test: nl_mkimage für OTA-Trailer-Erzeugung mit Tests anlegen

feat: nl_mkimage.py implementieren (Gegenstück zu nl_fwup_trailer.c aus Task 2)

tools/mkimage/test_nl_mkimage.py

@@ -0,0 +1,55 @@
+import hashlib
+import subprocess
+import sys
+from pathlib import Path
+
+SCRIPT = Path(__file__).with_name("nl_mkimage.py")
+
+
+def build(tmp_path, payload=b"\x01\x02\x03" * 100, device="evk", version="1.2.3"):
+    src = tmp_path / "fw_gz.img"
+    src.write_bytes(payload)
+    out = tmp_path / "fw_ota.img"
+    subprocess.run(
+        [sys.executable, str(SCRIPT), "--image", str(src), "--device", device,
+         "--version", version, "--out", str(out)],
+        check=True,
+    )
+    return src, out
+
+
+def test_appends_512_byte_trailer(tmp_path):
+    src, out = build(tmp_path)
+    data = out.read_bytes()
+    assert len(data) == len(src.read_bytes()) + 512
+    assert data[: len(src.read_bytes())] == src.read_bytes()
+    trailer = data[-512:]
+    assert trailer[0:4] == b"NINL"
+    assert trailer[4] == 1
+    assert trailer[5:21].rstrip(b"\x00") == b"evk"
+    assert trailer[21:37].rstrip(b"\x00") == b"1.2.3"
+    assert trailer[37:69] == hashlib.sha256(src.read_bytes()).digest()
+    assert set(trailer[69:]) == {0xFF}
+
+
+def test_rejects_long_fields(tmp_path):
+    src = tmp_path / "fw_gz.img"
+    src.write_bytes(b"x")
+    r = subprocess.run(
+        [sys.executable, str(SCRIPT), "--image", str(src), "--device", "0123456789abcdef",
+         "--version", "1", "--out", str(tmp_path / "o.img")],
+        capture_output=True, text=True,
+    )
+    assert r.returncode != 0
+    assert "device" in r.stderr
+
+
+def test_refuses_image_that_already_has_a_trailer(tmp_path):
+    _, out = build(tmp_path)
+    r = subprocess.run(
+        [sys.executable, str(SCRIPT), "--image", str(out), "--device", "evk",
+         "--version", "1.2.3", "--out", str(tmp_path / "again.img")],
+        capture_output=True, text=True,
+    )
+    assert r.returncode != 0
+    assert "trailer" in r.stderr