int cb_server_alpn()

in native/src/sslcontext.c [1350:1426]

• 54 lines of code
• 12 McCabe index (conditional complexity)

int cb_server_alpn(SSL *ssl,
                   const unsigned char **out, unsigned char *outlen,
                   const unsigned char *in, unsigned int inlen, void *arg)
{
    tcn_ssl_ctxt_t *tcsslctx = (tcn_ssl_ctxt_t *)arg;
    tcn_ssl_conn_t *con = (tcn_ssl_conn_t *)SSL_get_app_data(ssl);
    apr_array_header_t *client_protos;
    apr_array_header_t *proposed_protos;
    int i;
    size_t len;

    if (inlen == 0) {
        // Client specified an empty protocol list. Nothing to negotiate.
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    client_protos = apr_array_make(con->pool , 0, sizeof(char *));
    for (i = 0; i < inlen; /**/) {
        /* Grab length of next item from leading length byte */
        unsigned int plen = in[i++];
        if (plen + i > inlen) {
            // The protocol name extends beyond the declared length
            // of the protocol list.
            return SSL_TLSEXT_ERR_ALERT_FATAL;
        }
        APR_ARRAY_PUSH(client_protos, char*) = apr_pstrndup(con->pool, (const char *)in+i, plen);
        i += plen;
    }

    if (tcsslctx->alpn == NULL) {
        // Server supported protocol names not set.
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    if (tcsslctx->alpnlen == 0) {
        // Server supported protocols is an empty list
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    proposed_protos = apr_array_make(con->pool, 0, sizeof(char *));
    for (i = 0; i < tcsslctx->alpnlen; /**/) {
        /* Grab length of next item from leading length byte */
        unsigned int plen = tcsslctx->alpn[i++];
        if (plen + i > tcsslctx->alpnlen) {
            // The protocol name extends beyond the declared length
            // of the protocol list.
            return SSL_TLSEXT_ERR_ALERT_FATAL;
        }
        APR_ARRAY_PUSH(proposed_protos, char*) = apr_pstrndup(con->pool, (const char *)tcsslctx->alpn+i, plen);
        i += plen;
    }

    if (proposed_protos->nelts <= 0) {
        // Should never happen. The server did not specify any protocols.
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    /* Now select the most preferred protocol from the proposals. */
    *out = APR_ARRAY_IDX(proposed_protos, 0, const unsigned char *);
    for (i = 1; i < proposed_protos->nelts; ++i) {
        const char *proto = APR_ARRAY_IDX(proposed_protos, i, const char*);
        /* Do we prefer it over existing candidate? */
        if (ssl_cmp_alpn_protos(client_protos, (const char *)*out, proto) < 0) {
            *out = (const unsigned char*)proto;
        }
    }

    len = strlen((const char*)*out);
    if (len > 255) {
        // Agreed protocol name too long
        return SSL_TLSEXT_ERR_ALERT_FATAL;
    }

    *outlen = (unsigned char)len;

    return SSL_TLSEXT_ERR_OK;
}