The Tor Browser: image/decoders/nsGIFDecoder2.cpp@ac0c01689b40 (annotated)

image/decoders/nsGIFDecoder2.cpp@ac0c01689b40 (annotated)

image/decoders/nsGIFDecoder2.cpp

Thu, 15 Jan 2015 15:59:08 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 15 Jan 2015 15:59:08 +0100
branch: TOR_BUG_9701
changeset 10: ac0c01689b40
permissions: -rw-r--r--

Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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/. */
 /*
 The Graphics Interchange Format(c) is the copyright property of CompuServe
 Incorporated. Only CompuServe Incorporated is authorized to define, redefine,
 enhance, alter, modify or change in any way the definition of the format.
 CompuServe Incorporated hereby grants a limited, non-exclusive, royalty-free
 license for the use of the Graphics Interchange Format(sm) in computer
 software; computer software utilizing GIF(sm) must acknowledge ownership of the
 Graphics Interchange Format and its Service Mark by CompuServe Incorporated, in
 User and Technical Documentation. Computer software utilizing GIF, which is
 distributed or may be distributed without User or Technical Documentation must
 display to the screen or printer a message acknowledging ownership of the
 Graphics Interchange Format and the Service Mark by CompuServe Incorporated; in
 this case, the acknowledgement may be displayed in an opening screen or leading
 banner, or a closing screen or trailing banner. A message such as the following
 may be used:
     "The Graphics Interchange Format(c) is the Copyright property of
     CompuServe Incorporated. GIF(sm) is a Service Mark property of
     CompuServe Incorporated."
 For further information, please contact :
     CompuServe Incorporated
     Graphics Technology Department
 Arlington Center Boulevard
     Columbus, Ohio  43220
     U. S. A.
 CompuServe Incorporated maintains a mailing list with all those individuals and
 organizations who wish to receive copies of this document when it is corrected
 or revised. This service is offered free of charge; please provide us with your
 mailing address.
 */
 #include <stddef.h>
 #include "nsGIFDecoder2.h"
 #include "nsIInputStream.h"
 #include "RasterImage.h"
 #include "gfxColor.h"
 #include "gfxPlatform.h"
 #include "qcms.h"
 #include <algorithm>
 namespace mozilla {
 namespace image {
 /*
  * GETN(n, s) requests at least 'n' bytes available from 'q', at start of state 's'
  *
  * Colormaps are directly copied in the resp. global_colormap or the local_colormap of the PAL image frame
  * So a fixed buffer in gif_struct is good enough.
  * This buffer is only needed to copy left-over data from one GifWrite call to the next
  */
 #define GETN(n,s)                      \
   PR_BEGIN_MACRO                       \
     mGIFStruct.bytes_to_consume = (n); \
     mGIFStruct.state = (s);            \
   PR_END_MACRO
 /* Get a 16-bit value stored in little-endian format */
 #define GETINT16(p)   ((p)[1]<<8|(p)[0])
 //////////////////////////////////////////////////////////////////////
 // GIF Decoder Implementation
 nsGIFDecoder2::nsGIFDecoder2(RasterImage &aImage)
   : Decoder(aImage)
   , mCurrentRow(-1)
   , mLastFlushedRow(-1)
   , mOldColor(0)
   , mCurrentFrame(-1)
   , mCurrentPass(0)
   , mLastFlushedPass(0)
   , mGIFOpen(false)
   , mSawTransparency(false)
 {
   // Clear out the structure, excluding the arrays
   memset(&mGIFStruct, 0, sizeof(mGIFStruct));
   // Initialize as "animate once" in case no NETSCAPE2.0 extension is found
   mGIFStruct.loop_count = 1;
   // Start with the version (GIF89a|GIF87a)
   mGIFStruct.state = gif_type;
   mGIFStruct.bytes_to_consume = 6;
 }
 nsGIFDecoder2::~nsGIFDecoder2()
 {
   moz_free(mGIFStruct.local_colormap);
   moz_free(mGIFStruct.hold);
 }
 void
 nsGIFDecoder2::FinishInternal()
 {
   NS_ABORT_IF_FALSE(!HasError(), "Shouldn't call FinishInternal after error!");
   // If the GIF got cut off, handle it anyway
   if (!IsSizeDecode() && mGIFOpen) {
     if (mCurrentFrame == mGIFStruct.images_decoded)
       EndImageFrame();
     PostDecodeDone(mGIFStruct.loop_count - 1);
     mGIFOpen = false;
   }
 }
 // Push any new rows according to mCurrentPass/mLastFlushedPass and
 // mCurrentRow/mLastFlushedRow.  Note: caller is responsible for
 // updating mlastFlushed{Row,Pass}.
