Use StringBuilder to create new string in parse_html.

td/telegram/MessageEntity.cpp

@@ -24,6 +24,8 @@
 #include "td/utils/misc.h"
 #include "td/utils/Promise.h"
 #include "td/utils/SliceBuilder.h"
+#include "td/utils/StackAllocator.h"
+#include "td/utils/StringBuilder.h"
 #include "td/utils/unicode.h"
 #include "td/utils/utf8.h"
 
@@ -2994,6 +2996,9 @@ static Result<vector<MessageEntity>> do_parse_html(CSlice text, string &result)
   vector<MessageEntity> entities;
   int32 utf16_offset = 0;
 
+  auto buf = StackAllocator::alloc(text.size() + 30);
+  StringBuilder new_text(buf.as_slice(), true);
+
   struct EntityInfo {
     string tag_name;
     string argument;
@@ -3016,7 +3021,7 @@ static Result<vector<MessageEntity>> do_parse_html(CSlice text, string &result)
       if (ch != 0) {
         i--;  // i will be incremented in for
         utf16_offset += 1 + (ch > 0xffff);
-        append_utf8_character(result, ch);
+        append_utf8_character(new_text, ch);
         continue;
       }
     }
@@ -3024,7 +3029,7 @@ static Result<vector<MessageEntity>> do_parse_html(CSlice text, string &result)
       if (is_utf8_character_first_code_unit(c)) {
         utf16_offset += 1 + (c >= 0xf0);  // >= 4 bytes in symbol => surrogate pair
       }
-      result.push_back(text[i]);
+      new_text.push_back(text[i]);
       continue;
     }
 
@@ -3130,7 +3135,7 @@ static Result<vector<MessageEntity>> do_parse_html(CSlice text, string &result)
                                       << "Tag \"span\" must have class \"tg-spoiler\" at byte offset " << begin_pos);
       }
 
-      nested_entities.emplace_back(std::move(tag_name), std::move(argument), utf16_offset, result.size());
+      nested_entities.emplace_back(std::move(tag_name), std::move(argument), utf16_offset, new_text.size());
     } else {
       // end of an entity
       if (nested_entities.empty()) {
@@ -3177,7 +3182,7 @@ static Result<vector<MessageEntity>> do_parse_html(CSlice text, string &result)
         } else if (tag_name == "a") {
           auto url = std::move(nested_entities.back().argument);
           if (url.empty()) {
-            url = result.substr(nested_entities.back().entity_begin_pos);
+            url = new_text.as_cslice().substr(nested_entities.back().entity_begin_pos).str();
           }
           auto user_id = LinkManager::get_link_user_id(url);
           if (user_id.is_valid()) {
@@ -3226,6 +3231,7 @@ static Result<vector<MessageEntity>> do_parse_html(CSlice text, string &result)
 
   sort_entities(entities);
 
+  result = new_text.as_cslice().str();
   return std::move(entities);
 }
 

tdutils/td/utils/StringBuilder.h

@@ -32,6 +32,16 @@ class StringBuilder {
     current_ptr_--;
   }
 
+  void push_back(char c) {
+    if (unlikely(end_ptr_ <= current_ptr_)) {
+      if (!reserve_inner(RESERVED_SIZE)) {
+        on_error();
+        return;
+      }
+    }
+    *current_ptr_++ = c;
+  }
+
   MutableCSlice as_cslice() {
     if (current_ptr_ >= end_ptr_ + RESERVED_SIZE) {
       std::abort();  // shouldn't happen
@@ -40,6 +50,10 @@ class StringBuilder {
     return MutableCSlice(begin_ptr_, current_ptr_);
   }
 
+  size_t size() {
+    return static_cast<size_t>(current_ptr_ - begin_ptr_);
+  }
+
   bool is_error() const {
     return error_flag_;
   }
@@ -132,6 +146,7 @@ class StringBuilder {
     }
     return reserve_inner(RESERVED_SIZE);
   }
+
   bool reserve(size_t size) {
     if (end_ptr_ > current_ptr_ && static_cast<size_t>(end_ptr_ - current_ptr_) >= size) {
       return true;

tdutils/td/utils/utf8.cpp

@@ -62,24 +62,6 @@ bool check_utf8(CSlice str) {
   return false;
 }
 
-void append_utf8_character(string &str, uint32 ch) {
-  if (ch <= 0x7f) {
-    str.push_back(static_cast<char>(ch));
-  } else if (ch <= 0x7ff) {
-    str.push_back(static_cast<char>(0xc0 | (ch >> 6)));  // implementation-defined
-    str.push_back(static_cast<char>(0x80 | (ch & 0x3f)));
-  } else if (ch <= 0xffff) {
-    str.push_back(static_cast<char>(0xe0 | (ch >> 12)));  // implementation-defined
-    str.push_back(static_cast<char>(0x80 | ((ch >> 6) & 0x3f)));
-    str.push_back(static_cast<char>(0x80 | (ch & 0x3f)));
-  } else {
-    str.push_back(static_cast<char>(0xf0 | (ch >> 18)));  // implementation-defined
-    str.push_back(static_cast<char>(0x80 | ((ch >> 12) & 0x3f)));
-    str.push_back(static_cast<char>(0x80 | ((ch >> 6) & 0x3f)));
-    str.push_back(static_cast<char>(0x80 | (ch & 0x3f)));
-  }
-}
-
 const unsigned char *next_utf8_unsafe(const unsigned char *ptr, uint32 *code) {
   uint32 a = ptr[0];
   if ((a & 0x80) == 0) {

tdutils/td/utils/utf8.h

@@ -32,7 +32,24 @@ inline size_t utf8_length(Slice str) {
 size_t utf8_utf16_length(Slice str);
 
 /// appends a Unicode character using UTF-8 encoding
-void append_utf8_character(string &str, uint32 ch);
+template <class T>
+void append_utf8_character(T &str, uint32 ch) {
+  if (ch <= 0x7f) {
+    str.push_back(static_cast<char>(ch));
+  } else if (ch <= 0x7ff) {
+    str.push_back(static_cast<char>(0xc0 | (ch >> 6)));  // implementation-defined
+    str.push_back(static_cast<char>(0x80 | (ch & 0x3f)));
+  } else if (ch <= 0xffff) {
+    str.push_back(static_cast<char>(0xe0 | (ch >> 12)));  // implementation-defined
+    str.push_back(static_cast<char>(0x80 | ((ch >> 6) & 0x3f)));
+    str.push_back(static_cast<char>(0x80 | (ch & 0x3f)));
+  } else {
+    str.push_back(static_cast<char>(0xf0 | (ch >> 18)));  // implementation-defined
+    str.push_back(static_cast<char>(0x80 | ((ch >> 12) & 0x3f)));
+    str.push_back(static_cast<char>(0x80 | ((ch >> 6) & 0x3f)));
+    str.push_back(static_cast<char>(0x80 | (ch & 0x3f)));
+  }
+}
 
 /// moves pointer one UTF-8 character back
 inline const unsigned char *prev_utf8_unsafe(const unsigned char *ptr) {