Sending a POST using HttpSendRequestA fails with ERROR_HTTP_HEADER_NOT_FOUND?

Question

I'm trying to post data to a test .php script using XAMPP on my local machine, but it always fails with ERROR_HTTP_HEADER_NOT_FOUND. I check the server logs and no request was sent to Apache. I can manually do it via a web browser and the php script runs as expected.

Here's the C++ code that doesn't work. Can someone point out the problem?

static const char *accepttypes[]={ "application/x-www-form-urlencoded", NULL};
static const char headers[]="application/x-www-form-urlencoded\r\n";
    
// open session
HINTERNET hsession;
if ((hsession=InternetOpen(_T("Whatever"), INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0)) != NULL) {
    HINTERNET hconnect;
    if ((hconnect=InternetConnect(hsession, _T("127.0.0.1"), INTERNET_DEFAULT_HTTP_PORT, NULL, NULL, INTERNET_SERVICE_HTTP, 0, 0)) != NULL) {
        HINTERNET hpostreq;
        if ((hpostreq=HttpOpenRequestA(hconnect, "POST", "/mytest.php", NULL, NULL, accepttypes, INTERNET_FLAG_RELOAD, 0)) != NULL) {
            BYTE *data=(BYTE*)"xyz=1234";
            DWORD datasize=8;
            if (HttpSendRequestA(hpostreq, headers, sizeof(headers), (LPVOID) data, datasize)) {
                ....
              
                // ^^^^^ That always fails with ERROR_HTTP_HEADER_NOT_FOUND

Remy Lebeau · Accepted Answer · 2020-10-07 18:50:12Z

1

I see two mistakes in your call to HttpSendRequestA():

The value of headers needs to be changed from "application/x-www-form-urlencoded\r\n" to "Content-Type: application/x-www-form-urlencoded".
sizeof(headers) needs to be changed to either -1, sizeof(headers)-1, or strlen(headers). You are expected to pass in either -1 to let the function calculate the character length of the headers string, or you can pass in the actual character length. The string's null terminator is not to be included in that length.

edited Oct 7, 2020 at 18:50

answered Oct 7, 2020 at 18:44

Remy Lebeau

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1 Comment

user3161924 Over a year ago

It was the sizeof()-1 that was needed (I wondered about that). The Content-Type was missing because when I changed from octet-stream back to to the urlencoded I had commented out, I missed it on a copy/paste (ugh). Thanks!!

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