Return pdfium::span<wchar_t> from WideString::GetBuffer().

Adds bounds checking "for free", but beware of span outliving
a ReleaseBuffer() call.  Scoping as such avoids the possibility
of using an invalid span (and it is flagged as a lifetime issue).

Change-Id: Ica63f4b1429823d0254ec6951aeaeb08160cb93c
Reviewed-on: https://pdfium-review.googlesource.com/30310
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/core/fpdfapi/parser/fpdf_parser_decode.cpp b/core/fpdfapi/parser/fpdf_parser_decode.cpp
index d7114b66c5..90dca2edcb 100644
--- a/core/fpdfapi/parser/fpdf_parser_decode.cpp
+++ b/core/fpdfapi/parser/fpdf_parser_decode.cpp
@@ -425,6 +425,7 @@ bool PDF_DataDecode(const uint8_t* src_buf,
 }
 
 WideString PDF_DecodeText(const uint8_t* src_data, uint32_t src_len) {
+  int dest_pos = 0;
   WideString result;
   if (src_len >= 2 && ((src_data[0] == 0xfe && src_data[1] == 0xff) ||
                        (src_data[0] == 0xff && src_data[1] == 0xfe))) {
@@ -432,17 +433,15 @@ WideString PDF_DecodeText(const uint8_t* src_data, uint32_t src_len) {
     if (!max_chars)
       return result;
 
+    pdfium::span<wchar_t> dest_buf = result.GetBuffer(max_chars);
     bool bBE = src_data[0] == 0xfe || (src_data[0] == 0xff && !src_data[2]);
-    wchar_t* dest_buf = result.GetBuffer(max_chars);
     const uint8_t* uni_str = src_data + 2;
-    int dest_pos = 0;
     for (uint32_t i = 0; i < max_chars * 2; i += 2) {
       uint16_t unicode = GetUnicodeFromBytes(uni_str + i, bBE);
       if (unicode != 0x1b) {
         dest_buf[dest_pos++] = unicode;
         continue;
       }
-
       i += 2;
       while (i < max_chars * 2) {
         uint16_t unicode2 = GetUnicodeFromBytes(uni_str + i, bBE);
@@ -451,13 +450,13 @@ WideString PDF_DecodeText(const uint8_t* src_data, uint32_t src_len) {
           break;
       }
     }
-    result.ReleaseBuffer(dest_pos);
   } else {
-    wchar_t* dest_buf = result.GetBuffer(src_len);
+    pdfium::span<wchar_t> dest_buf = result.GetBuffer(src_len);
     for (uint32_t i = 0; i < src_len; ++i)
       dest_buf[i] = PDFDocEncoding[src_data[i]];
-    result.ReleaseBuffer(src_len);
+    dest_pos = src_len;
   }
+  result.ReleaseBuffer(dest_pos);
   return result;
 }