String:WriteUtf8: Add REPLACE_INVALID_UTF8 option

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4436 matching lines @@
 int String::Utf8Length() const {
   i::Handle<i::String> str = Utils::OpenHandle(this);
   i::Isolate* isolate = str->GetIsolate();
   return v8::Utf8Length(*str, isolate);
 }
 
 
 class Utf8WriterVisitor {
  public:
   Utf8WriterVisitor(
-      char* buffer, int capacity, bool skip_capacity_check)
-      : early_termination_(false),
-        last_character_(unibrow::Utf16::kNoPreviousCharacter),
-        buffer_(buffer),
-        start_(buffer),
-        capacity_(capacity),
-        skip_capacity_check_(capacity == -1 || skip_capacity_check),
-        utf16_chars_read_(0) {
+      char* buffer,
+      int capacity,
+      bool skip_capacity_check,
+      bool replace_invalid_utf8)
+    : early_termination_(false),
+      last_character_(unibrow::Utf16::kNoPreviousCharacter),
+      buffer_(buffer),
+      start_(buffer),
+      capacity_(capacity),
+      skip_capacity_check_(capacity == -1 || skip_capacity_check),
+      replace_invalid_utf8_(replace_invalid_utf8),
+      utf16_chars_read_(0) {
   }
 
   static int WriteEndCharacter(uint16_t character,
                                int last_character,
                                int remaining,
-                               char* const buffer) {
+                               char* const buffer,
+                               bool replace_invalid_utf8) {
     using namespace unibrow;
     ASSERT(remaining > 0);
     // We can't use a local buffer here because Encode needs to modify
     // previous characters in the stream.  We know, however, that
     // exactly one character will be advanced.
-    if (Utf16::IsTrailSurrogate(character) &&
-        Utf16::IsLeadSurrogate(last_character)) {
-      int written = Utf8::Encode(buffer, character, last_character);
+    if (Utf16::IsSurrogatePair(last_character, character)) {
+      int written = Utf8::Encode(buffer,
+                                 character,
+                                 last_character,
+                                 replace_invalid_utf8);
       ASSERT(written == 1);
       return written;
     }
     // Use a scratch buffer to check the required characters.
     char temp_buffer[Utf8::kMaxEncodedSize];
     // Can't encode using last_character as gcc has array bounds issues.
     int written = Utf8::Encode(temp_buffer,
                                character,
-                               Utf16::kNoPreviousCharacter);
+                               Utf16::kNoPreviousCharacter,
+                               replace_invalid_utf8);
     // Won't fit.
     if (written > remaining) return 0;
     // Copy over the character from temp_buffer.
     for (int j = 0; j < written; j++) {
       buffer[j] = temp_buffer[j];
     }
     return written;
   }
 
+  // Visit writes out a group of code units (chars) of a v8::String to the
+  // internal buffer_. This is done in two phases. The first phase calculates a
+  // pesimistic estimate (writable_length) on how many code units can be safely
+  // written without exceeding the buffer capacity and without writing the last
+  // code unit (it could be a lead surrogate). The estimated number of code
+  // units is then written out in one go, and the reported byte usage is used
+  // to correct the estimate. This is repeated until the estimate becomes <= 0
+  // or all code units have been written out. The second phase writes out code
+  // units until the buffer capacity is reached, would be exceeded by the next
+  // unit, or all units have been written out.
   template<typename Char>
   void Visit(const Char* chars, const int length) {
     using namespace unibrow;
     ASSERT(!early_termination_);
     if (length == 0) return;
     // Copy state to stack.
     char* buffer = buffer_;
     int last_character =
         sizeof(Char) == 1 ? Utf16::kNoPreviousCharacter : last_character_;
     int i = 0;
@@ skipping 17 matching lines @@
       // Write the characters to the stream.
       if (sizeof(Char) == 1) {
         for (; i < fast_length; i++) {
           buffer +=
               Utf8::EncodeOneByte(buffer, static_cast<uint8_t>(*chars++));
           ASSERT(capacity_ == -1 || (buffer - start_) <= capacity_);
         }
       } else {
         for (; i < fast_length; i++) {
           uint16_t character = *chars++;
-          buffer += Utf8::Encode(buffer, character, last_character);
+          buffer += Utf8::Encode(buffer,
+                                 character,
+                                 last_character,
+                                 replace_invalid_utf8_);
           last_character = character;
           ASSERT(capacity_ == -1 || (buffer - start_) <= capacity_);
         }
       }
       // Array is fully written. Exit.
       if (fast_length == length) {
         // Write state back out to object.
         last_character_ = last_character;
         buffer_ = buffer;
         utf16_chars_read_ += length;
         return;
       }
     }
     ASSERT(!skip_capacity_check_);
     // Slow loop. Must check capacity on each iteration.
     int remaining_capacity = capacity_ - static_cast<int>(buffer - start_);
     ASSERT(remaining_capacity >= 0);
     for (; i < length && remaining_capacity > 0; i++) {
       uint16_t character = *chars++;
+      // remaining_capacity is <= 3 bytes at this point, so we do not write out
+      // an umatched lead surrogate.
+      if (replace_invalid_utf8_ && Utf16::IsLeadSurrogate(character)) {
+        early_termination_ = true;
+        break;
+      }
       int written = WriteEndCharacter(character,
                                       last_character,
                                       remaining_capacity,
-                                      buffer);
+                                      buffer,
+                                      replace_invalid_utf8_);
       if (written == 0) {
         early_termination_ = true;
         break;
       }
       buffer += written;
       remaining_capacity -= written;
       last_character = character;
     }
     // Write state back out to object.
     last_character_ = last_character;
@@ skipping 27 matching lines @@
     return static_cast<int>(buffer_ - start_);
   }
 
