The Tor Browser: mobile/android/base/favicons/decoders/ICODecoder.java@fc2d59ddac77 (annotated)

mobile/android/base/favicons/decoders/ICODecoder.java@fc2d59ddac77 (annotated)

mobile/android/base/favicons/decoders/ICODecoder.java

Wed, 31 Dec 2014 07:22:50 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 07:22:50 +0100
branch: TOR_BUG_3246
changeset 4: fc2d59ddac77
permissions: -rw-r--r--

Correct previous dual key logic pending first delivery installment.

 /* 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/. */
 package org.mozilla.gecko.favicons.decoders;
 import android.graphics.Bitmap;
 import org.mozilla.gecko.favicons.Favicons;
 import org.mozilla.gecko.gfx.BitmapUtils;
 import android.util.SparseArray;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 /**
  * Utility class for determining the region of a provided array which contains the largest bitmap,
  * assuming the provided array is a valid ICO and the bitmap desired is square, and for pruning
  * unwanted entries from ICO files, if desired.
  *
  * An ICO file is a container format that may hold up to 255 images in either BMP or PNG format.
  * A mixture of image types may not exist.
  *
  * The format consists of a header specifying the number, n,  of images, followed by the Icon Directory.
  *
  * The Icon Directory consists of n Icon Directory Entries, each 16 bytes in length, specifying, for
  * the corresponding image, the dimensions, colour information, payload size, and location in the file.
  *
  * All numerical fields follow a little-endian byte ordering.
  *
  * Header format:
  *
  *  0               1               2               3
  *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |  Reserved field. Must be zero |  Type (1 for ICO, 2 for CUR)  |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |         Image count (n)       |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  *
  * The type field is expected to always be 1. CUR format images should not be used for Favicons.
  *
  *
  * Icon Directory Entry format:
  *
  *  0               1               2               3
  *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |  Image width  | Image height  | Palette size  | Reserved (0)  |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |       Colour plane count      |         Bits per pixel        |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |                   Size of image data, in bytes                |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  * |      Start of image data, as an offset from start of file     |
  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  *
  * Image dimensions of zero are to be interpreted as image dimensions of 256.
  *
  * The palette size field records the number of colours in the stored BMP, if a palette is used. Zero
  * if the payload is a PNG or no palette is in use.
  *
  * The number of colour planes is, usually, 0 (Not in use) or 1. Values greater than 1 are to be
  * interpreted not as a colour plane count, but as a multiplying factor on the bits per pixel field.
  * (Apparently 65535 was not deemed a sufficiently large maximum value of bits per pixel.)
  *
  *
  * The Icon Directory consists of n-many Icon Directory Entries in sequence, with no gaps.
  *
  * This class is not thread safe.
  */
 public class ICODecoder implements Iterable<Bitmap> {
     // The number of bytes that compacting will save for us to bother doing it.
     public static final int COMPACT_THRESHOLD = 4000;
     // Some geometry of an ICO file.
     public static final int ICO_HEADER_LENGTH_BYTES = 6;
     public static final int ICO_ICONDIRENTRY_LENGTH_BYTES = 16;
     // The buffer containing bytes to attempt to decode.
     private byte[] decodand;
     // The region of the decodand to decode.
     private int offset;
     private int len;
     private IconDirectoryEntry[] iconDirectory;
     private boolean isValid;
     private boolean hasDecoded;
     public ICODecoder(byte[] decodand, int offset, int len) {
         this.decodand = decodand;
         this.offset = offset;
         this.len = len;
     }
     /**
      * Decode the Icon Directory for this ICO and store the result in iconDirectory.
      *
      * @return true if ICO decoding was considered to probably be a success, false if it certainly
      *         was a failure.
      */
     private boolean decodeIconDirectoryAndPossiblyPrune() {
         hasDecoded = true;
         // Fail if the end of the described range is out of bounds.
         if (offset + len > decodand.length) {
             return false;
         }
         // Fail if we don't have enough space for the header.
         if (len < ICO_HEADER_LENGTH_BYTES) {
             return false;
         }
         // Check that the reserved fields in the header are indeed zero, and that the type field
         // specifies ICO. If not, we've probably been given something that isn't really an ICO.
         if (decodand[offset] != 0 ||
             decodand[offset + 1] != 0 ||
             decodand[offset + 2] != 1 ||
