Screenshot Creation and Uploading

Question

I'm trying to write an Image Uploading client. I use this code to grab the screenshot and write it into the variable hBitmap. Then I want to Upload it using the code under this one, but I don't know how to convert or maybe reformat the image. I don't want to write the Image into an File and then readout the file, that would be to easy ;)

// get the device context of the screen
HDC hScreenDC = CreateDC("DISPLAY", NULL, NULL, NULL);     
// and a device context to put it in
HDC hMemoryDC = CreateCompatibleDC(hScreenDC);

int x = GetDeviceCaps(hScreenDC, HORZRES);
int y = GetDeviceCaps(hScreenDC, VERTRES);

// maybe worth checking these are positive values
HBITMAP hBitmap = CreateCompatibleBitmap(hScreenDc, x, y);

// get a new bitmap
HBITMAP hOldBitmap = SelectObject(hMemoryDC, hBitmap);

BitBlt(hMemoryDC, 0, 0, width, height, hScreenDC, 0, 0, SRCCOPY);
hBitmap = SelectObject(hMemoryDC, hOldBitmap);

// clean up
DeleteDC(hMemoryDC);
DeleteDC(hScreenDC);

This is My Uploading code:

void HTTP_UPLOAD_REQUEST(char * Server,int Port,char * uploadscript,char* boundary,char*filetoup,char* data)
{
//Create Socket for sending data
WSADATA wsaData;
WSAStartup( MAKEWORD( 1,1 ), &wsaData );
SOCKET Socket = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP );
LPHOSTENT hostEntry;
hostEntry = gethostbyname( Server );//Get ip from Server by hostname
sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr = *((LPIN_ADDR)*hostEntry->h_addr_list);
addr.sin_port = htons( Port ); //Set Port
connect( Socket, (LPSOCKADDR) &addr, sizeof(struct sockaddr) );
//Socket created and connected to Server!

//Create HTTP POST Request
//construct POST Header
char header[512]="";
sprintf( header, "POST %s HTTP/1.0\r\nContent-Type: multipart/form-data; boundary=%s\r\nContent-Length: %u\r\n\r\n",uploadscript, boundary,2*strlen(data));

//construct Body(data part) of HTTP POST
char* body=new char[strlen(data)+4000];
sprintf( body, "--%s\r\nContent-Disposition: form-data; name=\"%s\"; filename=\"%s\"\r\n\r\n %s\r\n--%s\r\n",boundary,"data",filetoup,data,boundary);

//Put Header and Body together into Request
char * Request=new char[strlen(header)+strlen(body)+strlen(data)];
sprintf( Request, "%s%s", header,body );

//int bytestosend = strlen(Request);
int bytessend =send( Socket, Request, strlen(Request), 0 ); 


closesocket(Socket);//cleanup -!

}

Answer 1

1. What you have now is a raw bitmap data. Valid bitmap (*.bmp) file must contain BMP header also. There is a good article about it.

   Maybe then you'd like to convert the huge bmp file to jpeg or png format. Free image, for example, is able to perform such in-memory conversion.

2. If you need to upload data to the web consider using some reliable network library like libcurl. Your implementation has a few memory leaks.

   My recommendation also is to use std::string or std::vector wherever is possible. It gives you not only leak-free but also nicer code:

   void HTTP_UPLOAD_REQUEST(std::string Server, unsigned short Port, std::string uploadscript, std::string boundary, std::string filetoup, std::string data)
   {
       ...
   
       std::stringstream out;
   
       out << "POST " << uploadscript << " HTTP/1.0\r\n";
       out << "Content-Type: multipart/form-data; boundary=" << boundary << "\r\n";
       out << "Content-Length: " << data.size();
   
       out << "--" << boundary << "\r\n";
       out << "Content-Disposition: form-data; name=\"data\"; filename=\""
           << filetoup << "\"\r\n\r\n";
   
       out << data << "\r\n--" << boundary << "\r\n";
   
       std::string toSend = out.str();
       int bytessend = send( Socket, toSend.c_str(), toSend.size(), 0 ); 
       ...
   }
   

   Note that WSAStartup must be called only once in a program, not each call to HTTP_UPLOAD_REQUEST