Deserializing DateTime from unix timestamp is not implemented, despite description

[jmaximusix]

The Deserialize Trait can't deserialize DateTimes from timestamps despite the error message you get. I tried tracking it down in the source code, I hope the cited references are correct.

The Deserialize Trait only calls the deserialize_str() function

chrono/src/datetime/serde.rs

Lines 75 to 82 in f4adc28

	impl<'de> de::Deserialize<'de> for DateTime<FixedOffset> {
	fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
	where
	D: de::Deserializer<'de>,
	{
	deserializer.deserialize_str(DateTimeVisitor)
	}
	}

where, in spite of the expecting() stating it accepts "a formatted date and time string or a unix timestamp" it only calls the parse() function

chrono/src/datetime/serde.rs

Lines 53 to 66 in f4adc28

	impl<'de> de::Visitor<'de> for DateTimeVisitor {
	type Value = DateTime<FixedOffset>;
	fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
	formatter.write_str("a formatted date and time string or a unix timestamp")
	}
	fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
	where
	E: de::Error,
	{
	value.parse().map_err(E::custom)
	}
	}

which in turn is implemented to only try and deserialize rfc3339 strings

chrono/src/format/parse.rs

Lines 523 to 534 in f4adc28

	impl str::FromStr for DateTime<FixedOffset> {
	type Err = ParseError;
	fn from_str(s: &str) -> ParseResult<DateTime<FixedOffset>> {
	let mut parsed = Parsed::new();
	let (s, _) = parse_rfc3339_relaxed(&mut parsed, s)?;
	if !s.trim_start().is_empty() {
	return Err(TOO_LONG);
	}
	parsed.to_datetime()
	}
	}

[pitdicker]

That error message, "a formatted date and time string or a unix timestamp", seems not right indeed.

We do not really have a solution yet. There is an old PR to add deserializing from strings to the existing timestamp deserializers (#926). And another one to add full string serialization and deserialization modules (#1067).