 void
 nsGIFDecoder2::FlushImageData(uint32_t fromRow, uint32_t rows)
 {
   nsIntRect r(mGIFStruct.x_offset, mGIFStruct.y_offset + fromRow, mGIFStruct.width, rows);
   PostInvalidation(r);
 }
 void
 nsGIFDecoder2::FlushImageData()
 {
   switch (mCurrentPass - mLastFlushedPass) {
     case 0:  // same pass
       if (mCurrentRow - mLastFlushedRow)
         FlushImageData(mLastFlushedRow + 1, mCurrentRow - mLastFlushedRow);
       break;
     case 1:  // one pass on - need to handle bottom & top rects
       FlushImageData(0, mCurrentRow + 1);
       FlushImageData(mLastFlushedRow + 1, mGIFStruct.height - (mLastFlushedRow + 1));
       break;
     default:   // more than one pass on - push the whole frame
       FlushImageData(0, mGIFStruct.height);
   }
 }
 //******************************************************************************
 // GIF decoder callback methods. Part of public API for GIF2
 //******************************************************************************
 //******************************************************************************
 void nsGIFDecoder2::BeginGIF()
 {
   if (mGIFOpen)
     return;
   mGIFOpen = true;
   PostSize(mGIFStruct.screen_width, mGIFStruct.screen_height);
 }
 //******************************************************************************
 void nsGIFDecoder2::BeginImageFrame(uint16_t aDepth)
 {
   gfxImageFormat format;
   if (mGIFStruct.is_transparent)
     format = gfxImageFormat::ARGB32;
   else
     format = gfxImageFormat::RGB24;
   MOZ_ASSERT(HasSize());
   // Use correct format, RGB for first frame, PAL for following frames
   // and include transparency to allow for optimization of opaque images
   if (mGIFStruct.images_decoded) {
     // Image data is stored with original depth and palette
     NeedNewFrame(mGIFStruct.images_decoded, mGIFStruct.x_offset,
                  mGIFStruct.y_offset, mGIFStruct.width, mGIFStruct.height,
                  format, aDepth);
   }
   // Our first full frame is automatically created by the image decoding
   // infrastructure. Just use it as long as it matches up.
   else if (!GetCurrentFrame()->GetRect().IsEqualEdges(nsIntRect(mGIFStruct.x_offset,
                                                                 mGIFStruct.y_offset,
                                                                 mGIFStruct.width,
                                                                 mGIFStruct.height))) {
     // Regardless of depth of input, image is decoded into 24bit RGB
     NeedNewFrame(mGIFStruct.images_decoded, mGIFStruct.x_offset,
                  mGIFStruct.y_offset, mGIFStruct.width, mGIFStruct.height,
                  format);
   } else {
     // Our preallocated frame matches up, with the possible exception of alpha.
     if (format == gfxImageFormat::RGB24) {
       GetCurrentFrame()->SetHasNoAlpha();
     }
   }
   mCurrentFrame = mGIFStruct.images_decoded;
 }
 //******************************************************************************
 void nsGIFDecoder2::EndImageFrame()
 {
   FrameBlender::FrameAlpha alpha = FrameBlender::kFrameHasAlpha;
   // First flush all pending image data
   if (!mGIFStruct.images_decoded) {
     // Only need to flush first frame
     FlushImageData();
     // If the first frame is smaller in height than the entire image, send an
     // invalidation for the area it does not have data for.
     // This will clear the remaining bits of the placeholder. (Bug 37589)
     const uint32_t realFrameHeight = mGIFStruct.height + mGIFStruct.y_offset;
     if (realFrameHeight < mGIFStruct.screen_height) {
       nsIntRect r(0, realFrameHeight,
                   mGIFStruct.screen_width,
                   mGIFStruct.screen_height - realFrameHeight);
       PostInvalidation(r);
     }
     // This transparency check is only valid for first frame
     if (mGIFStruct.is_transparent && !mSawTransparency) {
       alpha = FrameBlender::kFrameOpaque;
     }
   }
   mCurrentRow = mLastFlushedRow = -1;
   mCurrentPass = mLastFlushedPass = 0;
   // Only add frame if we have any rows at all
   if (mGIFStruct.rows_remaining != mGIFStruct.height) {
     if (mGIFStruct.rows_remaining && mGIFStruct.images_decoded) {
       // Clear the remaining rows (only needed for the animation frames)
       uint8_t *rowp = mImageData + ((mGIFStruct.height - mGIFStruct.rows_remaining) * mGIFStruct.width);
       memset(rowp, 0, mGIFStruct.rows_remaining * mGIFStruct.width);
     }
   }
   // Unconditionally increment images_decoded, because we unconditionally
   // append frames in BeginImageFrame(). This ensures that images_decoded
   // always refers to the frame in mImage we're currently decoding,
   // even if some of them weren't decoded properly and thus are blank.
   mGIFStruct.images_decoded++;
   // Tell the superclass we finished a frame
   PostFrameStop(alpha,
                 FrameBlender::FrameDisposalMethod(mGIFStruct.disposal_method),
                 mGIFStruct.delay_time);
   // Reset the transparent pixel
   if (mOldColor) {
     mColormap[mGIFStruct.tpixel] = mOldColor;
     mOldColor = 0;
   }
   mCurrentFrame = -1;
 }
 //******************************************************************************
 // Send the data to the display front-end.
 uint32_t nsGIFDecoder2::OutputRow()
 {
   int drow_start, drow_end;
   drow_start = drow_end = mGIFStruct.irow;
   /* Protect against too much image data */
   if ((unsigned)drow_start >= mGIFStruct.height) {
     NS_WARNING("GIF2.cpp::OutputRow - too much image data");
     return 0;
   }
   if (!mGIFStruct.images_decoded) {
     /*
      * Haeberli-inspired hack for interlaced GIFs: Replicate lines while
      * displaying to diminish the "venetian-blind" effect as the image is
      * loaded. Adjust pixel vertical positions to avoid the appearance of the
      * image crawling up the screen as successive passes are drawn.
