Don't allocate memory for ZIP Central Directory data

Instead use `mmap`

Author: grendello

src/native/monodroid/embedded-assemblies-zip.cc

@@ -15,7 +15,7 @@
 using namespace xamarin::android::internal;
 
 force_inline bool
-EmbeddedAssemblies::zip_load_entry_common (size_t entry_index, std::vector<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX> &entry_name, ZipEntryLoadState &state) noexcept
+EmbeddedAssemblies::zip_load_entry_common (size_t entry_index, std::span<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX> &entry_name, ZipEntryLoadState &state) noexcept
 {
 	entry_name.clear ();
 
@@ -141,7 +141,7 @@ EmbeddedAssemblies::store_individual_assembly_data (dynamic_local_string<SENSIBL
 }
 
 force_inline void
-EmbeddedAssemblies::zip_load_individual_assembly_entries (std::vector<uint8_t> const& buf, uint32_t num_entries, [[maybe_unused]] monodroid_should_register should_register, ZipEntryLoadState &state) noexcept
+EmbeddedAssemblies::zip_load_individual_assembly_entries (std::span<uint8_t> const& buf, uint32_t num_entries, [[maybe_unused]] monodroid_should_register should_register, ZipEntryLoadState &state) noexcept
 {
 	// TODO: do away with all the string manipulation here. Replace it with generating xxhash for the entry name
 	dynamic_local_string<SENSIBLE_PATH_MAX> entry_name;
@@ -255,7 +255,7 @@ EmbeddedAssemblies::map_assembly_store (dynamic_local_string<SENSIBLE_PATH_MAX>
 }
 
 force_inline void
-EmbeddedAssemblies::zip_load_assembly_store_entries (std::vector<uint8_t> const& buf, uint32_t num_entries, ZipEntryLoadState &state) noexcept
+EmbeddedAssemblies::zip_load_assembly_store_entries (std::span<uint8_t> const& buf, uint32_t num_entries, ZipEntryLoadState &state) noexcept
 {
 	if (all_required_zip_entries_found ()) {
 		return;
@@ -326,26 +326,28 @@ EmbeddedAssemblies::zip_load_entries (int fd, const char *apk_name, [[maybe_unus
 			)
 		);
 	}
-#ifdef DEBUG
-	log_info (LOG_ASSEMBLY, "Central directory offset: %u", cd_offset);
-	log_info (LOG_ASSEMBLY, "Central directory size: %u", cd_size);
-	log_info (LOG_ASSEMBLY, "Central directory entries: %u", cd_entries);
-#endif
-	off_t retval = ::lseek (fd, static_cast<off_t>(cd_offset), SEEK_SET);
-	if (retval < 0) {
-		Helpers::abort_application (
-			LOG_ASSEMBLY,
-			Util::monodroid_strdup_printf (
-				"Failed to seek to central directory position in APK: %s. retval=%d errno=%d, File=%s",
-				std::strerror (errno),
-				retval,
-				errno,
-				apk_name
-			)
-		);
-	}
 
-	std::vector<uint8_t>  buf (cd_size);
+	md_mmap_info apk_map = md_mmap_apk_file (fd, cd_offset, cd_size, apk_name);
+
+	log_debug (LOG_ASSEMBLY, "Central directory offset: %u", cd_offset);
+	log_debug (LOG_ASSEMBLY, "Central directory size: %u", cd_size);
+	log_debug (LOG_ASSEMBLY, "Central directory entries: %u", cd_entries);
+
+	// off_t retval = ::lseek (fd, static_cast<off_t>(cd_offset), SEEK_SET);
+	// if (retval < 0) {
+	//	Helpers::abort_application (
+	//		LOG_ASSEMBLY,
+	//		Util::monodroid_strdup_printf (
+	//			"Failed to seek to central directory position in APK: %s. retval=%d errno=%d, File=%s",
+	//			std::strerror (errno),
+	//			retval,
+	//			errno,
+	//			apk_name
+	//		)
+	//	);
+	// }
+
+	std::span<uint8_t>  buf (reinterpret_cast<uint8_t*>(apk_map.area), apk_map.size);
 	const auto [prefix, prefix_len] = get_assemblies_prefix_and_length ();
 	ZipEntryLoadState state {
 		.file_fd             = fd,
@@ -381,6 +383,8 @@ EmbeddedAssemblies::zip_load_entries (int fd, const char *apk_name, [[maybe_unus
 	} else {
 		zip_load_individual_assembly_entries (buf, cd_entries, should_register, state);
 	}
+
+	// TODO: unmap here
 }
 
