Followup to r1670397+r1670434: even more ALPN goodness.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1670436 13f79535-47bb-0310-9956-ffa450edef68

modules/ssl/ssl_engine_kernel.c

@@ -2397,6 +2397,151 @@ int ssl_callback_AdvertiseNextProtos(SSL *ssl, const unsigned char **data_out,
 
 #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)