Update fetch for static page gen, fix DOM patching

go/httputil/fetch_test.go

@@ -0,0 +1,58 @@
+package httputil
+
+import (
+	"bytes"
+	"encoding/gob"
+	"testing"
+	"time"
+)
+
+type quote struct{ Author, Text string }
+
+// With no transport installed we are not on the client, so the fetch must not
+// happen and the callback must not fire — that is what leaves an SSR'd page in
+// its loading state (spinner/skeleton) rather than rendering a fetch error the
+// server had no way to avoid.
+func TestFetchWithoutTransportDoesNotCallBack(t *testing.T) {
+	defer SetClientTransport(nil)
+	SetClientTransport(nil)
+
+	called := make(chan error, 1)
+	FetchGob("/api/quotes", func(_ []quote, err error) { called <- err })
+	FetchJSON("/api/quotes", func(_ []quote, err error) { called <- err })
+
+	select {
+	case err := <-called:
+		t.Fatalf("callback ran with no transport installed (err=%v); SSR would render an error instead of the loading state", err)
+	case <-time.After(50 * time.Millisecond):
+	}
+}
+
+// The client path is unchanged: with a transport installed the body is fetched
+// and decoded into the same Go type the server encoded.
+func TestFetchGobWithTransport(t *testing.T) {
+	defer SetClientTransport(nil)
+	want := []quote{{Author: "Rob Pike", Text: "When in doubt, use brute force."}}
+	var buf bytes.Buffer
+	if err := gob.NewEncoder(&buf).Encode(want); err != nil {
+		t.Fatal(err)
+	}
+	SetClientTransport(func(string) ([]byte, error) { return buf.Bytes(), nil })
+
+	got := make(chan []quote, 1)
+	FetchGob("/api/quotes", func(qs []quote, err error) {
+		if err != nil {
+			t.Errorf("FetchGob: %v", err)
+		}
+		got <- qs
+	})
+
+	select {
+	case qs := <-got:
+		if len(qs) != 1 || qs[0] != want[0] {
+			t.Fatalf("decoded %v, want %v", qs, want)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("FetchGob callback never ran")
+	}
+}