perf: http/1 use table for lower case conversion (#231)

Author: mattklein123

source/common/http/http1/codec_impl.cc

@@ -244,28 +244,36 @@ http_parser_settings ConnectionImpl::settings_{
     nullptr  // on_chunk_complete
 };
 
-ConnectionImpl::ConnectionImpl(Network::Connection& connection, http_parser_type type)
-    : connection_(connection) {
-  http_parser_init(&parser_, type);
-  parser_.data = this;
+const ConnectionImpl::ToLowerTable ConnectionImpl::to_lower_table_;
+
+ConnectionImpl::ToLowerTable::ToLowerTable() {
+  for (size_t c = 0; c < 256; c++) {
+    table_[c] = c;
+    if ((c >= 'A') && (c <= 'Z')) {
+      table_[c] |= 0x20;
+    }
+  }
 }
 
-static void toLowerCase(HeaderString& text) {
+void ConnectionImpl::ToLowerTable::toLowerCase(HeaderString& text) const {
   char* buffer = text.buffer();
   uint32_t size = text.size();
   for (size_t i = 0; i < size; i++) {
-    char c = buffer[i];
-    if ((c >= 'A') && (c <= 'Z')) {
-      buffer[i] |= 0x20;
-    }
+    buffer[i] = table_[static_cast<uint8_t>(buffer[i])];
   }
 }
 
+ConnectionImpl::ConnectionImpl(Network::Connection& connection, http_parser_type type)
+    : connection_(connection) {
+  http_parser_init(&parser_, type);
+  parser_.data = this;
+}
+
 void ConnectionImpl::completeLastHeader() {
   conn_log_trace("completed header: key={} value={}", connection_, current_header_field_.c_str(),
                  current_header_value_.c_str());
   if (!current_header_field_.empty()) {
-    toLowerCase(current_header_field_);
+    to_lower_table_.toLowerCase(current_header_field_);
     current_header_map_->addViaMove(std::move(current_header_field_),
                                     std::move(current_header_value_));
   }

source/common/http/http1/codec_impl.h

@@ -148,6 +148,13 @@ class ConnectionImpl : public virtual Connection, protected Logger::Loggable<Log
 private:
   enum class HeaderParsingState { Field, Value, Done };
 
+  struct ToLowerTable {
+    ToLowerTable();
+    void toLowerCase(HeaderString& text) const;
+
+    std::array<uint8_t, 256> table_;
+  };
+
   /**
    * Called in order to complete an in progress header decode.
    */
@@ -219,6 +226,7 @@ class ConnectionImpl : public virtual Connection, protected Logger::Loggable<Log
   virtual void sendProtocolError() PURE;
 
   static http_parser_settings settings_;
+  static const ToLowerTable to_lower_table_;
 
   HeaderMapImplPtr current_header_map_;
   HeaderParsingState header_parsing_state_{HeaderParsingState::Field};