make custom inline headers bootstrap configurable

api/envoy/config/bootstrap/v3/bootstrap.proto

@@ -40,7 +40,7 @@ option (udpa.annotations.file_status).package_version_status = ACTIVE;
 // <config_overview_bootstrap>` for more detail.
 
 // Bootstrap :ref:`configuration overview <config_overview_bootstrap>`.
-// [#next-free-field: 32]
+// [#next-free-field: 33]
 message Bootstrap {
   option (udpa.annotations.versioning).previous_message_type =
       "envoy.config.bootstrap.v2.Bootstrap";
@@ -322,6 +322,13 @@ message Bootstrap {
   // field.
   // [#not-implemented-hide:]
   map<string, core.v3.TypedExtensionConfig> certificate_provider_instances = 25;
+
+  // Specifies a set of headers that need to be registered as inline header. This configuration
+  // allows users to customize the inline headers on-demand at Envoy startup without modifying
+  // Envoy's source code.
+  //
+  // Note that the 'set-cookie' header cannot be registered as inline header.
+  repeated CustomInlineHeader inline_headers = 32;
 }
 
 // Administration interface :ref:`operations documentation
@@ -595,3 +602,43 @@ message LayeredRuntime {
   // such that later layers in the list overlay earlier entries.
   repeated RuntimeLayer layers = 1;
 }
+
+// Used to specify the header that needs to be registered as an inline header.
+//
+// If request or response contain multiple headers with the same name and the header
+// name is registered as an inline header. Then multiple headers will be folded
+// into one, and multiple header values will be concatenated by a suitable delimiter.
+// The delimiter is generally a comma.
+//
+// For example, if 'foo' is registered as an inline header, and the headers contains
+// the following two headers:
+//
+// .. code-block:: text
+//
+//   foo: bar
+//   foo: eep
+//
+// Then they will eventually be folded into:
+//
+// .. code-block:: text
+//
+//   foo: bar, eep
+//
+// Inline headers provide O(1) search performance, but each inline header imposes
+// an additional memory overhead on all instances of the corresponding type of
+// HeaderMap or TrailerMap.
+message CustomInlineHeader {
+  enum InlineHeaderType {
+    REQUEST_HEADER = 0;
+    REQUEST_TRAILER = 1;
+    RESPONSE_HEADER = 2;
+    RESPONSE_TRAILER = 3;
+  }
+
+  // The name of the header that is expected to be set as the inline header.
+  string inline_header_name = 1
+      [(validate.rules).string = {min_len: 1 well_known_regex: HTTP_HEADER_NAME strict: false}];
+
+  // The type of the header that is expected to be set as the inline header.
+  InlineHeaderType inline_header_type = 2 [(validate.rules).enum = {defined_only: true}];
+}

docs/root/version_history/current.rst

@@ -28,6 +28,7 @@ Removed Config or Runtime
 
 New Features
 ------------
+* bootstrap: added :ref:`inline_headers <envoy_v3_api_field_config.bootstrap.v3.Bootstrap.inline_headers>` in the bootstrap to make custom inline headers bootstrap configurable.
 * http: added :ref:`string_match <envoy_v3_api_field_config.route.v3.HeaderMatcher.string_match>` in the header matcher.
 
 Deprecated

source/server/BUILD

@@ -515,6 +515,7 @@ envoy_cc_library(
         "//source/common/grpc:context_lib",
         "//source/common/http:codes_lib",
         "//source/common/http:context_lib",
+        "//source/common/http:headers_lib",
         "//source/common/init:manager_lib",
         "//source/common/local_info:local_info_lib",
         "//source/common/memory:heap_shrinker_lib",

source/server/server.cc

@@ -33,6 +33,7 @@
 #include "source/common/config/version_converter.h"
 #include "source/common/config/xds_resource.h"
 #include "source/common/http/codes.h"
+#include "source/common/http/headers.h"
 #include "source/common/local_info/local_info_impl.h"
 #include "source/common/memory/stats.h"
 #include "source/common/network/address_impl.h"
@@ -292,6 +293,46 @@ void loadBootstrap(absl::optional<uint32_t> bootstrap_version,
     throw EnvoyException(fmt::format("Unknown bootstrap version {}.", *bootstrap_version));
   }
 }
+
+bool canBeRegisteredAsInlineHeader(const Http::LowerCaseString& header_name) {
+  // 'set-cookie' cannot currently be registered as an inline header.
+  if (header_name == Http::Headers::get().SetCookie) {
+    return false;
+  }
+  return true;
+}
+
+void registerCustomInlineHeadersFromBootstrap(
+    const envoy::config::bootstrap::v3::Bootstrap& bootstrap) {
+  for (const auto& inline_header : bootstrap.inline_headers()) {
+    const Http::LowerCaseString lower_case_name(inline_header.inline_header_name());
+    if (!canBeRegisteredAsInlineHeader(lower_case_name)) {
+      throw EnvoyException(fmt::format("Header {} cannot be registered as an inline header.",
+                                       inline_header.inline_header_name()));
+    }
+    switch (inline_header.inline_header_type()) {
+    case envoy::config::bootstrap::v3::CustomInlineHeader::REQUEST_HEADER:
+      Http::CustomInlineHeaderRegistry::registerInlineHeader<
+          Http::RequestHeaderMap::header_map_type>(lower_case_name);
+      break;
+    case envoy::config::bootstrap::v3::CustomInlineHeader::REQUEST_TRAILER:
+      Http::CustomInlineHeaderRegistry::registerInlineHeader<
+          Http::RequestTrailerMap::header_map_type>(lower_case_name);
+      break;
+    case envoy::config::bootstrap::v3::CustomInlineHeader::RESPONSE_HEADER:
+      Http::CustomInlineHeaderRegistry::registerInlineHeader<
+          Http::ResponseHeaderMap::header_map_type>(lower_case_name);
+      break;
+    case envoy::config::bootstrap::v3::CustomInlineHeader::RESPONSE_TRAILER:
+      Http::CustomInlineHeaderRegistry::registerInlineHeader<
+          Http::ResponseTrailerMap::header_map_type>(lower_case_name);
+      break;
+    default:
+      NOT_IMPLEMENTED_GCOVR_EXCL_LINE;
+    }
+  }
+}
+
 } // namespace
 
 void InstanceUtil::loadBootstrapConfig(envoy::config::bootstrap::v3::Bootstrap& bootstrap,
@@ -353,8 +394,10 @@ void InstanceImpl::initialize(const Options& options,
     // setPrefix has a release assert verifying that setPrefix() is not called after prefix()
     ThreadSafeSingleton<Http::PrefixValue>::get().setPrefix(bootstrap_.header_prefix().c_str());
   }
-  // TODO(mattklein123): Custom O(1) headers can be registered at this point for creating/finalizing
-  // any header maps.
+
+  // Register Custom O(1) headers from bootstrap.
+  registerCustomInlineHeadersFromBootstrap(bootstrap_);
+
   ENVOY_LOG(info, "HTTP header map info:");
   for (const auto& info : Http::HeaderMapImplUtility::getAllHeaderMapImplInfo()) {
     ENVOY_LOG(info, "  {}: {} bytes: {}", info.name_, info.size_,