Fix Timestamps with dates before the Unix epoch that contain fractional seconds.

The Timestamp proto does not allow for negative nanos fields, so the seconds must be shifted and
a positive nanos then applied.

1 files changed, 9 insertions, 0 deletions

diff --git a/objectivec/GPBWellKnownTypes.m b/objectivec/GPBWellKnownTypes.m
index ed798a2e..83b1c833 100644
--- a/objectivec/GPBWellKnownTypes.m
+++ b/objectivec/GPBWellKnownTypes.m
@@ -50,6 +50,15 @@ static int32_t SecondsAndNanosFromTimeIntervalSince1970(NSTimeInterval time,
                                                         int64_t *outSeconds) {
   NSTimeInterval seconds;
   NSTimeInterval nanos = modf(time, &seconds);
+
+  // Per Timestamp.proto, nanos is non-negative and "Negative second values with
+  // fractions must still have non-negative nanos values that count forward in
+  // time. Must be from 0 to 999,999,999 inclusive."
+  if (nanos < 0) {
+    --seconds;
+    nanos = 1.0 + nanos;
+  }
+
   nanos *= 1e9;
   *outSeconds = (int64_t)seconds;
   return (int32_t)nanos;