在 C++cx 中的 WinRT HttpBufferContent 和非托管内存之间转换

Question

作为 WinRT C++cx 组件的一部分，使用 Windows::Web::Http::HttpBufferContent 来回转换非托管字节缓冲区（比如表示为 std::string）的最有效方法是什么？

这是我最终得到的结果，但它似乎不是很理想：

std::string 到 HttpBufferContent:

std::string m_body = ...;
auto writer = ref new DataWriter();
writer->WriteBytes(ArrayReference<unsigned char>(reinterpret_cast<unsigned char*>(const_cast<char*>(m_body.data())), m_body.length()));
auto content = ref new HttpBufferContent(writer->DetachBuffer());

HttpBufferContent 到 std::string:

HttpBufferContent^ content = ...
auto operation = content->ReadAsBufferAsync();
auto task = create_task(operation);
if (task.wait() == task_status::completed) {
    auto buffer = task.get();
    size_t length = buffer->Length;
    if (length > 0) {
        unsigned char* storage = static_cast<unsigned char*>(malloc(length));
        DataReader::FromBuffer(buffer)->ReadBytes(ArrayReference<unsigned char>(storage, length));
        auto m_body = std::string(reinterpret_cast<char*>(storage), length);
        free(storage);
    }
} else {
    abort();
}

更新： 这是我最终使用的版本（您可以从 Windows::Storage::Streams::IBuffer^ 简单地创建一个 HttpBufferContent^）：

void IBufferToString(IBuffer^ buffer, std::string& string) {
    Array<unsigned char>^ array = nullptr;
    CryptographicBuffer::CopyToByteArray(buffer, &array);  // TODO: Avoid copy
    string.assign(reinterpret_cast<char*>(array->Data), array->Length);
}

IBuffer^ StringToIBuffer(const std::string& string) {
    auto array = ArrayReference<unsigned char>(reinterpret_cast<unsigned char*>(const_cast<char*>(string.data())), string.length());
    return CryptographicBuffer::CreateFromByteArray(array);
}

Answer 1

我认为您在当前的 HttpBufferContent 方法中至少制作了一份不必要的数据副本 std::string，您可以通过直接访问 IBuffer 数据来改进这一点，请在此处查看已接受的答案：Getting an array of bytes out of Windows::Storage::Streams::IBuffer

Answer 2

我认为使用智能指针更好（不需要内存管理）:

#include <wrl.h>
#include <robuffer.h>
#include <memory>
using namespace Windows::Storage::Streams;
using namespace Microsoft::WRL;

IBuffer^ buffer;
ComPtr<IBufferByteAccess> byte_access;
reinterpret_cast<IInspectable*>(buffer)->QueryInterface(IID_PPV_ARGS(&byte_access));
std::unique_ptr<byte[]> raw_buffer = std::make_unique<byte[]>(buffer->Length);
byte_access->Buffer(raw_buffer.get());
std::string str(reinterpret_cast<char*>(raw_buffer.get())); // just 1 copy

在 C++cx 中的 WinRT HttpBufferContent 和非托管内存之间转换

Converting between WinRT HttpBufferContent and unmanaged memory in C++cx

unmanaged

visual-c++

windows-runtime

c++-cx

winrt-component