The Tor Browser: image/decoders/EXIF.cpp@b8a032363ba2 (annotated)

image/decoders/EXIF.cpp@b8a032363ba2 (annotated)

image/decoders/EXIF.cpp

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "EXIF.h"
 #include "mozilla/Endian.h"
 namespace mozilla {
 namespace image {
 // Section references in this file refer to the EXIF v2.3 standard, also known
 // as CIPA DC-008-Translation-2010.
 // See Section 4.6.4, Table 4.
 // Typesafe enums are intentionally not used here since we're comparing to raw
 // integers produced by parsing.
 enum EXIFTag
 {
   OrientationTag = 0x112,
 };
 // See Section 4.6.2.
 enum EXIFType
 {
   ByteType       = 1,
   ASCIIType      = 2,
   ShortType      = 3,
   LongType       = 4,
   RationalType   = 5,
   UndefinedType  = 7,
   SignedLongType = 9,
   SignedRational = 10,
 };
 static const char* EXIFHeader = "Exif\0\0";
 static const uint32_t EXIFHeaderLength = 6;
 /////////////////////////////////////////////////////////////
 // Parse EXIF data, typically found in a JPEG's APP1 segment.
 /////////////////////////////////////////////////////////////
 EXIFData
 EXIFParser::ParseEXIF(const uint8_t* aData, const uint32_t aLength)
 {
   if (!Initialize(aData, aLength))
     return EXIFData();
   if (!ParseEXIFHeader())
     return EXIFData();
   uint32_t offsetIFD;
   if (!ParseTIFFHeader(offsetIFD))
     return EXIFData();
   JumpTo(offsetIFD);
   Orientation orientation;
   if (!ParseIFD0(orientation))
     return EXIFData();
   // We only care about orientation at this point, so we don't bother with the
   // other IFDs. If we got this far we're done.
   return EXIFData(orientation);
 }
 /////////////////////////////////////////////////////////
 // Parse the EXIF header. (Section 4.7.2, Figure 30)
 /////////////////////////////////////////////////////////
 bool
 EXIFParser::ParseEXIFHeader()
 {
   return MatchString(EXIFHeader, EXIFHeaderLength);
 }
 /////////////////////////////////////////////////////////
 // Parse the TIFF header. (Section 4.5.2, Table 1)
 /////////////////////////////////////////////////////////
 bool
 EXIFParser::ParseTIFFHeader(uint32_t& aIFD0OffsetOut)
 {
   // Determine byte order.
   if (MatchString("MM\0*", 4))
     mByteOrder = ByteOrder::BigEndian;
   else if (MatchString("II*\0", 4))
     mByteOrder = ByteOrder::LittleEndian;
   else
     return false;
   // Determine offset of the 0th IFD. (It shouldn't be greater than 64k, which
   // is the maximum size of the entry APP1 segment.)
   uint32_t ifd0Offset;
   if (!ReadUInt32(ifd0Offset) || ifd0Offset > 64 * 1024)
     return false;
   // The IFD offset is relative to the beginning of the TIFF header, which
   // begins after the EXIF header, so we need to increase the offset
   // appropriately.
   aIFD0OffsetOut = ifd0Offset + EXIFHeaderLength;
   return true;
 }
 /////////////////////////////////////////////////////////
 // Parse the entries in IFD0. (Section 4.6.2)
 /////////////////////////////////////////////////////////
 bool
 EXIFParser::ParseIFD0(Orientation& aOrientationOut)
 {
   uint16_t entryCount;
   if (!ReadUInt16(entryCount))
     return false;
   for (uint16_t entry = 0 ; entry < entryCount ; ++entry) {
     // Read the fields of the entry.
     uint16_t tag;
     if (!ReadUInt16(tag))
       return false;
     // Right now, we only care about orientation, so we immediately skip to the
     // next entry if we find anything else.
     if (tag != OrientationTag) {
       Advance(10);
       continue;
     }
     uint16_t type;
     if (!ReadUInt16(type))
       return false;
     uint32_t count;
     if (!ReadUInt32(count))
       return false;
     // We should have an orientation value here; go ahead and parse it.
     Orientation orientation;
     if (!ParseOrientation(type, count, aOrientationOut))
       return false;
     // Since the orientation is all we care about, we're done.
     return true;
   }
   // We didn't find an orientation field in the IFD. That's OK; we assume the
