Invalid example for RFC3339 time layout - Invalid according to RFC and also time.Parse fails

[lazysegtree]

Go version

go version go1.21.6 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/kuknitin/Library/Caches/go-build'
GOENV='/Users/kuknitin/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/kuknitin/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/kuknitin/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.21.6/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.21.6/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.6'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/tp/8gddycn174j124g7lkl42trh0000gn/T/go-build1722890158=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Used the provided example for RFC3339 time layout (https://github.com/golang/go/blob/master/src/time/format.go#L119) , and tried to parse it via time.Parse

Go code

// Output is
// parsing time "2006-01-02T15:04:05Z07:00": extra text: "07:00"
package main 
import (
	"fmt"
	"time"
)
func main() {
	str_to_parse := time.RFC3339
	t,err := time.Parse(time.RFC3339, str_to_parse)
	if err!=nil {
		fmt.Println(err)
	} else {
		fmt.Println("Parse done : ", t)
	}
}

What did you see happen?

(.venv) ➜  ~/Workspace/kuknitin/shared/Misc/Go git:(main) ✗ [3:38:43] go run Learning/misc/time/rfc3339_bug.go
parsing time "2006-01-02T15:04:05Z07:00": extra text: "07:00"
(.venv) ➜  ~/Workspace/kuknitin/shared/Misc/Go git:(main) ✗ [3:40:00]

What did you expect to see?

Correct output with parse done.

[lazysegtree]

Also as per RFC - https://datatracker.ietf.org/doc/html/rfc3339#section-5.8, 2006-01-02T15:04:05Z07:00 is invalid.

Correct layout is 2006-01-02T15:04:05-07:00

[lazysegtree]

I went through the issue - #9346, and stackoverflow discussion.
But I dont understand how it is concluded.
Either

• we need to fix the example 2006-01-02T15:04:05Z07:00 to 2006-01-02T15:04:05-07:00 (correct)
• Or make the time.Parse() able to parse the 2006-01-02T15:04:05Z07:00 (even though its invalid as per RFC)

The failure of time.Parse(time.RFC3339, time.RFC3339) is completely unacceptable. Its like the language is not adhering to its own definitions

[gabyhelp]

Related Issues

• time.parse cann ot parse RFC3339 reference string (or any other I tried) #68527 (closed)
• time: documentation shows incorrect formatting of RFC3339 that does not parse #22135 (closed)
• time.RFC3339* cannot be parsed using time.RFC3339* as a format in time.Parse #38469 (closed)
• time.RFC3339 does not even parse with time.Parse #21443 (closed)
• time.RFC3339 does not support space between date and time #41461 (closed)
• time: layout string parser doesn't support all needed features to cover the RFC 3339 standard #63488 (closed)
• time: Weird behavior with RFC3339 parser #30341 (closed)
• time: doesn't parse RFC3339 properly #9346 (closed)
• time: ParseInLocation does not adjust timezone offset when seconds are not explicitly set #53919 (closed)
• time: no Parse format for GNU style RFC3339 #25937 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/643258 mentions this issue: time: fix example for RFC3339 time layout

[lazysegtree]

All the above issues and Stackoverflow discussion agree with that fact that package documentation for RFC3339 is wrong, and time.RFC3339 format is a case where the format string itself isn't a valid time at the moment.

So, the documentation and example should be fixed.

[lazysegtree]

This issue is indeed the duplicate of the above mentioned issues, but the above mentioned issues have been closed without a conclusion / fix.

I have created a PR for this - #71378

[lazysegtree]

@seankhliao Can you reopen this issue (Please see my above comments)

[seankhliao]

we've repeatedly stated that we need extra control over how exactly to parse or format the time. it's also stated in the docs:

Some valid layouts are invalid time values for time.Parse, due to formats such as _ for space padding and Z for zone information.

this is working as intended. the assumption that a layout time string has to be a valid time is unfounded.

[JoesSon72]

Jesus lovers 🇪🇭Sent from my iPhoneOn Jan 22, 2025, at 07:32, Sean Liao ***@***.***> wrote: we've repeatedly stated that we need extra control over how exactly to parse or format the time. it's also stated in the docs: Some valid layouts are invalid time values for time.Parse, due to formats such as _ for space padding and Z for zone information. —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[lazysegtree]

@seankhliao

the assumption that a layout time string has to be a valid time is unfounded.

This doesn't make sense. If its not a valid time string for the given layout, what is the purpose of the layout string value ? Why dont just define time.RFC3339 to any random unique identified.

Its clearly stated in the comments of the code https://github.com/golang/go/blob/master/src/time/format.go

// These are predefined layouts for use in [Time.Format] and [time.Parse].
// The reference time used in these layouts is the specific time stamp:
//
// 01/02 03:04:05PM '06 -0700
//
// (January 2, 15:04:05, 2006, in time zone seven hours west of GMT).

Then, time.RFC3339 string value should be exactly what is the correct value for the specified time in RFC33339 format, and nothing else.

we need extra control over how exactly to parse or format the time

I dont understand how having an invalid format example gives any extra control to parse the time.
time.RFC3339 is not used by the actual parser at all.

Some valid layouts are invalid time values for time.Parse

This is not true, 2006-01-02T15:04:05Z07:00 is neither a valid layout as per RFC3339, and nor a valid time value for time.Parse. This doesn't makes any sense to use a value in example that is both invalid per the RFC, and invalid per the time.Parse implementation.

[seankhliao]

as stated above, and in the docs, a layout is not necessarily a valid timestamp, it only describes the format which the time package should use to process the time. they are not example strings of valid timestamps, they are instructions to the parser and formatter. while in most cases it will look similar to a valid timestamp, that will not always be the case (_, Z).

for questions please refer to https://github.com/golang/go/wiki/Questions