Add 'dis' component

This commit adds a new 'dis' component to the distillery that serves a
list of all known instances for the moment.

cmd/dis_server.go

@@ -0,0 +1,43 @@
+package cmd
+
+import (
+	"net/http"
+
+	wisski_distillery "github.com/FAU-CDI/wisski-distillery"
+	"github.com/FAU-CDI/wisski-distillery/core"
+	"github.com/tkw1536/goprogram/exit"
+)
+
+// DisServer is the 'dis_server' command
+var DisServer wisski_distillery.Command = disServer{}
+
+type disServer struct {
+	Prefix string `short:"p" long:"prefix" description:"prefix to listen under"`
+	Bind   string `short:"b" long:"bind" description:"address to listen on" default:"127.0.0.1:8888"`
+}
+
+func (disServer) Description() wisski_distillery.Description {
+	return wisski_distillery.Description{
+		Requirements: core.Requirements{
+			NeedsDistillery: true,
+		},
+		Command:     "dis_server",
+		Description: "Starts a server with information about this distillery",
+	}
+}
+
+var errServerListen = exit.Error{
+	ExitCode: exit.ExitGeneric,
+	Message:  "Unable to listen",
+}
+
+func (s disServer) Run(context wisski_distillery.Context) error {
+	server := context.Environment.Server()
+
+	context.Printf("Listening on %s\n", s.Bind)
+	err := http.ListenAndServe(s.Bind, http.StripPrefix(s.Prefix, server))
+	if err == nil {
+		return nil
+	}
+	return errServerListen.Wrap(err)
+}