in the attempt to fix 627393, changed IFX_FileRead's readBlock to return the length it reads

core/fpdfapi/parser/cpdf_data_avail.cpp

Index: core/fpdfapi/parser/cpdf_data_avail.cpp
diff --git a/core/fpdfapi/parser/cpdf_data_avail.cpp b/core/fpdfapi/parser/cpdf_data_avail.cpp
index 3fe4b03da62012ae33d8cbf50944708e5572224f..d3d70adbe9731d609a1cde298d0fd3e17dcd2b1c 100644
--- a/core/fpdfapi/parser/cpdf_data_avail.cpp
+++ b/core/fpdfapi/parser/cpdf_data_avail.cpp
@@ -957,11 +957,13 @@ bool CPDF_DataAvail::GetNextChar(uint8_t& ch) {
     if ((FX_FILESIZE)(read_pos + read_size) > m_dwFileLen)
       read_pos = m_dwFileLen - read_size;
 
-    if (!m_pFileRead->ReadBlock(m_bufferData, read_pos, read_size))
+    uint32_t read_real_size =
+        m_pFileRead->ReadBlock(m_bufferData, read_pos, read_size);
+    if (read_real_size != read_size && !m_pFileRead->IsEOF())
       return false;
 
     m_bufferOffset = read_pos;
-    m_bufferSize = read_size;
+    m_bufferSize = read_real_size;
   }
   ch = m_bufferData[pos - m_bufferOffset];
   m_Pos++;
@@ -1062,7 +1064,8 @@ bool CPDF_DataAvail::CheckTrailer(DownloadHints* pHints) {
   int32_t iTrailerSize =
       (int32_t)(m_Pos + 512 > m_dwFileLen ? m_dwFileLen - m_Pos : 512);
   if (m_pFileAvail->IsDataAvail(m_Pos, iTrailerSize)) {
-    int32_t iSize = (int32_t)(m_Pos + iTrailerSize - m_dwTrailerOffset);
+    uint32_t iSize = pdfium::base::checked_cast<uint32_t>(m_Pos + iTrailerSize -
+                                                          m_dwTrailerOffset);
     CFX_BinaryBuf buf(iSize);
     uint8_t* pBuf = buf.GetBuffer();
     if (!pBuf) {
@@ -1070,10 +1073,11 @@ bool CPDF_DataAvail::CheckTrailer(DownloadHints* pHints) {
       return false;
     }
 
-    if (!m_pFileRead->ReadBlock(pBuf, m_dwTrailerOffset, iSize))
+    uint32_t readSize = m_pFileRead->ReadBlock(pBuf, m_dwTrailerOffset, iSize);
+    if (readSize != iSize && !m_pFileRead->IsEOF())
       return false;
 
-    ScopedFileStream file(FX_CreateMemoryStream(pBuf, (size_t)iSize, false));
+    ScopedFileStream file(FX_CreateMemoryStream(pBuf, (size_t)readSize, false));
     m_syntaxParser.InitParser(file.get(), 0);
 
     std::unique_ptr<CPDF_Object> pTrailer(