NPN/ALPN: allow disabling via command line

when using --http2 one can now selectively disable NPN or ALPN with
--no-alpn and --no-npn. for now honored with NSS only.

TODO: honor this option with GnuTLS and OpenSSL

docs/curl.1

@@ -133,6 +133,18 @@ version. (Added in 7.33.0)
 .IP "--http2"
 (HTTP) Tells curl to issue its requests using HTTP 2. This requires that the
 underlying libcurl was built to support it. (Added in 7.33.0)
+.IP "--no-npn"
+Disable the NPN TLS extension. NPN is enabled by default if libcurl was built
+with an SSL library that supports NPN. NPN is used by a libcurl that supports
+HTTP 2 to negoatiate HTTP 2 support with the server during https sessions.
+
+(Added in 7.36.0)
+.IP "--no-alpn"
+Disable the ALPN TLS extension. ALPN is enabled by default if libcurl was built
+with an SSL library that supports ALPN. ALPN is used by a libcurl that supports
+HTTP 2 to negoatiate HTTP 2 support with the server during https sessions.
+
+(Added in 7.36.0)
 .IP "-1, --tlsv1"
 (SSL)
 Forces curl to use TLS version 1 when negotiating with a remote TLS server.

docs/libcurl/symbols-in-versions

@@ -495,6 +495,8 @@ CURLOPT_SSLKEY                  7.9.3
 CURLOPT_SSLKEYPASSWD            7.9.3         7.17.0
 CURLOPT_SSLKEYTYPE              7.9.3
 CURLOPT_SSLVERSION              7.1
+CURLOPT_SSL_ENABLE_ALPN         7.36.0
+CURLOPT_SSL_ENABLE_NPN          7.36.0
 CURLOPT_SSL_CIPHER_LIST         7.9
 CURLOPT_SSL_CTX_DATA            7.10.6
 CURLOPT_SSL_CTX_FUNCTION        7.10.6

include/curl/curl.h

@@ -1571,6 +1571,12 @@ typedef enum {
   /* Set authentication options directly */
   CINIT(LOGIN_OPTIONS, OBJECTPOINT, 224),
 
+  /* Enable/disable TLS NPN extension (http2 over ssl might fail without) */
+  CINIT(SSL_ENABLE_NPN, LONG, 225),
+
+  /* Enable/disable TLS ALPN extension (http2 over ssl might fail without) */
+  CINIT(SSL_ENABLE_ALPN, LONG, 226),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 

lib/url.c

@@ -563,6 +563,8 @@ CURLcode Curl_init_userdefined(struct UserDefined *set)
   set->tcp_keepintvl = 60;
   set->tcp_keepidle = 60;
 
+  set->ssl_enable_npn = TRUE;
+  set->ssl_enable_alpn = TRUE;
   return res;
 }
 
@@ -2478,6 +2480,12 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
   case CURLOPT_TCP_KEEPINTVL:
     data->set.tcp_keepintvl = va_arg(param, long);
     break;
+  case CURLOPT_SSL_ENABLE_NPN:
+    data->set.ssl_enable_npn = (0 != va_arg(param, long))?TRUE:FALSE;
+    break;
+  case CURLOPT_SSL_ENABLE_ALPN:
+    data->set.ssl_enable_alpn = (0 != va_arg(param, long))?TRUE:FALSE;
+    break;
 
   default:
     /* unknown tag and its companion, just ignore: */

lib/urldata.h

@@ -1593,6 +1593,9 @@ struct UserDefined {
   long tcp_keepintvl;    /* seconds between TCP keepalive probes */
 
   size_t maxconnects;  /* Max idle connections in the connection cache */
+
+  bool ssl_enable_npn;  /* TLS NPN extension? */
+  bool ssl_enable_alpn; /* TLS ALPN extension? */
 };
 
 struct Names {

lib/vtls/nss.c

@@ -616,15 +616,16 @@ static void HandshakeCallback(PRFileDesc *sock, void *arg)
 {
   struct connectdata *conn = (struct connectdata*) arg;
 
-#ifndef USE_NGHTTP2
-  (void)sock;
-  (void)conn;
-#else
+#ifdef USE_NGHTTP2
   unsigned int buflenmax = 50;
   unsigned char buf[50];
   unsigned int buflen;
   SSLNextProtoState state;
 
+  if(!conn->data->set.ssl_enable_npn && !conn->data->set.ssl_enable_alpn) {
+    return;
+  }
+
   if(SSL_GetNextProto(sock, &state, buf, &buflen, buflenmax) == SECSuccess) {
 
     switch(state) {
@@ -1311,6 +1312,7 @@ CURLcode Curl_nss_connect(struct connectdata *conn, int sockindex)
 #endif
 #endif
 
+
   if(connssl->state == ssl_connection_complete)
     return CURLE_OK;
 
@@ -1485,32 +1487,45 @@ CURLcode Curl_nss_connect(struct connectdata *conn, int sockindex)
   }
 
 #ifdef USE_NGHTTP2
+  if(data->set.httpversion == CURL_HTTP_VERSION_2_0) {
 #ifdef SSL_ENABLE_NPN
-  if(SSL_OptionSet(connssl->handle, SSL_ENABLE_NPN, PR_TRUE) != SECSuccess)
-    goto error;
+    if(data->set.ssl_enable_npn) {
+      if(SSL_OptionSet(connssl->handle, SSL_ENABLE_NPN, PR_TRUE) != SECSuccess)
+        goto error;
+    }
 #endif
 
 #ifdef SSL_ENABLE_ALPN
-  if(SSL_OptionSet(connssl->handle, SSL_ENABLE_ALPN, PR_TRUE) != SECSuccess)
-    goto error;
+    if(data->set.ssl_enable_alpn) {
+      if(SSL_OptionSet(connssl->handle, SSL_ENABLE_ALPN, PR_TRUE)
+          != SECSuccess)
+        goto error;
+    }
 #endif
 
