Changed behaviour of spdylay_select_next_protocol()

We use following algorithm to select protocol:

 1. If server's list contains "spdy/2", this function selects
    "spdy/2" and returns 1. The following steps are not taken.

 2. If server's list contains "http/1.1", this function selects
    "http/1.1" and returns 0. The following step is not taken.

 3. This function selects "spdy/2" and returns -1. (So called
    non-overlap case).

lib/includes/spdylay/spdylay.h

@@ -461,10 +461,35 @@ int spdylay_submit_ping(spdylay_session *session);
 int spdylay_submit_goaway(spdylay_session *session);
 
 /*
- * A helper function for dealing with NPN.  This function always
- * selects "spdy/2" protocol.  NPN draft permits that client can
- * select any protocol even if server does not advertise it at the
- * time of this writing:
+ * A helper function for dealing with NPN in client side.
+ * |in| contains server's protocol in preferable order.
+ * The format of |in| is length-prefixed and not null-terminated.
+ * For example, "spdy/2" are "http/1.1" stored in |in| like this:
+ *
+ *  in[0] = 6
+ *  in[1..6] = "spdy/2"
+ *  in[7] = 8
+ *  in[8..15] = "http/1.1"
+ *  inlen = 16
+ *
+ * The selection algorithm is as follows:
+ *
+ * 1. If server's list contains "spdy/2", this function selects
+ *    "spdy/2" and returns 1. The following steps are not taken.
+ *
+ * 2. If server's list contains "http/1.1", this function selects
+ *    "http/1.1" and returns 0. The following step is not taken.
+ *
+ * 3. This function selects "spdy/2" and returns -1. (So called
+ *    non-overlap case).
+ *
+ * When spdylay supports updated version of SPDY in the future, this
+ * function may select updated protocol and application code which
+ * relies on spdylay for SPDY stuff needs not be modified.
+ *
+ * For rationale of step 3, NPN draft permits that client can select
+ * any protocol even if server does not advertise it at the time of
+ * this writing:
  *
  *   It's expected that a client will have a list of protocols that it
  *   supports, in preference order, and will only select a protocol if
@@ -481,9 +506,6 @@ int spdylay_submit_goaway(spdylay_session *session);
  * Selecting "spdy/2" means that "spdy/2" is written into |*out| and
  * length of "spdy/2" (which is 6) is assigned to |*outlen|.
  *
- * This function returns 0 if server advertised "spdy/2" and it is
- * selected, or -1.
- *
  * To use this method you should do something like:
  *
  * static int select_next_proto_cb(SSL* ssl,
@@ -491,7 +513,7 @@ int spdylay_submit_goaway(spdylay_session *session);
  *                                 const unsigned char *in, unsigned int inlen,
  *                                 void *arg)
  * {
- *   if (spdylay_select_next_protocol(out, outlen, in, inlen) == 0) {
+ *   if (spdylay_select_next_protocol(out, outlen, in, inlen) == 1) {
  *     ((MyType*)arg)->spdy = 1;
  *   }
  *   return SSL_TLSEXT_ERR_OK;

lib/spdylay_npn.c

@@ -29,13 +29,27 @@
 int spdylay_select_next_protocol(unsigned char **out, unsigned char *outlen,
                                  const unsigned char *in, unsigned int inlen)
 {
+  int http_selected = 0;
   unsigned int i = 0;
+  /* For non-overlap case */
   *out = (unsigned char*)"spdy/2";
   *outlen = 6;
   for(; i < inlen; i += in[i]+1) {
     if(in[i] == 6 && memcmp(&in[i+1], "spdy/2", in[i]) == 0) {
+      *out = &in[i+1];
+      *outlen = in[i];
+      return 1;
+    } else if(in[i] == 8 && memcmp(&in[i+1], "http/1.1", in[i]) == 0) {
+      http_selected = 1;
+      *out = &in[i+1];
+      *outlen = in[i];
+      /* Go through to the next iteration, because "spdy/2" may be
+         there */
+    }
+  }
+  if(http_selected) {
     return 0;
-    }
-  }
+  } else {
     return -1;
+  }
 }

tests/spdylay_npn_test.c

@@ -30,19 +30,34 @@
 static void spdy2()
 {
   const unsigned char spdy[] = {
-    8, 'h', 't', 't', 'p', '/', '1', '.', '0',
+    8, 'h', 't', 't', 'p', '/', '1', '.', '1',
     6, 's', 'p', 'd', 'y', '/', '2',
     6, 's', 'p', 'd', 'y', '/', '3'
   };
   unsigned char outlen;
   unsigned char* out;
-  CU_ASSERT(0 == spdylay_select_next_protocol(&out, &outlen,
+  CU_ASSERT(1 == spdylay_select_next_protocol(&out, &outlen,
                                               spdy, sizeof(spdy)));
   CU_ASSERT(6 == outlen);
   CU_ASSERT(memcmp("spdy/2", out, outlen) == 0);
 }
 
-static void spdy4()
+static void http11()
+{
+  const unsigned char spdy[] = {
+    6, 's', 'p', 'd', 'y', '/', '4',
+    8, 's', 'p', 'd', 'y', '/', '2', '.', '1',
+    8, 'h', 't', 't', 'p', '/', '1', '.', '1',
+  };
+  unsigned char outlen;
+  unsigned char* out;
+  CU_ASSERT(0 == spdylay_select_next_protocol(&out, &outlen,
+                                              spdy, sizeof(spdy)));
+  CU_ASSERT(8 == outlen);
+  CU_ASSERT(memcmp("http/1.1", out, outlen) == 0);
+}
+
+static void no_overlap()
 {
   const unsigned char spdy[] = {
     6, 's', 'p', 'd', 'y', '/', '4',
@@ -60,5 +75,6 @@ static void spdy4()
 void test_spdylay_npn()
 {
   spdy2();
-  spdy4();
+  http11();
+  no_overlap();
 }