HTTP Post Header Fields with libcurl

Question

First of, I'm very new to HTTP commands and the libcurl library, so there is a good chance that I'm not understanding something fundamental. That said, I'm attempting to replicate an HTTP POST command sent to a device via an internal server on a windows based MFC app. Essentially I'm sending a small bitmap image along with a command. I captured the command using Fiddler, and it looks something like:

POST /Service/MyCommand HTTP/1.1
Authorization: MyAuth

Content-Type: image/bmp
User-Agent: Mozilla/4.0 (Windows 7 6.1) Java/1.7.0_51
Host: MyHost:MyPort
Accept: MyAccept
Connection: MyConnection
Content-Length: 15606

/* BMP Data */

I'm having two problems replicating this (using libcurl). First, my post command of 'Service/MyCommand' appears at the very end of the header, rather than after the 'POST /'. I have attempted to move it around, but it will cease to appear on my WireShark filter window. Second, when I attempt to set my content length to 15606, as with the original, the protocol on WireShark switches from "POST" to "TCP". I've attached the code below.

int CHttpPost::fnSendContent()
{
using namespace std;
int Error = 0;
CString str;

CURL* curl;
CURLcode res;
struct curl_httppost *formpost=NULL;
struct curl_httppost *lastptr=NULL;
struct curl_slist *headerlist=NULL;
static const char buf[] = "a"; // not sure what to do with this

curl_global_init(CURL_GLOBAL_ALL);

curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "importfile", CURLFORM_FILE, "MyImage.bmp", CURLFORM_CONTENTTYPE, "image/bmp", CURLFORM_END);
curl_formadd(&formpost, &lastptr, CURLFORM_COPYNAME, "action", CURLFORM_COPYCONTENTS, "upload", CURLFORM_END);

curl = curl_easy_init();
headerlist = curl_slist_append(headerlist, buf);
headerlist = curl_slist_append(headerlist, "Authorization: MyAuth");
headerlist = curl_slist_append(headerlist, "Content-Type: image/bmp");
headerlist = curl_slist_append(headerlist, "User-Agent: Mozilla/4.0 (Windows 7 6.1) Java/1.7.0_51");
headerlist = curl_slist_append(headerlist, "Accept: MyAccept");
headerlist = curl_slist_append(headerlist, "Connection: MyConnection");
headerlist = curl_slist_append(headerlist, "Content-Length: 15606");


//Set URL to recevie POST
curl_easy_setopt(curl, CURLOPT_VERBOSE, true);
curl_easy_setopt(curl,CURLOPT_POST, true);
curl_easy_setopt(curl, CURLOPT_HEADER, true);
curl_easy_setopt(curl, CURLOPT_URL, "MyHost:MyPort");
curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "Service/MyCommand");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist);


res = curl_easy_perform(curl);

curl_easy_cleanup(curl);
curl_global_cleanup();

return Error;
}

Any other suggestions or corrections you have are much appreciated as well.

EDIT: I was being an idiot by placing the "Service/MyCommand" in the postfield rather than the URL. I apparently misunderstood one of the tutorials. My content-length question still stands however.

Answer 1

You can do this much simpler. You, just use CURLOPT_POSTFIELDS to point to the BMP data, and make CURLOPT_POSTFIELDSIZE_LARGE be the full size of that data (15606 I would guess in this particular case).

You do not want curl_formadd() and the formpost stuff you use. That's for the CURLOPT_HTTPPOST option, which is for multipart formposts but you don't want that.

char *bmp_array = [your data];
long bmp_size = 15606;

curl_easy_setopt(curl, CURLOPT_POSTFIELDS, bmp_array);
curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, bmp_size);