Avoid copying in TrimRight() and TrimLeft() if possible.

core/fxcrt/fx_basic_bstring_unittest.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/fxcrt/include/fx_string.h"
 #include "testing/fx_string_testhelpers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 TEST(fxcrt, ByteStringOperatorSubscript) {
   // CFX_ByteString includes the NUL terminator for non-empty strings.
@@ skipping 487 matching lines @@
 
   CFX_ByteString empty;
   empty.TrimRight("ERP");
   EXPECT_EQ("", empty);
   empty.TrimRight('E');
   EXPECT_EQ("", empty);
   empty.TrimRight();
   EXPECT_EQ("", empty);
 }
 
+TEST(fxcrt, ByteStringTrimRightCopies) {
+  {
+    // With a single reference, no copy takes place.
+    CFX_ByteString fred("  FRED  ");
+    const FX_CHAR* old_buffer = fred.c_str();
+    fred.TrimRight();
+    EXPECT_EQ("  FRED", fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, we must copy.
+    CFX_ByteString fred("  FRED  ");
+    CFX_ByteString other_fred = fred;
+    const FX_CHAR* old_buffer = fred.c_str();
+    fred.TrimRight();
+    EXPECT_EQ("  FRED", fred);
+    EXPECT_EQ("  FRED  ", other_fred);
+    EXPECT_NE(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, but no modifications, no copy.
+    CFX_ByteString fred("FRED");
+    CFX_ByteString other_fred = fred;
+    const FX_CHAR* old_buffer = fred.c_str();
+    fred.TrimRight();
+    EXPECT_EQ("FRED", fred);
+    EXPECT_EQ("FRED", other_fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+}
+
 TEST(fxcrt, ByteStringTrimLeft) {
   CFX_ByteString fred("  FRED  ");
   fred.TrimLeft();
   EXPECT_EQ("FRED  ", fred);
   fred.TrimLeft('E');
   EXPECT_EQ("FRED  ", fred);
   fred.TrimLeft('F');
   EXPECT_EQ("RED  ", fred);
   fred.TrimLeft("ERP");
   EXPECT_EQ("D  ", fred);
 
   CFX_ByteString blank("   ");
   blank.TrimLeft("ERP");
   EXPECT_EQ("   ", blank);
   blank.TrimLeft('E');
   EXPECT_EQ("   ", blank);
   blank.TrimLeft();
   EXPECT_EQ("", blank);
 
   CFX_ByteString empty;
   empty.TrimLeft("ERP");
   EXPECT_EQ("", empty);
   empty.TrimLeft('E');
   EXPECT_EQ("", empty);
   empty.TrimLeft();
   EXPECT_EQ("", empty);
 }
 
+TEST(fxcrt, ByteStringTrimLeftCopies) {
+  {
+    // With a single reference, no copy takes place.
+    CFX_ByteString fred("  FRED  ");
+    const FX_CHAR* old_buffer = fred.c_str();
+    fred.TrimLeft();
+    EXPECT_EQ("FRED  ", fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, we must copy.
+    CFX_ByteString fred("  FRED  ");
+    CFX_ByteString other_fred = fred;
+    const FX_CHAR* old_buffer = fred.c_str();
+    fred.TrimLeft();
+    EXPECT_EQ("FRED  ", fred);
+    EXPECT_EQ("  FRED  ", other_fred);
+    EXPECT_NE(old_buffer, fred.c_str());
+  }
+  {
+    // With multiple references, but no modifications, no copy.
+    CFX_ByteString fred("FRED");
+    CFX_ByteString other_fred = fred;
+    const FX_CHAR* old_buffer = fred.c_str();
+    fred.TrimLeft();
+    EXPECT_EQ("FRED", fred);
+    EXPECT_EQ("FRED", other_fred);
+    EXPECT_EQ(old_buffer, fred.c_str());
+  }
+}
+
 TEST(fxcrt, ByteStringCNotNull) {
   CFX_ByteStringC string3("abc");
   CFX_ByteStringC string6("abcdef");
   CFX_ByteStringC alternate_string3("abcdef", 3);
   CFX_ByteStringC embedded_nul_string7("abc\0def", 7);
   CFX_ByteStringC illegal_string7("abcdef", 7);
 
   EXPECT_EQ(3, string3.GetLength());
   EXPECT_EQ(6, string6.GetLength());
   EXPECT_EQ(3, alternate_string3.GetLength());
@@ skipping 352 matching lines @@
   }
 }
 
 TEST(fxcrt, EmptyByteString) {
   CFX_ByteString empty_str;
   EXPECT_TRUE(empty_str.IsEmpty());
   EXPECT_EQ(0, empty_str.GetLength());
   const FX_CHAR* cstr = empty_str.c_str();
   EXPECT_EQ(0, FXSYS_strlen(cstr));
 }