keep track of the position the input stream for decryption, makes it possible to give accurate progress information

src/org/thialfihar/android/apg/PositionAwareInputStream.java

@@ -0,0 +1,67 @@
+package org.thialfihar.android.apg;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+public class PositionAwareInputStream extends InputStream {
+    private InputStream mStream;
+    private long mPosition;
+
+    public PositionAwareInputStream(InputStream in) {
+        mStream = in;
+        mPosition = 0;
+    }
+
+    @Override
+    public int read() throws IOException {
+        int ch = mStream.read();
+        ++mPosition;
+        return ch;
+    }
+
+    @Override
+    public int available() throws IOException {
+        return mStream.available();
+    }
+
+    @Override
+    public void close() throws IOException {
+        mStream.close();
+    }
+
+    @Override
+    public boolean markSupported() {
+        return false;
+    }
+
+    @Override
+    public int read(byte[] b) throws IOException {
+        int result = mStream.read(b);
+        mPosition += result;
+        return result;
+    }
+
+    @Override
+    public int read(byte[] b, int offset, int length) throws IOException {
+        int result = mStream.read(b, offset, length);
+        mPosition += result;
+        return result;
+    }
+
+    @Override
+    public synchronized void reset() throws IOException {
+        mStream.reset();
+        mPosition = 0;
+    }
+
+    @Override
+    public long skip(long n) throws IOException {
+        long result = mStream.skip(n);
+        mPosition += result;
+        return result;
+    }
+
+    public long position() {
+        return mPosition;
+    }
+}