nghttpx: Don't apply max_header_fields and header_field_buffer limit to response

We modeled max_header_fields and header_field_buffer limit from Apache
configuration directives.  In Apache, they are only applied to request
header fields, while we applied both request and response.  Since
nghttpx is used as reverse proxy and backend server is relatively
"trusted", this commit removes the application to response header
fields.

src/shrpx.cc

@@ -1610,14 +1610,15 @@ HTTP:
               used several  times to  specify multiple  header fields.
               Example: --add-response-header="foo: bar"
   --header-field-buffer=<SIZE>
-              Set maximum  buffer size for incoming  HTTP header field
+              Set maximum buffer size for incoming HTTP request header
-              list.   This is  the sum  of  header name  and value  in
+              field list.  This is the sum of header name and value in
               bytes.
               Default: )"
       << util::utos_with_unit(get_config()->header_field_buffer) << R"(
   --max-header-fields=<N>
-              Set maximum number of incoming HTTP header fields, which
+              Set  maximum  number  of incoming  HTTP  request  header
-              appear in one request or response header field list.
+              fields, which  appear in one request  or response header
+              field list.
               Default: )" << get_config()->max_header_fields << R"(
 
 Debug:

src/shrpx_http2_session.cc

@@ -757,26 +757,6 @@ int on_header_callback(nghttp2_session *session, const nghttp2_frame *frame,
     auto trailer = frame->headers.cat == NGHTTP2_HCAT_HEADERS &&
                    !downstream->get_expect_final_response();
 
-    if (downstream->get_response_headers_sum() + namelen + valuelen >
-            get_config()->header_field_buffer ||
-        downstream->get_response_headers().size() >=
-            get_config()->max_header_fields) {
-      if (LOG_ENABLED(INFO)) {
-        DLOG(INFO, downstream)
-            << "Too large or many header field size="
-            << downstream->get_response_headers_sum() + namelen + valuelen
-            << ", num=" << downstream->get_response_headers().size() + 1;
-      }
-
-      if (trailer) {
-        // we don't care trailer part exceeds header size limit; just
-        // discard it.
-        return 0;
-      }
-
-      return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
-    }
-
     if (trailer) {
       // just store header fields for trailer part
       downstream->add_response_trailer(name, namelen, value, valuelen,
@@ -803,21 +783,6 @@ int on_header_callback(nghttp2_session *session, const nghttp2_frame *frame,
 
     assert(promised_downstream);
 
-    if (promised_downstream->get_request_headers_sum() + namelen + valuelen >
-            get_config()->header_field_buffer ||
-        promised_downstream->get_request_headers().size() >=
-            get_config()->max_header_fields) {
-      if (LOG_ENABLED(INFO)) {
-        DLOG(INFO, promised_downstream)
-            << "Too large or many header field size="
-            << promised_downstream->get_request_headers_sum() + namelen +
-                   valuelen << ", num="
-            << promised_downstream->get_request_headers().size() + 1;
-      }
-
-      return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
-    }
-
     auto token = http2::lookup_token(name, namelen);
     promised_downstream->add_request_header(name, namelen, value, valuelen,
                                             flags & NGHTTP2_NV_FLAG_NO_INDEX,

src/shrpx_http_downstream_connection.cc

@@ -562,29 +562,10 @@ int htp_hdrs_completecb(http_parser *htp) {
 namespace {
 int htp_hdr_keycb(http_parser *htp, const char *data, size_t len) {
   auto downstream = static_cast<Downstream *>(htp->data);
-
-  if (downstream->get_response_headers_sum() + len >
-      get_config()->header_field_buffer) {
-    if (LOG_ENABLED(INFO)) {
-      DLOG(INFO, downstream) << "Too large header block size="
-                             << downstream->get_response_headers_sum() + len;
-    }
-    return -1;
-  }
-
   if (downstream->get_response_state() == Downstream::INITIAL) {
     if (downstream->get_response_header_key_prev()) {
       downstream->append_last_response_header_key(data, len);
     } else {
-      if (downstream->get_response_headers().size() >=
-          get_config()->max_header_fields) {
-        if (LOG_ENABLED(INFO)) {
-          DLOG(INFO, downstream)
-              << "Too many header field num="
-              << downstream->get_response_headers().size() + 1;
-        }
-        return -1;
-      }
       downstream->add_response_header(std::string(data, len), "");
     }
   } else {
@@ -592,15 +573,6 @@ int htp_hdr_keycb(http_parser *htp, const char *data, size_t len) {
     if (downstream->get_response_trailer_key_prev()) {
       downstream->append_last_response_trailer_key(data, len);
     } else {
-      if (downstream->get_response_headers().size() >=
-          get_config()->max_header_fields) {
-        if (LOG_ENABLED(INFO)) {
-          DLOG(INFO, downstream)
-              << "Too many header field num="
-              << downstream->get_response_headers().size() + 1;
-        }
-        return -1;
-      }
       downstream->add_response_trailer(std::string(data, len), "");
     }
   }
@@ -611,14 +583,6 @@ int htp_hdr_keycb(http_parser *htp, const char *data, size_t len) {
 namespace {
 int htp_hdr_valcb(http_parser *htp, const char *data, size_t len) {
   auto downstream = static_cast<Downstream *>(htp->data);
-  if (downstream->get_response_headers_sum() + len >
-      get_config()->header_field_buffer) {
-    if (LOG_ENABLED(INFO)) {
-      DLOG(INFO, downstream) << "Too large header block size="
-                             << downstream->get_response_headers_sum() + len;
-    }
-    return -1;
-  }
   if (downstream->get_response_state() == Downstream::INITIAL) {
     if (downstream->get_response_header_key_prev()) {
       downstream->set_last_response_header_value(data, len);