(:system).with("xdg-open", "https://app.example.com")
+
+    run_command("open", config: :with_proxy_host)
+  end
+
+  test "open with primary host IP" do
+    RbConfig::CONFIG.stubs(:[]).with("host_os").returns("linux")
+    Object.any_instance.expects(:system).with("xdg-open", "http://1.1.1.1")
+
+    run_command("open")
+  end
+
   test "remove" do
     run_command("remove").tap do |output|
       assert_match /#{Regexp.escape("sh -c 'docker ps --latest --quiet --filter label=service=app --filter label=role=web --filter status=running --filter status=restarting --filter ancestor=$(docker image ls --filter reference=dhh/app:latest --format '\\''{{.ID}}'\\'') ; docker ps --latest --quiet --filter label=service=app --filter label=role=web --filter status=running --filter status=restarting' | head -1 | xargs docker stop")}/, output

test/fixtures/deploy_with_proxy_host.yml

@@ -0,0 +1,13 @@
+service: app
+image: dhh/app
+servers:
+  web:
+    - "1.1.1.1"
+proxy:
+  ssl: true
+  host: app.example.com
+registry:
+  username: user
+  password: pw
+builder:
+  arch: amd64