fix: send correct time unit when writing Points

src/main/java/com/influxdb/v3/client/internal/InfluxDBClientImpl.java

@@ -304,7 +304,13 @@ private <T> void writeData(@Nonnull final List<T> data, @Nonnull final WriteOpti
                     + "or use default configuration at 'ClientConfig.database'.");
         }
 
-        WritePrecision precision = options.precisionSafe(config);
+        WritePrecision precision;
+        if (!data.isEmpty() && data.get(0) instanceof Point) {
+            // When writing points, timestamp always be converted to nanoseconds.
+            precision = WritePrecision.NS;
+        } else {
+            precision = options.precisionSafe(config);
+        }
         options.validate(config);
 
         String path;

src/test/java/com/influxdb/v3/client/InfluxDBClientWriteTest.java

@@ -401,7 +401,7 @@ void writePointWithDefaultWriteOptionsCustomConfig() throws Exception {
         mockServer.enqueue(createResponse(200));
 
         ClientConfig cfg = new ClientConfig.Builder().host(baseURL).token("TOKEN".toCharArray()).database("DB")
-                .writePrecision(WritePrecision.S)
+                .writePrecision(WritePrecision.US)
                 .writeNoSync(true)
                 .gzipThreshold(1)
                 .build();
@@ -412,7 +412,10 @@ void writePointWithDefaultWriteOptionsCustomConfig() throws Exception {
             client.writePoint(point);
         }
 
-        checkWriteCalled("/api/v3/write_lp", "DB", "second", true, "true", null, true);
+        // When writing Point, precision send to the servers is always nanosecond
+        var expectedPrecision = "nanosecond";
+
+        checkWriteCalled("/api/v3/write_lp", "DB", expectedPrecision, true, "true", null, true);
     }
 
     @Test
@@ -447,7 +450,10 @@ void writePointsWithDefaultWriteOptionsCustomConfig() throws Exception {
             client.writePoints(List.of(point));
         }
 
-        checkWriteCalled("/api/v3/write_lp", "DB", "second", true, "true", null, true);
+        // When writing Point, precision send to the servers is always nanosecond
+        var expectedPrecision = "nanosecond";
+
+        checkWriteCalled("/api/v3/write_lp", "DB", expectedPrecision, true, "true", null, true);
     }
 
     private void checkWriteCalled(final String expectedPath, final String expectedDB,

src/test/java/com/influxdb/v3/client/integration/E2ETest.java

@@ -595,10 +595,43 @@ public void testMultipleQueries() throws Exception {
                 }
             }
         }
-
-
     }
 
+    @EnabledIfEnvironmentVariable(named = "TESTING_INFLUXDB_URL", matches = ".*")
+    @EnabledIfEnvironmentVariable(named = "TESTING_INFLUXDB_TOKEN", matches = ".*")
+    @EnabledIfEnvironmentVariable(named = "TESTING_INFLUXDB_DATABASE", matches = ".*")
+    @Test
+    public void testWriteWithDifferentTimeUnit() throws Exception {
+        // These tests make sure that timestamp always converted to nanoseconds when writing Points.
+        try (InfluxDBClient client = InfluxDBClient.getInstance(
+                System.getenv("TESTING_INFLUXDB_URL"),
+                System.getenv("TESTING_INFLUXDB_TOKEN").toCharArray(),
+                System.getenv("TESTING_INFLUXDB_DATABASE"),
+                null)) {
+            var writeOptions = new WriteOptions.Builder().precision(WritePrecision.MS).build();
+            String measurement = "test_" + Instant.now().toEpochMilli() % 1000;
+            List<Point> points = List.of(
+                    Point.measurement(measurement)
+                            .setTag("type", "test")
+                            .setFloatField("rads", 3.14)
+                            .setIntegerField("life", 42)
+                            .setTimestamp(Instant.now().toEpochMilli(), WritePrecision.MS),
+                    Point.measurement(measurement)
+                            .setTag("type", "test")
+                            .setFloatField("rads", 3.14)
+                            .setIntegerField("life", 12)
+                            .setTimestamp(Instant.now().plusSeconds(1).toEpochMilli() / 1000, WritePrecision.S),
+                    Point.measurement(measurement)
+                            .setTag("type", "test")
+                            .setFloatField("rads", 3.14)
+                            .setIntegerField("life", 432)
+                            .setTimestamp(Instant.now().plusSeconds(2).toEpochMilli() * 1000, WritePrecision.US)
+            );
+            client.writePoints(points, writeOptions);
+            var results = client.queryPoints("select * from " + measurement).collect(Collectors.toList());
+            Assertions.assertThat(results).hasSize(3);
+        }
+    }
 
     private void assertGetDataSuccess(@Nonnull final InfluxDBClient influxDBClient) {
         influxDBClient.writePoint(