impl(rest): improve http header representation

generator/integration_tests/tests/golden_thing_admin_rest_metadata_decorator_test.cc

@@ -312,7 +312,7 @@ TEST(ThingAdminRestMetadataDecoratorTest, DropDatabaseExplicitRoutingMatch) {
             EXPECT_THAT(context.GetHeader("x-goog-quota-user"), IsEmpty());
             EXPECT_THAT(context.GetHeader("x-server-timeout"), IsEmpty());
             EXPECT_THAT(
-                context.GetHeader("x-goog-request-params")[0],
+                context.GetHeader("x-goog-request-params").values().front(),
                 AllOf(
                     HasSubstr(std::string("project=projects%2Fmy_project")),
                     HasSubstr(std::string("instance=instances%2Fmy_instance")),

google/cloud/BUILD.bazel

@@ -256,6 +256,7 @@ cc_library(
     visibility = ["//:__subpackages__"],
     deps = [
         ":google_cloud_cpp_common",
+        "@abseil-cpp//absl/container:flat_hash_map",
         "@abseil-cpp//absl/functional:function_ref",
         "@abseil-cpp//absl/types:span",
         "@curl",

google/cloud/bigquery/v2/minimal/internal/log_wrapper.h

@@ -38,10 +38,11 @@ Result LogWrapper(Functor&& functor, rest_internal::RestContext& context,
                   TracingOptions const& options) {
   auto formatter = [options](std::string* out, auto const& header) {
     auto const* delim = options.single_line_mode() ? "&" : "\n";
-    absl::StrAppend(
-        out, " { name: \"", header.first, "\" value: \"",
-        internal::DebugString(absl::StrJoin(header.second, delim), options),
-        "\" }");
+    absl::StrAppend(out, " { name: \"", std::string_view{header.first},
+                    "\" value: \"",
+                    internal::DebugString(
+                        absl::StrJoin(header.second.values(), delim), options),
+                    "\" }");
   };
   GCP_LOG(DEBUG) << where << "() << "
                  << request.DebugString(request_name, options) << ", Context {"

google/cloud/bigquery/v2/minimal/internal/rest_stub_utils.h

@@ -48,7 +48,7 @@ StatusOr<rest_internal::RestRequest> PrepareRestRequest(
   if (!rest_context.headers().empty()) {
     for (auto const& h : rest_context.headers()) {
       if (!h.second.empty()) {
-        rest_request->AddHeader(h.first, absl::StrJoin(h.second, "&"));
+        rest_request->AddHeader(h.first, absl::StrJoin(h.second.values(), "&"));
       }
     }
   }

google/cloud/bigquery/v2/minimal/testing/metadata_test_utils.cc

@@ -30,13 +30,15 @@ static auto const kUserProject = "test-only-project";
 static auto const kQuotaUser = "test-quota-user";
 
 void VerifyMetadataContext(rest_internal::RestContext& context) {
-  EXPECT_THAT(context.GetHeader("x-goog-api-client"),
+  EXPECT_THAT(context.GetHeader("x-goog-api-client").values(),
               ElementsAre(internal::HandCraftedLibClientHeader()));
-  EXPECT_THAT(context.GetHeader("x-goog-request-params"), IsEmpty());
-  EXPECT_THAT(context.GetHeader("x-goog-user-project"),
+  EXPECT_THAT(context.GetHeader("x-goog-request-params").values(), IsEmpty());
+  EXPECT_THAT(context.GetHeader("x-goog-user-project").values(),
               ElementsAre(kUserProject));
-  EXPECT_THAT(context.GetHeader("x-goog-quota-user"), ElementsAre(kQuotaUser));
-  EXPECT_THAT(context.GetHeader("x-server-timeout"), ElementsAre("3.141"));
+  EXPECT_THAT(context.GetHeader("x-goog-quota-user").values(),
+              ElementsAre(kQuotaUser));
+  EXPECT_THAT(context.GetHeader("x-server-timeout").values(),
+              ElementsAre("3.141"));
 }
 
