Implement support for CoreCLR host to load assemblies from storage

This adds the missing bits to load assembly store from device's filesystem
instead of from the APK when running application which has the
`android:extractNativeLibs` attribute set to `true` in its manifest.

Author: grendello

src/native/clr/host/host.cc

@@ -1,4 +1,9 @@
+#include <sys/types.h>
+#include <dirent.h>
+
+#include <cerrno>
 #include <cstdio>
+#include <cstring>
 
 #include <coreclrhost.h>
 
@@ -62,10 +67,98 @@ auto Host::zip_scan_callback (std::string_view const& apk_path, int apk_fd, dyna
 	return false;
 }
 
+[[gnu::always_inline]]
+void Host::scan_filesystem_for_assemblies_and_libraries () noexcept
+{
+	std::string const& native_lib_dir = AndroidSystem::get_native_libraries_dir ();
+	log_debug (LOG_ASSEMBLY, "Looking for assemblies in '{}'", native_lib_dir);
+
+	DIR *lib_dir = opendir (native_lib_dir.c_str ());
+	if (lib_dir == nullptr) [[unlikely]] {
+		Helpers::abort_application (
+			LOG_ASSEMBLY,
+			std::format (
+				"Unable to open native library directory '{}'. {}",
+				native_lib_dir,
+				std::strerror (errno)
+			)
+		);
+	}
+
+	int dir_fd = dirfd (lib_dir);
+	if (dir_fd < 0) [[unlikely]] {
+		Helpers::abort_application (
+			LOG_ASSEMBLY,
+			std::format (
+				"Unable to obtain file descriptor for opened directory '{}'. {}",
+				native_lib_dir,
+				std::strerror (errno)
+			)
+		);
+	}
+
+	do {
+		errno = 0;
+		dirent *cur = readdir (lib_dir);
+		if (cur == nullptr) {
+			if (errno != 0) {
+				log_warn (LOG_ASSEMBLY, "Failed to open a directory entry from '{}': {}", native_lib_dir, std::strerror (errno));
+				continue; // No harm, keep going
+			}
+			break; // we're done
+		}
+
+		// We can ignore the obvious entries
+		if (cur->d_name[0] == '.') {
+			continue;
+		}
+
+		if (!found_assembly_store) {
+			found_assembly_store = Constants::assembly_store_file_name.compare (cur->d_name) == 0;
+			if (!found_assembly_store) {
+				continue;
+			}
+
+			log_debug (LOG_ASSEMBLY, "Found assembly store in '{}/{}'", native_lib_dir, Constants::assembly_store_file_name);
+			int store_fd = openat (dir_fd, cur->d_name, O_RDONLY);
+			if (store_fd < 0) {
+				Helpers::abort_application (
+					LOG_ASSEMBLY,
+					std::format (
+						"Unable to open assembly store '{}/{}' for reading. {}",
+						native_lib_dir,
+						Constants::assembly_store_file_name,
+						std::strerror (errno)
+					)
+				);
+			}
+
+			auto file_size = Util::get_file_size_at (dir_fd, cur->d_name);
+			if (!file_size) {
+				// get_file_size_at logged errno for us
+				Helpers::abort_application (
+					LOG_ASSEMBLY,
+					std::format (
+						"Unable to map assembly store '{}/{}'",
+						native_lib_dir,
+						Constants::assembly_store_file_name
+					)
+				);
+			}
+
+			AssemblyStore::map (store_fd, cur->d_name, 0, static_cast<uint32_t>(file_size.value ()));
+			close (store_fd);
+			break; // we've found all we need
+		}
+	} while (true);
+	closedir (lib_dir);
+}
+
 void Host::gather_assemblies_and_libraries (jstring_array_wrapper& runtimeApks, bool have_split_apks)
 {
 	if (!AndroidSystem::is_embedded_dso_mode_enabled ()) {
-		Helpers::abort_application ("Filesystem mode not supported yet.");
+		scan_filesystem_for_assemblies_and_libraries ();
+		return;
 	}
 
 	int64_t apk_count = static_cast<int64_t>(runtimeApks.get_length ());

src/native/clr/include/constants.hh

@@ -31,6 +31,7 @@ namespace xamarin::android {
 		static constexpr bool is_debug_build = true;
 #endif
 		static constexpr std::string_view MANGLED_ASSEMBLY_NAME_EXT { ".so" };
+		static constexpr std::string_view dso_suffix { ".so" };
 
 	private:
 		static constexpr std::string_view RUNTIME_CONFIG_BLOB_BASE_NAME       { "libarc.bin" };
@@ -94,7 +95,15 @@ namespace xamarin::android {
 	private:
 		static constexpr size_t split_config_abi_apk_name_size = calc_size (split_config_prefix, android_abi, split_config_extension);
 
+		static constexpr std::string_view assembly_store_prefix { "libassemblies." };
+		static constexpr std::string_view assembly_store_extension { ".blob" };
+		static constexpr size_t assembly_store_file_name_size = calc_size (assembly_store_prefix, android_lib_abi, assembly_store_extension, dso_suffix);
+		static constexpr auto assembly_store_file_name_array = concat_string_views<assembly_store_file_name_size> (assembly_store_prefix, android_lib_abi, assembly_store_extension, dso_suffix);
+
 	public:
+		// .data() must be used otherwise string_view length will include the trailing \0 in the array
+		static constexpr std::string_view assembly_store_file_name { assembly_store_file_name_array.data () };
+
 		static constexpr auto split_config_abi_apk_name = concat_string_views<split_config_abi_apk_name_size> (split_config_prefix, android_abi, split_config_extension);
 
