time: implement strict RFC 3339 during marshal and unmarshal

We add strict checking to marshal and unmarshal methods,
rather than Parse to maintain compatibility in Parse behavior.
Also, the Time.Format method has no ability to report errors.

The Time.Marshal{Text,JSON} and Time.Unmarshal{Time,JSON} methods
are already documented as complying with RFC 3339, but have
edge cases on both marshal and unmarshal where it is incorrect.
The Marshal methods already have at least one check to comply
with RFC 3339, so it seems sensible to expand this to cover
all known violations of the specification.
This commit fixes all known edge cases for full compliance.

Two optimizations are folded into this change:

	1. parseRFC3339 is made generic so that it can operate
	   directly on a []byte as well as string.
	   This avoids allocating or redundant copying
	   when converting from string to []byte.

	2. When marshaling, we verify for correctness based
	   on the serialized output, rather than calling
	   attribute methods on the Time type. For example,
	   it is faster to check that the 5th byte is '-'
	   rather than check that Time.Year is within [0,9999],
	   since Year is a relatively expensive operation.

Performance:

	name            old time/op  new time/op  delta
	MarshalJSON     109ns ± 2%    99ns ± 1%   -9.43%  (p=0.000 n=10+10)
	UnmarshalText   158ns ± 4%   143ns ± 1%   -9.17%  (p=0.000 n=9+9)

Updates #54580
Updates #54568
Updates #54571

Change-Id: I1222e45a7625d1ffd0629be5738670a84188d301
Reviewed-on: https://go-review.googlesource.com/c/go/+/444277
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>

0 files changed, 0 insertions, 0 deletions