PDF: Fix extra NUL characters from incorrect WriteInto() calls.

pdf/pdfium/pdfium_range.cc

 // Copyright (c) 2010 The Chromium 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 "pdf/pdfium/pdfium_range.h"
 
 #include "base/logging.h"
 #include "base/strings/string_util.h"
 
 namespace chrome_pdf {
@@ skipping 41 matching lines @@
     cached_screen_rects_.push_back(
         page_->PageToScreen(offset, zoom, left, top, right, bottom, rotation));
   }
 
   return cached_screen_rects_;
 }
 
 base::string16 PDFiumRange::GetText() {
   int index = char_index_;
   int count = char_count_;
-  if (!count)
-    return base::string16();
+  base::string16 rv;
   if (count < 0) {
     count *= -1;
     index -= count - 1;
   }
 
-  base::string16 rv;
-  unsigned short* data =
-      reinterpret_cast<unsigned short*>(WriteInto(&rv, count + 1));
-  if (data) {
+  if (count > 0) {
+    unsigned short* data =
+        reinterpret_cast<unsigned short*>(WriteInto(&rv, count + 1));
+    // |written| includes the trailing terminator, so get rid of the trailing
+    // NUL character by calling resize().

[raymes, 2015/01/06 05:43:24]

Not sure if you want to put this comment above your other similar change in
pdfium_engine.cc as well, it's a bit subtle.

In addition to the comment, it also seems like FPDF_GetText could write fewer
characters than specified, in which case you would also want to resize as well.

It's tricky to get a string out of the API!

[Lei Zhang, 2015/01/06 22:53:03]

Comment added. Some places call len = Foo(NULL_buffer, 0) to get the byte/char
count, then we use it immediately in Foo(buffer, len). In both of these
FPDF_GetText() calls, we have a character count that did not originate from
FPDF_GetText(), so we definitely should check the return value.

     int written = FPDFText_GetText(page_->GetTextPage(), index, count, data);
-    rv.reserve(written);
+    if (written < 1)
+      rv.resize(0);
+    else
+      rv.resize(written - 1);
   }
+
   return rv;
 }
 
 }  // namespace chrome_pdf