Reduce the odds of a collision in image keys

Fixes #27
bumptech · Oct 20, 2013 · 9600642 · 9600642
1 parent 775639a
commit 9600642
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Showing 3 changed files with 105 additions and 11 deletions.
diff --git a/library/src/com/bumptech/glide/resize/ImageManager.java b/library/src/com/bumptech/glide/resize/ImageManager.java
@@ -36,6 +36,12 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.io.UnsupportedEncodingException;
+import java.nio.ByteBuffer;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
@@ -68,6 +74,7 @@ public class ImageManager {
     private final MemoryCache memoryCache;
     private final ImageResizer resizer;
     private final DiskCache diskCache;
+    private final SafeKeyGenerator safeKeyGenerator = new SafeKeyGenerator();
 
     //special downsampler that doesn't check exif, and assumes inWidth and inHeight == outWidth and outHeight so it
     //doesn't need to read the image header for size information
@@ -389,7 +396,7 @@ public void onImageRemoved(Bitmap removed) {
     public ImageManagerJob getImage(String id, StreamLoader streamLoader, Transformation transformation, Downsampler downsampler, int width, int height, LoadedCallback cb) {
         if (shutdown) return null;
 
-        final String key = getKey(id, transformation.getId(), downsampler, width, height);
+        final String key = safeKeyGenerator.getSafeKey(id, transformation, downsampler, width, height);
 
         ImageManagerJob job = null;
         if (!returnFromCache(key, cb)) {
@@ -631,8 +638,84 @@ private void putInMemoryCache(String key, final Bitmap bitmap) {
         }
     }
 
-    private static String getKey(String id, String transformationId, Downsampler downsampler, int width, int height) {
-        return String.valueOf(Util.hash(id.hashCode(), downsampler.getId().hashCode(),
-                transformationId.hashCode(), width, height));
+    private static class SafeKeyGenerator {
+        private final Map<LoadId, String> loadIdToSafeHash = new HashMap<LoadId, String>();
+        private final ByteBuffer byteBuffer = ByteBuffer.allocate(8);
+        private MessageDigest messageDigest;
+
+        public SafeKeyGenerator() {
+            try {
+                messageDigest = MessageDigest.getInstance("SHA-256");
+            } catch (NoSuchAlgorithmException e) {
+                e.printStackTrace();
+            }
+        }
+
+        public String getSafeKey(String id, Transformation transformation, Downsampler downsampler, int width, int height) {
+            LoadId loadId = new LoadId(id, transformation.getId(), downsampler.getId(), width, height);
+            String safeKey = loadIdToSafeHash.get(loadId);
+            if (safeKey == null) {
+                try {
+                    safeKey = loadId.generateSafeKey();
+                } catch (UnsupportedEncodingException e) {
+                    e.printStackTrace();
+                }
+                loadIdToSafeHash.put(loadId, safeKey);
+            }
+            return safeKey;
+        }
+
+        private class LoadId {
+            private final String id;
+            private final String transformationId;
+            private final String downsamplerId;
+            private final int width;
+            private final int height;
+
+            public LoadId(String id, String transformationId, String downsamplerId, int width, int height) {
+                this.id = id;
+                this.transformationId = transformationId;
+                this.downsamplerId = downsamplerId;
+                this.width = width;
+                this.height = height;
+            }
+
+            public String generateSafeKey() throws UnsupportedEncodingException {
+                messageDigest.update(id.getBytes("UTF-8"));
+                messageDigest.update(transformationId.getBytes("UTF-8"));
+                messageDigest.update(downsamplerId.getBytes("UTF-8"));
+                byteBuffer.position(0);
+                byteBuffer.putInt(width);
+                byteBuffer.putInt(height);
+                messageDigest.update(byteBuffer.array());
+                return Util.sha256BytesToHex(messageDigest.digest());
+            }
+
+            @Override
+            public boolean equals(Object o) {
+                if (this == o) return true;
+                if (o == null || getClass() != o.getClass()) return false;
+
+                LoadId loadId = (LoadId) o;
+
+                if (height != loadId.height) return false;
+                if (width != loadId.width) return false;
+                if (!downsamplerId.equals(loadId.downsamplerId)) return false;
+                if (!id.equals(loadId.id)) return false;
+                if (!transformationId.equals(loadId.transformationId)) return false;
+
+                return true;
+            }
+
+            @Override
+            public int hashCode() {
+                int result = id.hashCode();
+                result = 31 * result + transformationId.hashCode();
+                result = 31 * result + downsamplerId.hashCode();
+                result = 31 * result + width;
+                result = 31 * result + height;
+                return result;
+            }
+        }
     }
 }
diff --git a/library/src/com/bumptech/glide/resize/cache/DiskLruCacheWrapper.java b/library/src/com/bumptech/glide/resize/cache/DiskLruCacheWrapper.java
@@ -18,12 +18,14 @@
  */
 public class DiskLruCacheWrapper implements DiskCache {
 
+    private static final int APP_VERSION = 1;
+    private static final int VALUE_COUNT = 1;
     private static DiskLruCache CACHE = null;
     private static DiskLruCacheWrapper WRAPPER = null;
 
     private synchronized static DiskLruCache getDiskLruCache(File directory, int maxSize) throws IOException {
         if (CACHE == null) {
-            CACHE = DiskLruCache.open(directory, 0, 1, maxSize);
+            CACHE = DiskLruCache.open(directory, APP_VERSION, VALUE_COUNT, maxSize);
         }
         return CACHE;
     }

diff --git a/library/src/com/bumptech/glide/util/Util.java b/library/src/com/bumptech/glide/util/Util.java
@@ -1,13 +1,22 @@
 package com.bumptech.glide.util;
 
 public class Util {
-    private static final int PRIME = 31;
+    private static final char[] hexArray = "0123456789abcdef".toCharArray();
+    private static final char[] sha256Chars = new char[64]; //32 bytes from sha-256 -> 64 hex chars
 
-    public static int hash(int... hashes) {
-        int result = 1;
-        for (int hash : hashes) {
-            result *= PRIME * hash;
+    public static String sha256BytesToHex(byte[] bytes) {
+        return bytesToHex(bytes, sha256Chars);
+    }
+
+    // Taken from:
+    // http://stackoverflow.com/questions/9655181/convert-from-byte-array-to-hex-string-in-java/9655275#9655275
+    private static String bytesToHex(byte[] bytes, char[] hexChars) {
+        int v;
+        for ( int j = 0; j < bytes.length; j++ ) {
+            v = bytes[j] & 0xFF;
+            hexChars[j * 2] = hexArray[v >>> 4];
+            hexChars[j * 2 + 1] = hexArray[v & 0x0F];
         }
-        return result;
+        return new String(hexChars);
     }
 }