Changed spdylay_select_next_protocol behaviour

It now always select "spdy/2" as a next protocol regardless whether or not
the server advertises it. The NPN draft allows this.
Returning integer version number is not flexible because the selected protcol
is just a string.
The function now returns 0 if the server advertised spdy/2, or -1.

examples/spdylay_ssl.cc

@@ -360,8 +360,7 @@ int select_next_proto_cb(SSL* ssl,
     }
   }
   if(spdylay_select_next_protocol(out, outlen, in, inlen) == -1) {
-    std::cerr << "Invalid protocol: "
-              << std::string((const char*)*out, (size_t)*outlen) << std::endl;
+    std::cerr << "Server did not advertise spdy/2 protocol." << std::endl;
     abort();
   }
   if(ssl_debug) {

lib/includes/spdylay/spdylay.h

@@ -435,16 +435,37 @@ int spdylay_submit_ping(spdylay_session *session);
 int spdylay_submit_goaway(spdylay_session *session);
 
 /*
- * A helper function for dealing with NPN. This function returns the
- * version of spdy that was negotiated, or -1. To use this method you
- * should do something like:
+ * 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:
+ *
+ *   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
+ *   the server supports it. In that case, the client SHOULD select
+ *   the first protocol advertised by the server that it also
+ *   supports. In the event that the client doesn't support any of
+ *   server's protocols, or the server doesn't advertise any, it
+ *   SHOULD select the first protocol that it supports.
+ *
+ *   There are cases where the client knows that a server supports an
+ *   unadvertised protocol. In these cases the client should simply
+ *   select that protocol.
+ *
+ * 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,
  *                                 unsigned char **out, unsigned char *outlen,
  *                                 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) == 0) {
  *     ((MyType*)arg)->spdy = 1;
  *   }
  *   return SSL_TLSEXT_ERR_OK;

lib/spdylay_npn.c

@@ -30,12 +30,11 @@ int spdylay_select_next_protocol(unsigned char **out, unsigned char *outlen,
                                  const unsigned char *in, unsigned int inlen)
 {
   unsigned int i = 0;
+  *out = (unsigned char*)"spdy/2";
+  *outlen = 6;
   for(; i < inlen; i += in[i]+1) {
-    /* Always assign to *out so that the last one is picked. */
-    *out = (unsigned char*)in+i+1;
-    *outlen = in[i];
     if(in[i] == 6 && memcmp(&in[i+1], "spdy/2", in[i]) == 0) {
-      return 2;
+      return 0;
     }
   }
   return -1;

tests/spdylay_npn_test.c

@@ -36,10 +36,10 @@ static void spdy2()
   };
   unsigned char outlen;
   unsigned char* out;
-  CU_ASSERT(2 == spdylay_select_next_protocol(&out, &outlen,
+  CU_ASSERT(0 == spdylay_select_next_protocol(&out, &outlen,
                                               spdy, sizeof(spdy)));
   CU_ASSERT(6 == outlen);
-  CU_ASSERT(memcmp("spdy/2", out, 6) == 0);
+  CU_ASSERT(memcmp("spdy/2", out, outlen) == 0);
 }
 
 static void spdy4()
@@ -53,8 +53,8 @@ static void spdy4()
   unsigned char* out;
   CU_ASSERT(-1 == spdylay_select_next_protocol(&out, &outlen,
                                                spdy, sizeof(spdy)));
-  CU_ASSERT(8 == outlen);
-  CU_ASSERT(memcmp("http/1.0", out, outlen) == 0);
+  CU_ASSERT(6 == outlen);
+  CU_ASSERT(memcmp("spdy/2", out, outlen) == 0);
 }
 
 void test_spdylay_npn()