Add week 7 materials

2026-10-21 23:03:28 +03:00
parent 4bb38fb0a8
commit a987b82834
22 changed files with 1265 additions and 0 deletions
@@ -0,0 +1,73 @@
+"""Inspect a torrent or demonstrate unchanged infohash and damaged piece detection."""
+import argparse
+import json
+from pathlib import Path
+import sys
+from metainfo import decode, encode, inspect, make_metainfo, verify
+
+
+def describe(raw):
+    meta, infohash = inspect(raw)
+    info = meta[b"info"]
+    print(json.dumps({
+        "announce": meta[b"announce"].decode(),
+        "name": info[b"name"].decode(),
+        "length": info[b"length"],
+        "piece length": info[b"piece length"],
+        "pieces (SHA-1)": [info[b"pieces"][i:i + 20].hex()
+                           for i in range(0, len(info[b"pieces"]), 20)],
+        "infohash (raw bencoded info)": infohash,
+    }, indent=2))
+
+
+def demo(directory):
+    directory.mkdir(parents=True, exist_ok=True)
+    data = bytes(range(256)) * 1024
+    original = encode(make_metainfo("lesson.bin", data))
+    meta, original_info = decode(original)
+    changed = dict(meta)
+    changed[b"announce"] = b"http://127.0.0.1:6970/announce"
+    changed[b"comment"] = b"A different comment"
+    modified = encode(changed)
+    assert decode(modified)[1] == original_info
+    damaged = bytearray(data)
+    damaged[65536 + 17] ^= 1
+    for name, content in [("lesson.bin", data), ("lesson.torrent", original),
+                          ("changed.torrent", modified), ("damaged.bin", damaged)]:
+        (directory / name).write_bytes(content)
+    describe(original)
+    print("Original infohash:", inspect(original)[1])
+    print("Changed  infohash:", inspect(modified)[1])
+    assert inspect(original)[1] == inspect(modified)[1]
+    good, _ = verify(original, data)
+    bad, indices = verify(original, damaged)
+    assert good and not bad and indices == [1]
+    print("PASS: changing announce/comment preserved infohash")
+    print("PASS: original file verified; damaged file rejected, piece index:", indices)
+    print("Files:", directory)
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    subs = parser.add_subparsers(dest="command", required=True)
+    p = subs.add_parser("demo")
+    p.add_argument("--directory", type=Path, default=Path(".local/metadata"))
+    p = subs.add_parser("inspect")
+    p.add_argument("torrent", type=Path)
+    p = subs.add_parser("verify")
+    p.add_argument("torrent", type=Path)
+    p.add_argument("file", type=Path)
+    args = parser.parse_args()
+    if args.command == "demo":
+        demo(args.directory)
+    elif args.command == "inspect":
+        describe(args.torrent.read_bytes())
+    else:
+        ok, bad = verify(args.torrent.read_bytes(), args.file.read_bytes())
+        print("OK" if ok else "FAILED", "bad pieces:", bad)
+        return 0 if ok else 1
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())