 Options GetMetadataOptions() {

google/cloud/google_cloud_cpp_rest_internal.cmake

@@ -137,7 +137,7 @@ add_library(
 target_link_libraries(
     google_cloud_cpp_rest_internal
     PUBLIC absl::span google-cloud-cpp::common CURL::libcurl
-           nlohmann_json::nlohmann_json)
+           absl::flat_hash_map nlohmann_json::nlohmann_json)
 if (WIN32)
     target_compile_definitions(google_cloud_cpp_rest_internal
                                PRIVATE WIN32_LEAN_AND_MEAN)
@@ -197,6 +197,7 @@ google_cloud_cpp_add_pkgconfig(
     "Provides REST Transport for the Google Cloud C++ Client Library."
     "google_cloud_cpp_common"
     "libcurl"
+    "absl_flat_hash_map"
     NON_WIN32_REQUIRES
     openssl
     WIN32_LIBS

google/cloud/internal/curl_impl.cc

@@ -297,10 +297,9 @@ void CurlImpl::MergeAndWriteHeaders(
   }
 }
 
-void CurlImpl::SetHeaders(
-    std::unordered_map<std::string, std::vector<std::string>> const& headers) {
+void CurlImpl::SetHeaders(HttpHeaders const& headers) {
   for (auto const& header : headers) {
-    SetHeader(HttpHeader(header.first, header.second));
+    SetHeader(header.second);
   }
 }
 

google/cloud/internal/curl_impl.h

@@ -35,7 +35,6 @@
 #include <map>
 #include <memory>
 #include <string>
-#include <utility>
 #include <vector>
 
 namespace google {
@@ -84,8 +83,7 @@ class CurlImpl {
   CurlImpl& operator=(CurlImpl&&) = default;
 
   void SetHeader(HttpHeader header);
-  void SetHeaders(
-      std::unordered_map<std::string, std::vector<std::string>> const& headers);
+  void SetHeaders(HttpHeaders const& headers);
 
   std::string MakeEscapedString(std::string const& s);
 

google/cloud/internal/curl_rest_client_test.cc

@@ -29,21 +29,21 @@ TEST(CurlRestClientStandaloneFunctions, HostHeader) {
     std::string expected;
   } cases[] = {
       {"https://storage.googleapis.com", "storage.googleapis.com",
-       "Host: storage.googleapis.com"},
-      {"https://storage.googleapis.com", "", "Host: storage.googleapis.com"},
-      {"https://storage.googleapis.com", "auth", "Host: auth"},
+       "host: storage.googleapis.com"},
+      {"https://storage.googleapis.com", "", "host: storage.googleapis.com"},
+      {"https://storage.googleapis.com", "auth", "host: auth"},
       {"https://storage.googleapis.com:443", "storage.googleapis.com",
-       "Host: storage.googleapis.com"},
+       "host: storage.googleapis.com"},
       {"https://restricted.googleapis.com", "storage.googleapis.com",
-       "Host: storage.googleapis.com"},
+       "host: storage.googleapis.com"},
       {"https://private.googleapis.com", "storage.googleapis.com",
-       "Host: storage.googleapis.com"},
+       "host: storage.googleapis.com"},
       {"https://restricted.googleapis.com", "iamcredentials.googleapis.com",
-       "Host: iamcredentials.googleapis.com"},
+       "host: iamcredentials.googleapis.com"},
       {"https://private.googleapis.com", "iamcredentials.googleapis.com",
-       "Host: iamcredentials.googleapis.com"},
+       "host: iamcredentials.googleapis.com"},
       {"http://localhost:8080", "", ""},
-      {"http://localhost:8080", "auth", "Host: auth"},
+      {"http://localhost:8080", "auth", "host: auth"},
       {"http://[::1]", "", ""},
       {"http://[::1]/", "", ""},
       {"http://[::1]/foo/bar", "", ""},

google/cloud/internal/http_header.cc

@@ -22,48 +22,50 @@ namespace cloud {
 namespace rest_internal {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
 
-HttpHeader::HttpHeader(std::string key) : key_(std::move(key)) {}
+HttpHeader::HttpHeader(HttpHeaderName key) : name_(std::move(key)) {}
 
-HttpHeader::HttpHeader(std::string key, std::string value)
-    : key_(std::move(key)), values_({std::move(value)}) {}
+HttpHeader::HttpHeader(std::pair<std::string, std::string> header)
+    : HttpHeader(std::move(header.first), std::move(header.second)) {}
 
-HttpHeader::HttpHeader(std::string key, std::vector<std::string> values)
-    : key_(std::move(key)), values_(std::move(values)) {}
+HttpHeader::HttpHeader(HttpHeaderName key, std::string value)
+    : name_(std::move(key)), values_({std::move(value)}) {}
 
