how to work CORRECTLY with SSL_read() and select()? - windows

Question

I try to make a C++ TLS client with OpenSSL which use non-blocking socket on Windows.
I want to work with SSL_read()/SSL_write() and select() functions but I don't find the algorithme which work well and the net not provide good and simple exemple. There is allready a timeout return by select() after the last block of data recved.
I don't understand OpenSSL api, SSL_pending() return already 0 and select a time out??
Select cause a criticale delay at last bloc of data.
My algorithme for recv_buffer() is this:
I have function which check if a socket is readable or writeable (work well):
int CSocket::socket_RWable(int rw_flag, const int time_out)
{
fd_set rwfs;
int error = 0;
struct timeval timeout;
try
{
memset(&timeout, 0, sizeof(struct timeval));
timeout.tv_sec = time_out;
while( 1 ) // boucle de surveillance
{
FD_ZERO(&rwfs);
FD_SET(m_socket, &rwfs);
// surveiller la socket en lecture ou ecriture
if(rw_flag == R_MODE)
error = select(m_socket+1, &rwfs, NULL, NULL, &timeout);
else if(rw_flag == W_MODE)
error = select(m_socket+1, NULL, &rwfs, NULL, &timeout);
if(error < 0) // echec de select
throw 1;
else if(error == 0) // fin du time out
throw 2;
// Une opération d' entree/sortie sur la socket est disponible
if(FD_ISSET(m_socket, &rwfs) != 0)
{
FD_CLR(m_socket, &rwfs );
return 0;
}
}
}
catch(int ret)
{
FD_CLR(m_socket, &rwfs );
if(ret == 1) throw CErreur("[-] CSocket : select : ", CWinUtil::Win_sys_error(NET_ERROR));
else if(ret == 2) return -1;
}
return -1;
}
UPDATE:
and this function recve the data into a buffer and cause a time out after the las block of data:
int CTLSClient::recv_buffer(char *buffer, const int buffer_size, const int time_out)
{
int selectErr = 0;
int sslErr = 0;
int retRead = 0;
int recvData = 0;
selectErr = m_socket->socket_RWable(R_MODE, time_out);
while(selectErr == 0)
{
retRead = SSL_read(m_ssl, buffer+recvData, buffer_size-recvData);
sslErr = SSL_get_error(m_ssl, retRead);
if(sslErr == SSL_ERROR_NONE)
{
cout<<"DEBUG 2 SSL_ERROR_NONE recv data="<<retRead<<endl;
recvData += retRead;
}
else if(sslErr == SSL_ERROR_WANT_READ)
{
cout<<"DEBUG 3 SSL_ERROR_WANT_READ select()"<<endl;
selectErr = m_socket->socket_RWable(R_MODE, time_out);
}
else if(sslErr == SSL_ERROR_WANT_WRITE)
{
cout<<"DEBUG 4 SSL_ERROR_WANT_WRITE select()"<<endl;
selectErr = m_socket->socket_RWable(W_MODE, time_out);
}
else if(sslErr == SSL_ERROR_ZERO_RETURN)
{
return -1;
}
else
return -1;
}
return recvData;
}
this is a output with connection to a POP3 server:
DEBUG 2 SSL_ERROR_NONE recv data=35
DEBUG 3 SSL_ERROR_WANT_READ select()
[S]+OK BLU0-POP617 POP3 server ready
total data -> 35
DEBUG 2 SSL_ERROR_NONE recv data=23
DEBUG 3 SSL_ERROR_WANT_READ select()
[S]+OK password required
total data -> 23
DEBUG 2 SSL_ERROR_NONE recv data=30
DEBUG 3 SSL_ERROR_WANT_READ select()
[S]+OK mailbox has 180 messages
total data -> 30
DEBUG 2 SSL_ERROR_NONE recv data=18
DEBUG 3 SSL_ERROR_WANT_READ select()
[S]+OK 180 12374432
total data -> 18
DEBUG 2 SSL_ERROR_NONE recv data=13
DEBUG 3 SSL_ERROR_WANT_READ select()
[S]+OK 1 23899
total data -> 13
DEBUG 2 SSL_ERROR_NONE recv data=5
DEBUG 3 SSL_ERROR_WANT_READ select()
DEBUG 2 SSL_ERROR_NONE recv data=8192
DEBUG 2 SSL_ERROR_NONE recv data=8192
DEBUG 3 SSL_ERROR_WANT_READ select()
DEBUG 3 SSL_ERROR_WANT_READ select()
DEBUG 2 SSL_ERROR_NONE recv data=7521
DEBUG 3 SSL_ERROR_WANT_READ select()
[S]total data -> 23910

Answer 1

Assuming you have already read the headers, for some reason SSL_read() hangs after reading the email message and returns SSL_WANT_READ. I solved this problem by looping through the message body one line at a time until I find the ending period. When I reach this line, I call SSL_pending(). Although there is no pending data, it prevents an endless loop where SSL_read() returns SSL_WANT_READ. However, I am looking for a better solution.
for(;;)
{
char *line = ReadLine(ssl, buf, sizeof(buf));
if(line != NULL)
{
if(*line == '.')
{
int pending = SSL_pending(ssl);
if(pending > 0)
{
int read = SSL_read(ssl,buf,pending);
}
}
}
}
This function reads one character at a time until it reaches an end of line character and returns the line.
char *ReadLine(SSL *ssl, char *buf, int size)
{
int i = 0;
char *ptr = NULL;
for (ptr = str; size > 1; size--, ptr++)
{
i = SSL_read(out, ptr, 1);
switch (SSL_get_error(out, i)){
case SSL_ERROR_NONE:
break;
case SSL_ERROR_ZERO_RETURN:
break;
case SSL_ERROR_WANT_READ:
break;
case SSL_ERROR_WANT_WRITE:
break;
default:
TRACE("SSL problem\r\n");
}
if (*ptr == '\n')
break;
if (*ptr == '\r'){
ptr--;
}
}
*ptr = '\0';
return(str);
}