From 52fe3cf3c87edb220831232bfd3325690920ec30 Mon Sep 17 00:00:00 2001
From: rbygrave <robin.bygrave@gmail.com>
Date: Thu, 29 Jul 2021 11:40:05 +1200
Subject: [PATCH] Change from MD5 to Checksum (Adler32) for json content dirty
 detection

---
 .../server/deploy/BeanPropertyJsonMapper.java | 12 +++++++----
 .../ebeaninternal/server/util/Checksum.java   | 20 +++++++++++++++++++
 .../io/ebeaninternal/server/util/Md5.java     |  1 -
 .../server/util/ChecksumTest.java             | 18 +++++++++++++++++
 4 files changed, 46 insertions(+), 5 deletions(-)
 create mode 100644 ebean-core/src/main/java/io/ebeaninternal/server/util/Checksum.java
 create mode 100644 ebean-core/src/test/java/io/ebeaninternal/server/util/ChecksumTest.java

diff --git a/ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyJsonMapper.java b/ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyJsonMapper.java
index 38c9ebb9f..747df5130 100644
--- a/ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyJsonMapper.java
+++ b/ebean-core/src/main/java/io/ebeaninternal/server/deploy/BeanPropertyJsonMapper.java
@@ -7,7 +7,7 @@ import io.ebean.core.type.DataReader;
 import io.ebean.core.type.ScalarType;
 import io.ebean.text.TextException;
 import io.ebeaninternal.server.deploy.meta.DeployBeanProperty;
-import io.ebeaninternal.server.util.Md5;
+import io.ebeaninternal.server.util.Checksum;
 
 import javax.persistence.PersistenceException;
 import java.sql.SQLException;
@@ -66,10 +66,14 @@ public class BeanPropertyJsonMapper extends BeanProperty {
 
   private static class Md5MutableHash implements MutableHash {
 
-    private final String md5;
+    private final String hash;
 
     Md5MutableHash(String json) {
-      md5 = Md5.hash(json);
+      this.hash = hash(json);
+    }
+
+    private String hash(String json) {
+      return String.valueOf(Checksum.checksum(json));
     }
 
     @Override
@@ -79,7 +83,7 @@ public class BeanPropertyJsonMapper extends BeanProperty {
 
     @Override
     public boolean isEqualToJson(String json) {
-      return Md5.hash(json).equals(md5);
+      return hash(json).equals(hash);
     }
 
     @Override
diff --git a/ebean-core/src/main/java/io/ebeaninternal/server/util/Checksum.java b/ebean-core/src/main/java/io/ebeaninternal/server/util/Checksum.java
new file mode 100644
index 000000000..87ee6e7e8
--- /dev/null
+++ b/ebean-core/src/main/java/io/ebeaninternal/server/util/Checksum.java
@@ -0,0 +1,20 @@
+package io.ebeaninternal.server.util;
+
+import java.nio.charset.StandardCharsets;
+import java.util.zip.Adler32;
+
+/**
+ * Compute a checksum for String content. Use when we desire cheaper option than MD5.
+ */
+public final class Checksum {
+
+  /**
+   * Return the checksum for the given String input.
+   */
+  public static long checksum(String input) {
+    Adler32 adler32 = new Adler32();
+    final byte[] bytes = input.getBytes(StandardCharsets.UTF_8);
+    adler32.update(bytes, 0, bytes.length);
+    return adler32.getValue();
+  }
+}
diff --git a/ebean-core/src/main/java/io/ebeaninternal/server/util/Md5.java b/ebean-core/src/main/java/io/ebeaninternal/server/util/Md5.java
index 1c848f55d..7329d3f25 100644
--- a/ebean-core/src/main/java/io/ebeaninternal/server/util/Md5.java
+++ b/ebean-core/src/main/java/io/ebeaninternal/server/util/Md5.java
@@ -21,7 +21,6 @@ public final class Md5 {
    * Convert the digest into a hex value.
    */
   private static String digestToHex(byte[] digest) {
-
     StringBuilder sb = new StringBuilder();
     for (byte aDigest : digest) {
       sb.append(Integer.toString((aDigest & 0xff) + 0x100, 16).substring(1));
diff --git a/ebean-core/src/test/java/io/ebeaninternal/server/util/ChecksumTest.java b/ebean-core/src/test/java/io/ebeaninternal/server/util/ChecksumTest.java
new file mode 100644
index 000000000..58342df80
--- /dev/null
+++ b/ebean-core/src/test/java/io/ebeaninternal/server/util/ChecksumTest.java
@@ -0,0 +1,18 @@
+package io.ebeaninternal.server.util;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ChecksumTest {
+
+  @Test
+  public void checksum() {
+
+    final long val = Checksum.checksum("Hello world");
+    assertThat(val).isEqualTo(413860925L);
+
+    assertThat(Checksum.checksum("Hello world")).isEqualTo(val);
+    assertThat(Checksum.checksum("hello world")).isNotEqualTo(val);
+  }
+}