-HttpHeader::HttpHeader(std::string key,
+HttpHeader::HttpHeader(HttpHeaderName key, std::vector<std::string> values)
+    : name_(std::move(key)), values_(std::move(values)) {}
+
+HttpHeader::HttpHeader(HttpHeaderName key,
                        std::initializer_list<char const*> values)
-    : key_(std::move(key)) {
+    : name_(std::move(key)) {
   for (auto&& v : values) values_.emplace_back(v);
 }
 
 bool operator==(HttpHeader const& lhs, HttpHeader const& rhs) {
-  return absl::AsciiStrToLower(lhs.key_) == absl::AsciiStrToLower(rhs.key_) &&
-         lhs.values_ == rhs.values_;
+  return lhs.name_ == rhs.name_ && lhs.values_ == rhs.values_;
 }
 
 bool operator<(HttpHeader const& lhs, HttpHeader const& rhs) {
-  return absl::AsciiStrToLower(lhs.key_) < absl::AsciiStrToLower(rhs.key_);
+  return lhs.name_ < rhs.name_;
 }
 
-bool HttpHeader::IsSameKey(std::string const& key) const {
-  return absl::AsciiStrToLower(key_) == absl::AsciiStrToLower(key);
+bool HttpHeader::IsSameKey(HttpHeaderName const& name) const {
+  return name_ == name.name();
 }
 
 bool HttpHeader::IsSameKey(HttpHeader const& other) const {
-  return IsSameKey(other.key_);
+  return name_ == other.name_;
 }
 
 HttpHeader::operator std::string() const {
-  if (key_.empty()) return {};
-  if (values_.empty()) return absl::StrCat(key_, ":");
-  return absl::StrCat(key_, ": ", absl::StrJoin(values_, ","));
+  if (name_.empty()) return {};
+  if (values_.empty()) return absl::StrCat(name_.name(), ":");
+  return absl::StrCat(name_.name(), ": ", absl::StrJoin(values_, ","));
 }
 
 std::string HttpHeader::DebugString() const {
-  if (key_.empty()) return {};
-  if (values_.empty()) return absl::StrCat(key_, ":");
+  if (name_.empty()) return {};
+  if (values_.empty()) return absl::StrCat(name_.name(), ":");
   return absl::StrCat(
-      key_, ": ",
+      name_.name(), ": ",
       absl::StrJoin(values_, ",", [](std::string* out, std::string const& v) {
         absl::StrAppend(out, v.substr(0, 10));
       }));

google/cloud/internal/http_header.h

@@ -16,6 +16,13 @@
 #define GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_INTERNAL_HTTP_HEADER_H
 
 #include "google/cloud/version.h"
+#include "absl/strings/ascii.h"
+#include <cstdint>
+#if UINTPTR_MAX == UINT64_MAX
+#include "absl/container/flat_hash_map.h"
+#else
+#include <unordered_map>
+#endif  // UINTPTR_MAX == UINT64_MAX
 #include <string>
 #include <vector>
 
@@ -24,17 +31,67 @@ namespace cloud {
 namespace rest_internal {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
 
