ext_proc: avoid copies introduced by auto assignment (#44657)

Commit Message: auto is great, not so much when it creates unnecessary
copies
Additional Description: part of issue
#44795
Risk Level: LOW
Testing:
Docs Changes:
Release Notes:
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional [API
Considerations](https://github.com/envoyproxy/envoy/blob/main/api/review_checklist.md):]

---------

Signed-off-by: Xin Zhuang <stevenzzz@google.com>

Author: stevenzzzz

source/extensions/filters/http/ext_proc/config.cc

@@ -88,7 +88,7 @@ ExternalProcessingFilterConfig::createFilterFactoryFromProtoTyped(
       PROTOBUF_GET_MS_OR_DEFAULT(proto_config, message_timeout, DefaultMessageTimeoutMs);
   const uint32_t max_message_timeout_ms =
       PROTOBUF_GET_MS_OR_DEFAULT(proto_config, max_message_timeout, DefaultMaxMessageTimeoutMs);
-  const auto filter_config = std::make_shared<FilterConfig>(
+  auto filter_config = std::make_shared<FilterConfig>(
       proto_config, std::chrono::milliseconds(message_timeout_ms), max_message_timeout_ms,
       dual_info.scope, stats_prefix, dual_info.is_upstream,
       Envoy::Extensions::Filters::Common::Expr::getBuilder(context), context);
@@ -140,7 +140,7 @@ ExternalProcessingFilterConfig::createFilterFactoryFromProtoWithServerContextTyp
       PROTOBUF_GET_MS_OR_DEFAULT(proto_config, message_timeout, DefaultMessageTimeoutMs);
   const uint32_t max_message_timeout_ms =
       PROTOBUF_GET_MS_OR_DEFAULT(proto_config, max_message_timeout, DefaultMaxMessageTimeoutMs);
-  const auto filter_config = std::make_shared<FilterConfig>(
+  auto filter_config = std::make_shared<FilterConfig>(
       proto_config, std::chrono::milliseconds(message_timeout_ms), max_message_timeout_ms,
       server_context.scope(), stats_prefix, false,
       Envoy::Extensions::Filters::Common::Expr::getBuilder(server_context), server_context);

source/extensions/filters/http/ext_proc/ext_proc.cc

@@ -718,7 +718,7 @@ void Filter::sendRequest(const ProcessorState& state, ProcessingRequest&& req, b
 
 void Filter::onComplete(ProcessingResponse& response) {
   ENVOY_STREAM_LOG(debug, "Received successful response from server", *decoder_callbacks_);
-  std::unique_ptr<ProcessingResponse> resp_ptr = std::make_unique<ProcessingResponse>(response);
+  auto resp_ptr = std::make_unique<ProcessingResponse>(response);
   onReceiveMessage(std::move(resp_ptr));
 }
 
@@ -1538,7 +1538,7 @@ void Filter::addDynamicMetadata(const ProcessorState& state, ProcessingRequest&
   envoy::config::core::v3::Metadata forwarding_metadata;
 
   // Forward cluster metadata if so configured.
-  const auto cluster_info = cb->streamInfo().upstreamClusterInfo();
+  const auto& cluster_info = cb->streamInfo().upstreamClusterInfo();
   if (cluster_info) {
     const auto& cluster_metadata = cluster_info->metadata().filter_metadata();
     for (const auto& context_key : state.untypedClusterMetadataForwardingNamespaces()) {
@@ -1599,7 +1599,7 @@ void Filter::addDynamicMetadata(const ProcessorState& state, ProcessingRequest&
     }
   }
 
-  *req.mutable_metadata_context() = forwarding_metadata;
+  *req.mutable_metadata_context() = std::move(forwarding_metadata);
 }
 
 void Filter::addAttributes(ProcessorState& state, ProcessingRequest& req) {
@@ -1615,7 +1615,7 @@ void Filter::addAttributes(ProcessorState& state, ProcessingRequest& req) {
   auto attributes = state.evaluateAttributes(config_->expressionManager(), *activation_ptr);
 
   state.setSentAttributes(true);
-  (*req.mutable_attributes())[FilterName] = attributes;
+  (*req.mutable_attributes())[FilterName] = std::move(attributes);
 }
 
 void Filter::setDynamicMetadata(Http::StreamFilterCallbacks* cb, const ProcessorState& state,
@@ -1630,8 +1630,8 @@ void Filter::setDynamicMetadata(Http::StreamFilterCallbacks* cb, const Processor
     return;
   }
 
