Implement component metadata protocol

src/CMakeLists.txt

@@ -40,6 +40,7 @@ hunter_add_package(jsoncpp)
 hunter_add_package(CURL)
 
 find_package(CURL REQUIRED)
+find_package(LibLZMA REQUIRED)
 
 if(BUILD_TESTS AND (IOS OR ANDROID))
     message(STATUS "Building for iOS or Android: forcing BUILD_TESTS to FALSE...")

src/mavsdk/core/CMakeLists.txt

@@ -22,6 +22,8 @@ target_sources(mavsdk
     system.cpp
     system_impl.cpp
     flight_mode.cpp
+    fs_utils.cpp
+    inflate_lzma.cpp
     math_conversions.cpp
     mavsdk.cpp
     mavsdk_impl.cpp
@@ -63,6 +65,11 @@ cmake_policy(SET CMP0079 NEW)
 target_link_libraries(mavsdk
     PRIVATE
     Threads::Threads
+    ${LIBLZMA_LIBRARIES}
+)
+target_include_directories(mavsdk
+    PRIVATE
+    ${LIBLZMA_INCLUDE_DIRS}
 )
 
 if (NOT BUILD_WITHOUT_CURL)

src/mavsdk/core/fs_utils.cpp

@@ -0,0 +1,115 @@
+
+#include "fs_utils.h"
+#include "log.h"
+#include <fstream>
+#include <random>
+
+#if defined(LINUX) || defined(APPLE)
+#include <pwd.h>
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
+#ifdef WINDOWS
+#include <windows.h>
+#include <shlobj.h>
+#endif
+
+namespace mavsdk {
+
+#ifdef WINDOWS
+static std::optional<std::filesystem::path> get_known_windows_path(REFKNOWNFOLDERID folderId)
+{
+    std::filesystem::path path;
+    PWSTR path_tmp;
+
+    /* Attempt to get user's AppData folder
+     *
+     * Microsoft Docs:
+     * https://learn.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-shgetknownfolderpath
+     * https://learn.microsoft.com/en-us/windows/win32/shell/knownfolderid
+     */
+    auto get_folder_path_ret = SHGetKnownFolderPath(folderId, 0, nullptr, &path_tmp);
+
+    /* Error check */
+    if (get_folder_path_ret != S_OK) {
+        CoTaskMemFree(path_tmp);
+        return std::nullopt;
+    }
+
+    /* Convert the Windows path type to a C++ path */
+    path = path_tmp;
+
+    CoTaskMemFree(path_tmp);
+    return path;
+}
+#endif
+
+std::optional<std::filesystem::path> get_cache_directory()
+{
+    // Windows: %LOCALAPPDATA%
+    // Android: /data/data/<package>/cache
+    // Linux: ~/.cache
+    // macOS: ~/Library/Caches
+#if defined(WINDOWS)
+    auto path = get_known_windows_path(FOLDERID_LocalAppData);
+    if (path) {
+        return path->append("mavsdk_cache");
+    }
+#elif defined(ANDROID)
+    // Read /proc/self/cmdline
+    std::ifstream cmdline("/proc/self/cmdline");
+    std::string line;
+    if (std::getline(cmdline, line)) {
+        // line might have a trailing \0
+        if (line.length() > 0 && *line.end() == 0) {
+            line.pop_back();
+        }
+        return "/data/data/" + line + "/mavsdk_cache";
+    }
+#elif defined(APPLE) || defined(LINUX)
+    const char* homedir;
+    if ((homedir = getenv("HOME")) == NULL) {
+        homedir = getpwuid(getuid())->pw_dir;
+    }
+    if (!homedir) {
+        return std::nullopt;
+    }
+#if defined(APPLE)
+    return std::filesystem::path(homedir) / "Library" / "Caches" / "mavsdk";
+#else // Linux
+    return std::filesystem::path(homedir) / ".cache" / "mavsdk";
+#endif
+#else
+#error "Unsupported platform"
+#endif
+
+    return std::nullopt;
+}
+
+std::optional<std::filesystem::path> create_tmp_directory(const std::string& prefix)
+{
+    // Inspired by https://stackoverflow.com/a/58454949/8548472
+    const auto tmp_dir = std::filesystem::temp_directory_path();
+
+    std::random_device dev;
+    std::mt19937 prng(dev());
+    std::uniform_int_distribution<uint32_t> rand(0);
+
+    static constexpr unsigned max_tries = 100;
+
+    for (unsigned i = 0; i < max_tries; ++i) {
+        std::stringstream ss;
+        ss << prefix << '-' << std::hex << rand(prng);
+        auto path = tmp_dir / ss.str();
+
+        const auto created = std::filesystem::create_directory(path);
+        if (created) {
+            return path.string();
+        }
+    }
+
+    LogErr() << "Could not create a temporary directory, aborting.";
+    return std::nullopt;
+}
+} // namespace mavsdk

src/mavsdk/core/fs_utils.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <optional>
+#include <filesystem>
+
+namespace mavsdk {
+
+/**
+ * Get the path to the system's cache directory with a MAVSDK-specific subdirectory.
+ * The path does not necessarily exist yet.
+ */
+std::optional<std::filesystem::path> get_cache_directory();
+
+/**
+ * Create a random subdirectory in the system's tmp directory
+ * @param prefix directory prefix
+ */
+std::optional<std::filesystem::path> create_tmp_directory(const std::string& prefix);
+
+} // namespace mavsdk