fix: checksum format (#1178)

Fix checksum format to match the server's format -- unsigned long.

datastore-v1-proto-client/src/main/java/com/google/datastore/v1/client/ChecksumEnforcingInputStream.java

@@ -76,7 +76,7 @@ public int read(byte[] b, int off, int len) throws IOException {
       endToEndChecksumHandler.update(b, off, i);
     } else {
       // no more payload to read. compute checksum and verify
-      if (!expectedChecksum.equalsIgnoreCase(endToEndChecksumHandler.hash())) {
+      if (!expectedChecksum.equals(endToEndChecksumHandler.hash())) {
         throw new IOException("possible memory corruption on payload detected");
       }
     }

datastore-v1-proto-client/src/main/java/com/google/datastore/v1/client/EndToEndChecksumHandler.java

@@ -40,7 +40,11 @@ static String computeChecksum(byte[] bytes) {
       return null;
     }
     HashCode hc = getNewCrc32cHasher().putBytes(bytes).hash();
-    return hc.toString();
+    return hashToString(hc);
+  }
+
+  private static String hashToString(HashCode hc) {
+    return String.valueOf(Integer.toUnsignedLong(hc.asInt()));
   }
 
   private static Hasher getNewCrc32cHasher() {
@@ -59,7 +63,7 @@ static boolean validateChecksum(String checksum, byte[] bytes) {
         && !checksum.isEmpty()
         && bytes != null
         && bytes.length > 0
-        && checksum.equalsIgnoreCase(computeChecksum(bytes));
+        && checksum.equals(computeChecksum(bytes));
   }
 
   static boolean hasChecksumHeader(HttpResponse response) {
@@ -76,6 +80,6 @@ void update(byte[] bytes, int off, int len) {
   }
 
   String hash() {
-    return hasher.hash().toString();
+    return hashToString(hasher.hash());
   }
 }

datastore-v1-proto-client/src/test/java/com/google/datastore/v1/client/EndToEndChecksumHandlerTest.java

@@ -16,6 +16,7 @@
 package com.google.datastore.v1.client;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
@@ -27,14 +28,23 @@
 /** Test for {@link EndToEndChecksumHandler}. */
 @RunWith(JUnit4.class)
 public class EndToEndChecksumHandlerTest {
-  private byte[] payloadBytes = "This is a long string with numbers 1234, 134.56 ".getBytes(UTF_8);
+  private final byte[] payloadBytes =
+      "This is a long string with numbers 1234, 134.56 ".getBytes(UTF_8);
+  private final byte[] payloadForUnsignedLongChecksum = "aaa".getBytes(UTF_8);
+  private final String unsignedLongChecksum = "3818383321";
 
   @Test
   public void validateChecksum_correctChecksum() {
     String computed = EndToEndChecksumHandler.computeChecksum(payloadBytes);
     assertTrue(EndToEndChecksumHandler.validateChecksum(computed, payloadBytes));
   }
 
+  @Test
+  public void computeChecksum_returnsUnsignedLongAsStringValue() {
+    String computed = EndToEndChecksumHandler.computeChecksum(payloadForUnsignedLongChecksum);
+    assertEquals("computeChecksum return value", unsignedLongChecksum, computed);
+  }
+
   @Test
   public void validateChecksum_incorrectChecksum() {
     String computed = EndToEndChecksumHandler.computeChecksum("random string".getBytes(UTF_8));

datastore-v1-proto-client/src/test/java/com/google/datastore/v1/client/RemoteRpcTest.java

@@ -176,7 +176,7 @@ public void testHttpHeaders_expectE2eChecksumHeader() throws IOException {
         httpRequest
             .getHeaders()
             .getFirstHeaderStringValue(EndToEndChecksumHandler.HTTP_REQUEST_CHECKSUM_HEADER);
-    assertEquals(8, header.length());
+    assertEquals(9, header.length());
   }
 
   @Test