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