writable_file: fix mapping permissions

Was outright missing write permissions on windows and private/non-shared
on linux.

Author: pknowles

include/decodeless/detail/mappedfile_linux.hpp

@@ -182,9 +182,9 @@ template <bool Writable>
 class MappedFile {
 public:
     using data_type = std::conditional_t<Writable, void*, const void*>;
-    MappedFile(const fs::path& path, int mapFlags = MAP_PRIVATE)
+    MappedFile(const fs::path& path)
         : m_file(path, Writable ? O_RDWR : O_RDONLY)
-        , m_mapped(nullptr, m_file.size(), mapFlags, m_file, 0) {}
+        , m_mapped(nullptr, m_file.size(), Writable ? MAP_SHARED : MAP_PRIVATE, m_file, 0) {}
 
     data_type data() const { return m_mapped.address(); }
     size_t    size() const { return m_mapped.size(); }

include/decodeless/detail/mappedfile_windows.hpp

@@ -174,8 +174,8 @@ class MappedFile {
                  FILE_SHARE_READ | (Writable ? FILE_SHARE_WRITE : 0), nullptr, OPEN_EXISTING,
                  FILE_ATTRIBUTE_NORMAL, nullptr)
         , m_size(m_file.size())
-        , m_mapping(m_file, nullptr, PAGE_READONLY, m_size, nullptr)
-        , m_rawView(m_mapping, FILE_MAP_READ) {}
+        , m_mapping(m_file, nullptr, Writable ? PAGE_READWRITE : PAGE_READONLY, m_size, nullptr)
+        , m_rawView(m_mapping, FILE_MAP_READ | (Writable ? FILE_MAP_WRITE : 0)) {}
     data_type data() const { return m_rawView.address(); }
     size_t    size() const { return m_size; }
 

test/src/mappedfile.cpp

@@ -26,7 +26,21 @@ class MappedFileFixture : public ::testing::Test {
 
 TEST_F(MappedFileFixture, ReadOnly) {
     file mapped(m_tmpFile);
-    EXPECT_EQ(*reinterpret_cast<const int*>(mapped.data()), 42);
+    EXPECT_EQ(*static_cast<const int*>(mapped.data()), 42);
+}
+
+TEST_F(MappedFileFixture, Writable) {
+    {
+        writable_file mapped(m_tmpFile);
+        ASSERT_GE(mapped.size(), sizeof(int));
+        *static_cast<int*>(mapped.data()) = 123;
+    }
+    {
+        std::ifstream ifile(m_tmpFile, std::ios::binary);
+        int           contents;
+        ifile.read(reinterpret_cast<char*>(&contents), sizeof(contents));
+        EXPECT_EQ(contents, 123);
+    }
 }
 
 #ifdef _WIN32