optimize access to ssl_cert. specifically the case where there is none, avoid pessimisation of the common case

include/libtorrent/announce_entry.hpp

@@ -36,6 +36,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/config.hpp"
 #include "libtorrent/time.hpp"
 #include "libtorrent/error_code.hpp"
+#include "libtorrent/string_view.hpp"
 
 #include <string>
 #include <cstdint>
@@ -47,7 +48,7 @@ namespace libtorrent
 	struct TORRENT_EXPORT announce_entry
 	{
 		// constructs a tracker announce entry with ``u`` as the URL.
-		explicit announce_entry(std::string u);
+		explicit announce_entry(string_view u);
 		announce_entry();
 		~announce_entry();
 		announce_entry(announce_entry const&) = default;

include/libtorrent/torrent.hpp

@@ -1202,7 +1202,7 @@ namespace libtorrent
 
 		bool verify_peer_cert(bool preverified, boost::asio::ssl::verify_context& ctx);
 
-		void init_ssl(std::string const& cert);
+		void init_ssl(string_view cert);
 #endif
 
 		void setup_peer_class();

include/libtorrent/torrent_info.hpp

@@ -400,7 +400,7 @@ namespace libtorrent
 		// Returns the SSL root certificate for the torrent, if it is an SSL
 		// torrent. Otherwise returns an empty string. The certificate is
 		// the the public certificate in x509 format.
-		std::string ssl_cert() const;
+		string_view ssl_cert() const;
 
 		// returns true if this torrent_info object has a torrent loaded.
 		// This is primarily used to determine if a magnet link has had its
@@ -643,7 +643,11 @@ namespace libtorrent
 			// domain in its hostname. This means the DHT and LSD
 			// features are disabled for this torrent (unless the
 			// settings allows mixing i2p peers with regular peers)
-			i2p = 4
+			i2p = 4,
+
+			// this flag is set if we found an ssl-cert field in the info
+			// dictionary
+			ssl_torrent = 8,
 		};
 
 		// any combination of values from flags_t enum

src/announce_entry.cpp

@@ -46,8 +46,8 @@ namespace libtorrent
 		minutes32 constexpr tracker_retry_delay_max{60};
 	}
 
-	announce_entry::announce_entry(std::string u)
-		: url(std::move(u))
+	announce_entry::announce_entry(string_view u)
+		: url(u.to_string())
 		, fails(0)
 		, updating(false)
 		, source(0)

src/torrent.cpp

@@ -1468,7 +1468,7 @@ namespace libtorrent
 #endif
 	}
 
-	void torrent::init_ssl(std::string const& cert)
+	void torrent::init_ssl(string_view cert)
 	{
 		using boost::asio::ssl::context;
 
@@ -1537,7 +1537,7 @@ namespace libtorrent
 
 		// wrap the PEM certificate in a BIO, for openssl to read
 		BIO* bp = BIO_new_mem_buf(
-			const_cast<void*>(static_cast<void const*>(cert.c_str()))
+			const_cast<void*>(static_cast<void const*>(cert.data()))
 			, int(cert.size()));
 
 		// parse the certificate into OpenSSL's internal
@@ -1646,7 +1646,7 @@ namespace libtorrent
 		if (int(m_file_priority.size()) > m_torrent_file->num_files())
 			m_file_priority.resize(m_torrent_file->num_files());
 
-		std::string cert = m_torrent_file->ssl_cert();
+		auto cert = m_torrent_file->ssl_cert();
 		if (!cert.empty())
 		{
 			m_ssl_torrent = true;

src/torrent_info.cpp

@@ -1017,18 +1017,22 @@ namespace libtorrent
 		swap(m_flags, ti.m_flags);
 	}
 
-	std::string torrent_info::ssl_cert() const
+	string_view torrent_info::ssl_cert() const
 	{
+		if ((m_flags & ssl_torrent) == 0) return "";
+
 		// this is parsed lazily
 		if (!m_info_dict)
 		{
 			error_code ec;
 			bdecode(m_info_section.get(), m_info_section.get()
 				+ m_info_section_size, m_info_dict, ec);
+			TORRENT_ASSERT(!ec);
 			if (ec) return "";
 		}
+		TORRENT_ASSERT(m_info_dict.type() == bdecode_node::dict_t);
 		if (m_info_dict.type() != bdecode_node::dict_t) return "";
-		return m_info_dict.dict_find_string_value("ssl-cert").to_string();
+		return m_info_dict.dict_find_string_value("ssl-cert");
 	}
 
 	bool torrent_info::parse_info_section(bdecode_node const& info
@@ -1207,6 +1211,9 @@ namespace libtorrent
 		}
 #endif // TORRENT_DISABLE_MUTABLE_TORRENTS
 
+		if (info.dict_find_string("ssl-cert"))
+			m_flags |= ssl_torrent;
+
 		// now, commit the files structure we just parsed out
 		// into the torrent_info object.
 		m_files.swap(files);
@@ -1411,7 +1418,7 @@ namespace libtorrent
 
 		if (m_urls.empty())
 		{
-			announce_entry e(torrent_file.dict_find_string_value("announce").to_string());
+			announce_entry e(torrent_file.dict_find_string_value("announce"));
 			e.fail_limit = 0;
 			e.source = announce_entry::source_torrent;
 			e.trim();