Move InstawebHandler initialization after validity checks.

Creating an instaweb handler will run MakeRequestUrl, which assumes that
request->unparsed_uri is non-null.  So move the creation to after where
we check that it's non-null.  To be safe, move it all the way down to
where it's first needed, in case some other validity checks end up being
relevant.

Fixes #1248

net/instaweb/apache/instaweb_context.cc

@@ -370,6 +370,12 @@ const char* InstawebContext::MakeRequestUrl(
     // as an absolute URL. So we check if request->unparsed_uri is already
     // an absolute URL first. If so, use it as-is, otherwise ap_construct_url().
     if (url == NULL) {
+      if (request->unparsed_uri == NULL) {
+        LOG(DFATAL) <<
+            "build_context_for_request should verify unparsed_uri is non-null.";
+        return NULL;
+      }
+
       GoogleUrl gurl(request->unparsed_uri);
       if (gurl.IsAnyValid()) {
         url = apr_pstrdup(request->pool, request->unparsed_uri);

net/instaweb/apache/mod_instaweb.cc

@@ -371,10 +371,6 @@ InstawebContext* build_context_for_request(request_rec* request) {
     return NULL;
   }
 
-  InstawebHandler instaweb_handler(request);
-  const RewriteOptions* options = instaweb_handler.options();
-  instaweb_handler.SetupSpdyConnectionIfNeeded();
-
   if (request->unparsed_uri == NULL) {
     // TODO(jmarantz): consider adding Debug message if unparsed_uri is NULL,
     // possibly of request->the_request which was non-null in the case where
@@ -439,6 +435,10 @@ InstawebContext* build_context_for_request(request_rec* request) {
     return NULL;
   }
 
+  InstawebHandler instaweb_handler(request);
+  const RewriteOptions* options = instaweb_handler.options();
+  instaweb_handler.SetupSpdyConnectionIfNeeded();
+
   const GoogleUrl& stripped_gurl = instaweb_handler.stripped_gurl();
   if (!stripped_gurl.IsWebValid()) {
     ap_log_rerror(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, request,

net/instaweb/apache/system_test.sh

@@ -2672,6 +2672,11 @@ start_test Base config has purging disabled.  Check error message syntax.
 OUT=$($WGET_DUMP "$HOSTNAME/pagespeed_admin/cache?purge=*")
 check_from "$OUT" fgrep -q "ModPagespeedEnableCachePurge on"
 
+start_test long url handling
+# This is an extremely long url, enough that it should give a 4xx server error.
+OUT=$($CURL -sS -D- "$TEST_ROOT/$(head -c 10000 < /dev/zero | tr '\0' 'a')")
+check_from "$OUT" grep -q "414 Request-URI Too Large"
+
 # Cleanup
 rm -rf $OUTDIR