Add byte transformes class and crc32 transformer

Author: patrickfav

src/main/java/at/favre/lib/bytes/BytesTransformers.java

@@ -0,0 +1,57 @@
+package at.favre.lib.bytes;
+
+import java.util.Objects;
+import java.util.zip.CRC32;
+import java.util.zip.Checksum;
+
+public final class BytesTransformers {
+
+    private BytesTransformers() {
+    }
+
+    public static BytesTransformer appendCrc32() {
+        return new ChecksumTransformer(new CRC32(), ChecksumTransformer.Mode.APPEND, 4);
+    }
+
+    /**
+     * Adds or converts to arbitrary checksum
+     */
+    final static class ChecksumTransformer implements BytesTransformer {
+        enum Mode {
+            /**
+             * Appends checksum to given byte array
+             */
+            APPEND,
+            /**
+             * Transforms byte array and returns only checksum
+             */
+            TRANSFORM
+        }
+
+        private final Checksum checksum;
+        private final Mode mode;
+        private final int checksumLengthByte;
+
+        public ChecksumTransformer(Checksum checksum, Mode mode, int checksumLengthByte) {
+            if (checksumLengthByte < 0 || checksumLengthByte > 8)
+                throw new IllegalArgumentException("checksumlength must be between 1 and 8 bytes");
+
+            Objects.requireNonNull(checksum, "checksum instance must not be null");
+            this.checksum = checksum;
+            this.mode = mode;
+            this.checksumLengthByte = checksumLengthByte;
+        }
+
+        @Override
+        public byte[] transform(byte[] currentArray, boolean inPlace) {
+            checksum.update(currentArray, 0, currentArray.length);
+            byte[] checksumBytes = Bytes.from(checksum.getValue()).resize(checksumLengthByte).array();
+
+            if (mode == Mode.TRANSFORM) {
+                return checksumBytes;
+            } else {
+                return Bytes.from(currentArray, checksumBytes).array();
+            }
+        }
+    }
+}