+// This class represents a case-insensitive HTTP header name by storing all
+// strings in lower-case.
+class HttpHeaderName {
+ public:
+  HttpHeaderName() = default;
+  HttpHeaderName(std::string name)  // NOLINT(google-explicit-constructor)
+      : name_(std::move(name)) {
+    absl::AsciiStrToLower(&name_);
+  }
+  HttpHeaderName(std::string_view name)  // NOLINT(google-explicit-constructor)
+      : HttpHeaderName(std::string{name}) {}
+  HttpHeaderName(char const* name)  // NOLINT(google-explicit-constructor)
+      : HttpHeaderName(std::string{name}) {}
+
+  operator std::string() const {  // NOLINT(google-explicit-constructor)
+    return name_;
+  }
+  operator std::string_view() const {  // NOLINT(google-explicit-constructor)
+    return name_;
+  }
+  operator char const*() const {  // NOLINT(google-explicit-constructor)
+    return name_.c_str();
+  }
+
+  bool empty() const { return name_.empty(); }
+  std::string const& name() const { return name_; }
+
+  friend bool operator==(HttpHeaderName const& lhs, HttpHeaderName const& rhs) {
+    return lhs.name_ == rhs.name_;
+  }
+  friend bool operator<(HttpHeaderName const& lhs, HttpHeaderName const& rhs) {
+    return lhs.name_ < rhs.name_;
+  }
+  friend bool operator!=(HttpHeaderName const& lhs, HttpHeaderName const& rhs) {
+    return !(lhs == rhs);
+  }
+  friend bool operator>(HttpHeaderName const& lhs, HttpHeaderName const& rhs) {
+    return !(lhs < rhs) && (lhs != rhs);
+  }
+  friend bool operator>=(HttpHeaderName const& lhs, HttpHeaderName const& rhs) {
+    return !(lhs < rhs);
+  }
+  friend bool operator<=(HttpHeaderName const& lhs, HttpHeaderName const& rhs) {
+    return !(lhs > rhs);
+  }
+
+ private:
+  std::string name_;
+};
+
 /**
  * This class represents an HTTP header field.
  */
 class HttpHeader {
  public:
   HttpHeader() = default;
-  explicit HttpHeader(std::string key);
-  HttpHeader(std::string key, std::string value);
-  HttpHeader(std::string key, std::initializer_list<char const*> values);
-
-  HttpHeader(std::string key, std::vector<std::string> values);
+  explicit HttpHeader(HttpHeaderName key);
+  explicit HttpHeader(std::pair<std::string, std::string> header);
+  HttpHeader(HttpHeaderName key, std::string value);
+  HttpHeader(HttpHeaderName key, std::initializer_list<char const*> values);
+  HttpHeader(HttpHeaderName key, std::vector<std::string> values);
 
   HttpHeader(HttpHeader&&) = default;
   HttpHeader& operator=(HttpHeader&&) = default;
@@ -57,14 +114,20 @@ class HttpHeader {
   friend bool operator<(HttpHeader const& lhs, HttpHeader const& rhs);
 
   // If the key is empty, the entire HttpHeader is considered empty.
-  bool empty() const { return key_.empty(); }
+  bool empty() const { return name_.empty(); }
+
+  // Number of values.
+  std::size_t size() const { return values_.size(); }
 
   // Checks to see if the values are empty. Does not inspect the key field.
   bool EmptyValues() const { return values_.empty(); }
 
   // Performs a case-insensitive comparison of the key.
   bool IsSameKey(HttpHeader const& other) const;
-  bool IsSameKey(std::string const& key) const;
+  bool IsSameKey(HttpHeaderName const& name) const;
+
+  std::string name() const { return name_; }
+  std::vector<std::string> const& values() const { return values_; }
 
   // While the RFCs indicate that header keys are case-insensitive, no attempt
   // to convert them to all lowercase is made. Header keys are printed in the
@@ -83,14 +146,44 @@ class HttpHeader {
   HttpHeader& MergeHeader(HttpHeader const& other);
   HttpHeader& MergeHeader(HttpHeader&& other);
 
+  using value_type = std::string;
+  using const_iterator = std::vector<value_type>::const_iterator;
+  const_iterator begin() const { return values_.begin(); }
+  const_iterator end() const { return values_.end(); }
+  const_iterator cbegin() const { return begin(); }
+  const_iterator cend() const { return end(); }
+
  private:
-  std::string key_;
+  HttpHeaderName name_;
   std::vector<std::string> values_;
 };
 
+// Abseil does not guarantee compatibility with 32-bit platforms that they do
+// not test with. Support for such platforms is a community effort. Using
+// std::unordered_map on 32-bit platforms reduces the likelihood of issues
+// arising due to this arrangement.
+#if UINTPTR_MAX == UINT64_MAX
+// 64-bit architecture
+using HttpHeaders = absl::flat_hash_map<HttpHeaderName, HttpHeader>;
+#else
+// 32-bit architecture
+using HttpHeaders = std::unordered_map<HttpHeaderName, HttpHeader>;
+#endif  // UINTPTR_MAX == UINT64_MAX
+
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace rest_internal
 }  // namespace cloud
 }  // namespace google
 
+#if UINTPTR_MAX != UINT64_MAX
+// This specialization has to be in the global namespace.
+template <>
+struct std::hash<google::cloud::rest_internal::HttpHeaderName> {
+  std::size_t operator()(
+      google::cloud::rest_internal::HttpHeaderName const& k) const noexcept {
+    return std::hash<std::string>()(k.name());
+  }
+};
+#endif  // UINTPTR_MAX != UINT64_MAX
+
 #endif  // GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_INTERNAL_HTTP_HEADER_H