magic: improve error handling

3 files changed, 25 insertions, 12 deletions

diff --git a/cabinet/magic.cpp b/cabinet/magic.cpp
index 08b3046..96b78a3 100644
--- a/cabinet/magic.cpp
+++ b/cabinet/magic.cpp
@@ -53,24 +53,35 @@ namespace cab
     return *this;
   }
 
-  auto magic::process(std::filesystem::path path) -> std::expected<std::string, std::string>
+  auto magic::process(std::filesystem::path path) -> std::expected<std::string, std::error_code>
   {
-    auto result = ::magic_file(m_cookie, path.native().c_str());
-    if (!result)
+    return handle_result(::magic_file(m_cookie, path.native().c_str()));
+  }
+
+  auto magic::process(int file_descriptor) -> std::expected<std::string, std::error_code>
+  {
+    if (file_descriptor < 0)
     {
-      return std::unexpected{std::string{::magic_error(m_cookie)}};
+      return std::unexpected{std::make_error_code(std::errc::invalid_argument)};
     }
-    return result;
+
+    return handle_result(::magic_descriptor(m_cookie, file_descriptor));
   }
 
-  auto magic::process(int file_descriptor) -> std::expected<std::string, std::string>
+  auto magic::handle_result(char const * result) -> std::expected<std::string, std::error_code>
   {
-    auto result = ::magic_descriptor(m_cookie, file_descriptor);
+    auto errno_copy = errno;
+
     if (!result)
     {
-      return std::unexpected{std::string{::magic_error(m_cookie)}};
+      auto magic_errno = ::magic_errno(m_cookie);
+      if (!magic_errno && !errno)
+      {
+        return std::unexpected{std::make_error_code(std::errc::invalid_argument)};
+      }
     }
-    return result;
+
+    return std::string{result};
   }
 
   auto swap(magic & lhs, magic & rhs) noexcept -> void
diff --git a/cabinet/magic.hpp b/cabinet/magic.hpp
index 96f4b08..9e078de 100644
--- a/cabinet/magic.hpp
+++ b/cabinet/magic.hpp
@@ -54,10 +54,12 @@ namespace cab
     auto operator=(magic const &) -> magic & = delete;
     auto operator=(magic && other) noexcept -> magic &;
 
-    auto process(std::filesystem::path path) -> std::expected<std::string, std::string>;
-    auto process(int file_descriptor) -> std::expected<std::string, std::string>;
+    auto process(std::filesystem::path path) -> std::expected<std::string, std::error_code>;
+    auto process(int file_descriptor) -> std::expected<std::string, std::error_code>;
 
   private:
+    auto handle_result(char const * result) -> std::expected<std::string, std::error_code>;
+
     explicit magic(::magic_t cookie) noexcept;
 
     ::magic_t m_cookie{};
diff --git a/cabinet/main.cpp b/cabinet/main.cpp
index db2d43b..ff35d34 100644
--- a/cabinet/main.cpp
+++ b/cabinet/main.cpp
@@ -27,7 +27,7 @@ auto main(int argc, char ** argv) -> int
   auto mime_type = magic->process(fd);
   if (!mime_type)
   {
-    std::println(std::cerr, "Failed to determine file type: {}", mime_type.error());
+    std::println(std::cerr, "Failed to determine file type: {}", mime_type.error().message());
     return EXIT_FAILURE;
   }
   std::println("{}: {}", argv[1], mime_type.value());