--- /dev/null
+#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)
+{
+ static char tx_msg[384], host_port[300];
+ 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 = NULL;
+
+ if (argc < 3) {
+ fprintf(stderr, "usage: %s host port\n", argv[0]);
+ goto fail;
+ }
+
+ snprintf(host_port, sizeof(host_port), "%s:%s", argv[1], argv[2]);
+ snprintf(tx_msg, sizeof(tx_msg),
+ "GET / HTTP/1.0\r\nHost: %s\r\n\r\n", argv[1]);
+
+ ctx = create_ssl_ctx();
+ if (ctx == NULL) {
+ fprintf(stderr, "cannot create SSL context\n");
+ goto fail;
+ }
+
+ conn = new_conn(ctx, host_port);
+ 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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