Add InputStream mode for signing zips

app/src/main/java/com/topjohnwu/magisk/container/ByteArrayStream.java

@@ -0,0 +1,34 @@
+package com.topjohnwu.magisk.container;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+public class ByteArrayStream extends ByteArrayOutputStream {
+    public byte[] getBuf() {
+        return buf;
+    }
+    public synchronized void readFrom(InputStream is) {
+        readFrom(is, Integer.MAX_VALUE);
+    }
+    public synchronized void readFrom(InputStream is, int len) {
+        int read;
+        byte buffer[] = new byte[4096];
+        try {
+            while ((read = is.read(buffer, 0, len < buffer.length ? len : buffer.length)) > 0) {
+                write(buffer, 0, read);
+                len -= read;
+            }
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+    public synchronized void writeTo(OutputStream out, int off, int len) throws IOException {
+        out.write(buf, off, len);
+    }
+    public ByteArrayInputStream getInputStream() {
+        return new ByteArrayInputStream(buf, 0, count);
+    }
+}