doc/designs/ddd/ddd-03-fd-blocking.c

#include <openssl/ssl.h>

/*
 * Demo 3: Client — Client Creates FD — Blocking
 * =============================================
 *
 * This is an example of (part of) an application which uses libssl in a simple,
 * synchronous, blocking fashion. The client is responsible for creating the
 * socket and passing it to libssl. The functions show all interactions with
 * libssl the application makes, and would hypothetically be linked into a
 * larger application.
 */

/*
 * 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;

#ifdef USE_QUIC
    ctx = SSL_CTX_new(OSSL_QUIC_client_method());
#else
    ctx = SSL_CTX_new(TLS_client_method());
#endif
    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" used for certificate validation.
 */
SSL *new_conn(SSL_CTX *ctx, int fd, const char *bare_hostname)
{
    SSL *ssl;
#ifdef USE_QUIC
    static const unsigned char alpn[] = { 5, 'd', 'u', 'm', 'm', 'y' };
#endif

    ssl = SSL_new(ctx);
    if (ssl == NULL)
        return NULL;

    SSL_set_connect_state(ssl); /* cannot fail */

    if (SSL_set_fd(ssl, fd) <= 0) {
        SSL_free(ssl);
        return NULL;
    }

    if (SSL_set1_host(ssl, bare_hostname) <= 0) {
        SSL_free(ssl);
        return NULL;
    }

    if (SSL_set_tlsext_host_name(ssl, bare_hostname) <= 0) {
        SSL_free(ssl);
        return NULL;
    }

#ifdef USE_QUIC
    /* Configure ALPN, which is required for QUIC. */
    if (SSL_set_alpn_protos(ssl, alpn, sizeof(alpn))) {
        /* Note: SSL_set_alpn_protos returns 1 for failure. */
        SSL_free(ssl);
        return NULL;
    }
#endif

    return ssl;
}

/*
 * The application wants to send some block of data to the peer.
 * This is a blocking call.
 */
int tx(SSL *ssl, const void *buf, int buf_len)
{
    return SSL_write(ssl, buf, buf_len);
}

/*
 * The application wants to receive some block of data from
 * the peer. This is a blocking call.
 */
int rx(SSL *ssl, void *buf, int buf_len)
{
    return SSL_read(ssl, buf, buf_len);
}

/*
 * The application wants to close the connection and free bookkeeping
 * structures.
 */
void teardown(SSL *ssl)
{
    SSL_free(ssl);
}

/*
 * 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.
 */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/signal.h>
#include <netdb.h>
#include <unistd.h>

int main(int argc, char **argv)
{
    int rc, fd = -1, l, mlen, res = 1;
    static char msg[300];
    struct addrinfo hints = { 0 }, *result = NULL;
    SSL *ssl = NULL;
    SSL_CTX *ctx = NULL;
    char buf[2048];

    if (argc < 3) {
        fprintf(stderr, "usage: %s host port\n", argv[0]);
        goto fail;
    }

    mlen = snprintf(msg, sizeof(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 context\n");
        goto fail;
    }

    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    rc = getaddrinfo(argv[1], argv[2], &hints, &result);
    if (rc < 0) {
        fprintf(stderr, "cannot resolve\n");
        goto fail;
    }

    signal(SIGPIPE, SIG_IGN);

#ifdef USE_QUIC
    fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
#else
    fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
#endif
    if (fd < 0) {
        fprintf(stderr, "cannot create socket\n");
        goto fail;
    }

    rc = connect(fd, result->ai_addr, result->ai_addrlen);
    if (rc < 0) {
        fprintf(stderr, "cannot connect\n");
        goto fail;
    }

    ssl = new_conn(ctx, fd, argv[1]);
    if (ssl == NULL) {
        fprintf(stderr, "cannot create connection\n");
        goto fail;
    }

    l = tx(ssl, msg, mlen);
    if (l < mlen) {
        fprintf(stderr, "tx error\n");
        goto fail;
    }

    for (;;) {
        l = rx(ssl, buf, sizeof(buf));
        if (l <= 0)
            break;
        fwrite(buf, 1, l, stdout);
    }

    res = 0;
fail:
    if (ssl != NULL)
        teardown(ssl);
    if (ctx != NULL)
        teardown_ctx(ctx);
    if (fd >= 0)
        close(fd);
    if (result != NULL)
        freeaddrinfo(result);
    return res;
}