content: /*
   * Copyright (C) 2013 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.android.ex.photo.util;
  
  import android.util.Log;
  
  import java.io.ByteArrayInputStream;
  import java.io.InputStream;
  
  public class Exif {
      private static final String TAG = "CameraExif";
  
      /**
       * Returns the degrees in clockwise. Values are 0, 90, 180, or 270.
       * @param inputStream The input stream will not be closed for you.
       * @param byteSize Recommended parameter declaring the length of the input stream. If you
       *                 pass in -1, we will have to read more from the input stream.
       * @return 0, 90, 180, or 270.
       */
      public static int getOrientation(final InputStream inputStream, final long byteSize) {
          if (inputStream == null) {
              return 0;
          }
  
          /*
            Looking at this algorithm, we never look ahead more than 8 bytes. As long as we call
            advanceTo() at the end of every loop, we should never have to reallocate a larger buffer.
  
            Also, the most we ever read backwards is 4 bytes. pack() reads backwards if the encoding
            is in little endian format. These following two lines potentially reads 4 bytes backwards:
  
            int tag = pack(jpeg, offset, 4, false);
            count = pack(jpeg, offset - 2, 2, littleEndian);
  
            To be safe, we will always advance to some index-4, so we'll need 4 more for the +8
            look ahead, which makes it a +12 look ahead total. Use 16 just in case my analysis is off.
  
            This means we only need to allocate a single 16 byte buffer.
  
            Note: If you do not pass in byteSize parameter, a single large allocation will occur.
            For a 1MB image, I see one 30KB allocation. This is due to the line containing:
  
            has(jpeg, byteSize, offset + length - 1)
  
            where length is a variable int (around 30KB above) read from the EXIF headers.
  
            This is still much better than allocating a 1MB byte[] which we were doing before.
           */
  
          final int lookAhead = 16;
          final int readBackwards = 4;
          final InputStreamBuffer jpeg = new InputStreamBuffer(inputStream, lookAhead, false);
  
          int offset = 0;
          int length = 0;
  
          if (has(jpeg, byteSize, 1)) {
              // JPEG image files begin with FF D8. Only JPEG images have EXIF data.
              final boolean possibleJpegFormat = jpeg.get(0) == (byte) 0xFF
                      && jpeg.get(1) == (byte) 0xD8;
              if (!possibleJpegFormat) {
                  return 0;
              }
          }
  
          // ISO/IEC 10918-1:1993(E)
          while (has(jpeg, byteSize, offset + 3) && (jpeg.get(offset++) & 0xFF) == 0xFF) {
              final int marker = jpeg.get(offset) & 0xFF;
  
              // Check if the marker is a padding.
              if (marker == 0xFF) {
                  continue;
              }
              offset++;
  
              // Check if the marker is SOI or TEM.
              if (marker == 0xD8 || marker == 0x01) {
                  continue;
              }
              // Check if the marker is EOI or SOS.
              if (marker == 0xD9 || marker == 0xDA) {
                  // Loop ends.
                  jpeg.advanceTo(offset - readBackwards);
                  break;
              }
  
              // Get the length and check if it is reasonable.
              length = pack(jpeg, offset, 2, false);
              if (length < 2 || !has(jpeg, byteSize, offset + length - 1)) {
                  Log.e(TAG, "Invalid length");
                  return 0;
              }
  
              // Break if the marker is EXIF in APP1.
              if (marker == 0xE1 && length >= 8 &&
                      pack(jpeg, offset + 2, 4, false) == 0x45786966 &&
                      pack(jpeg, offset + 6, 2, false) == 0) {
                  offset += 8;
                  length -= 8;
                  // Loop ends.
                  jpeg.advanceTo(offset - readBackwards);
                  break;
              }
  
              // Skip other markers.
              offset += length;
              length = 0;
  
              // Loop ends.
              jpeg.advanceTo(offset - readBackwards);
          }
  
          // JEITA CP-3451 Exif Version 2.2
          if (length > 8) {
              // Identify the byte order.
              int tag = pack(jpeg, offset, 4, false);
              if (tag != 0x49492A00 && tag != 0x4D4D002A) {
                  Log.e(TAG, "Invalid byte order");
                  return 0;
              }
              final boolean littleEndian = (tag == 0x49492A00);
  
              // Get the offset and check if it is reasonable.
              int count = pack(jpeg, offset + 4, 4, littleEndian) + 2;
              if (count < 10 || count > length) {
                  Log.e(TAG, "Invalid offset");
                  return 0;
              }
              offset += count;
              length -= count;
  
              // Offset has changed significantly.
              jpeg.advanceTo(offset - readBackwards);
  
              // Get the count and go through all the elements.
              count = pack(jpeg, offset - 2, 2, littleEndian);
  
              while (count-- > 0 && length >= 12) {
                  // Get the tag and check if it is orientation.
                  tag = pack(jpeg, offset, 2, littleEndian);
                  if (tag == 0x0112) {
                      // We do not really care about type and count, do we?
                      final int orientation = pack(jpeg, offset + 8, 2, littleEndian);
                      switch (orientation) {
                          case 1:
                              return 0;
                          case 3:
                              return 180;
                          case 6:
                              return 90;
                          case 8:
                              return 270;
                      }
                      Log.i(TAG, "Unsupported orientation");
                      return 0;
                  }
                  offset += 12;
                  length -= 12;
  
                  // Loop ends.
                  jpeg.advanceTo(offset - readBackwards);
              }
          }
  
          return 0;
      }
  
      private static int pack(final InputStreamBuffer bytes, int offset, int length,
              final boolean littleEndian) {
          int step = 1;
          if (littleEndian) {
              offset += length - 1;
              step = -1;
          }
  
          int value = 0;
          while (length-- > 0) {
              value = (value << 8) | (bytes.get(offset) & 0xFF);
              offset += step;
          }
          return value;
      }
  
      private static boolean has(final InputStreamBuffer jpeg, final long byteSize, final int index) {
          if (byteSize >= 0) {
              return index < byteSize;
          } else {
              // For large values of index, this will cause the internal buffer to resize.
              return jpeg.has(index);
          }
      }
  
      @Deprecated
      public static int getOrientation(final byte[] jpeg) {
          return getOrientation(new ByteArrayInputStream(jpeg), jpeg.length);
      }
  }
  