Add a read_announce_list() to TorrentRead

announce-list is very annoyingly a list of lists. I don't
have any useful primitive to manage that case in TorrentRead,
so for now I've done a not-so-elegant implementation where I
step around the visitor, use my knowledge of the variant and
access the outer list directly through boost::get(). I'm not
necessarily convinced that this is bad since on the other hand
the solution consistent with the rest of the implementation
would involve searching for "/[[x]]/[[y]]" which has its own
overhead. I mean, variant contains a vector, I can access it
normally. Visitor is a convenience thing, I don't see why
parser's client code should be obliged to pretend the variant
cannot be accessed directly.

src/main.cpp

@@ -49,6 +49,16 @@ int main(int argc, const char* argv[]) {
 	std::cout << "Creation date: " << torrent.read_creation_date() << '\n';
 	std::cout << "Comment: " << torrent.read_comment() << '\n';
 	std::cout << "Announce: " << torrent.read_announce() << '\n';
+	{
+		std::size_t z = 0;
+		for (const std::vector<std::string_view>& sublist : torrent.read_announce_list()) {
+			std::cout << '\t' << ++z << ": < ";
+			for (std::string_view announce : sublist) {
+				std::cout << '"' << announce << "\", ";
+			}
+			std::cout << " >\n";
+		}
+	}
 	std::cout << "Is private: " << std::boolalpha << torrent.read_is_private() << '\n';
 
 	torrent.print(std::cout);

src/torrent_read.cpp

@@ -87,6 +87,31 @@ std::string_view build_fast_search_path (
 
 	return retval;
 }
+
+std::vector<std::string_view> grab_all_strings_in_list (const TorrentValue& node) {
+	const auto path_size = find_int<std::int_fast32_t>("/[[size]]", node);
+	std::vector<std::string_view> retval;
+	retval.reserve(path_size);
+
+	{
+		constexpr char prefix[] = "/[[";
+		constexpr char postfix[] = "]]";
+		constexpr std::size_t prefix_size = sizeof(prefix) / sizeof(prefix[0]) - 1u;
+		constexpr std::size_t postfix_size = sizeof(postfix) / sizeof(postfix[0]) - 1u;
+		char buff[4 + prefix_size + postfix_size];
+		std::string buff2;
+
+		for (std::int_fast32_t z = 0; z < path_size; ++z) {
+			std::string_view piece = find_string(
+				build_fast_search_path(prefix, postfix, z, buff, buff2),
+				node
+			);
+			retval.push_back(piece);
+		}
+	}
+
+	return retval;
+}
 } //unnamed namespace
 
 TorrentRead::TorrentRead (std::string_view torrent_path, std::filesystem::path workdir) :
@@ -129,7 +154,6 @@ std::int_fast32_t TorrentRead::read_file_count() const {
 
 std::vector<std::string_view> TorrentRead::read_file_path(std::size_t index) const {
 	const TorrentValue* path_variant;
-	std::string buff2;
 
 	{
 		constexpr char prefix[] = "/[[";
@@ -140,6 +164,7 @@ std::vector<std::string_view> TorrentRead::read_file_path(std::size_t index) con
 		//see comment in read_file_size()
 		//in this case a search should look like "/[[1234]]/path"
 		char buff[4 + prefix_size + postfix_size];
+		std::string buff2;
 
 		auto found = find_variant(
 			build_fast_search_path(prefix, postfix, index, buff, buff2),
@@ -151,25 +176,7 @@ std::vector<std::string_view> TorrentRead::read_file_path(std::size_t index) con
 		path_variant = &found->get();
 	}
 
-	const auto path_size = find_int<std::int_fast32_t>("/[[size]]", *path_variant);
-	std::vector<std::string_view> retval;
-	retval.reserve(path_size);
-
-	{
-		constexpr char prefix[] = "/[[";
-		constexpr char postfix[] = "]]";
-		constexpr std::size_t prefix_size = sizeof(prefix) / sizeof(prefix[0]) - 1u;
-		constexpr std::size_t postfix_size = sizeof(postfix) / sizeof(postfix[0]) - 1u;
-		char buff[4 + prefix_size + postfix_size];
-		for (std::int_fast32_t z = 0; z < path_size; ++z) {
-			std::string_view piece = find_string(
-				build_fast_search_path(prefix, postfix, z, buff, buff2),
-				*path_variant
-			);
-			retval.push_back(piece);
-		}
-	}
-	return retval;
+	return grab_all_strings_in_list(*path_variant);
 }
 
 std::string TorrentRead::read_joint_file_path(std::size_t index, char sep) const {
@@ -224,6 +231,29 @@ std::string_view TorrentRead::read_announce() const {
 	return find_string("/announce", m_parsed_values);
 }
 
+std::vector<std::vector<std::string_view>> TorrentRead::read_announce_list() const {
+	typedef boost::spirit::x3::forward_ast<std::vector<TorrentValue>> TorrentListType;
+
+	//see https://bittorrent.org/beps/bep_0012.html it's a list of lists
+	auto list_variant = find_variant("/announce-list", m_parsed_values);
+	if (list_variant) {
+		auto* node_list = boost::get<TorrentListType>(&list_variant->get());
+		std::vector<std::vector<std::string_view>> retval;
+		if (node_list) {
+			const auto list_size = static_cast<std::int_fast32_t>(node_list->get().size());
+			retval.reserve(list_size);
+			for (std::int_fast32_t z = 0; z < list_size; ++z) {
+				retval.push_back(grab_all_strings_in_list(node_list->get()[z]));
+			}
+		}
+		return retval;
+	}
+	else {
+		//from my tests this node is optional
+		return {};
+	}
+}
+
 std::time_t TorrentRead::read_creation_date() const {
 	return find_int<std::time_t>("/creation date", m_parsed_values);
 }

src/torrent_read.hpp

@@ -55,6 +55,7 @@ public:
 	std::string_view read_hashes() const;
 	std::string_view read_created_by() const;
 	std::string_view read_announce() const;
+	std::vector<std::vector<std::string_view>> read_announce_list() const;
 	std::time_t read_creation_date() const;
 
 private: