add doh support

core/doh_test.go

@@ -0,0 +1,96 @@
+package core
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"testing"
+
+	"golang.org/x/net/dns/dnsmessage"
+)
+
+func TestResolveViaDoHServers(t *testing.T) {
+	t.Parallel()
+
+	want := netip.AddrFrom4([4]byte{93, 184, 216, 34})
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("method = %s, want POST", r.Method)
+		}
+		if ct := r.Header.Get("Content-Type"); ct != dohContentType {
+			t.Errorf("Content-Type = %q, want %q", ct, dohContentType)
+		}
+		w.Header().Set("Content-Type", dohContentType)
+		_, _ = w.Write(packAResponse(t, "example.com.", [4]byte{93, 184, 216, 34}))
+	}))
+	defer srv.Close()
+
+	got, err := resolveViaDoHServers(context.Background(), []string{srv.URL}, "example.com")
+	if err != nil {
+		t.Fatalf("resolveViaDoHServers() error: %v", err)
+	}
+	if got != want {
+		t.Fatalf("resolveViaDoHServers() = %v, want %v", got, want)
+	}
+}
+
+func TestResolveViaDoHServersFallsThrough(t *testing.T) {
+	t.Parallel()
+
+	// First endpoint errors; the second answers. Confirms the loop advances past
+	// a failing server instead of giving up.
+	bad := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer bad.Close()
+	good := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", dohContentType)
+		_, _ = w.Write(packAResponse(t, "example.com.", [4]byte{1, 2, 3, 4}))
+	}))
+	defer good.Close()
+
+	got, err := resolveViaDoHServers(context.Background(), []string{bad.URL, good.URL}, "example.com")
+	if err != nil {
+		t.Fatalf("resolveViaDoHServers() error: %v", err)
+	}
+	if want := netip.AddrFrom4([4]byte{1, 2, 3, 4}); got != want {
+		t.Fatalf("resolveViaDoHServers() = %v, want %v", got, want)
+	}
+}
+
+func TestResolveViaDoHServersNoServers(t *testing.T) {
+	t.Parallel()
+
+	if _, err := resolveViaDoHServers(context.Background(), nil, "example.com"); err == nil {
+		t.Fatal("resolveViaDoHServers() with no servers returned nil error, want error")
+	}
+}
+
+// packAResponse builds a minimal DNS response carrying a single A record.
+func packAResponse(t *testing.T, name string, ip [4]byte) []byte {
+	t.Helper()
+	dnsName, err := dnsmessage.NewName(name)
+	if err != nil {
+		t.Fatalf("NewName: %v", err)
+	}
+	msg := dnsmessage.Message{
+		Header: dnsmessage.Header{Response: true},
+		Answers: []dnsmessage.Resource{
+			{
+				Header: dnsmessage.ResourceHeader{
+					Name:  dnsName,
+					Type:  dnsmessage.TypeA,
+					Class: dnsmessage.ClassINET,
+				},
+				Body: &dnsmessage.AResource{A: ip},
+			},
+		},
+	}
+	b, err := msg.Pack()
+	if err != nil {
+		t.Fatalf("Pack: %v", err)
+	}
+	return b
+}