Function TestMapDecodedSizeTooLarge

control/tsp/map_test.go:338–365

TestMapDecodedSizeTooLarge verifies that a small on-wire frame (well under the cap) which decompresses into a huge JSON payload is rejected. This is the "zstd bomb" case: a tiny compressed frame that would explode into a huge decoded payload for json.Decoder to consume.

(t *testing.T)

// This is the "zstd bomb" case: a tiny compressed frame that would
// explode into a huge decoded payload for json.Decoder to consume.
func TestMapDecodedSizeTooLarge(t *testing.T) {
	const max = 4 << 20
	big := strings.Repeat("a", 5<<20) // 5 MiB of 'a'
	raw, err := json.Marshal(&tailcfg.MapResponse{Domain: big})
	if err != nil {
		t.Fatal(err)
	}
	if int64(len(raw)) <= max {
		t.Fatalf("raw JSON unexpectedly small: %d", len(raw))
	}
	compressed := zstdFrame(t, raw)
	if int64(len(compressed)) >= max {
		t.Fatalf("compressed too large (%d); test needs a more compressible payload", len(compressed))
	}

	var wire bytes.Buffer
	wireFrame(&wire, compressed)

	jdec := newTestPipeline(t, wire.Bytes(), max)
	var resp tailcfg.MapResponse
	err = jdec.Decode(&resp)
	if err == nil {
		t.Fatal("Decode: got nil error, want decoded-size-exceeded")
	}
	if !strings.Contains(err.Error(), "exceeds max") {
		t.Errorf("Decode error = %q, want one containing %q", err, "exceeds max")
	}
}

// TestMapBudgetResetsBetweenFrames verifies that the per-message decoded
// budget is reset at each new frame boundary. Two consecutive 3-MiB frames