      */
     if (mGIFStruct.progressive_display && mGIFStruct.interlaced && (mGIFStruct.ipass < 4)) {
       /* ipass = 1,2,3 results in resp. row_dup = 7,3,1 and row_shift = 3,1,0 */
       const uint32_t row_dup = 15 >> mGIFStruct.ipass;
       const uint32_t row_shift = row_dup >> 1;
       drow_start -= row_shift;
       drow_end = drow_start + row_dup;
       /* Extend if bottom edge isn't covered because of the shift upward. */
       if (((mGIFStruct.height - 1) - drow_end) <= row_shift)
         drow_end = mGIFStruct.height - 1;
       /* Clamp first and last rows to upper and lower edge of image. */
       if (drow_start < 0)
         drow_start = 0;
       if ((unsigned)drow_end >= mGIFStruct.height)
         drow_end = mGIFStruct.height - 1;
     }
     // Row to process
     const uint32_t bpr = sizeof(uint32_t) * mGIFStruct.width;
     uint8_t *rowp = mImageData + (mGIFStruct.irow * bpr);
     // Convert color indices to Cairo pixels
     uint8_t *from = rowp + mGIFStruct.width;
     uint32_t *to = ((uint32_t*)rowp) + mGIFStruct.width;
     uint32_t *cmap = mColormap;
     for (uint32_t c = mGIFStruct.width; c > 0; c--) {
       *--to = cmap[*--from];
     }
     // check for alpha (only for first frame)
     if (mGIFStruct.is_transparent && !mSawTransparency) {
       const uint32_t *rgb = (uint32_t*)rowp;
       for (uint32_t i = mGIFStruct.width; i > 0; i--) {
         if (*rgb++ == 0) {
           mSawTransparency = true;
           break;
         }
       }
     }
     // Duplicate rows
     if (drow_end > drow_start) {
       // irow is the current row filled
       for (int r = drow_start; r <= drow_end; r++) {
         if (r != int(mGIFStruct.irow)) {
           memcpy(mImageData + (r * bpr), rowp, bpr);
         }
       }
     }
   }
   mCurrentRow = drow_end;
   mCurrentPass = mGIFStruct.ipass;
   if (mGIFStruct.ipass == 1)
     mLastFlushedPass = mGIFStruct.ipass;   // interlaced starts at 1
   if (!mGIFStruct.interlaced) {
     mGIFStruct.irow++;
   } else {
     static const uint8_t kjump[5] = { 1, 8, 8, 4, 2 };
     do {
       // Row increments resp. per 8,8,4,2 rows
       mGIFStruct.irow += kjump[mGIFStruct.ipass];
       if (mGIFStruct.irow >= mGIFStruct.height) {
         // Next pass starts resp. at row 4,2,1,0
         mGIFStruct.irow = 8 >> mGIFStruct.ipass;
         mGIFStruct.ipass++;
       }
     } while (mGIFStruct.irow >= mGIFStruct.height);
   }
   return --mGIFStruct.rows_remaining;
 }
 //******************************************************************************
 /* Perform Lempel-Ziv-Welch decoding */
 bool
 nsGIFDecoder2::DoLzw(const uint8_t *q)
 {
   if (!mGIFStruct.rows_remaining)
     return true;
   /* Copy all the decoder state variables into locals so the compiler
    * won't worry about them being aliased.  The locals will be homed
    * back into the GIF decoder structure when we exit.
