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 +322,11 @@ 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.
+  repeated CustomInlineHeader inline_headers = 32;
 }
 
 // Administration interface :ref:`operations documentation
@@ -595,3 +600,22 @@ 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.
+// 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}];
+
+  // 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}];
+}

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_,

test/server/server_test.cc

@@ -334,6 +334,60 @@ INSTANTIATE_TEST_SUITE_P(IpVersions, ServerInstanceImplTest,
                          testing::ValuesIn(TestEnvironment::getIpVersionsForTest()),
                          TestUtility::ipTestParamsToString);
 
+// The finalize() of Http::CustomInlineHeaderRegistry will be called When InstanceImpl is
+// instantiated. For this reason, the test case for inline headers must precede all other test
+// cases.
+
+// Test the case where inline headers contain names that cannot be registered as inline headers.
+TEST_P(ServerInstanceImplTest, WithErrorCustomInlineHeaders) {
+  EXPECT_THROW_WITH_MESSAGE(
+      initialize("test/server/test_data/server/bootstrap_inline_headers_error.yaml"),
+      EnvoyException, "Header set-cookie cannot be registered as an inline header.");
+}
+
+TEST_P(ServerInstanceImplTest, WithDeathCustomInlineHeaders) {
+#if !defined(NDEBUG)
+  // The finalize() of Http::CustomInlineHeaderRegistry will be called after the first successful
+  // instantiation of InstanceImpl. If InstanceImpl is instantiated again and the inline header is
+  // registered again, the assertion will be triggered.
+  EXPECT_DEATH(
+      {
+        initialize("test/server/test_data/server/bootstrap_inline_headers.yaml");
+        initialize("test/server/test_data/server/bootstrap_inline_headers.yaml");
+      },
+      "");
+#endif // !defined(NDEBUG)
+}
+
+// Test whether the custom inline headers can be registered correctly.
+TEST_P(ServerInstanceImplTest, WithCustomInlineHeaders) {
+  static bool is_registered = false;
+
+  if (!is_registered) {
+    // Avoid repeated registration of custom inline headers in the current process after the
+    // finalize() of Http::CustomInlineHeaderRegistry has already been called.
+    EXPECT_NO_THROW(initialize("test/server/test_data/server/bootstrap_inline_headers.yaml"));
+    is_registered = true;
+  }
+
+  EXPECT_TRUE(
+      Http::CustomInlineHeaderRegistry::getInlineHeader<Http::RequestHeaderMap::header_map_type>(
+          Http::LowerCaseString("test1"))
+          .has_value());
+  EXPECT_TRUE(
+      Http::CustomInlineHeaderRegistry::getInlineHeader<Http::RequestTrailerMap::header_map_type>(
+          Http::LowerCaseString("test2"))
+          .has_value());
+  EXPECT_TRUE(
+      Http::CustomInlineHeaderRegistry::getInlineHeader<Http::ResponseHeaderMap::header_map_type>(
+          Http::LowerCaseString("test3"))
+          .has_value());
+  EXPECT_TRUE(
+      Http::CustomInlineHeaderRegistry::getInlineHeader<Http::ResponseTrailerMap::header_map_type>(
+          Http::LowerCaseString("test4"))
+          .has_value());
+}
+
 // Validates that server stats are flushed even when server is stuck with initialization.
 TEST_P(ServerInstanceImplTest, StatsFlushWhenServerIsStillInitializing) {
   CustomStatsSinkFactory factory;

test/server/test_data/server/bootstrap_inline_headers.yaml

@@ -0,0 +1,9 @@
+inline_headers:
+- inline_header_name: test1
+  inline_header_type: REQUEST_HEADER
+- inline_header_name: test2
+  inline_header_type: REQUEST_TRAILER
+- inline_header_name: test3
+  inline_header_type: RESPONSE_HEADER
+- inline_header_name: test4
+  inline_header_type: RESPONSE_TRAILER

test/server/test_data/server/bootstrap_inline_headers_error.yaml

@@ -0,0 +1,3 @@
+inline_headers:
+- inline_header_name: set-cookie
+  inline_header_type: RESPONSE_HEADER