refactor: wrap std::filesystem::space calls (#8284)

Co-authored-by: Charles Kerr <charles@charleskerr.com>

libtransmission/file.cc

@@ -11,7 +11,6 @@
 
 #include "libtransmission/error.h"
 #include "libtransmission/file.h"
-#include "libtransmission/tr-assert.h"
 
 std::string tr_sys_path_resolve(std::string_view path, tr_error* error)
 {
@@ -65,3 +64,19 @@ std::vector<std::string> tr_sys_dir_get_files(
         }
     }
 }
+
+std::optional<std::filesystem::space_info> tr_sys_path_get_capacity(std::filesystem::path const& path, tr_error* error)
+{
+    auto ec = std::error_code{};
+    auto space = std::filesystem::space(path, ec);
+    if (!ec)
+    {
+        return space;
+    }
+
+    if (error != nullptr)
+    {
+        error->set(ec.value(), ec.message());
+    }
+    return {};
+}

libtransmission/file.h

@@ -102,6 +102,28 @@ struct tr_sys_path_info
     }
 };
 
+/**
+ * Temporary replacement of deprecated `std::filesystem::u8path()` while we migrate
+ * from char to char8_t strings.
+ *
+ * https://stackoverflow.com/a/57635139/11390656
+ * @{
+ */
+
+template<typename InputIt>
+[[nodiscard]] std::filesystem::path tr_u8path(InputIt begin, InputIt end)
+{
+    auto const view = std::ranges::subrange(begin, end) | std::views::transform([](char const c) -> char8_t { return c; });
+    return { view.begin(), view.end() };
+}
+
+[[nodiscard]] inline std::filesystem::path tr_u8path(std::string_view path)
+{
+    return tr_u8path(path.begin(), path.end());
+}
+
+/// @}
+
 /**
  * @name Platform-specific wrapper functions
  *
@@ -144,6 +166,23 @@ bool tr_sys_path_copy(std::string_view src_path, std::string_view dst_path, tr_e
     int flags = 0,
     tr_error* error = nullptr);
 
+/**
+ * @brief Get disk capacity and free disk space (in bytes) for the specified folder.
+ *
+ * @param[in]  path  Path to directory.
+ * @param[out] error Pointer to error object. Optional, pass `nullptr` if you
+ *                   are not interested in error details.
+ */
+[[nodiscard]] std::optional<std::filesystem::space_info> tr_sys_path_get_capacity(
+    std::filesystem::path const& path,
+    tr_error* error = nullptr);
+[[nodiscard]] inline std::optional<std::filesystem::space_info> tr_sys_path_get_capacity(
+    std::string_view path,
+    tr_error* error = nullptr)
+{
+    return tr_sys_path_get_capacity(tr_u8path(path), error);
+}
+
 /**
  * @brief Portability wrapper for `access()`.
  *
@@ -510,25 +549,3 @@ bool tr_sys_dir_close(tr_sys_dir_t handle, tr_error* error = nullptr);
 
 /** @} */
 /** @} */
-
-/**
- * Temporary replacement of deprecated `std::filesystem::u8path()` while we migrate
- * from char to char8_t strings.
- *
- * https://stackoverflow.com/a/57635139/11390656
- * @{
- */
-
-template<typename InputIt>
-[[nodiscard]] std::filesystem::path tr_u8path(InputIt begin, InputIt end)
-{
-    auto const view = std::ranges::subrange(begin, end) | std::views::transform([](char const c) -> char8_t { return c; });
-    return { view.begin(), view.end() };
-}
-
-[[nodiscard]] inline std::filesystem::path tr_u8path(std::string_view path)
-{
-    return tr_u8path(path.begin(), path.end());
-}
-
-/// @}

libtransmission/rpcimpl.cc

@@ -2231,9 +2231,12 @@ using SessionAccessors = std::pair<SessionGetter, SessionSetter>;
         TR_KEY_download_dir_free_space,
         [](tr_session const& src) -> tr_variant
         {
-            auto ec = std::error_code{};
-            auto const space = std::filesystem::space(tr_u8path(src.downloadDir()), ec);
-            return !ec ? space.available : tr_variant{ -1 };
+            // TODO(C++23): use std::optional::transform() instead
+            if (auto const space = tr_sys_path_get_capacity(std::string_view{ src.downloadDir() }))
+            {
+                return space->available;
+            }
+            return -1;
         },
         nullptr);
 
@@ -2736,17 +2739,17 @@ using SessionAccessors = std::pair<SessionGetter, SessionSetter>;
     }
 
     // get the free space
-    auto ec = std::error_code{};
-    auto const capacity = std::filesystem::space(tr_u8path(*path), ec);
+    auto error = tr_error{};
+    auto const capacity = tr_sys_path_get_capacity(*path, &error);
 
     // response
     args_out.try_emplace(TR_KEY_path, *path);
-    args_out.try_emplace(TR_KEY_size_bytes, !ec ? capacity.available : tr_variant{ -1 });
-    args_out.try_emplace(TR_KEY_total_size, !ec ? capacity.capacity : tr_variant{ -1 });
+    args_out.try_emplace(TR_KEY_size_bytes, capacity ? capacity->available : tr_variant{ -1 });
+    args_out.try_emplace(TR_KEY_total_size, capacity ? capacity->capacity : tr_variant{ -1 });
 
-    if (ec)
+    if (error)
     {
-        return { Error::SYSTEM_ERROR, ec.message() };
+        return { Error::SYSTEM_ERROR, std::string{ error.message() } };
     }
     return { Error::SUCCESS, {} };
 }