c++ - 无法使用 wininet 获取 POST 请求响应

Question

我需要向 API 发出 POST 请求以获取一些 XML 数据 (http://freecite.library.brown.edu/welcome/api_instructions)。这适用于 curl:

curl -H "Accept: application/xml" --data "citation=Udvarhelyi, I.S., Gatsonis, C.A., Epstein, A.M., Pashos, C.L., Newhouse, J.P. and McNeil, B.J. Acute Myocardial Infarction in the Medicare population: process of care and clinical outcomes. Journal of the American Medical Association, 1992; 18:2530-2536. " http://freecite.library.brown.edu:80/citations/create

所以我正在尝试使用 Win32 SDK 做类似的事情。这是我的代码:

void LoadData()
{
    wil::unique_hinternet hInternet(InternetOpen(L"Dummy", INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0));
    wil::unique_hinternet hConnect(InternetConnect(hInternet.get(), L"http://freecite.library.brown.edu", 80, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 0));
    wil::unique_hinternet hRequest(HttpOpenRequest(hConnect.get(), L"POST", L"/citations/create", NULL, NULL, NULL, NULL, NULL));
    wstring data = L"citation=Udvarhelyi, I.S., Gatsonis, C.A., Epstein, A.M., Pashos, C.L., Newhouse, J.P. and McNeil, B.J. Acute Myocardial Infarction in the Medicare population: process of care and clinical outcomes. Journal of the American Medical Association, 1992; 18:2530-2536.";
    PCWSTR szHeaders = L"Accept: application/xml";

    HttpSendRequest(hRequest.get(), szHeaders, 0, (LPVOID)data.c_str(), static_cast<int>(data.length()));

    DWORD availableBytes = 0;
    InternetQueryDataAvailable(hRequest.get(), &availableBytes, 0, 0);
    PBYTE outputBuffer = (PBYTE)HeapAlloc(GetProcessHeap(), 0, availableBytes);
    PBYTE nextBytes = outputBuffer;
    DWORD bytesUsed = 0; // number of used bytes.
    while (availableBytes)
    {
        DWORD downloadedBytes;
        InternetReadFile(hRequest.get(), nextBytes, availableBytes, &downloadedBytes);
        bytesUsed = bytesUsed + downloadedBytes;

        InternetQueryDataAvailable(hRequest.get(), &availableBytes, 0, 0);
        if (availableBytes > 0)
        {
            // lazy buffer growth here. Only alloc for what we need. could be optimized if we end up with huge payloads (>10MB).
            // otherwise, this is good enough.
            outputBuffer = (PBYTE)HeapReAlloc(GetProcessHeap(), 0, outputBuffer, bytesUsed + availableBytes);
            nextBytes = outputBuffer + bytesUsed; // careful, pointer might have moved! Update cursor.
        }
    }

    // Convert outputed XML to wide char
    int size_needed = MultiByteToWideChar(CP_UTF8, 0, (PCCH)outputBuffer, bytesUsed, NULL, 0);
    std::wstring wstrTo(size_needed, 0);
    MultiByteToWideChar(CP_UTF8, 0, (PCCH)outputBuffer, bytesUsed, &wstrTo[0], size_needed);

    wstring res = wstrTo;
}

问题是，在进入 for 循环之前，即使在调用 InternetQueryDataAvailable 之后，availableBytes 的结果也是 0。作为一个结果，我最终得到一个空白字符串作为响应，而我期待的是 XML 响应。

谁能指出我做错了什么，以及如何解决？

Answer 1

InternetConnect需要服务器名称或 IP 地址，因此不要在地址中包含 "http://"。更改为:

InternetConnect(handle, L"freecite.library.brown.edu"...);

data 使用 UTF-8。 WinAPI 函数的其他参数正确使用 UTF-16，它们会自动进行必要的转换。

更改标题:

std::wstring szHeaders = L"Content-Type: application/x-www-form-urlencoded\r\n";

accept 应该通过HttpOpenRequest

发送

const wchar_t *accept[] = { L"text/xml", NULL };
HINTERNET hrequest = HttpOpenRequest(hconnect, L"POST", L"/citations/create",
    NULL, NULL, accept, 0, 0);

请注意，如果您不指定 accept(在其位置使用 NULL)，则结果可以是纯 html。

下面的例子应该返回 XML。

注意，为简单起见，我将optional 设置为ANSI 字符串，但它应该是UTF8，然后将其转换为UTF16 woptional 并发送。 result 将是 UTF8 字符串，需要将其转换为 UTF16 以便 Windows 显示。

#include <iostream>
#include <string>
#include <Windows.h>
#include <WinINet.h>

#pragma comment(lib, "wininet.lib")//include WinINet library

int main()
{
    std::string result;
    std::wstring server = L"freecite.library.brown.edu";
    std::wstring objectname = L"/citations/create"; //file in this case!
    std::wstring header = L"Content-Type: application/x-www-form-urlencoded\r\n";
    std::string optional = "citation=Udvarhelyi, I.S., Gatsonis, C.A., Epstein";

    HINTERNET hsession = InternetOpen(L"appname", 
        INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0);

    HINTERNET hconnect = InternetConnect(hsession, server.c_str(),
        INTERNET_DEFAULT_HTTP_PORT, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 0);

    const wchar_t* accept[] = { L"text/xml", NULL };
    HINTERNET hrequest = HttpOpenRequest(hconnect, L"POST", objectname.c_str(),
        NULL, NULL, accept, 0, 0);

    if(HttpSendRequest(hrequest, header.c_str(), header.size(),
        &optional[0], optional.size()))
    {
        DWORD blocksize = 4096;
        DWORD received = 0;
        std::string block(blocksize, 0);
        while (InternetReadFile(hrequest, &block[0], blocksize, &received) 
            && received)
        {
            block.resize(received);
            result += block;
        }
        std::cout << result << std::endl;
    }

    if (hrequest)  InternetCloseHandle(hrequest);
    if (hconnect)  InternetCloseHandle(hconnect);
    if (hsession)  InternetCloseHandle(hsession);
    return 0;
}