I've semplified a bit my code. I've removed all CURLOPT_APPEND and now I'm
using only CURLOPT_RESUME_FROM. I've again the same problem: all writes
consecutive to a CURLOPT_RESUME_FROM are translated to an APPE ftp comand. I
think it's not the correct behavior, expecially if seek back to EOF and
overwrite some data is needed ( like in my case ).
Every advice is appreciated,
Daniele

2008/8/27 Daniele Pianu <muogoro_at_gmail.com>

> Hi to all,
> I'm working to a library that simulates Unix I/O read/write/seek operations
> using different streams/protocols. The plugin which uses FTP protocol is
> built using libcURL. While I'm doing consecutive writes there's no problems:
> I set the CURLOPT_APPEND and all data is appended beyond the EOF. I've some
> problems when I seek back and want to overwrite some data inside the file.
> My writing function code is something like this:
>
> /* Setup curl library for upload */
> curl_easy_setopt( handle, CURLOPT_UPLOAD, 1L );
>
> /* If file size is equal to file offset and this isn't the first write
> (channelSize != 0), append data to the end of file .....*/
> if( channelSize )
> {
> if( channelPos == channelSize )
> {
> curl_easy_setopt( handle, CURLOPT_APPEND, 1L );
> }
> else
> {
> /* ... else, set resume */
> curl_easy_setopt( handle, CURLOPT_RESUME_FROM,
> channelPos );
> }
>
> /* Check if the buffer write need to write data beyond the EOF */
> if( channelPos + size > channelSize )
> {
> /* Write up to channelSize - curl->channelPos bytes */
> retVal = Curl_write( libraryInstance, buffer,
> channelSize - channelPos );
> /* Append remaining bytes */
> curl_easy_setopt( handle, CURLOPT_RESUME_FROM, 0L );
> curl_easy_setopt( handle, CURLOPT_APPEND, 1L );
> retVal = Curl_write( libraryInstance, (unsigned char*)buffer +
> retVal,
> size - retVal );
> }
> else
> {
> /* overwrite data inside the file */
> Curl_write( libraryInstance, buffer, size );
> }
>
> }
> else
> {
> /* First write */
> Curl_write( libraryInstance, buffer, size );
> }
>
> /* Reset curl library options for next transfers */
> curl_easy_setopt( handle, CURLOPT_UPLOAD, 0L );
> curl_easy_setopt( handle, CURLOPT_APPEND, 0L );
> curl_easy_setopt( handle, CURLOPT_RESUME_FROM, 0L );
>
> return retVal;
>
> channelSize is the size of the file, channelPos is the offset.
> libraryInstance is the library instance, Curl_write is the plugin write
> function, which use my own defined callbacks. A callback that prevents seek
> operation in the input stream is also provided, so resume operations move
> the offset only inside the ftp server file ( that is, transfer starts ALWAYS
> from the begin of the file ). Supposing I've this file:
>
> foo!!!
> foobar!!!
>
> and I seek back to 7-th byte (the second line), if I want to write the
> string "bar!!!\n", I've this output file in the server
>
> foo!!!
> foobar!!!
> bar!!!
>
> and not this
>
> foo!!!
> bar!!!
> bar!!!
>
> seek ( and, so, resume) operations are ignored: if I enable verbose mode I
> see the every write operation is resolved to a APPEND command (except for
> the first write).
>
> Every help is appreciated,
> Daniele
>
> P.S.: excuse me for my bad english :)
>
Received on 2008-08-27