 template<bool NeedsNameAlloc>
@@ -636,7 +640,7 @@ EmbeddedAssemblies::zip_read_field (T const& buf, size_t index, size_t count, dy
 }
 
 bool
-EmbeddedAssemblies::zip_read_entry_info (std::vector<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX>& file_name, ZipEntryLoadState &state)
+EmbeddedAssemblies::zip_read_entry_info (std::span<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX>& file_name, ZipEntryLoadState &state)
 {
 	constexpr size_t CD_COMPRESSION_METHOD_OFFSET = 10uz;
 	constexpr size_t CD_UNCOMPRESSED_SIZE_OFFSET  = 24uz;

src/native/monodroid/embedded-assemblies.hh

@@ -9,6 +9,7 @@
 #include <string_view>
 #include <tuple>
 #include <vector>
+#include <span>
 
 #include <dirent.h>
 #include <elf.h>
@@ -248,9 +249,9 @@ namespace xamarin::android::internal {
 		void get_assembly_data (AssemblyStoreSingleAssemblyRuntimeData const& e, uint8_t*& assembly_data, uint32_t& assembly_data_size) noexcept;
 
 		void zip_load_entries (int fd, const char *apk_name, monodroid_should_register should_register);
-		void zip_load_individual_assembly_entries (std::vector<uint8_t> const& buf, uint32_t num_entries, monodroid_should_register should_register, ZipEntryLoadState &state) noexcept;
-		void zip_load_assembly_store_entries (std::vector<uint8_t> const& buf, uint32_t num_entries, ZipEntryLoadState &state) noexcept;
-		bool zip_load_entry_common (size_t entry_index, std::vector<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX> &entry_name, ZipEntryLoadState &state) noexcept;
+		void zip_load_individual_assembly_entries (std::span<uint8_t> const& buf, uint32_t num_entries, monodroid_should_register should_register, ZipEntryLoadState &state) noexcept;
+		void zip_load_assembly_store_entries (std::span<uint8_t> const& buf, uint32_t num_entries, ZipEntryLoadState &state) noexcept;
+		bool zip_load_entry_common (size_t entry_index, std::span<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX> &entry_name, ZipEntryLoadState &state) noexcept;
 		bool zip_read_cd_info (int fd, uint32_t& cd_offset, uint32_t& cd_size, uint16_t& cd_entries);
 		bool zip_adjust_data_offset (int fd, ZipEntryLoadState &state);
 
@@ -272,7 +273,7 @@ namespace xamarin::android::internal {
 		template<ByteArrayContainer T>
 		bool zip_read_field (T const& buf, size_t index, size_t count, dynamic_local_string<SENSIBLE_PATH_MAX>& characters) const noexcept;
 
-		bool zip_read_entry_info (std::vector<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX>& file_name, ZipEntryLoadState &state);
+		bool zip_read_entry_info (std::span<uint8_t> const& buf, dynamic_local_string<SENSIBLE_PATH_MAX>& file_name, ZipEntryLoadState &state);
 
 		[[gnu::always_inline]]
 		static std::tuple<void*, size_t> get_wrapper_dso_payload_pointer_and_size (md_mmap_info const& map_info, const  char *file_name) noexcept