    */
   int avail       = mGIFStruct.avail;
   int bits        = mGIFStruct.bits;
   int codesize    = mGIFStruct.codesize;
   int codemask    = mGIFStruct.codemask;
   int count       = mGIFStruct.count;
   int oldcode     = mGIFStruct.oldcode;
   const int clear_code = ClearCode();
   uint8_t firstchar = mGIFStruct.firstchar;
   int32_t datum     = mGIFStruct.datum;
   uint16_t *prefix  = mGIFStruct.prefix;
   uint8_t *stackp   = mGIFStruct.stackp;
   uint8_t *suffix   = mGIFStruct.suffix;
   uint8_t *stack    = mGIFStruct.stack;
   uint8_t *rowp     = mGIFStruct.rowp;
   uint32_t bpr = mGIFStruct.width;
   if (!mGIFStruct.images_decoded)
     bpr *= sizeof(uint32_t);
   uint8_t *rowend   = mImageData + (bpr * mGIFStruct.irow) + mGIFStruct.width;
 #define OUTPUT_ROW()                                        \
   PR_BEGIN_MACRO                                            \
     if (!OutputRow())                                       \
       goto END;                                             \
     rowp = mImageData + mGIFStruct.irow * bpr;              \
     rowend = rowp + mGIFStruct.width;                       \
   PR_END_MACRO
   for (const uint8_t* ch = q; count-- > 0; ch++)
   {
     /* Feed the next byte into the decoder's 32-bit input buffer. */
     datum += ((int32_t) *ch) << bits;
     bits += 8;
     /* Check for underflow of decoder's 32-bit input buffer. */
     while (bits >= codesize)
     {
       /* Get the leading variable-length symbol from the data stream */
       int code = datum & codemask;
       datum >>= codesize;
       bits -= codesize;
       /* Reset the dictionary to its original state, if requested */
       if (code == clear_code) {
         codesize = mGIFStruct.datasize + 1;
         codemask = (1 << codesize) - 1;
         avail = clear_code + 2;
         oldcode = -1;
         continue;
       }
       /* Check for explicit end-of-stream code */
       if (code == (clear_code + 1)) {
         /* end-of-stream should only appear after all image data */
         return (mGIFStruct.rows_remaining == 0);
       }
       if (oldcode == -1) {
         if (code >= MAX_BITS)
           return false;
         *rowp++ = suffix[code] & mColorMask; // ensure index is within colormap
         if (rowp == rowend)
           OUTPUT_ROW();
         firstchar = oldcode = code;
         continue;
       }
       int incode = code;
       if (code >= avail) {
         *stackp++ = firstchar;
         code = oldcode;
         if (stackp >= stack + MAX_BITS)
           return false;
       }
       while (code >= clear_code)
       {
         if ((code >= MAX_BITS) || (code == prefix[code]))
           return false;
         *stackp++ = suffix[code];
         code = prefix[code];
         if (stackp == stack + MAX_BITS)
           return false;
       }
       *stackp++ = firstchar = suffix[code];
       /* Define a new codeword in the dictionary. */
       if (avail < 4096) {
         prefix[avail] = oldcode;
         suffix[avail] = firstchar;
         avail++;
         /* If we've used up all the codewords of a given length
          * increase the length of codewords by one bit, but don't
          * exceed the specified maximum codeword size of 12 bits.
          */
         if (((avail & codemask) == 0) && (avail < 4096)) {
           codesize++;
           codemask += avail;
         }
       }
       oldcode = incode;
       /* Copy the decoded data out to the scanline buffer. */
       do {
         *rowp++ = *--stackp & mColorMask; // ensure index is within colormap
         if (rowp == rowend)
           OUTPUT_ROW();
       } while (stackp > stack);
     }
   }
   END:
   /* Home the local copies of the GIF decoder state variables */
   mGIFStruct.avail = avail;
   mGIFStruct.bits = bits;
   mGIFStruct.codesize = codesize;
   mGIFStruct.codemask = codemask;
   mGIFStruct.count = count;
   mGIFStruct.oldcode = oldcode;
   mGIFStruct.firstchar = firstchar;
   mGIFStruct.datum = datum;
   mGIFStruct.stackp = stackp;
   mGIFStruct.rowp = rowp;
   return true;
 }
 /**
  * Expand the colormap from RGB to Packed ARGB as needed by Cairo.
  * And apply any LCMS transformation.
  */
 static void ConvertColormap(uint32_t *aColormap, uint32_t aColors)
 {
   // Apply CMS transformation if enabled and available
   if (gfxPlatform::GetCMSMode() == eCMSMode_All) {
     qcms_transform *transform = gfxPlatform::GetCMSRGBTransform();
     if (transform)
       qcms_transform_data(transform, aColormap, aColormap, aColors);
   }
   // Convert from the GIF's RGB format to the Cairo format.
   // Work from end to begin, because of the in-place expansion
   uint8_t *from = ((uint8_t *)aColormap) + 3 * aColors;
   uint32_t *to = aColormap + aColors;
   // Convert color entries to Cairo format
   // set up for loops below
   if (!aColors) return;
   uint32_t c = aColors;
   // copy as bytes until source pointer is 32-bit-aligned
   // NB: can't use 32-bit reads, they might read off the end of the buffer
   for (; (NS_PTR_TO_UINT32(from) & 0x3) && c; --c) {
     from -= 3;
     *--to = gfxPackedPixel(0xFF, from[0], from[1], from[2]);
   }
   // bulk copy of pixels.
   while (c >= 4) {
     from -= 12;
     to   -=  4;
     c    -=  4;
     GFX_BLOCK_RGB_TO_FRGB(from,to);
   }
   // copy remaining pixel(s)
   // NB: can't use 32-bit reads, they might read off the end of the buffer
   while (c--) {
     from -= 3;
     *--to = gfxPackedPixel(0xFF, from[0], from[1], from[2]);
   }
 }
 void
 nsGIFDecoder2::WriteInternal(const char *aBuffer, uint32_t aCount, DecodeStrategy)
 {
   NS_ABORT_IF_FALSE(!HasError(), "Shouldn't call WriteInternal after error!");
   // These variables changed names, and renaming would make a much bigger patch :(
   const uint8_t *buf = (const uint8_t *)aBuffer;
   uint32_t len = aCount;
   const uint8_t *q = buf;
   // Add what we have sofar to the block
   // If previous call to me left something in the hold first complete current block
   // Or if we are filling the colormaps, first complete the colormap
   uint8_t* p = (mGIFStruct.state == gif_global_colormap) ? (uint8_t*)mGIFStruct.global_colormap :
                (mGIFStruct.state == gif_image_colormap) ? (uint8_t*)mColormap :
                (mGIFStruct.bytes_in_hold) ? mGIFStruct.hold : nullptr;
   if (len == 0 && buf == nullptr) {
     // We've just gotten the frame we asked for. Time to use the data we
     // stashed away.
