model: redirect mappings (RedirectTo, RedirectPermanent, RedirectKeepPath)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

model/model_test.go

@@ -0,0 +1,25 @@
+package model
+
+import "testing"
+
+func TestRedirectLocation(t *testing.T) {
+	cases := []struct {
+		m    Mapping
+		uri  string
+		want string
+	}{
+		{Mapping{RedirectTo: "https://new.example.com"}, "/a?b=1", "https://new.example.com"},
+		{Mapping{RedirectTo: "https://new.example.com", RedirectKeepPath: true}, "/a?b=1", "https://new.example.com/a?b=1"},
+		{Mapping{RedirectTo: "https://new.example.com/", RedirectKeepPath: true}, "/", "https://new.example.com/"},
+		{Mapping{RedirectTo: "https://new.example.com/base", RedirectKeepPath: true}, "/x/y", "https://new.example.com/base/x/y"},
+		{Mapping{RedirectTo: "https://new.example.com", RedirectKeepPath: true}, "", "https://new.example.com/"},
+	}
+	for _, c := range cases {
+		if got := c.m.RedirectLocation(c.uri); got != c.want {
+			t.Errorf("%+v %q: got %q, want %q", c.m, c.uri, got, c.want)
+		}
+	}
+	if (Mapping{}).IsRedirect() || !(Mapping{RedirectTo: "https://x"}).IsRedirect() {
+		t.Error("IsRedirect is wrong")
+	}
+}