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[英]Is WinHTTP downloading null bytes or am I copying the results buffer incorrectly?
[英]WinHTTP stops downloading after 8 KiB
我正在使用 WinHTTP(通过 HTTPS)从repo1.maven.org
libraries.minecraft.net
.jar
文件。 这是 function:
// Namespace alias, all stdfs mentions in the function refer to std::filesystem
namespace stdfs = std::filesystem;
bool downloadFile(DLElement element) {
HINTERNET session = WinHttpOpen(
// Identify as Firefox
L"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0",
// Don't care about proxies
WINHTTP_ACCESS_TYPE_DEFAULT_PROXY, WINHTTP_NO_PROXY_NAME, WINHTTP_NO_PROXY_BYPASS, 0);
if (session == nullptr) return false;
HINTERNET connection;
connection = WinHttpConnect(session, element.hostname.c_str(),
element.https ? INTERNET_DEFAULT_HTTPS_PORT : INTERNET_DEFAULT_HTTP_PORT, 0);
// Accept `.jar` files
const wchar_t** acceptTypes = new const wchar_t* [2];
acceptTypes[0] = L"application/java-archive";
acceptTypes[1] = nullptr;
HINTERNET request = WinHttpOpenRequest(connection, L"GET", element.object.c_str(),
nullptr, WINHTTP_NO_REFERER, acceptTypes, element.https ? WINHTTP_FLAG_SECURE : 0);
bool result = WinHttpSendRequest(request, WINHTTP_NO_ADDITIONAL_HEADERS, 0, WINHTTP_NO_REQUEST_DATA, 0, 0, 0);
if (!result) {
DWORD hr = GetLastError();
checkHresult(hr, window, false);
}
if (!result) {
failRet:
WinHttpCloseHandle(request);
WinHttpCloseHandle(connection);
WinHttpCloseHandle(session);
return false;
}
result = WinHttpReceiveResponse(request, nullptr);
DWORD size = 0;
DWORD downloaded = 0;
std::vector<uint8_t> file;
if (!result) goto failRet;
do {
if (!WinHttpQueryDataAvailable(request, &size)) {
goto failRet;
}
uint8_t* buffer;
alloc:
try {
buffer = new uint8_t[size];
}
catch (std::bad_alloc&) {
MessageBox(window, lstr(VCLS_OUT_OF_MEMORY_DESC), lstr(VCLS_OUT_OF_MEMORY_TITLE), MB_ICONERROR);
goto alloc;
}
// Dunno why, do I even need this memset?
memset(buffer, 0, size);
if (!WinHttpReadData(request, buffer, size, &downloaded)) {
delete[] buffer;
checkHresult(GetLastError(), window, false);
goto failRet;
}
size_t vectSize = file.size();
file.reserve(vectSize + size);
for (size_t i = vectSize; i < size; i++) {
// Might as well rewrite this and make this more efficient
file.push_back(buffer[i]);
}
delete[] buffer;
} while (size > 0);
WinHttpCloseHandle(request);
WinHttpCloseHandle(connection);
WinHttpCloseHandle(session);
element.path.make_preferred();
stdfs::path dir = stdfs::path(element.path).remove_filename();
std::wstring fdirStr = dir.wstring();
fdirStr.pop_back();
dir = fdirStr;
tryCreateDir:
try {
stdfs::create_directories(mcFolderPath/dir);
}
catch (const std::bad_alloc&) {
MessageBox(window, lstr(VCLS_OUT_OF_MEMORY_DESC), lstr(VCLS_OUT_OF_MEMORY_TITLE), MB_ICONERROR);
goto tryCreateDir;
}
catch (const stdfs::filesystem_error& e) {
// Error handling removed for brevity
return false;
}
std::basic_ofstream<uint8_t> ofs(mcFolderPath/element.path, std::ios::binary | std::ios::trunc);
ofs.write(file.data(), file.size());
ofs.close();
return true;
}
DLElement
定义如下:
struct DLElement {
std::wstring hostname; std::wstring object; stdfs::path path; std::string sha1hex;
bool hasSha = true; bool https = false;
};
问题是,由于某种原因,这个 function 只下载了8 KiB 的实际文件,这恰好是 WinHTTP 的缓冲区大小。 此代码是经过修改的Microsoft WinHTTP 示例,因此我假设它的正确性和获取超过 8 KiB 数据的能力。 我做错了什么,为什么WinHttpQueryDataAvailable
一旦达到 8 KiB 就会返回 0 size
?
操作系统:Windows 10 专业版,更新 1903
架构: x86-64
CPU, x86-64
操作系统
CPU : Intel Core i5-2300 @ 2.8 GHz
内存: 8 GiB
交换文件: 16000 MB
buffer = new uint8_t[size]; size_t vectSize = file.size(); file.reserve(vectSize + size); ... for (size_t i = vectSize; i < size; i++) { // Might as well rewrite this and make this more efficient file.push_back(buffer[i]); }
这段代码应该是 append buffer
到file
,所以for
循环应该从零开始,而不是vectSize
。 将其更改为:
for (size_t i = 0; i < size; i++)
file.push_back(buffer[i]);
看来您正在使用 C++11 或更新版本,因此您可以使用std::vector
而不是new
。 考虑用以下内容替换你的do
循环:
while(true)
{
if(!WinHttpQueryDataAvailable(request, &size))
break;
if(!size)
break;
std::vector<uint8_t> buffer(size);
if(!WinHttpReadData(request, buffer.data(), size, &downloaded))
break;
if(!downloaded)
break;
buffer.resize(downloaded);
file.insert(file.end(), buffer.begin(), buffer.end());
}
或者直接写入主缓冲区:
while(true)
{
if(!WinHttpQueryDataAvailable(request, &size))
break;
if(!size)
break;
size_t current_size = file.size();
file.resize(current_size + size);
downloaded = 0;
result = WinHttpReadData(request, file.data() + current_size, size, &downloaded);
file.resize(current_size + downloaded);
if(!result || !downloaded)
break;
}
与错误无关:
不需要将缓冲区初始化为零。 它在 Microsoft 示例中完成,但该示例使用以 null 结尾的字符串,它只需将最后一个字节设置为零。
考虑使用 WinINet 而不是 WinHTTP。 如果您不需要服务器,WinINet 更容易。
Barmak Shemirani 的回答为我解决了这个问题,尽管还有另一种方法可以解决这个问题,同时仍然使用缓冲区。 (我提到的答案仍然更快、更优雅。)下面的单行替换了for
循环:
file.insert(file.end(), &buffer[0], &buffer[size]);
这是“C++ 方式”到 append 可迭代到std::vector
。 尽管如此,首先写入vector
显然更快。 如果你可以指定在哪里写,那就是。
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