     len = mGIFStruct.bytes_in_hold;
     q = buf = p;
   } else if (p) {
     // Add what we have sofar to the block
     uint32_t l = std::min(len, mGIFStruct.bytes_to_consume);
     memcpy(p+mGIFStruct.bytes_in_hold, buf, l);
     if (l < mGIFStruct.bytes_to_consume) {
       // Not enough in 'buf' to complete current block, get more
       mGIFStruct.bytes_in_hold += l;
       mGIFStruct.bytes_to_consume -= l;
       return;
     }
     // Point 'q' to complete block in hold (or in colormap)
     q = p;
   }
   // Invariant:
   //    'q' is start of current to be processed block (hold, colormap or buf)
   //    'bytes_to_consume' is number of bytes to consume from 'buf'
   //    'buf' points to the bytes to be consumed from the input buffer
   //    'len' is number of bytes left in input buffer from position 'buf'.
   //    At entrance of the for loop will 'buf' will be moved 'bytes_to_consume'
   //    to point to next buffer, 'len' is adjusted accordingly.
   //    So that next round in for loop, q gets pointed to the next buffer.
   for (;len >= mGIFStruct.bytes_to_consume; q=buf, mGIFStruct.bytes_in_hold = 0) {
     // Eat the current block from the buffer, q keeps pointed at current block
     buf += mGIFStruct.bytes_to_consume;
     len -= mGIFStruct.bytes_to_consume;
     switch (mGIFStruct.state)
     {
     case gif_lzw:
       if (!DoLzw(q)) {
         mGIFStruct.state = gif_error;
         break;
       }
       GETN(1, gif_sub_block);
       break;
     case gif_lzw_start:
     {
       // Make sure the transparent pixel is transparent in the colormap
       if (mGIFStruct.is_transparent) {
         // Save old value so we can restore it later
         if (mColormap == mGIFStruct.global_colormap)
             mOldColor = mColormap[mGIFStruct.tpixel];
         mColormap[mGIFStruct.tpixel] = 0;
       }
       /* Initialize LZW parser/decoder */
       mGIFStruct.datasize = *q;
       const int clear_code = ClearCode();
       if (mGIFStruct.datasize > MAX_LZW_BITS ||
           clear_code >= MAX_BITS) {
         mGIFStruct.state = gif_error;
         break;
       }
       mGIFStruct.avail = clear_code + 2;
       mGIFStruct.oldcode = -1;
       mGIFStruct.codesize = mGIFStruct.datasize + 1;
       mGIFStruct.codemask = (1 << mGIFStruct.codesize) - 1;
       mGIFStruct.datum = mGIFStruct.bits = 0;
       /* init the tables */
       for (int i = 0; i < clear_code; i++)
         mGIFStruct.suffix[i] = i;
       mGIFStruct.stackp = mGIFStruct.stack;
       GETN(1, gif_sub_block);
     }
     break;
     /* All GIF files begin with "GIF87a" or "GIF89a" */
     case gif_type:
       if (!strncmp((char*)q, "GIF89a", 6)) {
         mGIFStruct.version = 89;
       } else if (!strncmp((char*)q, "GIF87a", 6)) {
         mGIFStruct.version = 87;
       } else {
         mGIFStruct.state = gif_error;
         break;
       }
       GETN(7, gif_global_header);
       break;
     case gif_global_header:
       /* This is the height and width of the "screen" or
        * frame into which images are rendered.  The
        * individual images can be smaller than the
        * screen size and located with an origin anywhere
        * within the screen.
