On Wed, 22 Apr 1998, Eduardo Marcel Macan wrote:
> I need to implement a server/client that can handle multiple
> non-blocking connections, and I keep seeing things about the BIO ,
> it really looks like a damn good thing, is there any documentation
> available concerning the BIO interface?
A quick BIO summery for 0.9.0
BIO *ssl_bio,*conn_bio,*bio;
conn_bio=BIO_new_connect("remote.host.name.org:443");
ssl_bio=BIO_new_ssl_connect(SSL_CTX *ctx);
/* We have 2 options, you can do a BIO_do_handshake(conn_bio)
* until you get 1 or 0 to establish a connection, then push it
* onto the SSL BIO, and then do a BIO_do_handshake(ssl_bio)
* until 0 or 1 which means the SSL handshake has finished (worked
* or failed. or we can simply do the following */
bio=BIO_push(ssl_bio,conn_bio);
/* Into program logic, we can either do BIO_do_handshake() until
* 0 or 1, or we can just start reading/writing as follows, in all
* cases the non-blocking logic is outlined */
i=BIO_read(bio,buf,num); /* or */
i=BIO_write(bio,buf,num); /* or */
i=BIO_do_handshake(bio);
/* one of the above three can be done, then follow it with this logic
*/
if (i > 0)
{
read/written data or the 'initialisation' has finished.
For connect, this means a non-blocking connect has finished
and for read/write it means data was read or written.
}
else if (i == 0)
{
protocol failed or connection closed. Anyway, it is finished.
}
else if (i < 0)
{
if (BIO_should_retry(bio))
{ /* Was a non-blocking IO condition */
if (BIO_should_read(bio))
{ /* set select(2) flags accordingly */
}
else if (BIO_should_write(bio))
{ /* set select(2) flags accordingly */
}
else if (BIO_io_special(bio))
{
j=BIO_get_retry_reason(bio);
if (j == BIO_RR_CONNECT)
{
/* non-blocking connect, this
* is currently the only 'special'
* retry reason */
}
}
}
else
{
/* A system error of some type */
}
}
Now the reason for this stuff is because in the SSL protocol, during an
initial handshake or a session-renegotiation (which can occur at any time),
a program read can fail because the OS wanted to write and the other way
round. The program can get a little tricky when you then have to know that
when you are able to 'read' you actually want to do a BIO_write() call :-).
AS for the BIO interface, there is BIO_read(), BIO_write() which are basicaly
the same as read(2) and write(2); the 'should retry' stuff, and BIO_ctrl()
which is used to get and set values. There are lots and lots of macros that
map into BIO_ctrl().
BIOs can be pushed and poped. For the above SSL example, if we want some
buffering, so each BIO_write() does not generate a packet on the wire,
bbio=BIO_new(BIO_f_buffer());
bio=BIO_push(bbio,bio);
BIO_set_read_buffer_size(bbio,0);
BIO_set_write_buffer_size(bbio,1024*10);
etc...
eric
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