test: add a test case to parse the torrent file for Ubuntu 22.04

libbencode/BUILD.bazel

@@ -35,3 +35,14 @@ cc_test(
     srcs = ["test/test_decode_dictionary.cc"],
     deps = [":assertm", ":libbencode"],
 )
+
+cc_test(
+    name = "test_parse_torrent_file",
+    srcs = ["test/test_parse_torrent_file.cc"],
+    deps = [
+        ":assertm",
+        ":libbencode",
+        "@bazel_tools//tools/cpp/runfiles",
+    ],
+    data = [":test/data/ubuntu-22.04.1-desktop-amd64.iso.torrent"],
+)

libbencode/test/test_parse_torrent_file.cc

@@ -0,0 +1,98 @@
+#include <array>
+#include <cstddef>
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+
+#include "tools/cpp/runfiles/runfiles.h"
+
+#include "libbencode/assertm.h"
+#include "libbencode/libbencode.h"
+
+template <typename... Bytes>
+std::array<std::byte, sizeof...(Bytes)> make_byte_array(Bytes... bytes) {
+  return {std::byte(bytes)...};
+}
+
+std::string get_runfile(const std::string& runfile_rel_path) {
+  using bazel::tools::cpp::runfiles::Runfiles;
+  std::string runfiles_error;
+  std::unique_ptr<Runfiles> runfiles(Runfiles::CreateForTest(&runfiles_error));
+
+  assertm(runfiles, runfiles_error);
+
+  return runfiles->Rlocation(runfile_rel_path);
+}
+
+std::string read_file(const std::string& pathname) {
+  std::ifstream f(pathname);
+  assertm(f.is_open(), "Failed to open file for reading.");
+  std::stringstream file_contents;
+  file_contents << f.rdbuf();
+  return file_contents.str();
+}
+
+int main() {
+  using libbencode::BencodeDict;
+  using libbencode::BencodeList;
+  using libbencode::DecodeDict;
+
+  std::string torrent_file_path =
+      get_runfile("libbencode/libbencode/test/data/"
+                  "ubuntu-22.04.1-desktop-amd64.iso.torrent");
+  std::string torrent_bencode = read_file(torrent_file_path);
+
+  auto [torrent_info, _] = DecodeDict(torrent_bencode);
+  assertm(std::get<std::string>(torrent_info["announce"]) ==
+              std::string("https://torrent.ubuntu.com/announce"),
+          "'announce' did not match expectations.");
+
+  BencodeList bencode_list =
+      std::get<BencodeList>(torrent_info["announce-list"]);
+  BencodeList sublist_1 = std::get<BencodeList>(bencode_list[0]);
+  assertm(std::get<std::string>(sublist_1[0]) ==
+              std::string("https://torrent.ubuntu.com/announce"),
+          "Sublist 1 from 'announce-list' did not match expectations.");
+  BencodeList sublist_2 = std::get<BencodeList>(bencode_list[1]);
+  assertm(std::get<std::string>(sublist_2[0]) ==
+              std::string("https://ipv6.torrent.ubuntu.com/announce"),
+          "Sublist 2 from 'announce-list' did not match expectations.");
+
+  assertm(std::get<std::string>(torrent_info["comment"]) ==
+              std::string("Ubuntu CD releases.ubuntu.com"),
+          "'comment' did not match expectations.");
+  assertm(std::get<std::string>(torrent_info["created by"]) ==
+              std::string("mktorrent 1.1"),
+          "'created by' did not match expectations.");
+  assertm(std::get<int64_t>(torrent_info["creation date"]) == 1660215352,
+          "'creation date' did not match expectations.");
+
+  BencodeDict info_dict = std::get<BencodeDict>(torrent_info["info"]);
+
+  assertm(std::get<int64_t>(info_dict["length"]) == 3826831360,
+          "info_dict['length'] did not match expectations.");
+  assertm(std::get<std::string>(info_dict["name"]) ==
+              std::string("ubuntu-22.04.1-desktop-amd64.iso"),
+          "info_dict['name'] did not match expectations.");
+  assertm(std::get<int64_t>(info_dict["piece length"]) == 262144,
+          "info_dict['piece length'] did not match expectations.");
+
+  // "pieces" is a string of concatenated SHA-1 hashes. SHA-1 hashes are 20
+  // bytes in length, so the length of "pieces" must be divisible by 20.
+  std::string pieces = std::get<std::string>(info_dict["pieces"]);
+  assertm(pieces.size() % 20 == 0,
+          "info_dict['pieces'] did not match expectations.");
+
+  // Check the first 20-byte hash.
+  auto hash = make_byte_array(0x56, 0x7b, 0x9b, 0x5c, 0x3d, 0x06, 0x17, 0xb2,
+                              0xda, 0xab, 0x0c, 0xe8, 0x88, 0xed, 0x2b, 0x9a,
+                              0xc2, 0x33, 0x02, 0xfc);
+  for (auto i = 0; i < hash.size(); i++) {
+    assertm(std::byte(static_cast<uint8_t>(pieces[i])) == hash[i],
+            "Hash value mismatch.");
+  }
+
+  return 0;
+}