Revert 3c573272

It may violate draft-09 section 8.1.3.1. Proxy should perseve
host header field.

src/http2.cc

@@ -160,7 +160,6 @@ namespace {
 const char *IGN_HD[] = {
   "connection",
   "expect",
-  "host",
   "http2-settings",
   "keep-alive",
   "proxy-connection",

src/shrpx_http2_downstream_connection.cc

@@ -267,15 +267,11 @@ int Http2DownstreamConnection::push_request_headers()
       nva.push_back(http2::make_nv_ls
                     (":authority",
                      downstream_->get_request_http2_authority()));
-    } else {
-      auto host = downstream_->get_norm_request_header("host");
-      if(host == end_headers) {
-        if(LOG_ENABLED(INFO)) {
-          DCLOG(INFO, this) << "host header field missing";
-        }
-        return -1;
+    } else if(downstream_->get_norm_request_header("host") == end_headers) {
+      if(LOG_ENABLED(INFO)) {
+        DCLOG(INFO, this) << "host header field missing";
       }
-      nva.push_back(http2::make_nv_ls("host", (*host).second));
+      return -1;
     }
   } else {
     // The upstream is HTTP/1
@@ -322,15 +318,11 @@ int Http2DownstreamConnection::push_request_headers()
         authority += util::utos(u.port);
       }
       nva.push_back(http2::make_nv_ls(":authority", authority));
-    } else {
-      auto host = downstream_->get_norm_request_header("host");
-      if(host == end_headers) {
-        if(LOG_ENABLED(INFO)) {
-          DCLOG(INFO, this) << "host header field missing";
-        }
-        return -1;
+    } else if(downstream_->get_norm_request_header("host") == end_headers) {
+      if(LOG_ENABLED(INFO)) {
+        DCLOG(INFO, this) << "host header field missing";
       }
-      nva.push_back(http2::make_nv_ls("host", (*host).second));
+      return -1;
     }
   }