Re: TCP & curl-loader question

[Gary F. <ga...@in...>]

Hello Robert,

Thanks for all your help so far. Now I've run into a possible bug, and  
I want to see what you think. In loader.c, setup_curl_handle_init(),  
there is this code:

   if (url->upload_file)
     {
       if (! url->upload_file_ptr)
         {
           if (! (url->upload_file_ptr = fopen (url->upload_file,  
"rb")))
             {
               fprintf (stderr,
                        "%s - error: failed to open() %s with errno %d. 
\n",
                        __func__, url->upload_file, errno);
               return -1;
             }
         }

       /* Enable uploading */
       curl_easy_setopt(handle, CURLOPT_UPLOAD, 1);
...


Now if this is a cycling URL, we're going to want to upload the file  
many times. But after the first upload, the file pointer will be set  
to the end of the file, and subsequent reads will return eof. So I  
changed the code to this:

   if (url->upload_file)
     {
       if (! url->upload_file_ptr)
         {
           if (! (url->upload_file_ptr = fopen (url->upload_file,  
"rb")))
             {
               fprintf (stderr,
                        "%s - error: failed to open() %s with errno %d. 
\n",
                        __func__, url->upload_file, errno);
               return -1;
             }
         }
       else
         {
         rewind(url->upload_file_ptr); /* Added by GF October 2008 */
         }

       /* Enable uploading */
       curl_easy_setopt(handle, CURLOPT_UPLOAD, 1);

This seems to fix the problem when a single client is cycling the url.  
But now I'm worried about multiple clients. As it is, all the clients  
share this url context, and so they all share this single  
upload_file_ptr. What if client A begins the upload, and while the  
upload is proceeding in stages, client B comes along and tries to use  
the same pointer? It seems that this could certainly happen when we're  
running clients in multiple threads, and it looks as though it could  
happen even with multiple clients in a single thread.

I'm thinking that each upload url has to keep a file offset for each  
client, and arrange to use that offset for each read. What do you think?

Thanks,
Gary