Add permissions model for files.

1 files changed, 191 insertions, 0 deletions

diff --git a/include/fud_permissions.hpp b/include/fud_permissions.hpp
new file mode 100644
index 0000000..66eec0c
--- /dev/null
+++ b/include/fud_permissions.hpp
@@ -0,0 +1,191 @@
+/*
+ * libfud
+ * Copyright 2024 Dominick Allen
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FUD_PERMISSIONS_HPP
+#define FUD_PERMISSIONS_HPP
+
+#include <climits>
+#include <cstdint>
+#include <sys/stat.h>
+#include <type_traits>
+
+namespace fud {
+
+static_assert(CHAR_BIT == 8, "Assume that uint8_t has 8 bits");
+static_assert(sizeof(uint8_t) == 1, "Assume that uint8_t is 1 byte");
+
+enum class PermissionType : uint8_t
+{
+    None = 0x00,
+    Exec = 0x01,
+    Write = 0x02,
+    Read = 0x04
+};
+
+struct PermissionField {
+    explicit constexpr PermissionField(PermissionType permissionType) :
+        m_permissions{static_cast<uint8_t>(permissionType)}
+    {
+    }
+
+    constexpr PermissionField(PermissionType lhs, PermissionType rhs)
+    {
+        m_permissions = static_cast<uint8_t>(lhs) | static_cast<uint8_t>(rhs);
+    }
+
+    constexpr PermissionField(PermissionType lhs, PermissionField rhs)
+    {
+        m_permissions = static_cast<uint8_t>(lhs) | rhs.m_permissions;
+    }
+
+    constexpr PermissionField(PermissionField lhs, PermissionType rhs)
+    {
+        m_permissions = lhs.m_permissions | static_cast<uint8_t>(rhs);
+    }
+
+    constexpr PermissionField(PermissionField lhs, PermissionField rhs)
+    {
+        m_permissions = lhs.m_permissions | rhs.m_permissions;
+    }
+
+    constexpr uint16_t operator()()
+    {
+        return m_permissions;
+    }
+
+    uint8_t m_permissions{};
+};
+
+enum class PermissionSpecialType : uint8_t
+{
+    None = 0x00,
+    Sticky = 0x01,
+    SetGroupId = 0x02,
+    SetUserId = 0x04
+};
+
+struct PermissionSpecial {
+    explicit constexpr PermissionSpecial(PermissionSpecialType permissionType) :
+        m_permissions{static_cast<uint8_t>(permissionType)}
+    {
+    }
+
+    constexpr PermissionSpecial(PermissionSpecialType lhs, PermissionSpecialType rhs)
+    {
+        m_permissions = static_cast<uint8_t>(lhs) | static_cast<uint8_t>(rhs);
+    }
+
+    constexpr PermissionSpecial(PermissionSpecialType lhs, PermissionSpecial rhs)
+    {
+        m_permissions = static_cast<uint8_t>(lhs) | rhs.m_permissions;
+    }
+
+    constexpr PermissionSpecial(PermissionSpecial lhs, PermissionSpecialType rhs)
+    {
+        m_permissions = lhs.m_permissions | static_cast<uint8_t>(rhs);
+    }
+
+    constexpr PermissionSpecial(PermissionSpecial lhs, PermissionSpecial rhs)
+    {
+        m_permissions = lhs.m_permissions | rhs.m_permissions;
+    }
+
+    constexpr uint16_t operator()()
+    {
+        return m_permissions;
+    }
+
+    uint8_t m_permissions{0};
+};
+
+class Permissions {
+  public:
+    static constexpr uint8_t GroupShift = 3;
+    static constexpr uint8_t UserShift = GroupShift + 3;
+    static constexpr uint8_t SpecialShift = UserShift + 3;
+
+    constexpr Permissions(PermissionField user, PermissionField group, PermissionField others)
+    {
+        m_permissions = user() << UserShift | group() << GroupShift | others();
+    }
+
+    template <typename U, typename G, typename O>
+    constexpr Permissions(U user, G group, O others)
+    {
+        m_permissions = PermissionField{user}() << UserShift | PermissionField{group}() << GroupShift |
+            PermissionField{others}();
+    }
+
+    constexpr Permissions(
+        PermissionField user,
+        PermissionField group,
+        PermissionField others,
+        PermissionSpecial special)
+    {
+        m_permissions = special() << SpecialShift | user() << UserShift | group() << GroupShift | others();
+    }
+
+    template <typename U, typename G, typename O, typename S>
+    constexpr Permissions(
+        PermissionField user,
+        PermissionField group,
+        PermissionField others,
+        PermissionSpecial special)
+    {
+        m_permissions = special() << SpecialShift | PermissionField{user}() << UserShift |
+            PermissionField{group}() << GroupShift | PermissionField{others}();
+    }
+
+    constexpr int32_t operator()()
+    {
+        return m_permissions;
+    }
+
+    constexpr mode_t mode()
+    {
+        return static_cast<mode_t>(m_permissions);
+    }
+
+  private:
+    int32_t m_permissions{0};
+};
+
+constexpr PermissionField operator|(PermissionType lhs, PermissionType rhs)
+{
+    return PermissionField{lhs, rhs};
+}
+
+constexpr PermissionField operator|(PermissionType lhs, PermissionField rhs)
+{
+    return PermissionField{lhs, rhs};
+}
+
+constexpr PermissionField operator|(PermissionField lhs, PermissionType rhs)
+{
+    return PermissionField{lhs, rhs};
+}
+
+constexpr PermissionField operator|(PermissionField lhs, PermissionField rhs)
+{
+    return PermissionField{lhs, rhs};
+}
+
+constexpr PermissionField PermReadWrite = PermissionType::Read | PermissionType::Write;
+
+} // namespace fud
+
+#endif