-  auto response_metadata = response.dynamic_metadata().fields();
-  auto receiving_namespaces = state.untypedReceivingMetadataNamespaces();
+  const auto& response_metadata = response.dynamic_metadata().fields();
+  const auto& receiving_namespaces = state.untypedReceivingMetadataNamespaces();
   for (const auto& context_key : response_metadata) {
     bool found_allowed_namespace = false;
     if (auto metadata_it =

source/extensions/filters/http/ext_proc/http_client/http_client_impl.cc

@@ -46,7 +46,8 @@ void ExtProcHttpClient::sendRequest(envoy::service::ext_proc::v3::ProcessingRequ
   // Transcode req message into JSON string.
   auto req_in_json = MessageUtil::getJsonStringFromMessage(req);
   if (req_in_json.ok()) {
-    const auto http_uri = config_.http_service().http_service().http_uri();
+    const envoy::config::core::v3::HttpUri& http_uri =
+        config_.http_service().http_service().http_uri();
     Http::RequestHeaderMapPtr headers = buildHttpRequestHeaders(http_uri.uri(), stream_id);
     headers_applicator_->apply(*headers);
 
@@ -76,12 +77,14 @@ void ExtProcHttpClient::onSuccess(const Http::AsyncClient::Request&,
   if (status.has_value()) {
     uint64_t status_code = status.value();
     if (status_code == Envoy::enumToInt(Envoy::Http::Code::OK)) {
-      std::string msg_body = response->body().toString();
-      ENVOY_LOG(debug, "Response status is OK, message body length {}", msg_body.size());
+      const size_t body_len = response->body().length();
       envoy::service::ext_proc::v3::ProcessingResponse response_msg;
-      if (!msg_body.empty()) {
+      if (body_len > 0) {
+        const absl::string_view msg_body(
+            static_cast<const char*>(response->body().linearize(body_len)), body_len);
         bool has_unknown_field;
-        auto status = MessageUtil::loadFromJsonNoThrow(msg_body, response_msg, has_unknown_field);
+        const absl::Status& status =
+            MessageUtil::loadFromJsonNoThrow(msg_body, response_msg, has_unknown_field);
         if (!status.ok()) {
           ENVOY_LOG(
               error,

source/extensions/filters/http/ext_proc/matching_utils.cc

@@ -19,7 +19,8 @@ ExpressionManager::initExpressions(const Protobuf::RepeatedPtrField<std::string>
     if (expressions.contains(matcher)) {
       continue;
     }
-    auto parse_status = google::api::expr::parser::Parse(matcher);
+    const absl::StatusOr<cel::expr::ParsedExpr> parse_status =
+        google::api::expr::parser::Parse(matcher);
     if (!parse_status.ok()) {
       throw EnvoyException("Unable to parse descriptor expression: " +
                            parse_status.status().ToString());
@@ -55,7 +56,8 @@ ExpressionManager::evaluateAttributes(const Filters::Common::Expr::Activation& a
 
   for (const auto& hash_entry : expr) {
     Protobuf::Arena arena;
-    const auto result = hash_entry.second.evaluate(activation, &arena);
+    const absl::StatusOr<google::api::expr::runtime::CelValue>& result =
+        hash_entry.second.evaluate(activation, &arena);
     if (!result.ok()) {
       // TODO: Stats?
       continue;

source/extensions/filters/http/ext_proc/mutation_utils.cc

@@ -76,8 +76,8 @@ void MutationUtils::headersToProto(
                       &disallowed_headers](const Http::HeaderEntry& e) -> Http::HeaderMap::Iterate {
     if (headerCanBeForwarded(e.key().getStringView(), allowed_headers, disallowed_headers)) {
       auto* new_header = proto_out.add_headers();
-      new_header->set_key(std::string(e.key().getStringView()));
-      new_header->set_raw_value(std::string(e.value().getStringView()));
+      new_header->set_key(e.key().getStringView());
+      new_header->set_raw_value(e.value().getStringView());
     }
     return Http::HeaderMap::Iterate::Continue;
   });