Improve String::WriteAscii and add PRESERVE_ASCII_NULL option.

test/cctest/test-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 5552 matching lines @@
   return len;
 }
 
 
 THREADED_TEST(StringWrite) {
   LocalContext context;
   v8::HandleScope scope;
   v8::Handle<String> str = v8_str("abcde");
   // abc<Icelandic eth><Unicode snowman>.
   v8::Handle<String> str2 = v8_str("abc\303\260\342\230\203");
+  v8::Handle<String> str3 = v8::String::New("abc\0def", 7);
   const int kStride = 4;  // Must match stride in for loops in JS below.
   CompileRun(
       "var left = '';"
       "for (var i = 0; i < 0xd800; i += 4) {"
       "  left = left + String.fromCharCode(i);"
       "}");
   CompileRun(
       "var right = '';"
       "for (var i = 0; i < 0xd800; i += 4) {"
       "  right = String.fromCharCode(i) + right;"
@@ skipping 190 matching lines @@
   utf8buf[8] = 'X';
   len = str2->WriteUtf8(utf8buf, sizeof(utf8buf), &charlen,
                         String::NO_NULL_TERMINATION);
   CHECK_EQ(8, len);
   CHECK_EQ('X', utf8buf[8]);
   CHECK_EQ(5, charlen);
   CHECK_EQ(0, strncmp(utf8buf, "abc\303\260\342\230\203", 8));
   CHECK_NE(0, strcmp(utf8buf, "abc\303\260\342\230\203"));
   utf8buf[8] = '\0';
   CHECK_EQ(0, strcmp(utf8buf, "abc\303\260\342\230\203"));
+
+  memset(utf8buf, 0x1, sizeof(utf8buf));
+  utf8buf[5] = 'X';
+  len = str->WriteUtf8(utf8buf, sizeof(utf8buf), &charlen,
+                        String::NO_NULL_TERMINATION);
+  CHECK_EQ(5, len);
+  CHECK_EQ('X', utf8buf[5]);  // Test that the sixth character is untouched.
+  CHECK_EQ(5, charlen);
+  utf8buf[5] = '\0';
+  CHECK_EQ(0, strcmp(utf8buf, "abcde"));
+
+  memset(buf, 0x1, sizeof(buf));
+  len = str3->WriteAscii(buf);
+  CHECK_EQ(7, len);
+  CHECK_EQ(0, strcmp("abc def", buf));
+
+  memset(buf, 0x1, sizeof(buf));
+  len = str3->WriteAscii(buf, 0, -1, String::PRESERVE_ASCII_NULL);
+  CHECK_EQ(7, len);
+  CHECK_EQ(0, strcmp("abc", buf));
+  CHECK_EQ(0, buf[3]);
+  CHECK_EQ(0, strcmp("def", buf + 4));
 }
 
 
 static void Utf16Helper(
     LocalContext& context,
     const char* name,
     const char* lengths_name,
     int len) {
   Local<v8::Array> a =
       Local<v8::Array>::Cast(context->Global()->Get(v8_str(name)));
@@ skipping 11201 matching lines @@
   v8::HandleScope scope;
   LocalContext context;
 
   // Compile a try-finally clause where the finally block causes a GC
   // while there still is a message pending for external reporting.
   TryCatch try_catch;
   try_catch.SetVerbose(true);
   CompileRun("try { throw new Error(); } finally { gc(); }");
   CHECK(try_catch.HasCaught());
 }