userdb: Add a method to remove users

This patch adds a method to userdb to remove users.
It will not be used by chasquid, but by the command-line tool.

internal/userdb/userdb.go

@@ -191,6 +191,17 @@ func (db *DB) AddUser(name, plainPassword string) error {
 	return nil
 }
 
+// RemoveUser from the database. Returns True if the user was there, False
+// otherwise.
+func (db *DB) RemoveUser(name string) bool {
+	db.mu.Lock()
+
+	_, present := db.db.Users[name]
+	delete(db.db.Users, name)
+	db.mu.Unlock()
+	return present
+}
+
 ///////////////////////////////////////////////////////////
 // Encryption schemes
 //

internal/userdb/userdb_test.go

@@ -256,5 +256,30 @@ func TestReload(t *testing.T) {
 	if len(db.db.Users) != 2 {
 		t.Errorf("expected 2 users, got %d", len(db.db.Users))
 	}
-
+}
+
+func TestRemoveUser(t *testing.T) {
+	fname := mustCreateDB(t, "")
+	defer removeIfSuccessful(t, fname)
+	db := mustLoad(t, fname)
+
+	if ok := db.RemoveUser("unknown"); ok {
+		t.Errorf("removal of unknown user succeeded")
+	}
+
+	if err := db.AddUser("user", "passwd"); err != nil {
+		t.Fatalf("error adding user: %v", err)
+	}
+
+	if ok := db.RemoveUser("unknown"); ok {
+		t.Errorf("removal of unknown user succeeded")
+	}
+
+	if ok := db.RemoveUser("user"); !ok {
+		t.Errorf("removal of existing user failed")
+	}
+
+	if ok := db.RemoveUser("user"); ok {
+		t.Errorf("removal of unknown user succeeded")
+	}
 }