             decodand[offset + 3] != 0) {
             return false;
         }
         // Here, and in many other places, byte values are ANDed with 0xFF. This is because Java
         // bytes are signed - to obtain a numerical value of a longer type which holds the unsigned
         // interpretation of the byte of interest, we do this.
         int numEncodedImages = (decodand[offset + 4] & 0xFF) |
                                (decodand[offset + 5] & 0xFF) << 8;
         // Fail if there are no images or the field is corrupt.
         if (numEncodedImages <= 0) {
             return false;
         }
         final int headerAndDirectorySize = ICO_HEADER_LENGTH_BYTES + (numEncodedImages * ICO_ICONDIRENTRY_LENGTH_BYTES);
         // Fail if there is not enough space in the buffer for the stated number of icondir entries,
         // let alone the data.
         if (len < headerAndDirectorySize) {
             return false;
         }
         // Put the pointer on the first byte of the first Icon Directory Entry.
         int bufferIndex = offset + ICO_HEADER_LENGTH_BYTES;
         // We now iterate over the Icon Directory, decoding each entry as we go. We also need to
         // discard all entries except one >= the maximum interesting size.
         // Size of the smallest image larger than the limit encountered.
         int minimumMaximum = Integer.MAX_VALUE;
         // Used to track the best entry for each size. The entries we want to keep.
         SparseArray<IconDirectoryEntry> preferenceArray = new SparseArray<IconDirectoryEntry>();
         for (int i = 0; i < numEncodedImages; i++, bufferIndex += ICO_ICONDIRENTRY_LENGTH_BYTES) {
             // Decode the Icon Directory Entry at this offset.
             IconDirectoryEntry newEntry = IconDirectoryEntry.createFromBuffer(decodand, offset, len, bufferIndex);
             newEntry.index = i;
             if (newEntry.isErroneous) {
                 continue;
             }
             if (newEntry.width > Favicons.largestFaviconSize) {
                 // If we already have a smaller image larger than the maximum size of interest, we
                 // don't care about the new one which is larger than the smallest image larger than
                 // the maximum size.
                 if (newEntry.width >= minimumMaximum) {
                     continue;
                 }
                 // Remove the previous minimum-maximum.
                 preferenceArray.delete(minimumMaximum);
                 minimumMaximum = newEntry.width;
             }
             IconDirectoryEntry oldEntry = preferenceArray.get(newEntry.width);
             if (oldEntry == null) {
                 preferenceArray.put(newEntry.width, newEntry);
                 continue;
             }
             if (oldEntry.compareTo(newEntry) < 0) {
                 preferenceArray.put(newEntry.width, newEntry);
             }
         }
         final int count = preferenceArray.size();
         // Abort if no entries are desired (Perhaps all are corrupt?)
         if (count == 0) {
             return false;
         }
         // Allocate space for the icon directory entries in the decoded directory.
         iconDirectory = new IconDirectoryEntry[count];
         // The size of the data in the buffer that we find useful.
         int retainedSpace = ICO_HEADER_LENGTH_BYTES;
         for (int i = 0; i < count; i++) {
             IconDirectoryEntry e = preferenceArray.valueAt(i);
             retainedSpace += ICO_ICONDIRENTRY_LENGTH_BYTES + e.payloadSize;
             iconDirectory[i] = e;
         }
         isValid = true;
         // Set the number of images field in the buffer to reflect the number of retained entries.
         decodand[offset + 4] = (byte) iconDirectory.length;
         decodand[offset + 5] = (byte) (iconDirectory.length >>> 8);
         if ((len - retainedSpace) > COMPACT_THRESHOLD) {
             compactingCopy(retainedSpace);
         }
         return true;
     }
     /**
      * Copy the buffer into a new array of exactly the required size, omitting any unwanted data.
      */
     private void compactingCopy(int spaceRetained) {
         byte[] buf = new byte[spaceRetained];
         // Copy the header.
         System.arraycopy(decodand, offset, buf, 0, ICO_HEADER_LENGTH_BYTES);
         int headerPtr = ICO_HEADER_LENGTH_BYTES;
         int payloadPtr = ICO_HEADER_LENGTH_BYTES + (iconDirectory.length * ICO_ICONDIRENTRY_LENGTH_BYTES);
         int ind = 0;
         for (IconDirectoryEntry entry : iconDirectory) {
             // Copy this entry.
             System.arraycopy(decodand, offset + entry.getOffset(), buf, headerPtr, ICO_ICONDIRENTRY_LENGTH_BYTES);
             // Copy its payload.
             System.arraycopy(decodand, offset + entry.payloadOffset, buf, payloadPtr, entry.payloadSize);
             // Update the offset field.
             buf[headerPtr + 12] = (byte) payloadPtr;
             buf[headerPtr + 13] = (byte) (payloadPtr >>> 8);
             buf[headerPtr + 14] = (byte) (payloadPtr >>> 16);