        */
       mGIFStruct.screen_width = GETINT16(q);
       mGIFStruct.screen_height = GETINT16(q + 2);
       mGIFStruct.global_colormap_depth = (q[4]&0x07) + 1;
       if (IsSizeDecode()) {
         MOZ_ASSERT(!mGIFOpen, "Gif should not be open at this point");
         PostSize(mGIFStruct.screen_width, mGIFStruct.screen_height);
         return;
       }
       // screen_bgcolor is not used
       //mGIFStruct.screen_bgcolor = q[5];
       // q[6] = Pixel Aspect Ratio
       //   Not used
       //   float aspect = (float)((q[6] + 15) / 64.0);
       if (q[4] & 0x80) { /* global map */
         // Get the global colormap
         const uint32_t size = (3 << mGIFStruct.global_colormap_depth);
         if (len < size) {
           // Use 'hold' pattern to get the global colormap
           GETN(size, gif_global_colormap);
           break;
         }
         // Copy everything, go to colormap state to do CMS correction
         memcpy(mGIFStruct.global_colormap, buf, size);
         buf += size;
         len -= size;
         GETN(0, gif_global_colormap);
         break;
       }
       GETN(1, gif_image_start);
       break;
     case gif_global_colormap:
       // Everything is already copied into global_colormap
       // Convert into Cairo colors including CMS transformation
       ConvertColormap(mGIFStruct.global_colormap, 1<<mGIFStruct.global_colormap_depth);
       GETN(1, gif_image_start);
       break;
     case gif_image_start:
       switch (*q) {
         case GIF_TRAILER:
           mGIFStruct.state = gif_done;
           break;
         case GIF_EXTENSION_INTRODUCER:
           GETN(2, gif_extension);
           break;
         case GIF_IMAGE_SEPARATOR:
           GETN(9, gif_image_header);
           break;
         default:
           /* If we get anything other than GIF_IMAGE_SEPARATOR,
            * GIF_EXTENSION_INTRODUCER, or GIF_TRAILER, there is extraneous data
            * between blocks. The GIF87a spec tells us to keep reading
            * until we find an image separator, but GIF89a says such
            * a file is corrupt. We follow GIF89a and bail out. */
           if (mGIFStruct.images_decoded > 0) {
             /* The file is corrupt, but one or more images have
              * been decoded correctly. In this case, we proceed
              * as if the file were correctly terminated and set
              * the state to gif_done, so the GIF will display.
              */
             mGIFStruct.state = gif_done;
           } else {
             /* No images decoded, there is nothing to display. */
             mGIFStruct.state = gif_error;
           }
       }
       break;
     case gif_extension:
       mGIFStruct.bytes_to_consume = q[1];
       if (mGIFStruct.bytes_to_consume) {
         switch (*q) {
         case GIF_GRAPHIC_CONTROL_LABEL:
           // The GIF spec mandates that the GIFControlExtension header block length is 4 bytes,
           // and the parser for this block reads 4 bytes, so we must enforce that the buffer
           // contains at least this many bytes. If the GIF specifies a different length, we
           // allow that, so long as it's larger; the additional data will simply be ignored.
           mGIFStruct.state = gif_control_extension;
           mGIFStruct.bytes_to_consume = std::max(mGIFStruct.bytes_to_consume, 4u);
           break;
         // The GIF spec also specifies the lengths of the following two extensions' headers
         // (as 12 and 11 bytes, respectively). Because we ignore the plain text extension entirely
         // and sanity-check the actual length of the application extension header before reading it,
         // we allow GIFs to deviate from these values in either direction. This is important for
         // real-world compatibility, as GIFs in the wild exist with application extension headers
         // that are both shorter and longer than 11 bytes.
         case GIF_APPLICATION_EXTENSION_LABEL:
           mGIFStruct.state = gif_application_extension;
           break;
         case GIF_PLAIN_TEXT_LABEL:
           mGIFStruct.state = gif_skip_block;
           break;
         case GIF_COMMENT_LABEL:
           mGIFStruct.state = gif_consume_comment;
           break;
         default:
           mGIFStruct.state = gif_skip_block;
         }
       } else {
         GETN(1, gif_image_start);
       }
       break;
     case gif_consume_block:
       if (!*q)
         GETN(1, gif_image_start);
       else
         GETN(*q, gif_skip_block);
       break;
     case gif_skip_block:
       GETN(1, gif_consume_block);
       break;
     case gif_control_extension:
       mGIFStruct.is_transparent = *q & 0x1;
       mGIFStruct.tpixel = q[3];
       mGIFStruct.disposal_method = ((*q) >> 2) & 0x7;
       // Some specs say 3rd bit (value 4), other specs say value 3
       // Let's choose 3 (the more popular)
       if (mGIFStruct.disposal_method == 4)
         mGIFStruct.disposal_method = 3;
       mGIFStruct.delay_time = GETINT16(q + 1) * 10;
       GETN(1, gif_consume_block);
       break;
     case gif_comment_extension:
       if (*q)
         GETN(*q, gif_consume_comment);
       else
         GETN(1, gif_image_start);
       break;
     case gif_consume_comment:
       GETN(1, gif_comment_extension);
       break;
     case gif_application_extension:
       /* Check for netscape application extension */
       if (mGIFStruct.bytes_to_consume == 11 &&
           (!strncmp((char*)q, "NETSCAPE2.0", 11) ||
            !strncmp((char*)q, "ANIMEXTS1.0", 11)))
         GETN(1, gif_netscape_extension_block);
       else
         GETN(1, gif_consume_block);
       break;
     /* Netscape-specific GIF extension: animation looping */
     case gif_netscape_extension_block:
       if (*q)
         // We might need to consume 3 bytes in
         // gif_consume_netscape_extension, so make sure we have at least that.
         GETN(std::max(3, static_cast<int>(*q)), gif_consume_netscape_extension);
       else
         GETN(1, gif_image_start);
       break;
     /* Parse netscape-specific application extensions */
     case gif_consume_netscape_extension:
       switch (q[0] & 7) {
         case 1:
           /* Loop entire animation specified # of times.  Only read the
              loop count during the first iteration. */
           mGIFStruct.loop_count = GETINT16(q + 1);
           GETN(1, gif_netscape_extension_block);
           break;
         case 2:
           /* Wait for specified # of bytes to enter buffer */
           // Don't do this, this extension doesn't exist (isn't used at all)
           // and doesn't do anything, as our streaming/buffering takes care of it all...
