Correctly set FileOffsets in WriteHandle (#14562)

* Correctly set FileOffsets in WriteHandle

* Apply PR suggestions

src/windows/common/relay.cpp

@@ -1443,7 +1443,7 @@ void HTTPChunkBasedReadHandle::OnRead(const gsl::span<char>& Input)
 }
 
 WriteHandle::WriteHandle(HandleWrapper&& MovedHandle, const std::vector<char>& Buffer) :
-    Handle(std::move(MovedHandle)), Buffer(Buffer)
+    Handle(std::move(MovedHandle)), Buffer(Buffer), Offset(InitializeFileOffset(Handle.Get()))
 {
     Overlapped.hEvent = Event.get();
 }
@@ -1475,10 +1475,15 @@ void WriteHandle::Schedule()
 
     Event.ResetEvent();
 
+    Overlapped.Offset = Offset.LowPart;
+    Overlapped.OffsetHigh = Offset.HighPart;
+
     // Schedule the write.
     DWORD bytesWritten{};
     if (WriteFile(Handle.Get(), Buffer.data(), static_cast<DWORD>(Buffer.size()), &bytesWritten, &Overlapped))
     {
+        Offset.QuadPart += bytesWritten;
+
         Buffer.erase(Buffer.begin(), Buffer.begin() + bytesWritten);
         if (Buffer.empty())
         {
@@ -1505,6 +1510,7 @@ void WriteHandle::Collect()
     // Complete the write.
     DWORD bytesWritten{};
     THROW_IF_WIN32_BOOL_FALSE(GetOverlappedResult(Handle.Get(), &Overlapped, &bytesWritten, false));
+    Offset.QuadPart += bytesWritten;
 
     Buffer.erase(Buffer.begin(), Buffer.begin() + bytesWritten);
     if (Buffer.empty())

src/windows/common/relay.hpp

@@ -361,6 +361,7 @@ private:
     wil::unique_event Event{wil::EventOptions::ManualReset};
     OVERLAPPED Overlapped{};
     std::vector<char> Buffer;
+    LARGE_INTEGER Offset{};
 };
 
 template <typename TRead = ReadHandle>

test/windows/WSLCTests.cpp

@@ -4688,6 +4688,70 @@ class WSLCTests
         runTest({"3\r\nfoo\r\n3\r\nbar\r\n0", "\r\n\r\n"}, {"foo", "bar"});
     }
 
+    TEST_METHOD(WriteHandleContent)
+    {
+        WSL2_TEST_ONLY();
+
+        // Validate that writing to a pipe works as expected.
+        {
+            const std::string expectedData = "Pipe-test";
+            std::vector<char> writeBuffer{expectedData.begin(), expectedData.end()};
+
+            auto [readPipe, writePipe] = wsl::windows::common::wslutil::OpenAnonymousPipe(16 * 1024, true, false);
+
+            std::string readData;
+            wsl::windows::common::relay::MultiHandleWait io;
+
+            io.AddHandle(std::make_unique<wsl::windows::common::relay::ReadHandle>(std::move(readPipe), [&](const gsl::span<char>& buffer) {
+                if (!buffer.empty())
+                {
+                    readData.append(buffer.data(), buffer.size());
+                }
+            }));
+
+            io.AddHandle(std::make_unique<WriteHandle>(std::move(writePipe), writeBuffer));
+
+            io.Run({});
+
+            VERIFY_ARE_EQUAL(expectedData, readData);
+        }
+
+        // Validate that writing to files work as expected.
+        // Use a large buffer to make sure that overlapped writes correctly handle offsets.
+        {
+            constexpr size_t fileSize = 50 * 1024 * 1024;
+
+            std::vector<char> writeBuffer(fileSize);
+            for (size_t i = 0; i < fileSize; i++)
+            {
+                writeBuffer[i] = static_cast<char>(i % 251);
+            }
+
+            auto outputFile = wil::open_or_create_file(L"write-handle-test", GENERIC_WRITE | GENERIC_READ, 0, nullptr);
+
+            auto cleanup = wil::scope_exit_log(WI_DIAGNOSTICS_INFO, [&]() {
+                outputFile.reset();
+                std::filesystem::remove("write-handle-test");
+            });
+
+            wsl::windows::common::relay::MultiHandleWait io;
+            io.AddHandle(std::make_unique<WriteHandle>(outputFile.get(), writeBuffer));
+            io.Run({});
+
+            VERIFY_ARE_NOT_EQUAL(SetFilePointer(outputFile.get(), 0, nullptr, FILE_BEGIN), INVALID_SET_FILE_POINTER);
+
+            LARGE_INTEGER size{};
+            VERIFY_WIN32_BOOL_SUCCEEDED(GetFileSizeEx(outputFile.get(), &size));
+            VERIFY_ARE_EQUAL(static_cast<long long>(fileSize), size.QuadPart);
+
+            std::vector<char> readBuffer(fileSize);
+            DWORD bytesRead = 0;
+            VERIFY_IS_TRUE(ReadFile(outputFile.get(), readBuffer.data(), static_cast<DWORD>(fileSize), &bytesRead, nullptr));
+            VERIFY_ARE_EQUAL(static_cast<DWORD>(fileSize), bytesRead);
+            VERIFY_IS_TRUE(readBuffer == writeBuffer);
+        }
+    }
+
     TEST_METHOD(DockerIORelay)
     {
         using namespace wsl::windows::common::relay;