  private:
   bool early_termination_;
   int last_character_;
   char* buffer_;
   char* const start_;
   int capacity_;
   bool const skip_capacity_check_;
+  bool const replace_invalid_utf8_;
   int utf16_chars_read_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(Utf8WriterVisitor);
 };
 
 
 static bool RecursivelySerializeToUtf8(i::String* current,
                                        Utf8WriterVisitor* writer,
                                        int recursion_budget) {
   while (!writer->IsDone()) {
     i::ConsString* cons_string = i::String::VisitFlat(writer, current);
@@ skipping 18 matching lines @@
                       int options) const {
   i::Isolate* isolate = Utils::OpenHandle(this)->GetIsolate();
   LOG_API(isolate, "String::WriteUtf8");
   ENTER_V8(isolate);
   i::Handle<i::String> str = Utils::OpenHandle(this);
   if (options & HINT_MANY_WRITES_EXPECTED) {
     FlattenString(str);  // Flatten the string for efficiency.
   }
   const int string_length = str->length();
   bool write_null = !(options & NO_NULL_TERMINATION);
+  bool replace_invalid_utf8 = (options & REPLACE_INVALID_UTF8);
+  int max16BitCodeUnitSize = unibrow::Utf8::kMax16BitCodeUnitSize;
   // First check if we can just write the string without checking capacity.
-  if (capacity == -1 || capacity / 3 >= string_length) {
-    Utf8WriterVisitor writer(buffer, capacity, true);
+  if (capacity == -1 || capacity / max16BitCodeUnitSize >= string_length) {
+    Utf8WriterVisitor writer(buffer, capacity, true, replace_invalid_utf8);
     const int kMaxRecursion = 100;
     bool success = RecursivelySerializeToUtf8(*str, &writer, kMaxRecursion);
     if (success) return writer.CompleteWrite(write_null, nchars_ref);
   } else if (capacity >= string_length) {
     // First check that the buffer is large enough.
     int utf8_bytes = v8::Utf8Length(*str, str->GetIsolate());
     if (utf8_bytes <= capacity) {
       // ASCII fast path.
       if (utf8_bytes == string_length) {
         WriteOneByte(reinterpret_cast<uint8_t*>(buffer), 0, capacity, options);
         if (nchars_ref != NULL) *nchars_ref = string_length;
         if (write_null && (utf8_bytes+1 <= capacity)) {
           return string_length + 1;
         }
         return string_length;
       }
       if (write_null && (utf8_bytes+1 > capacity)) {
         options |= NO_NULL_TERMINATION;
       }
       // Recurse once without a capacity limit.
       // This will get into the first branch above.
       // TODO(dcarney) Check max left rec. in Utf8Length and fall through.
       return WriteUtf8(buffer, -1, nchars_ref, options);
     }
   }
   // Recursive slow path can potentially be unreasonable slow. Flatten.
   str = FlattenGetString(str);
-  Utf8WriterVisitor writer(buffer, capacity, false);
+  Utf8WriterVisitor writer(buffer, capacity, false, replace_invalid_utf8);
   i::String::VisitFlat(&writer, *str);
   return writer.CompleteWrite(write_null, nchars_ref);
 }
 
 
 template<typename CharType>
 static inline int WriteHelper(const String* string,
                               CharType* buffer,
                               int start,
                               int length,
@@ skipping 2739 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(info.GetIsolate());
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 } }  // namespace v8::internal