           // See: http://semmix.pl/color/exgraf/eeg24.htm
           GETN(1, gif_netscape_extension_block);
           break;
         default:
           // 0,3-7 are yet to be defined netscape extension codes
           mGIFStruct.state = gif_error;
       }
       break;
     case gif_image_header:
     {
       /* Get image offsets, with respect to the screen origin */
       mGIFStruct.x_offset = GETINT16(q);
       mGIFStruct.y_offset = GETINT16(q + 2);
       /* Get image width and height. */
       mGIFStruct.width  = GETINT16(q + 4);
       mGIFStruct.height = GETINT16(q + 6);
       if (!mGIFStruct.images_decoded) {
         /* Work around broken GIF files where the logical screen
          * size has weird width or height.  We assume that GIF87a
          * files don't contain animations.
          */
         if ((mGIFStruct.screen_height < mGIFStruct.height) ||
             (mGIFStruct.screen_width < mGIFStruct.width) ||
             (mGIFStruct.version == 87)) {
           mGIFStruct.screen_height = mGIFStruct.height;
           mGIFStruct.screen_width = mGIFStruct.width;
           mGIFStruct.x_offset = 0;
           mGIFStruct.y_offset = 0;
         }
         // Create the image container with the right size.
         BeginGIF();
         if (HasError()) {
           // Setting the size led to an error.
           mGIFStruct.state = gif_error;
           return;
         }
         // If we were doing a size decode, we're done
         if (IsSizeDecode())
           return;
       }
       /* Work around more broken GIF files that have zero image
          width or height */
       if (!mGIFStruct.height || !mGIFStruct.width) {
         mGIFStruct.height = mGIFStruct.screen_height;
         mGIFStruct.width = mGIFStruct.screen_width;
         if (!mGIFStruct.height || !mGIFStruct.width) {
           mGIFStruct.state = gif_error;
           break;
         }
       }
       /* Depth of colors is determined by colormap */
       /* (q[8] & 0x80) indicates local colormap */
       /* bits per pixel is (q[8]&0x07 + 1) when local colormap is set */
       uint32_t depth = mGIFStruct.global_colormap_depth;
       if (q[8] & 0x80)
         depth = (q[8]&0x07) + 1;
       uint32_t realDepth = depth;
       while (mGIFStruct.tpixel >= (1 << realDepth) && (realDepth < 8)) {
         realDepth++;
       }
       // Mask to limit the color values within the colormap
       mColorMask = 0xFF >> (8 - realDepth);
       BeginImageFrame(realDepth);
       if (NeedsNewFrame()) {
         // We now need a new frame from the decoder framework. We leave all our
         // data in the buffer as if it wasn't consumed, copy to our hold and return
         // to the decoder framework.
         uint32_t size = len + mGIFStruct.bytes_to_consume + mGIFStruct.bytes_in_hold;
         if (size) {
           if (SetHold(q, mGIFStruct.bytes_to_consume + mGIFStruct.bytes_in_hold, buf, len)) {
             // Back into the decoder infrastructure so we can get called again.
             GETN(9, gif_image_header_continue);
             return;
           }
         }
         break;
       } else {
         // FALL THROUGH
       }
     }
     case gif_image_header_continue:
     {
       // While decoders can reuse frames, we unconditionally increment
       // mGIFStruct.images_decoded when we're done with a frame, so we both can
       // and need to zero out the colormap and image data after every new frame.
       memset(mImageData, 0, mImageDataLength);
       if (mColormap) {
         memset(mColormap, 0, mColormapSize);
       }
       if (!mGIFStruct.images_decoded) {
         // Send a onetime invalidation for the first frame if it has a y-axis offset.
