Added tests and readme

internal/transport/frame_test.go

@@ -0,0 +1,76 @@
+package transport
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+func TestFrameRoundtrip(t *testing.T) {
+	cases := [][]byte{
+		nil,
+		{},
+		[]byte("hello"),
+		bytes.Repeat([]byte("x"), 1<<14),
+	}
+	for _, payload := range cases {
+		var buf bytes.Buffer
+		if err := writeFrame(&buf, payload); err != nil {
+			t.Fatalf("write %d bytes: %v", len(payload), err)
+		}
+		out, err := readFrame(&buf)
+		if err != nil {
+			t.Fatalf("read %d bytes: %v", len(payload), err)
+		}
+		if !bytes.Equal(out, payload) {
+			t.Errorf("roundtrip lost data for %d bytes", len(payload))
+		}
+	}
+}
+
+func TestFrameRejectsOversize(t *testing.T) {
+	var buf bytes.Buffer
+	if err := writeFrame(&buf, bytes.Repeat([]byte{0}, MaxFrameSize+1)); err == nil {
+		t.Error("oversized write was accepted")
+	}
+}
+
+func TestFrameRejectsOversizeOnRead(t *testing.T) {
+	// hand-crafted header announcing a size beyond the cap
+	var buf bytes.Buffer
+	buf.Write([]byte{0xFF, 0xFF, 0xFF, 0xFF}) // ~4GiB
+	if _, err := readFrame(&buf); err == nil {
+		t.Error("oversized read was accepted")
+	}
+}
+
+func TestFrameReportsShortRead(t *testing.T) {
+	var buf bytes.Buffer
+	// header says 10 bytes, body only 3
+	buf.Write([]byte{0, 0, 0, 10})
+	buf.WriteString("abc")
+	if _, err := readFrame(&buf); err == nil {
+		t.Error("short body did not error")
+	}
+}
+
+func TestMultipleFramesInOneStream(t *testing.T) {
+	var buf bytes.Buffer
+	for _, s := range []string{"first", "second", "third"} {
+		if err := writeFrame(&buf, []byte(s)); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, want := range []string{"first", "second", "third"} {
+		got, err := readFrame(&buf)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if string(got) != want {
+			t.Errorf("got %q want %q", got, want)
+		}
+	}
+	if _, err := readFrame(&buf); err != io.EOF {
+		t.Errorf("expected EOF, got %v", err)
+	}
+}