From 79549aab5b9ca8f0cad4f00bc8ad68b7091ab65f Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Fri, 5 Jun 2026 10:12:56 +0200
Subject: magic: implement buffer processing support

---
 cabinet/magic.cpp |  7 +++++++
 cabinet/magic.hpp |  3 +++
 cabinet/main.cpp  | 18 ++++++++++++++++--
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/cabinet/magic.cpp b/cabinet/magic.cpp
index 96b78a3..3c36881 100644
--- a/cabinet/magic.cpp
+++ b/cabinet/magic.cpp
@@ -3,8 +3,10 @@
 #include <magic.h>
 
 #include <cerrno>
+#include <cstddef>
 #include <expected>
 #include <filesystem>
+#include <span>
 #include <string>
 #include <string_view>
 #include <system_error>
@@ -68,6 +70,11 @@ namespace cab
     return handle_result(::magic_descriptor(m_cookie, file_descriptor));
   }
 
+  auto magic::process(std::span<std::byte> data) -> std::expected<std::string, std::error_code>
+  {
+    return handle_result(::magic_buffer(m_cookie, data.data(), data.size_bytes()));
+  }
+
   auto magic::handle_result(char const * result) -> std::expected<std::string, std::error_code>
   {
     auto errno_copy = errno;
diff --git a/cabinet/magic.hpp b/cabinet/magic.hpp
index 9e078de..68177f9 100644
--- a/cabinet/magic.hpp
+++ b/cabinet/magic.hpp
@@ -3,8 +3,10 @@
 
 #include <magic.h>
 
+#include <cstddef>
 #include <expected>
 #include <filesystem>
+#include <span>
 #include <string>
 #include <string_view>
 #include <system_error>
@@ -56,6 +58,7 @@ namespace cab
 
     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>;
+    auto process(std::span<std::byte> data) -> std::expected<std::string, std::error_code>;
 
   private:
     auto handle_result(char const * result) -> std::expected<std::string, std::error_code>;
diff --git a/cabinet/main.cpp b/cabinet/main.cpp
index ff35d34..3602142 100644
--- a/cabinet/main.cpp
+++ b/cabinet/main.cpp
@@ -1,8 +1,13 @@
 #include <cabinet/magic.hpp>
 
 #include <fcntl.h>
+#include <unistd.h>
 
+#include <array>
+#include <cerrno>
+#include <cstddef>
 #include <cstdlib>
+#include <cstring>
 #include <iostream>
 #include <print>
 
@@ -23,12 +28,21 @@ auto main(int argc, char ** argv) -> int
     return EXIT_FAILURE;
   }
 
-  auto fd = open(argv[1], O_RDONLY);
-  auto mime_type = magic->process(fd);
+  auto fd = ::open(argv[1], O_RDONLY);
+  if (fd < 0)
+  {
+    std::println(std::cerr, "Failed to determine file type: {}", ::strerror(errno));
+    return EXIT_FAILURE;
+  }
+
+  std::array<std::byte, 512> buffer{};
+  ::read(fd, buffer.data(), buffer.size());
+  auto mime_type = magic->process(buffer);
   if (!mime_type)
   {
     std::println(std::cerr, "Failed to determine file type: {}", mime_type.error().message());
     return EXIT_FAILURE;
   }
+
   std::println("{}: {}", argv[1], mime_type.value());
 }
-- 
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