   // default orientation in that case.
   aOrientationOut = Orientation();
   return true;
 }
 bool
 EXIFParser::ParseOrientation(uint16_t aType, uint32_t aCount, Orientation& aOut)
 {
   // Sanity check the type and count.
   if (aType != ShortType || aCount != 1)
     return false;
   uint16_t value;
   if (!ReadUInt16(value))
     return false;
   switch (value) {
     case 1: aOut = Orientation(Angle::D0,   Flip::Unflipped);  break;
     case 2: aOut = Orientation(Angle::D0,   Flip::Horizontal); break;
     case 3: aOut = Orientation(Angle::D180, Flip::Unflipped);  break;
     case 4: aOut = Orientation(Angle::D180, Flip::Horizontal); break;
     case 5: aOut = Orientation(Angle::D90,  Flip::Horizontal); break;
     case 6: aOut = Orientation(Angle::D90,  Flip::Unflipped);  break;
     case 7: aOut = Orientation(Angle::D270, Flip::Horizontal); break;
     case 8: aOut = Orientation(Angle::D270, Flip::Unflipped);  break;
     default: return false;
   }
   // This is a 32-bit field, but the orientation value only occupies the first
   // 16 bits. We need to advance another 16 bits to consume the entire field.
   Advance(2);
   return true;
 }
 bool
 EXIFParser::Initialize(const uint8_t* aData, const uint32_t aLength)
 {
   if (aData == nullptr)
     return false;
   // An APP1 segment larger than 64k violates the JPEG standard.
   if (aLength > 64 * 1024)
     return false;
   mStart = mCurrent = aData;
   mLength = mRemainingLength = aLength;
   mByteOrder = ByteOrder::Unknown;
   return true;
 }
 void
 EXIFParser::Advance(const uint32_t aDistance)
 {
   if (mRemainingLength >= aDistance) {
     mCurrent += aDistance;
     mRemainingLength -= aDistance;
   } else {
     mCurrent = mStart;
     mRemainingLength = 0;
   }
 }
 void
 EXIFParser::JumpTo(const uint32_t aOffset)
 {
   if (mLength >= aOffset) {
     mCurrent = mStart + aOffset;
     mRemainingLength = mLength - aOffset;
   } else {
     mCurrent = mStart;
     mRemainingLength = 0;
   }
 }
 bool
 EXIFParser::MatchString(const char* aString, const uint32_t aLength)
 {
   if (mRemainingLength < aLength)
     return false;
   for (uint32_t i = 0 ; i < aLength ; ++i) {
     if (mCurrent[i] != aString[i])
       return false;
   }
   Advance(aLength);
   return true;
 }
 bool
 EXIFParser::MatchUInt16(const uint16_t aValue)
 {
   if (mRemainingLength < 2)
     return false;
   bool matched;
   switch (mByteOrder) {
     case ByteOrder::LittleEndian:
       matched = LittleEndian::readUint16(mCurrent) == aValue;
       break;
     case ByteOrder::BigEndian:
       matched = BigEndian::readUint16(mCurrent) == aValue;
       break;
     default:
       NS_NOTREACHED("Should know the byte order by now");
       matched = false;
   }
   if (matched)
     Advance(2);
   return matched;
 }
 bool
 EXIFParser::ReadUInt16(uint16_t& aValue)
 {
   if (mRemainingLength < 2)
     return false;
   bool matched = true;
   switch (mByteOrder) {
     case ByteOrder::LittleEndian:
       aValue = LittleEndian::readUint16(mCurrent);
       break;
     case ByteOrder::BigEndian:
       aValue = BigEndian::readUint16(mCurrent);
       break;
     default:
       NS_NOTREACHED("Should know the byte order by now");
       matched = false;
   }
   if (matched)
     Advance(2);
   return matched;
 }
 bool
 EXIFParser::ReadUInt32(uint32_t& aValue)
 {
   if (mRemainingLength < 4)
     return false;
   bool matched = true;
   switch (mByteOrder) {
     case ByteOrder::LittleEndian:
       aValue = LittleEndian::readUint32(mCurrent);
       break;
     case ByteOrder::BigEndian:
       aValue = BigEndian::readUint32(mCurrent);
       break;
     default:
       NS_NOTREACHED("Should know the byte order by now");
       matched = false;
   }
   if (matched)
     Advance(4);
   return matched;
 }
 } // namespace image
 } // namespace mozilla

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image/decoders/EXIF.cpp@b8a032363ba2 (annotated)

image/decoders/EXIF.cpp