Improve accuracy for UtcDatetime conversion from timestamp

Author: matsimitsu

src/decoder.rs

@@ -25,7 +25,8 @@ use std::io::{self, Read};
 use std::{str, error, fmt};
 
 use byteorder::{self, LittleEndian, ReadBytesExt};
-use chrono::{DateTime, NaiveDateTime, UTC};
+use chrono::{UTC};
+use chrono::offset::TimeZone;
 
 use spec::{self, BinarySubtype};
 use bson::{Bson, Array, Document};
@@ -215,7 +216,7 @@ fn decode_bson<R: Read + ?Sized>(reader: &mut R, tag: u8) -> DecoderResult<Bson>
         Some(TimeStamp) => read_i64(reader).map(Bson::TimeStamp),
         Some(UtcDatetime) => {
             let time = try!(read_i64(reader));
-            Ok(Bson::UtcDatetime(DateTime::from_utc(NaiveDateTime::from_timestamp(time / 1000, 0), UTC)))
+            Ok(Bson::UtcDatetime(UTC.timestamp(time / 1000, (time % 1000) as u32 * 1000000)))
         },
 	Some(Deprecated) |
         Some(Undefined) |

src/encoder.rs

@@ -24,6 +24,7 @@
 use std::io::{self, Write};
 use std::iter::IntoIterator;
 use std::{mem, error, fmt};
+use chrono::Timelike;
 
 use byteorder::{self, LittleEndian, WriteBytesExt};
 
@@ -162,7 +163,9 @@ fn encode_bson<W: Write + ?Sized>(writer: &mut W, key: &str, val: &Bson) -> Enco
             try!(writer.write_u8(From::from(subtype)));
             writer.write_all(data).map_err(From::from)
         },
-        &Bson::UtcDatetime(ref v) => write_i64(writer, v.timestamp() * 1000),
+        &Bson::UtcDatetime(ref v) => {
+            write_i64(writer, (v.timestamp() * 1000) + (v.nanosecond()  / 1000000)  as i64)
+        },
         &Bson::Null => Ok(())
     }
 }