First pass at a forwarded port collision middleware

lib/vagrant/action/builtin/handle_forwarded_port_collisions.rb

@@ -0,0 +1,93 @@
+require "set"
+
+require "log4r"
+
+require "vagrant/util/is_port_open"
+
+module Vagrant
+  module Action
+    module Builtin
+      # This middleware class will detect and handle collisions with
+      # forwarded ports, whether that means raising an error or repairing
+      # them automatically.
+      #
+      # Parameters it takes from the environment hash:
+      #
+      #   * `:port_collision_repair` - If true, it will attempt to repair
+      #     port collisions. If false, it will raise an exception when
+      #     there is a collision.
+      #
+      class HandleForwardedPortCollisions
+        include Util::IsPortOpen
+
+        def initialize(app, env)
+          @app    = app
+          @logger = Log4r::Logger.new("vagrant::action::builtin::handle_port_collisions")
+        end
+
+        def call(env)
+          @logger.debug("Detecting any forwarded port collisions...")
+
+          # Determine the handler we'll use if we have any port collisions
+          repair = !!env[:port_collision_repair]
+
+          # Determine a list of usable ports for repair
+          usable_ports = Set.new(env[:machine].config.vm.usable_port_range)
+
+          # Pass one, remove all defined host ports from usable ports
+          with_forwarded_ports do |args|
+            usable_ports.delete(args[1])
+          end
+
+          # Pass two, detect/handle any collisions
+          with_forwarded_ports do |args|
+            # Get the host port of this forwarded port
+            # TODO: handle overrides in the case that an existing VM is
+            # already running with auto-corrected ports.
+            guest_port = args[0]
+            host_port  = args[1]
+
+            # If the port is open (listening for TCP connections)
+            if is_port_open?("127.0.0.1", host_port)
+              if !repair
+                raise Errors::ForwardPortCollision,
+                  :guest_port => guest_port.to_s,
+                  :host_port  => host_port.to_s
+              end
+
+              @logger.info("Attempting to repair FP collision: #{host_port}")
+
+              # If we have no usable ports then we can't repair
+              if usable_ports.empty?
+                raise Errors::ForwardPortAutolistEmpty,
+                  :vm_name    => env[:machine].name,
+                  :guest_port => guest_port.to_s,
+                  :host_port  => host_port.to_s
+              end
+
+              # Attempt to repair the forwarded port
+              repaired_port = usable_ports.to_a.sort[0]
+              usable_ports.delete(repaired_port)
+
+              # Modify the args in place
+              args[1] = repaired_port
+
+              @logger.info("Repaired FP collision: #{host_port} to #{repaired_port}")
+            end
+          end
+        end
+
+        protected
+
+        def with_forwarded_ports
+          env[:machine].config.vm.networks.each do |type, args|
+            # Ignore anything but forwarded ports
+            next if type != :forwarded_port
+
+            yield args
+          end
+        end
+      end
+    end
+  end
+end