#endif /* HAVE_TLS_NPN */
+static int ssl_array_index(apr_array_header_t *array,
+ const char *s)
+{
+ int i;
+ for (i = 0; i < array->nelts; i++) {
+ const char *p = APR_ARRAY_IDX(array, i, const char*);
+ if (!strcmp(p, s)) {
+ return i;
+ }
+ }
+ return -1;
+}
+
+#ifdef HAVE_TLS_ALPN
+/*
+ * Compare to ALPN protocol proposal. Result is similar to strcmp():
+ * 0 gives same precedence, >0 means proto1 is prefered.
+ */
+static int ssl_cmp_alpn_protos(modssl_ctx_t *ctx,
+ const char *proto1,
+ const char *proto2)
+{
+ /* TODO: we should have a mod_ssl configuration parameter. */
+ if (ctx && ctx->ssl_alpn_pref) {
+ int index1 = ssl_array_index(ctx->ssl_alpn_pref, proto1);
+ int index2 = ssl_array_index(ctx->ssl_alpn_pref, proto2);
+ if (index2 > index1) {
+ return (index1 >= 0)? 1 : -1;
+ }
+ else if (index1 > index2) {
+ return (index2 >= 0)? -1 : 1;
+ }
+ }
+ /* both have the same index (mabye -1 or no pref configured) and we compare
+ * the names so that spdy3 gets precedence over spdy2. That makes
+ * the outcome at least deterministic. */
+ return strcmp((const char *)proto1, (const char *)proto2);
+}
+
+/*
+ * This callback function is executed when the TLS Application Layer
+ * Protocol Negotiate Extension (ALPN, RFC 7301) is triggered by the client
+ * hello, giving a list of desired protocol names (in descending preference)
+ * to the server.
+ * The callback has to select a protocol name or return an error if none of
+ * the clients preferences is supported.
+ * The selected protocol does not have to be on the client list, according
+ * to RFC 7301, so no checks are performed.
+ * The client protocol list is serialized as length byte followed by ascii
+ * characters (not null-terminated), followed by the next protocol name.
+ */
+int ssl_callback_alpn_select(SSL *ssl,
+ const unsigned char **out, unsigned char *outlen,
+ const unsigned char *in, unsigned int inlen, void *arg)
+{
+ conn_rec *c = (conn_rec*)SSL_get_app_data(ssl);
+ SSLConnRec *sslconn = myConnConfig(c);
+ server_rec *s = mySrvFromConn(c);
+ SSLSrvConfigRec *sc = mySrvConfig(s);
+ modssl_ctx_t *mctx = myCtxConfig(sslconn, sc);
+ const char *alpn_http1 = "http/1.1";
+ apr_array_header_t *client_protos;
+ apr_array_header_t *proposed_protos;
+ int i;
+
+ /* If the connection object is not available,
+ * then there's nothing for us to do. */
+ if (c == NULL) {
+ return SSL_TLSEXT_ERR_OK;
+ }
+
+ if (inlen == 0) {
+ // someone tries to trick us?
+ ap_log_cerror(APLOG_MARK, APLOG_ERR, 0, c, APLOGNO(02837)
+ "alpn client protocol list empty");
+ return SSL_TLSEXT_ERR_ALERT_FATAL;
+ }
+
+ client_protos = apr_array_make(c->pool, 0, sizeof(char *));
+ for (i = 0; i < inlen; /**/) {
+ unsigned int plen = in[i++];
+ if (plen + i > inlen) {
+ // someone tries to trick us?
+ ap_log_cerror(APLOG_MARK, APLOG_ERR, 0, c, APLOGNO(02838)
+ "alpn protocol identier too long");
+ return SSL_TLSEXT_ERR_ALERT_FATAL;
+ }
+ APR_ARRAY_PUSH(client_protos, char*) =
+ apr_pstrndup(c->pool, (const char *)in+i, plen);
+ i += plen;
+ }
+
+ /* Regardless of installed hooks, the http/1.1 protocol is always
+ * supported by us. Add it to the proposals if the client also
+ * offers it. */
+ proposed_protos = apr_array_make(c->pool, client_protos->nelts+1,
+ sizeof(char *));
+ if (ssl_array_index(client_protos, alpn_http1) >= 0) {
+ APR_ARRAY_PUSH(proposed_protos, const char*) = alpn_http1;
+ }
+
+ if (sslconn->alpn_proposefns != NULL) {
+ /* Invoke our alpn_propos_proto hooks, giving other modules a chance to
+ * propose protocol names for selection. We might have several such
+ * hooks installed and if two make a proposal, we need to give
+ * preference to one.
+ */
+ for (i = 0; i < sslconn->alpn_proposefns->nelts; i++) {
+ ssl_alpn_propose_protos fn =
+ APR_ARRAY_IDX(sslconn->alpn_proposefns, i,
+ ssl_alpn_propose_protos);
+
+ if (fn(c, client_protos, proposed_protos) == DONE)
+ break;
+ }
+ }
+
+ if (proposed_protos->nelts <= 0) {
+ ap_log_cerror(APLOG_MARK, APLOG_ERR, 0, c, APLOGNO(02839)
+ "none of the client alpn protocols are supported");
+ 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(mctx, (const char *)*out, proto) < 0) {
+ *out = (const unsigned char*)proto;
+ }
+ }
+
+ size_t len = strlen((const char*)*out);
+ if (len > 255) {
+ ap_log_cerror(APLOG_MARK, APLOG_ERR, 0, c, APLOGNO(02840)
+ "alpn negotiated protocol name too long");
+ return SSL_TLSEXT_ERR_ALERT_FATAL;
+ }
+ *outlen = (unsigned char)len;
+
+ return SSL_TLSEXT_ERR_OK;
+}
+#endif /* HAVE_TLS_ALPN */
+
#ifdef HAVE_SRP
int ssl_callback_SRPServerParams(SSL *ssl, int *ad, void *arg)
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