Adds a database.

This is a really simple map. Calls to it just check if the key exists
and return a bool. In case of a false it adds the key.
The key is just a string which might or might not be sufficient.

database.go

@@ -0,0 +1,33 @@
+/*
+Credits go to github.com/SlyMarbo/rss for inspiring this solution.
+*/
+package feeder
+
+type database struct {
+	request  chan string
+	response chan bool
+	known    map[string]struct{}
+}
+
+func (d *database) Run() {
+	d.known = make(map[string]struct{})
+	var s string
+
+	for {
+		s = <-d.request
+		if _, ok := d.known[s]; ok {
+			d.response <- true
+		} else {
+			d.response <- false
+			d.known[s] = struct{}{}
+		}
+	}
+}
+
+func NewDatabase() *database {
+	database := new(database)
+	database.request = make(chan string)
+	database.response = make(chan bool)
+	go database.Run()
+	return database
+}