 #if defined(SSL_ENABLE_NPN) || defined(SSL_ENABLE_ALPN)
-  alpn_protos[cur] = NGHTTP2_PROTO_VERSION_ID_LEN;
-  cur++;
-  memcpy(&alpn_protos[cur], NGHTTP2_PROTO_VERSION_ID,
-      NGHTTP2_PROTO_VERSION_ID_LEN);
-  cur += NGHTTP2_PROTO_VERSION_ID_LEN;
-  alpn_protos[cur] = ALPN_HTTP_1_1_LENGTH;
-  cur++;
-  memcpy(&alpn_protos[cur], ALPN_HTTP_1_1, ALPN_HTTP_1_1_LENGTH);
+    if(data->set.ssl_enable_npn || data->set.ssl_enable_alpn) {
+      alpn_protos[cur] = NGHTTP2_PROTO_VERSION_ID_LEN;
+      cur++;
+      memcpy(&alpn_protos[cur], NGHTTP2_PROTO_VERSION_ID,
+          NGHTTP2_PROTO_VERSION_ID_LEN);
+      cur += NGHTTP2_PROTO_VERSION_ID_LEN;
+      alpn_protos[cur] = ALPN_HTTP_1_1_LENGTH;
+      cur++;
+      memcpy(&alpn_protos[cur], ALPN_HTTP_1_1, ALPN_HTTP_1_1_LENGTH);
 
-  if(SSL_SetNextProtoNego(connssl->handle, alpn_protos, alpn_protos_len)
-      != SECSuccess)
-    goto error;
+      if(SSL_SetNextProtoNego(connssl->handle, alpn_protos, alpn_protos_len)
+          != SECSuccess)
+        goto error;
+    }
+    else {
+      infof(data, "SSL, can't negotiate HTTP/2.0 with neither NPN nor ALPN\n");
+    }
 #endif
+  }
 #endif
 
+
   /* Force handshake on next I/O */
   SSL_ResetHandshake(connssl->handle, /* asServer */ PR_FALSE);
 

src/tool_cfgable.h

@@ -214,6 +214,8 @@ struct Configurable {
   bool test_event_based;
 #endif
   char *xoauth2_bearer;       /* XOAUTH2 bearer token */
+  bool nonpn;                 /* enable/disable TLS NPN extension */
+  bool noalpn;                /* enable/disable TLS ALPN extension */
 
   struct Configurable* prev;
   struct Configurable* next;  /* Always last in the struct */

src/tool_getparam.c

@@ -90,7 +90,9 @@ static const struct LongShort aliases[]= {
 #endif
   {"*F", "dns-servers",              TRUE},
   {"*g", "trace",                    TRUE},
+  {"*G", "npn",                      FALSE},
   {"*h", "trace-ascii",              TRUE},
+  {"*H", "alpn",                     FALSE},
   {"*i", "limit-rate",               TRUE},
   {"*j", "compressed",               FALSE},
   {"*J", "tr-encoding",              FALSE},
@@ -554,6 +556,9 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
           warnf(config, "--trace overrides an earlier trace/verbose option\n");
         config->tracetype = TRACE_BIN;
         break;
+      case 'G': /* --npn */
+        config->nonpn = (!toggle)?TRUE:FALSE;
+        break;
       case 'h': /* --trace-ascii */
         GetStr(&config->trace_dump, nextarg);
         if(config->tracetype && (config->tracetype != TRACE_ASCII))
@@ -561,6 +566,9 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
                 "--trace-ascii overrides an earlier trace/verbose option\n");
         config->tracetype = TRACE_ASCII;
         break;
+      case 'H': /* --alpn */
+        config->noalpn = (!toggle)?TRUE:FALSE;
+        break;
       case 'i': /* --limit-rate */
       {
         /* We support G, M, K too */

src/tool_help.c

@@ -105,6 +105,8 @@ static const char *const helptext[] = {
   " -0, --http1.0       Use HTTP 1.0 (H)",
   "     --http1.1       Use HTTP 1.1 (H)",
   "     --http2         Use HTTP 2 (H)",
+  "     --no-npn        Disable the NPN TLS extension",
+  "     --no-alpn       Disable the ALPN TLS extension",
   "     --ignore-content-length  Ignore the HTTP Content-Length header",
   " -i, --include       Include protocol headers in the output (H/F)",
   " -k, --insecure      Allow connections to SSL sites without certs (H)",

src/tool_operate.c

@@ -1350,6 +1350,14 @@ static int operate_do(struct Configurable *config)
         if(config->sasl_ir)
           my_setopt(curl, CURLOPT_SASL_IR, 1L);
 
+        if(config->nonpn) {
+          my_setopt(curl, CURLOPT_SSL_ENABLE_NPN, 0L);
+        }
+
+        if(config->noalpn) {
+          my_setopt(curl, CURLOPT_SSL_ENABLE_ALPN, 0L);
+        }
+
         /* initialize retry vars for loop below */
         retry_sleep_default = (config->retry_delay) ?
           config->retry_delay*1000L : RETRY_SLEEP_DEFAULT; /* ms */

src/tool_setopt.c

@@ -145,6 +145,8 @@ const NameValue setopt_nv_CURLPROTO[] = {
 static const NameValue setopt_nv_CURLNONZERODEFAULTS[] = {
   NV1(CURLOPT_SSL_VERIFYPEER, 1),
   NV1(CURLOPT_SSL_VERIFYHOST, 1),
+  NV1(CURLOPT_SSL_ENABLE_NPN, 1),
+  NV1(CURLOPT_SSL_ENABLE_ALPN, 1),
   NVEND
 };