magic: improve error handling

1 files changed, 20 insertions, 9 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