 		//

src/native/clr/include/host/host.hh

@@ -33,6 +33,7 @@ namespace xamarin::android {
 		static void create_xdg_directories_and_environment (jstring_wrapper &homeDir) noexcept;
 		static auto zip_scan_callback (std::string_view const& apk_path, int apk_fd, dynamic_local_string<SENSIBLE_PATH_MAX> const& entry_name, uint32_t offset, uint32_t size) -> bool;
 		static void gather_assemblies_and_libraries (jstring_array_wrapper& runtimeApks, bool have_split_apks);
+		static void scan_filesystem_for_assemblies_and_libraries () noexcept;
 
 		static size_t clr_get_runtime_property (const char *key, char *value_buffer, size_t value_buffer_size, void *contract_context) noexcept;
 		static bool clr_external_assembly_probe (const char *path, void **data_start, int64_t *size) noexcept;

src/native/clr/include/runtime-base/android-system.hh

@@ -70,6 +70,11 @@ namespace xamarin::android {
 			primary_override_dir = determine_primary_override_dir (home);
 		}
 
+		static auto get_native_libraries_dir () noexcept -> std::string const&
+		{
+			return native_libraries_dir;
+		}
+
 		static void create_update_dir (std::string const& override_dir) noexcept
 		{
 			if constexpr (Constants::is_release_build) {
@@ -141,6 +146,7 @@ namespace xamarin::android {
 		static inline bool running_in_emulator = false;
 		static inline bool embedded_dso_mode_enabled = false;
 		static inline std::string primary_override_dir;
+		static inline std::string native_libraries_dir;
 
 #if defined (DEBUG)
 		static inline std::unordered_map<std::string, std::string> bundled_properties;

src/native/clr/include/runtime-base/util.hh

@@ -8,6 +8,7 @@
 #include <cerrno>
 #include <concepts>
 #include <cstdio>
+#include <optional>
 #include <string_view>
 
 #include "../constants.hh"
@@ -88,6 +89,17 @@ namespace xamarin::android {
 			return file_exists (file.get ());
 		}
 
+		static auto get_file_size_at (int dirfd, const char *file_name) noexcept -> std::optional<size_t>
+		{
+			struct stat sbuf;
+			if (fstatat (dirfd, file_name, &sbuf, 0) == -1) {
+				log_warn (LOG_ASSEMBLY, "Failed to stat file '{}': {}", file_name, std::strerror (errno));
+				return std::nullopt;
+			}
+
+			return static_cast<size_t>(sbuf.st_size);
+		}
+
 		static void set_environment_variable (std::string_view const& name, jstring_wrapper& value) noexcept
 		{
 			::setenv (name.data (), value.get_cstr (), 1);

src/native/clr/include/startup/zip.hh

@@ -59,23 +59,12 @@ namespace xamarin::android {
 		// .data() must be used otherwise string_view length will include the trailing \0 in the array
 		static constexpr std::string_view lib_prefix { lib_prefix_array.data () };
 
-		static constexpr std::string_view dso_suffix { ".so" };
-
-        static constexpr std::string_view assembly_store_prefix { "libassemblies." };
-        static constexpr std::string_view assembly_store_extension { ".blob" };
-
-        static constexpr size_t assembly_store_file_name_size = calc_size (assembly_store_prefix, Constants::android_lib_abi, assembly_store_extension, dso_suffix);
-        static constexpr auto assembly_store_file_name_array = concat_string_views<assembly_store_file_name_size> (assembly_store_prefix, Constants::android_lib_abi, assembly_store_extension, dso_suffix);
-
-        // .data() must be used otherwise string_view length will include the trailing \0 in the array
-        static constexpr std::string_view assembly_store_file_name { assembly_store_file_name_array.data () };
-
-        static constexpr size_t assembly_store_file_path_size = calc_size(lib_prefix, assembly_store_file_name);
-        static constexpr auto assembly_store_file_path_array = concat_string_views<assembly_store_file_path_size> (lib_prefix, assembly_store_file_name);
+		static constexpr size_t assembly_store_file_path_size = calc_size(lib_prefix, Constants::assembly_store_file_name);
+		static constexpr auto assembly_store_file_path_array = concat_string_views<assembly_store_file_path_size> (lib_prefix, Constants::assembly_store_file_name);
 
 	public:
-        // .data() must be used otherwise string_view length will include the trailing \0 in the array
-        static constexpr std::string_view assembly_store_file_path { assembly_store_file_path_array.data () };
+		// .data() must be used otherwise string_view length will include the trailing \0 in the array
+		static constexpr std::string_view assembly_store_file_path { assembly_store_file_path_array.data () };
 
 	public:
 		// Scans the ZIP archive for any entries matching the `lib/{ARCH}/` prefix and calls `entry_cb`

src/native/clr/runtime-base/android-system.cc

@@ -277,6 +277,7 @@ AndroidSystem::detect_embedded_dso_mode (jstring_array_wrapper& appDirs) noexcep
 	} else {
 		log_debug (LOG_ASSEMBLY, "Native libs extracted to {}, assuming application/android:extractNativeLibs == true", appDirs[Constants::APP_DIRS_DATA_DIR_INDEX].get_cstr ());
 		set_embedded_dso_mode_enabled (false);
+		native_libraries_dir.assign (appDirs[Constants::APP_DIRS_DATA_DIR_INDEX].get_cstr ());
 	}
 }