             buf[headerPtr + 15] = (byte) (payloadPtr >>> 24);
             entry.payloadOffset = payloadPtr;
             entry.index = ind;
             payloadPtr += entry.payloadSize;
             headerPtr += ICO_ICONDIRENTRY_LENGTH_BYTES;
             ind++;
         }
         decodand = buf;
         offset = 0;
         len = spaceRetained;
     }
     /**
      * Decode and return the bitmap represented by the given index in the Icon Directory, if valid.
      *
      * @param index The index into the Icon Directory of the image of interest.
      * @return The decoded Bitmap object for this image, or null if the entry is invalid or decoding
      *         fails.
      */
     public Bitmap decodeBitmapAtIndex(int index) {
         final IconDirectoryEntry iconDirEntry = iconDirectory[index];
         if (iconDirEntry.payloadIsPNG) {
             // PNG payload. Simply extract it and decode it.
             return BitmapUtils.decodeByteArray(decodand, offset + iconDirEntry.payloadOffset, iconDirEntry.payloadSize);
         }
         // The payload is a BMP, so we need to do some magic to get the decoder to do what we want.
         // We construct an ICO containing just the image we want, and let Android do the rest.
         byte[] decodeTarget = new byte[ICO_HEADER_LENGTH_BYTES + ICO_ICONDIRENTRY_LENGTH_BYTES + iconDirEntry.payloadSize];
         // Set the type field in the ICO header.
         decodeTarget[2] = 1;
         // Set the num-images field in the header to 1.
         decodeTarget[4] = 1;
         // Copy the ICONDIRENTRY we need into the new buffer.
         System.arraycopy(decodand, offset + iconDirEntry.getOffset(), decodeTarget, ICO_HEADER_LENGTH_BYTES, ICO_ICONDIRENTRY_LENGTH_BYTES);
         // Copy the payload into the new buffer.
         final int singlePayloadOffset =  ICO_HEADER_LENGTH_BYTES + ICO_ICONDIRENTRY_LENGTH_BYTES;
         System.arraycopy(decodand, offset + iconDirEntry.payloadOffset, decodeTarget, singlePayloadOffset, iconDirEntry.payloadSize);
         // Update the offset field of the ICONDIRENTRY to make the new ICO valid.
         decodeTarget[ICO_HEADER_LENGTH_BYTES + 12] = (byte) singlePayloadOffset;
         decodeTarget[ICO_HEADER_LENGTH_BYTES + 13] = (byte) (singlePayloadOffset >>> 8);
         decodeTarget[ICO_HEADER_LENGTH_BYTES + 14] = (byte) (singlePayloadOffset >>> 16);
         decodeTarget[ICO_HEADER_LENGTH_BYTES + 15] = (byte) (singlePayloadOffset >>> 24);
         // Decode the newly-constructed singleton-ICO.
         return BitmapUtils.decodeByteArray(decodeTarget);
     }
     /**
      * Fetch an iterator over the images in this ICO, or null if this ICO seems to be invalid.
      *
      * @return An iterator over the Bitmaps stored in this ICO, or null if decoding fails.
      */
     @Override
     public ICOIterator iterator() {
         // If a previous call to decode concluded this ICO is invalid, abort.
         if (hasDecoded && !isValid) {
             return null;
         }
         // If we've not been decoded before, but now fail to make any sense of the ICO, abort.
         if (!hasDecoded) {
             if (!decodeIconDirectoryAndPossiblyPrune()) {
                 return null;
             }
         }
         // If decoding was a success, return an iterator over the images in this ICO.
         return new ICOIterator();
     }
     /**
      * Decode this ICO and return the result as a LoadFaviconResult.
      * @return A LoadFaviconResult representing the decoded ICO.
      */
     public LoadFaviconResult decode() {
         // The call to iterator returns null if decoding fails.
         Iterator<Bitmap> bitmaps = iterator();
         if (bitmaps == null) {
             return null;
         }
         LoadFaviconResult result = new LoadFaviconResult();
         result.bitmapsDecoded = bitmaps;
         result.faviconBytes = decodand;
         result.offset = offset;
         result.length = len;
         result.isICO = true;
         return result;
     }
     /**
      * Inner class to iterate over the elements in the ICO represented by the enclosing instance.
      */
     private class ICOIterator implements Iterator<Bitmap> {
         private int mIndex = 0;
         @Override
         public boolean hasNext() {
             return mIndex < iconDirectory.length;
         }
         @Override
         public Bitmap next() {
             if (mIndex > iconDirectory.length) {
                 throw new NoSuchElementException("No more elements in this ICO.");
             }
             return decodeBitmapAtIndex(mIndex++);
         }
         @Override
         public void remove() {
             if (iconDirectory[mIndex] == null) {
                 throw new IllegalStateException("Remove already called for element " + mIndex);
             }
             iconDirectory[mIndex] = null;
         }
     }
 }

The Tor Browser / annotate

mobile/android/base/favicons/decoders/ICODecoder.java@fc2d59ddac77 (annotated)

mobile/android/base/favicons/decoders/ICODecoder.java