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Fix #2435: allow mmap to open files held open for writing (#2438)

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* Add test for #2435 mmap::open with concurrent writer

Verifies that detail::mmap can open a file held open with GENERIC_WRITE
by another handle (e.g. an active log file). Currently fails on Windows
because CreateFile2 omits FILE_SHARE_WRITE.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Fix #2435: allow mmap to open files held open for writing

Add FILE_SHARE_WRITE to the share mode passed to ::CreateFile2 so
detail::mmap can open a file even when another process holds it open
with GENERIC_WRITE (e.g. an active log file). Without this, CreateFile2
fails with ERROR_SHARING_VIOLATION because the new opener's share mode
must permit the existing handle's access mode.

This brings the Windows path's behavior in line with the POSIX path
which uses ::open(O_RDONLY) and is unaffected by other processes'
write handles.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
yhirose
2026-04-29 12:42:38 +09:00
committed by GitHub
co-authored by Claude Opus 4.7
parent 0cbeafe6a4
commit c2678f0186
2 changed files with 28 additions and 2 deletions
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httplib.h
+3 -2
View File
@@ -5319,8 +5319,9 @@ inline bool mmap::open(const char *path) {
auto wpath = u8string_to_wstring(path);
if (wpath.empty()) { return false; }
hFile_ = ::CreateFile2(wpath.c_str(), GENERIC_READ, FILE_SHARE_READ,
OPEN_EXISTING, NULL);
hFile_ =
::CreateFile2(wpath.c_str(), GENERIC_READ,
FILE_SHARE_READ | FILE_SHARE_WRITE, OPEN_EXISTING, NULL);
if (hFile_ == INVALID_HANDLE_VALUE) { return false; }
test/test.cc
+25
View File
@@ -7939,6 +7939,31 @@ TEST(MountTest, MultibytesPathName) {
EXPECT_EQ(U8("日本語コンテンツ"), res->body);
}
#ifdef _WIN32
// Issue #2435: mmap::open() must succeed even when another handle holds
// the file open for writing (e.g. an active log file).
TEST(MmapTest, OpenWhileFileHeldForWriting) {
const char *path = "mmap_concurrent_writer_test.txt";
const char *content = "hello";
{
std::ofstream f(path, std::ios::binary);
f.write(content, static_cast<std::streamsize>(strlen(content)));
}
auto file_cleanup = detail::scope_exit([&] { std::remove(path); });
HANDLE writer = ::CreateFileA(path, GENERIC_WRITE, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
ASSERT_NE(INVALID_HANDLE_VALUE, writer);
auto handle_cleanup = detail::scope_exit([&] { ::CloseHandle(writer); });
detail::mmap m(path);
ASSERT_TRUE(m.is_open());
EXPECT_EQ(strlen(content), m.size());
EXPECT_EQ(0, std::memcmp(content, m.data(), strlen(content)));
}
#endif
TEST(KeepAliveTest, ReadTimeout) {
Server svr;