Rewrite lower level details of extracting text from page

The current implementation of text extraction was difficult to
understand, duplicated logic that existed in other methods, and wasn't
clear about the units the inputs were in. It also didn't handle
control characters correctly.

The new implementation leans on the methods for converting indices
between the text buffer index and character list index spaces to avoid
duplication of code. It also makes it clear to the reader that inputs
are in the character list index space. Finally, it fixes issues being
seen in Chrome with respect of ranges being slightly off.

This CL also adds a test for extracting text that has control
characters.

BUG=pdfium:942,chromium:654578

Change-Id: Id9d1f360c2d7492c7b5a48d6c9ae29f530892742
Reviewed-on: https://pdfium-review.googlesource.com/20014
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>

1 files changed, 17 insertions, 39 deletions

diff --git a/core/fpdftext/cpdf_textpage.cpp b/core/fpdftext/cpdf_textpage.cpp
index 7ea2061c26..8ef5522bae 100644
--- a/core/fpdftext/cpdf_textpage.cpp
+++ b/core/fpdftext/cpdf_textpage.cpp
@@ -436,49 +436,27 @@ void CPDF_TextPage::CheckMarkedContentObject(int32_t& start,
   }
 }
 
-WideString CPDF_TextPage::GetPageText(int start, int nCount) const {
-  if (!m_bIsParsed || nCount == 0)
+WideString CPDF_TextPage::GetPageText(int start, int count) const {
+  if (start < 0 || start >= CountChars() || count <= 0 || !m_bIsParsed ||
+      m_CharList.empty() || m_TextBuf.GetLength() == 0) {
     return L"";
-
-  if (start < 0)
-    start = 0;
-
-  if (nCount == -1) {
-    nCount = pdfium::CollectionSize<int>(m_CharList) - start;
-    WideStringView wsTextBuf = m_TextBuf.AsStringView();
-    return WideString(wsTextBuf.Right(wsTextBuf.GetLength() - start));
   }
-  if (nCount <= 0 || m_CharList.empty())
-    return L"";
-  if (nCount + start > pdfium::CollectionSize<int>(m_CharList) - 1)
-    nCount = pdfium::CollectionSize<int>(m_CharList) - start;
-  if (nCount <= 0)
+
+  int text_start = TextIndexFromCharIndex(start);
+  if (text_start < 0)
     return L"";
-  CheckMarkedContentObject(start, nCount);
-  int startindex = 0;
-  PAGECHAR_INFO charinfo = m_CharList[start];
-  int startOffset = 0;
-  while (charinfo.m_Index == -1) {
-    startOffset++;
-    if (startOffset > nCount ||
-        start + startOffset >= pdfium::CollectionSize<int>(m_CharList)) {
-      return L"";
-    }
-    charinfo = m_CharList[start + startOffset];
-  }
-  startindex = charinfo.m_Index;
-  charinfo = m_CharList[start + nCount - 1];
-  int nCountOffset = 0;
-  while (charinfo.m_Index == -1) {
-    nCountOffset++;
-    if (nCountOffset >= nCount)
-      return L"";
-    charinfo = m_CharList[start + nCount - nCountOffset - 1];
-  }
-  nCount = start + nCount - nCountOffset - startindex;
-  if (nCount <= 0)
+
+  count = std::min(count, CountChars() - start);
+
+  int last = start + count - 1;
+  int text_last = TextIndexFromCharIndex(last);
+  if (text_last < 0 || text_last < text_start)
     return L"";
-  return WideString(m_TextBuf.AsStringView().Mid(startindex, nCount));
+
+  int text_count = text_last - text_start + 1;
+
+  return WideString(m_TextBuf.AsStringView().Mid(
+      static_cast<size_t>(text_start), static_cast<size_t>(text_count)));
 }
 
 int CPDF_TextPage::CountRects(int start, int nCount) {