Merge pull request #421 from wsot/master

Fix issue #410: DecryptingPartInputStream could return more data than re...

src/org/thoughtcrime/securesms/crypto/DecryptingPartInputStream.java

@@ -24,6 +24,7 @@ import java.security.InvalidAlgorithmParameterException;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
 import java.util.Arrays;
+import java.lang.System;
 
 import javax.crypto.BadPaddingException;
 import javax.crypto.Cipher;
@@ -53,6 +54,7 @@ public class DecryptingPartInputStream extends FileInputStream {
   private boolean done;
   private long totalDataSize;
   private long totalRead;
+  private byte[] overflowBuffer;
 	
   public DecryptingPartInputStream(File file, MasterSecret masterSecret) throws FileNotFoundException {
     super(file);
@@ -122,6 +124,25 @@ public class DecryptingPartInputStream extends FileInputStream {
   }
 	
   private int readIncremental(byte[] buffer, int offset, int length) throws IOException {
+    int readLength = 0;
+    if (null != overflowBuffer) {
+      if (overflowBuffer.length > length) {
+        System.arraycopy(overflowBuffer, 0, buffer, offset, length);
+        overflowBuffer = Arrays.copyOfRange(overflowBuffer, length, overflowBuffer.length);
+        return length;
+      } else if (overflowBuffer.length == length) {
+        System.arraycopy(overflowBuffer, 0, buffer, offset, length);
+        overflowBuffer = null;
+        return length;
+      } else {
+        System.arraycopy(overflowBuffer, 0, buffer, offset, overflowBuffer.length);
+        readLength += overflowBuffer.length;
+        offset += readLength;
+        length -= readLength;
+        overflowBuffer = null;
+      }
+    }
+
     if (length + totalRead > totalDataSize)
       length = (int)(totalDataSize - totalRead);
 		
@@ -131,7 +152,25 @@ public class DecryptingPartInputStream extends FileInputStream {
 		
     try {
       mac.update(internalBuffer, 0, read);
-      return cipher.update(internalBuffer, 0, read, buffer, offset);
+
+      int outputLen = cipher.getOutputSize(read);
+
+      if (outputLen <= length) {
+        readLength += cipher.update(internalBuffer, 0, read, buffer, offset);
+        return readLength;
+      }
+
+      byte[] transientBuffer = new byte[outputLen];
+      outputLen = cipher.update(internalBuffer, 0, read, transientBuffer, 0);
+      if (outputLen <= length) {
+        System.arraycopy(transientBuffer, 0, buffer, offset, outputLen);
+        readLength += outputLen;
+      } else {
+        System.arraycopy(transientBuffer, 0, buffer, offset, length);
+        overflowBuffer = Arrays.copyOfRange(transientBuffer, length, outputLen);
+        readLength += length;
+      }
+      return readLength;
     } catch (ShortBufferException e) {
       throw new AssertionError(e);
     }