gpgme_data_new_from_mem works, gpgme_data_write doesn't

[Marcus Brinkmann]

At Mon, 7 Jul 2008 00:10:10 +0200,
Nico Schottelius <nico-gnupg-dev-0 at schottelius.org> wrote:
> 
> [1  <multipart/signed (7bit)>]
> [1.1  <text/plain; us-ascii (quoted-printable)>]
> Hello!
> 
> I am testing around with gpgme and it seems I am doing something
> wrong with gpgme_data_write():
> 
> If I do
> 
>    gerr = gpgme_data_new(&g_test);
>    if(gerr != GPG_ERR_NO_ERROR) return 20;
>    i = strlen(b_encrypt);  
> 
>    /* THIS WORKS */
>    gerr = gpgme_data_new_from_mem(&g_encrypt_send, b_encrypt, i, 1);
>    if(gerr != GPG_ERR_NO_ERROR) return 24;
> 
>    /* decrypt: from gpgme_data_new_from_mem()  */
>    gerr = gpgme_op_decrypt(g_context, g_encrypt_send, g_plain_recv);
>    if(gerr != GPG_ERR_NO_ERROR) {
>       printf("gerr=%d\n",gerr);
>       return 19;
>    }
> 
> 
> it works. If I do
> 
>    gerr = gpgme_data_new(&g_test);
>    if(gerr != GPG_ERR_NO_ERROR) return 20;
>    i = strlen(b_encrypt);  
>    printf("strlen(%s) = %d\n",b_encrypt,i);
> 
>    /* THIS DOES NOT WORK */
>    tmp = gpgme_data_write(g_test, b_encrypt, i);
>    printf("gpgmedatawrite: %d\n", tmp);
> 
>    /* decrypt: from gpgme_data_write() */
>    gerr = gpgme_op_decrypt(g_context, g_test, g_plain_recv2);
>    if(gerr != GPG_ERR_NO_ERROR) {
>       printf("gerr=%d\n",gerr);
>       return 41;
>    }
> 
> it does *NOT* work.

As I wrote before: "gpgme data objects have a file pointer that must
be rewound to read written data (gpgme_data_seek).  To use the seek
function make sure you compile with large file support.  See the
documentation."

The gpgme_data_write() above works just fine, but after it the file
pointer is at the end of the data, and the gpgme_op_decrypt sees an
empty data buffer:

  g_test: some-data
                   ^
                   | "file" pointer

You need to rewind the file pointer to the beginning after
gpgme_data_write.  Please see the documentation, and take notice of
the large file support necessary when using gpgme_data_seek.

Thanks,
Marcus