         // Otherwise, the area may never be refreshed and the placeholder will remain
         // on the screen. (Bug 37589)
         if (mGIFStruct.y_offset > 0) {
           nsIntRect r(0, 0, mGIFStruct.screen_width, mGIFStruct.y_offset);
           PostInvalidation(r);
         }
       }
       if (q[8] & 0x40) {
         mGIFStruct.interlaced = true;
         mGIFStruct.ipass = 1;
       } else {
         mGIFStruct.interlaced = false;
         mGIFStruct.ipass = 0;
       }
       /* Only apply the Haeberli display hack on the first frame */
       mGIFStruct.progressive_display = (mGIFStruct.images_decoded == 0);
       /* Clear state from last image */
       mGIFStruct.irow = 0;
       mGIFStruct.rows_remaining = mGIFStruct.height;
       mGIFStruct.rowp = mImageData;
       /* Depth of colors is determined by colormap */
       /* (q[8] & 0x80) indicates local colormap */
       /* bits per pixel is (q[8]&0x07 + 1) when local colormap is set */
       uint32_t depth = mGIFStruct.global_colormap_depth;
       if (q[8] & 0x80)
         depth = (q[8]&0x07) + 1;
       uint32_t realDepth = depth;
       while (mGIFStruct.tpixel >= (1 << realDepth) && (realDepth < 8)) {
         realDepth++;
       }
       if (q[8] & 0x80) /* has a local colormap? */
       {
         mGIFStruct.local_colormap_size = 1 << depth;
         if (!mGIFStruct.images_decoded) {
           // First frame has local colormap, allocate space for it
           // as the image frame doesn't have its own palette
           mColormapSize = sizeof(uint32_t) << realDepth;
           if (!mGIFStruct.local_colormap) {
             mGIFStruct.local_colormap = (uint32_t*)moz_xmalloc(mColormapSize);
           }
           mColormap = mGIFStruct.local_colormap;
         }
         const uint32_t size = 3 << depth;
         if (mColormapSize > size) {
           // Clear the notfilled part of the colormap
           memset(((uint8_t*)mColormap) + size, 0, mColormapSize - size);
         }
         if (len < size) {
           // Use 'hold' pattern to get the image colormap
           GETN(size, gif_image_colormap);
           break;
         }
         // Copy everything, go to colormap state to do CMS correction
         memcpy(mColormap, buf, size);
         buf += size;
         len -= size;
         GETN(0, gif_image_colormap);
         break;
       } else {
         /* Switch back to the global palette */
         if (mGIFStruct.images_decoded) {
           // Copy global colormap into the palette of current frame
           memcpy(mColormap, mGIFStruct.global_colormap, mColormapSize);
         } else {
           mColormap = mGIFStruct.global_colormap;
         }
       }
       GETN(1, gif_lzw_start);
     }
     break;
     case gif_image_colormap:
       // Everything is already copied into local_colormap
       // Convert into Cairo colors including CMS transformation
       ConvertColormap(mColormap, mGIFStruct.local_colormap_size);
       GETN(1, gif_lzw_start);
       break;
     case gif_sub_block:
       mGIFStruct.count = *q;
       if (mGIFStruct.count) {
         /* Still working on the same image: Process next LZW data block */
         /* Make sure there are still rows left. If the GIF data */
         /* is corrupt, we may not get an explicit terminator.   */
         if (!mGIFStruct.rows_remaining) {
 #ifdef DONT_TOLERATE_BROKEN_GIFS
           mGIFStruct.state = gif_error;
           break;
 #else
           /* This is an illegal GIF, but we remain tolerant. */
           GETN(1, gif_sub_block);
 #endif
           if (mGIFStruct.count == GIF_TRAILER) {
             /* Found a terminator anyway, so consider the image done */
             GETN(1, gif_done);
             break;
           }
         }
         GETN(mGIFStruct.count, gif_lzw);
       } else {
         /* See if there are any more images in this sequence. */
         EndImageFrame();
         GETN(1, gif_image_start);
       }
       break;
     case gif_done:
       MOZ_ASSERT(!IsSizeDecode(), "Size decodes shouldn't reach gif_done");
       FinishInternal();
       goto done;
     case gif_error:
       PostDataError();
       return;
     // We shouldn't ever get here.
     default:
       break;
     }
   }
   // if an error state is set but no data remains, code flow reaches here
   if (mGIFStruct.state == gif_error) {
       PostDataError();
       return;
   }
   // Copy the leftover into mGIFStruct.hold
   if (len) {
     // Add what we have sofar to the block
     if (mGIFStruct.state != gif_global_colormap && mGIFStruct.state != gif_image_colormap) {
       if (!SetHold(buf, len)) {
         PostDataError();
         return;
       }
     } else {
       uint8_t* p = (mGIFStruct.state == gif_global_colormap) ? (uint8_t*)mGIFStruct.global_colormap :
                                                                (uint8_t*)mColormap;
       memcpy(p, buf, len);
       mGIFStruct.bytes_in_hold = len;
     }
     mGIFStruct.bytes_to_consume -= len;
   }
 // We want to flush before returning if we're on the first frame
 done:
   if (!mGIFStruct.images_decoded) {
     FlushImageData();
     mLastFlushedRow = mCurrentRow;
     mLastFlushedPass = mCurrentPass;
   }
   return;
 }
 bool
 nsGIFDecoder2::SetHold(const uint8_t* buf1, uint32_t count1, const uint8_t* buf2 /* = nullptr */, uint32_t count2 /* = 0 */)
 {
   // We have to handle the case that buf currently points to hold
   uint8_t* newHold = (uint8_t *) moz_malloc(std::max(uint32_t(MIN_HOLD_SIZE), count1 + count2));
   if (!newHold) {
     mGIFStruct.state = gif_error;
     return false;
   }
   memcpy(newHold, buf1, count1);
   if (buf2) {
     memcpy(newHold + count1, buf2, count2);
   }
   moz_free(mGIFStruct.hold);
   mGIFStruct.hold = newHold;
   mGIFStruct.bytes_in_hold = count1 + count2;
   return true;
 }
 Telemetry::ID
 nsGIFDecoder2::SpeedHistogram()
 {
   return Telemetry::IMAGE_DECODE_SPEED_GIF;
 }
 } // namespace image
 } // namespace mozilla

The Tor Browser / annotate

image/decoders/nsGIFDecoder2.cpp@ac0c01689b40 (annotated)

image/decoders/nsGIFDecoder2.cpp