Viewing file:  ddd-02-conn-nonblocking.c (7.08 KB) -rw-r--r--
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#include <sys/poll.h>
#include <openssl/ssl.h>
/*
* Demo 2: Client — Managed Connection — Asynchronous Nonblocking
* ==============================================================
*
* This is an example of (part of) an application which uses libssl in an
* asynchronous, nonblocking fashion. The functions show all interactions with
* libssl the application makes, and would hypothetically be linked into a
* larger application.
*
* In this example, libssl still makes syscalls directly using an fd, which is
* configured in nonblocking mode. As such, the application can still be
* abstracted from the details of what that fd is (is it a TCP socket? is it a
* UDP socket?); this code passes the application an fd and the application
* simply calls back into this code when poll()/etc. indicates it is ready.
*/
typedef struct app_conn_st {
SSL *ssl;
BIO *ssl_bio;
int rx_need_tx, tx_need_rx;
} APP_CONN;
/*
* The application is initializing and wants an SSL_CTX which it will use for
* some number of outgoing connections, which it creates in subsequent calls to
* new_conn. The application may also call this function multiple times to
* create multiple SSL_CTX.
*/
SSL_CTX *create_ssl_ctx(void)
{
SSL_CTX *ctx;
ctx = SSL_CTX_new(TLS_client_method());
if (ctx == NULL)
return NULL;
/* Enable trust chain verification. */
SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER, NULL);
/* Load default root CA store. */
if (SSL_CTX_set_default_verify_paths(ctx) == 0) {
SSL_CTX_free(ctx);
return NULL;
}
return ctx;
}
/*
* The application wants to create a new outgoing connection using a given
* SSL_CTX.
*
* hostname is a string like "openssl.org:443" or "[::1]:443".
*/
APP_CONN *new_conn(SSL_CTX *ctx, const char *hostname)
{
APP_CONN *conn;
BIO *out, *buf;
SSL *ssl = NULL;
const char *bare_hostname;
conn = calloc(1, sizeof(APP_CONN));
if (conn == NULL)
return NULL;
out = BIO_new_ssl_connect(ctx);
if (out == NULL) {
free(conn);
return NULL;
}
if (BIO_get_ssl(out, &ssl) == 0) {
BIO_free_all(out);
free(conn);
return NULL;
}
buf = BIO_new(BIO_f_buffer());
if (buf == NULL) {
BIO_free_all(out);
free(conn);
return NULL;
}
BIO_push(out, buf);
if (BIO_set_conn_hostname(out, hostname) == 0) {
BIO_free_all(out);
free(conn);
return NULL;
}
/* Returns the parsed hostname extracted from the hostname:port string. */
bare_hostname = BIO_get_conn_hostname(out);
if (bare_hostname == NULL) {
BIO_free_all(out);
free(conn);
return NULL;
}
/* Tell the SSL object the hostname to check certificates against. */
if (SSL_set1_host(ssl, bare_hostname) <= 0) {
BIO_free_all(out);
free(conn);
return NULL;
}
/* Make the BIO nonblocking. */
BIO_set_nbio(out, 1);
conn->ssl_bio = out;
return conn;
}
/*
* Non-blocking transmission.
*
* Returns -1 on error. Returns -2 if the function would block (corresponds to
* EWOULDBLOCK).
*/
int tx(APP_CONN *conn, const void *buf, int buf_len)
{
int l;
conn->tx_need_rx = 0;
l = BIO_write(conn->ssl_bio, buf, buf_len);
if (l <= 0) {
if (BIO_should_retry(conn->ssl_bio)) {
conn->tx_need_rx = BIO_should_read(conn->ssl_bio);
return -2;
} else {
return -1;
}
}
return l;
}
/*
* Non-blocking reception.
*
* Returns -1 on error. Returns -2 if the function would block (corresponds to
* EWOULDBLOCK).
*/
int rx(APP_CONN *conn, void *buf, int buf_len)
{
int l;
conn->rx_need_tx = 0;
l = BIO_read(conn->ssl_bio, buf, buf_len);
if (l <= 0) {
if (BIO_should_retry(conn->ssl_bio)) {
conn->rx_need_tx = BIO_should_write(conn->ssl_bio);
return -2;
} else {
return -1;
}
}
return l;
}
/*
* The application wants to know a fd it can poll on to determine when the
* SSL state machine needs to be pumped.
*/
int get_conn_fd(APP_CONN *conn)
{
return BIO_get_fd(conn->ssl_bio, NULL);
}
/*
* These functions returns zero or more of:
*
* POLLIN: The SSL state machine is interested in socket readability events.
*
* POLLOUT: The SSL state machine is interested in socket writeability events.
*
* POLLERR: The SSL state machine is interested in socket error events.
*
* get_conn_pending_tx returns events which may cause SSL_write to make
* progress and get_conn_pending_rx returns events which may cause SSL_read
* to make progress.
*/
int get_conn_pending_tx(APP_CONN *conn)
{
return (conn->tx_need_rx ? POLLIN : 0) | POLLOUT | POLLERR;
}
int get_conn_pending_rx(APP_CONN *conn)
{
return (conn->rx_need_tx ? POLLOUT : 0) | POLLIN | POLLERR;
}
/*
* The application wants to close the connection and free bookkeeping
* structures.
*/
void teardown(APP_CONN *conn)
{
BIO_free_all(conn->ssl_bio);
free(conn);
}
/*
* The application is shutting down and wants to free a previously
* created SSL_CTX.
*/
void teardown_ctx(SSL_CTX *ctx)
{
SSL_CTX_free(ctx);
}
/*
* ============================================================================
* Example driver for the above code. This is just to demonstrate that the code
* works and is not intended to be representative of a real application.
*/
int main(int argc, char **argv)
{
const char tx_msg[] = "GET / HTTP/1.0\r\nHost: www.openssl.org\r\n\r\n";
const char *tx_p = tx_msg;
char rx_buf[2048];
int res = 1, l, tx_len = sizeof(tx_msg)-1;
int timeout = 2000 /* ms */;
APP_CONN *conn = NULL;
SSL_CTX *ctx;
ctx = create_ssl_ctx();
if (ctx == NULL) {
fprintf(stderr, "cannot create SSL context\n");
goto fail;
}
conn = new_conn(ctx, "www.openssl.org:443");
if (conn == NULL) {
fprintf(stderr, "cannot establish connection\n");
goto fail;
}
/* TX */
while (tx_len != 0) {
l = tx(conn, tx_p, tx_len);
if (l > 0) {
tx_p += l;
tx_len -= l;
} else if (l == -1) {
fprintf(stderr, "tx error\n");
} else if (l == -2) {
struct pollfd pfd = {0};
pfd.fd = get_conn_fd(conn);
pfd.events = get_conn_pending_tx(conn);
if (poll(&pfd, 1, timeout) == 0) {
fprintf(stderr, "tx timeout\n");
goto fail;
}
}
}
/* RX */
for (;;) {
l = rx(conn, rx_buf, sizeof(rx_buf));
if (l > 0) {
fwrite(rx_buf, 1, l, stdout);
} else if (l == -1) {
break;
} else if (l == -2) {
struct pollfd pfd = {0};
pfd.fd = get_conn_fd(conn);
pfd.events = get_conn_pending_rx(conn);
if (poll(&pfd, 1, timeout) == 0) {
fprintf(stderr, "rx timeout\n");
goto fail;
}
}
}
res = 0;
fail:
if (conn != NULL)
teardown(conn);
if (ctx != NULL)
teardown_ctx(ctx);
return res;
}
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