fix: fix conversion for pre-epoch timestamps (#160)

* test: failing test for parsing a negative timestamp * fix: fix conversion for pre-epoch timestamps * chore: add comment, rename test variable names

Author: chingor13

google-cloud-core/src/main/java/com/google/cloud/Timestamp.java

@@ -119,7 +119,19 @@ public static Timestamp now() {
  * @throws IllegalArgumentException if the timestamp is outside the representable range
  */
  public static Timestamp of(java.sql.Timestamp timestamp) {
- return ofTimeSecondsAndNanos(timestamp.getTime() / 1000, timestamp.getNanos());
+ int nanos = timestamp.getNanos();
+
+ // A pre-epoch timestamp will be off by one second because of the way that integer division
+ // works. For example, -1001 / 1000 == -1. In this case of timestamps, we want this result to be
+ // -2. This causes any pre-epoch timestamp to be off by 1 second - fix this by adjusting the
+ // seconds value by 1 if the timestamp < 0.
+ // TODO: replace with Math.floorDiv when we drop Java 7 support
+ long seconds = timestamp.getTime() / 1000;
+ if (seconds < 0) {
+ --seconds;
+ }
+
+ return Timestamp.ofTimeSecondsAndNanos(seconds, nanos);
  }
 
  /**

google-cloud-core/src/test/java/com/google/cloud/TimestampTest.java

@@ -80,6 +80,30 @@ public void ofDate() {
  assertThat(timestamp.getNanos()).isEqualTo(expectedNanos);
  }
 
+ @Test
+ public void ofSqlTimestamp() {
+ String expectedTimestampString = "1970-01-01T00:00:12.345000000Z";
+ java.sql.Timestamp input = new java.sql.Timestamp(12345);
+ Timestamp timestamp = Timestamp.of(input);
+ assertThat(timestamp.toString()).isEqualTo(expectedTimestampString);
+ }
+
+ @Test
+ public void ofSqlTimestampPreEpoch() {
+ String expectedTimestampString = "1969-12-31T23:59:47.655000000Z";
+ java.sql.Timestamp input = new java.sql.Timestamp(-12345);
+ Timestamp timestamp = Timestamp.of(input);
+ assertThat(timestamp.toString()).isEqualTo(expectedTimestampString);
+ }
+
+ @Test
+ public void ofSqlTimestampOnEpoch() {
+ String expectedTimestampString = "1970-01-01T00:00:00Z";
+ java.sql.Timestamp input = new java.sql.Timestamp(0);
+ Timestamp timestamp = Timestamp.of(input);
+ assertThat(timestamp.toString()).isEqualTo(expectedTimestampString);
+ }
+
  @Test
  public void ofDatePreEpoch() {
  Timestamp timestamp = Timestamp.of(TEST_DATE_PRE_EPOCH);