feat: add url_aggregator::replace_and_resize (#302)

* feat: add url_aggregator::replace_and_resize

* perf: improve update_base_pathname performance

Author: anonrig

include/ada/url_aggregator-inl.h

@@ -87,6 +87,26 @@ inline void url_aggregator::update_unencoded_base_hash(std::string_view input) {
   ADA_ASSERT_TRUE(validate());
 }
 
+ada_really_inline uint32_t url_aggregator::replace_and_resize(uint32_t start, uint32_t end, std::string_view input) {
+  uint32_t current_length = end - start;
+  uint32_t input_size = uint32_t(input.size());
+  uint32_t new_difference = input_size - current_length;
+
+  if (current_length == 0) {
+    buffer.insert(start, input);
+  } else if (input_size == current_length) {
+    buffer.replace(start, input_size, input);
+  } else if (input_size < current_length) {
+    buffer.erase(start, current_length - input_size);
+    buffer.replace(start, input_size, input);
+  } else {
+    buffer.replace(start, current_length, input.substr(0, current_length));
+    buffer.insert(start + current_length, input.substr(current_length));
+  }
+
+  return new_difference;
+}
+
 inline void url_aggregator::update_base_hostname(const std::string_view input) {
   ada_log("url_aggregator::update_base_hostname ", input, " [", input.size(), " bytes], buffer is '", buffer, "' [", buffer.size()," bytes]");
   ADA_ASSERT_TRUE(validate());
@@ -95,21 +115,13 @@ inline void url_aggregator::update_base_hostname(const std::string_view input) {
   // This next line is required for when parsing a URL like `foo://`
   add_authority_slashes_if_needed();
 
-  bool has_credential = components.protocol_end + 2 < components.host_start;
-  uint32_t current_length = components.host_end - components.host_start;
-  // next line could overflow but unsigned arithmetic has well-defined overflows.
-  uint32_t new_difference = uint32_t(input.size()) - current_length;
-  // The common case is current_length == 0.
-  buffer.erase(components.host_start, current_length);
-
-  uint32_t host_start = components.host_start;
-  // The common case is components.host_start == buffer.size().
-  if (has_credential) {
-    buffer.insert(host_start, "@");
-    host_start++;
+  bool has_credentials = components.protocol_end + 2 < components.host_start;
+  uint32_t new_difference = replace_and_resize(components.host_start, components.host_end, input);
+
+  if (has_credentials) {
+    buffer.insert(components.host_start, "@");
     new_difference++;
   }
-  buffer.insert(host_start, input);
   components.host_end += new_difference;
   components.pathname_start += new_difference;
   if (components.search_start != url_components::omitted) { components.search_start += new_difference; }
@@ -203,27 +215,22 @@ inline void url_aggregator::update_base_pathname(const std::string_view input) {
   ada_log("url_aggregator::update_base_pathname '", input, "' [", input.size(), " bytes] \n", to_diagram());
   ADA_ASSERT_TRUE(!helpers::overlaps(input, buffer));
   ADA_ASSERT_TRUE(validate());
+
   const bool begins_with_dashdash = checkers::begins_with(input, "//");
-  // uncommon branch:
   if(!begins_with_dashdash && has_dash_dot()) {
     ada_log("url_aggregator::update_base_pathname has /.: \n", to_diagram());
     // We must delete the ./
     delete_dash_dot();
   }
-  uint32_t current_length = get_pathname_length();
-  uint32_t difference = uint32_t(input.size()) - current_length;
-  // The common case is current_length == 0.
-  buffer.erase(components.pathname_start, current_length);
-  // next line is very uncommon and we should seek to optimize it accordingly.
-  if (begins_with_dashdash && !has_opaque_path && !has_authority()) {
+
+  if (begins_with_dashdash && !has_opaque_path && !has_authority() && !has_dash_dot()) {
     // If url’s host is null, url does not have an opaque path, url’s path’s size is greater than 1,
     // then append U+002F (/) followed by U+002E (.) to output.
     buffer.insert(components.pathname_start, "/.");
     components.pathname_start += 2;
-    difference += 2;
   }
-  // The common case is components.pathname_start == buffer.size() so this is effectively an append.
-  buffer.insert(components.pathname_start, input);
+
+  uint32_t difference = replace_and_resize(components.pathname_start, components.pathname_start + get_pathname_length(), input);
   if (components.search_start != url_components::omitted) { components.search_start += difference; }
   if (components.hash_start != url_components::omitted) { components.hash_start += difference; }
   ada_log("url_aggregator::update_base_pathname end '", input, "' [", input.size(), " bytes] \n", to_diagram());

include/ada/url_aggregator.h

@@ -231,6 +231,9 @@ namespace ada {
     template <bool has_state_override = false>
     [[nodiscard]] ada_really_inline bool parse_scheme_with_colon(const std::string_view input);
 
+    /** @private */
+    ada_really_inline uint32_t replace_and_resize(uint32_t start, uint32_t end, std::string_view input);
+
     /**
      * Useful for implementing efficient serialization for the URL.
      *