fs: add tmp file creation routines

CMakeLists.txt

@@ -342,6 +342,8 @@ list (
     float.hpp
     fourcc.cpp
     fourcc.hpp
+    fs/tmp_posix.cpp
+    fs/tmp.hpp
     functor.hpp
     geom/fwd.hpp
     geom/aabb.cpp
@@ -706,6 +708,8 @@ if (TESTS)
         extent
         fixed
         float
+        fs/scoped
+        fs/tmp
         geom/aabb
         geom/ellipse
         geom/frustum

fs/tmp.hpp

@@ -0,0 +1,23 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 2022, Danny Robson <danny@nerdcruft.net>
+ */
+
+#pragma once
+
+#include <filesystem>
+
+namespace cruft::fs {
+    /// Create a temporary directory and return the path to the a newly
+    /// created directory (in a system appropriate location).
+    ///
+    /// It is the caller's responsibility to clean up this directory if
+    /// required.
+    ///
+    /// No guarantees are made about the longevity of the directory after
+    /// the application terminates.
+    std::filesystem::path mktmpdir [[nodiscard]] (void);
+}

fs/tmp_posix.cpp

@@ -0,0 +1,36 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 2022, Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "./tmp.hpp"
+
+#include "./paths.hpp"
+#include "./posix/except.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+std::filesystem::path
+cruft::fs::mktmpdir (void)
+{
+    // The pattern suffix we'll append to the temp directory.
+    //
+    // * It needs a slash to ensure we don't try to create a new directory.
+    // * We might as well append the package name for clarity
+    // * The libc call REQUIRES the string end with "XXXXXX"
+    char const SUFFIX[] = "/" PACKAGE_NAME "-XXXXXX";
+
+    auto const root = cruft::paths::temp ();
+    std::string path;
+    path.reserve (root.string ().size () + sizeof (SUFFIX));
+    path = root.string ();
+    path += SUFFIX;
+
+    if (!mkdtemp (path.data ()))
+        cruft::posix::error::throw_code ();
+
+    return path;
+}