header: HeaderListView implementation (envoyproxy#10733)

This is an abstraction of HeaderList. This is required for us to return all of headers from HeaderMap to implement List/Map expression processor for google/cel which is not implemented right now.

Signed-off-by: shikugawa <rei@tetrate.io>

source/common/http/BUILD

@@ -253,6 +253,15 @@ envoy_cc_library(
     ],
 )
 
+envoy_cc_library(
+    name = "header_list_view_lib",
+    srcs = ["header_list_view.cc"],
+    hdrs = ["header_list_view.h"],
+    deps = [
+        "//include/envoy/http:header_map_interface",
+    ],
+)
+
 envoy_cc_library(
     name = "header_map_lib",
     srcs = ["header_map_impl.cc"],

source/common/http/header_list_view.cc

@@ -0,0 +1,19 @@
+#include "common/http/header_list_view.h"
+
+namespace Envoy {
+namespace Http {
+
+HeaderListView::HeaderListView(const HeaderMap& header_map) {
+  header_map.iterate(
+      [](const Http::HeaderEntry& header, void* context) -> HeaderMap::Iterate {
+        auto* context_ptr = static_cast<HeaderListView*>(context);
+        context_ptr->keys_.emplace_back(std::reference_wrapper<const HeaderString>(header.key()));
+        context_ptr->values_.emplace_back(
+            std::reference_wrapper<const HeaderString>(header.value()));
+        return HeaderMap::Iterate::Continue;
+      },
+      this);
+}
+
+} // namespace Http
+} // namespace Envoy

source/common/http/header_list_view.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <vector>
+
+#include "envoy/http/header_map.h"
+
+namespace Envoy {
+namespace Http {
+
+class HeaderListView {
+public:
+  using HeaderStringRefs = std::vector<std::reference_wrapper<const HeaderString>>;
+
+  HeaderListView(const HeaderMap& header_map);
+  const HeaderStringRefs& keys() const { return keys_; }
+  const HeaderStringRefs& values() const { return values_; }
+
+private:
+  HeaderStringRefs keys_;
+  HeaderStringRefs values_;
+};
+
+} // namespace Http
+} // namespace Envoy

test/common/http/BUILD

@@ -278,6 +278,7 @@ envoy_cc_test(
     name = "header_map_impl_test",
     srcs = ["header_map_impl_test.cc"],
     deps = [
+        "//source/common/http:header_list_view_lib",
         "//source/common/http:header_map_lib",
         "//source/common/http:header_utility_lib",
         "//test/test_common:utility_lib",

test/common/http/header_map_impl_test.cc

@@ -1,6 +1,8 @@
+#include <algorithm>
 #include <memory>
 #include <string>
 
+#include "common/http/header_list_view.h"
 #include "common/http/header_map_impl.h"
 #include "common/http/header_utility.h"
 
@@ -9,6 +11,7 @@
 
 #include "gtest/gtest.h"
 
+using ::testing::ElementsAre;
 using ::testing::InSequence;
 
 namespace Envoy {
@@ -920,6 +923,24 @@ TEST(HeaderMapImplTest, Get) {
   }
 }
 
+TEST(HeaderMapImplTest, TestHeaderList) {
+  std::array<Http::LowerCaseString, 2> keys{Headers::get().Path, LowerCaseString("hello")};
+  std::array<std::string, 2> values{"/", "world"};
+
+  auto headers = createHeaderMap<TestHeaderMapImpl>({{keys[0], values[0]}, {keys[1], values[1]}});
+  HeaderListView header_list(headers->header_map_);
+  auto to_string_views =
+      [](const HeaderListView::HeaderStringRefs& strs) -> std::vector<absl::string_view> {
+    std::vector<absl::string_view> str_views(strs.size());
+    std::transform(strs.begin(), strs.end(), str_views.begin(),
+                   [](auto value) -> absl::string_view { return value.get().getStringView(); });
+    return str_views;
+  };
+
+  EXPECT_THAT(to_string_views(header_list.keys()), ElementsAre(":path", "hello"));
+  EXPECT_THAT(to_string_views(header_list.values()), ElementsAre("/", "world"));
+}
+
 TEST(HeaderMapImplTest, TestAppendHeader) {
   // Test appending to a string with a value.
   {