Save an image from JPEG to PNG using libCurl and GdkPixBuff

Question

I'm trying to build up an algorithm that downloads a JPEG image from an URL and saves it as a PNG into the disk. To achieve this I've used libCurl, for download, and GdkPixbuff library for the other stuffs (for a project limitation I'm sticked to Gdk libraries)

Here the code to achieve data:

CURL     *curl;
GError   *error = NULL;

struct context ctx;
memset(&ctx, 0, sizeof(struct context));

curl = curl_easy_init();

if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, *file_to_download*);

    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeDownloadedPic);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &ctx);

    curl_easy_perform(curl);
    curl_easy_cleanup(curl);
}

where context is defined like that:

struct context
{
    unsigned char *data;
    int allocation_size;
    int length;
};

and writeDownloadedPic in this way:

size_t writeDownloadedPic (void *buffer, size_t size, size_t nmemb, void *userp)
{
   struct context *ctx = (struct context *) userp;

   if(ctx->data ==  NULL)
   {
    ctx->allocation_size = 31014;
    if((ctx->data = (unsigned char *) malloc(ctx->allocation_size)) == NULL)
    {
        fprintf(stderr, "malloc(%d) failed\n", ctx->allocation_size);
        return -1;
    }
   }

   if(ctx->length + nmemb > ctx->allocation_size)
   {
    fprintf(stderr, "full\n");
    return -1;
   }

   memcpy(ctx->data + ctx->length, buffer, nmemb);
   ctx->length += nmemb;

   return nmemb;

}

and in the end I try to save the image in that way:

GdkPixbuf   *pixbuf;
pixbuf = gdk_pixbuf_new_from_data(ctx.data,
                         GDK_COLORSPACE_RGB,
                         FALSE, 8,
                         222, 310,
                         222 * 3,
                         NULL, NULL);

gdk_pixbuf_save(pixbuf, "src/pics/image.png", "png", &error, NULL);

but, what I got is a missy png image with a bunch of random pixel and not form at all. Now, I know for sure dimension of image, width and height, but I think I've done some mess with the RowStride which I've calculated as width * 3.

Where am I wrong?

Answer 1

gdk_pixbuf_new_from_data doesn't support JPEG format. You will either have to save the JPEG to a file first and load it with gdk_pixbuf_new_from_file. Or create a GInputStream around ctx.data and use gdk_pixbuf_new_from_stream.