Serialize time to RFC3339 compliant string

[zhxnlai]

According to the documentation, OffsetDateTime's toString method uses this format uuuu-MM-dd'T'HH:mmXXXXX when seconds is zero. This is incompatible with RFC3339 and cannot be parsed by other cloud events SDKs.

Here is an demo of the incompatibility:
https://play.golang.org/p/9db3zuJTM_k

[matejvasek]

In general looks good, but it breaks some test since it adds unnecessary zeros to fraction part of date (2018-04-26T14:48:09.123400Z instead of 2018-04-26T14:48:09.1234Z).
Maybe:

    public static final DateTimeFormatter RFC3339_DATE_FORMAT = new DateTimeFormatterBuilder()	
        .appendPattern("yyyy-MM-dd'T'HH:mm:ss")	
        .appendFraction(ChronoField.NANO_OF_SECOND, 0, 9, true)	
        .appendOffsetId()	
        .toFormatter();

would work better than java.time.format.DateTimeFormatter.ISO_OFFSET_DATE_TIME

the above was used in previous version https://github.com/cloudevents/sdk-java/pull/216/files#diff-bac8dca098ba932b36f5b17870212371L34.

Or maybe we could change assertions in the test, I think that would be acceptable too.

/cc @slinkydeveloper

[zhxnlai]

@matejvasek fixed the test. It looks like ISO_OFFSET_DATE_TIME actually removes unnecessary zeros in the test 😉

[slinkydeveloper]

I personally don't care about the more zeroes, if that's compliant to the spec, fine. I would love to avoid adding custom formats

[slinkydeveloper]

@matejvasek can you double check this one?

[matejvasek]

@zhxnlai my bad, I mistaken expected with actual in the test output.

[matejvasek]

LGTM

[matejvasek]

Note: when reading input we allow missing seconds, but for input it's OK to be less strict as is doesn't affect compatibility.

[zhxnlai]

@matejvasek @slinkydeveloper any chance we could roll this out soon?

[matejvasek]

@zhxnlai I am not maintainer here (@slinkydeveloper is), but I would say probably not. This was merged just one day after releasing 2.0.0 Milestone 3, and there hasn't been much done for M4.

[zhxnlai]

Technically this is a bug fix. My java application is stuck with milestone1 because it needs to interop with a go application that uses the go SDK. I am waiting for this fix to go out so that I can upgrade it to the latest Java SDK

[slinkydeveloper]

@zhxnlai hopefully another release will be out soon, we're trying to solve this issue first #250 😄

[slinkydeveloper]

@zhxnlai Meanwhile you can use the snapshot packages, which should include this fix