time: one-digit hour is accepted for 15:04:05 template

[tredoe]

What version of Go are you using (go version)?

$ go version
go version go1.11.4 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

https://play.golang.org/p/EBxIIXatR1Y

What did you expect to see?

I expected to see an error at parsing the time "3:04:05" for layout "15:04:05", of the same way that it fails at parsing the minutes ("03:4:05") or the seconds ("03:04:5").

What did you see instead?

No error.

[mattn]

Please try this instead https://play.golang.org/p/k7kmlXt15zF
See https://golang.org/pkg/time/#pkg-constants

[tredoe]

I want not to accept hours, minutes neither seconds with an only digit. And it is parsed correctly for both minutes and seconds with the layout "15:04:05".

[mattn]

Ah, I undestand just now. Sorry.

[FiloSottile]

I'm afraid there is no way to require 24-hour zero-padded hours with a time.Parse template.

/cc @rsc to confirm

[FiloSottile]

@Virepri You can open a proposal if you want to discuss such a big change, but in general we try not to provide two different ways of doing very similar things in the standard library.

This might be better as an external package.

[gopherbot]

Change https://go.dev/cl/425044 mentions this issue: time: fix Parse to reject single digit hour in RFC3339

[arp242]

This might be better as an external package.

Seems a bit much to maintain and/or import an external package for such a minor feature?

Anyway, this is what I came up with for the time being:

// time.Parse() will accept numbers without a leading zero; there isn't any way
// to require it. https://github.com/golang/go/issues/29911
//
// The separators (- and :) should always be at the same location for the layout
// and date string.
func missingLeadingZero(d, l string) bool {
	for i, c := range []byte(l) {
		if c == '.' || c == 'Z' {
			return false
		}
		if (c < '0' || c > '9') && d[i] != c {
			return true
		}
	}
	return false
}