time.Parse in Go with varying fractional second length - go

Question

I am parsing a timestamp from a DB. My layout is the following:
layout = "2006-01-02 15:04:05.000000000 -0700 MST"
pipelineTS, err := time.Parse(layout, rawPipelineTS)
The issue is that sometimes the fractional seconds are not 9 digits, for example:
2018-12-18 15:25:08.73728596 +0000 UTC
When it finds a value like this, it errors out. Any ideas on how to fix this? The timestamps come from a DB table. I need it to take any number of fractional second digits.

Answer 1

Package time
A decimal point followed by one or more zeros represents a fractional
second, printed to the given number of decimal places. A decimal point
followed by one or more nines represents a fractional second, printed
to the given number of decimal places, with trailing zeros removed.
Use nines, not zeros, for the layout fractional seconds.
For example,
package main
import (
"fmt"
"time"
)
func main() {
layout := "2006-01-02 15:04:05.999999999 -0700 MST"
input := "2018-12-18 15:25:08.73728596 +0000 UTC" // 8 digits
t, err := time.Parse(layout, input)
fmt.Println(t, err)
input = "2018-12-18 15:25:08.7372 +0000 UTC" // 4 digits
t, err = time.Parse(layout, input)
fmt.Println(t, err)
input = "2018-12-18 15:25:08 +0000 UTC" // 0 digits
t, err = time.Parse(layout, input)
fmt.Println(t, err)
}
Playground: https://play.golang.org/p/j4WBmz3ENke
Output:
2018-12-18 15:25:08.73728596 +0000 UTC <nil>
2018-12-18 15:25:08.7372 +0000 UTC <nil>
2018-12-18 15:25:08 +0000 UTC <nil>

Answer 2

From the time.Parse docs:
When parsing (only), the input may contain a fractional second
field immediately after the seconds field, even if the layout does not
signify its presence. In that case either a comma or a decimal point
followed by a maximal series of digits is parsed as a fractional second.
Fractional seconds are truncated to nanosecond precision.
For time parsing:
If you don't specify fractional seconds in the layout, time.Parse will still accept it in the input, with full resolution (the "maximal series of digits"). (source)
If you specify fractional seconds with one or more zeros, time.Parse requires the input to have that exact number of fractional digits. (source)
If you specify fractional seconds with one or more nines, time.Parse actually accepts any number of fractional digits (up to 9) in the input. That is, the behavior is the same as if you didn't specify fractional seconds at all (case #1). I think the docs are not clear on this point at all, but for parsing (not formatting), .9, .99, .999, .999999, etc. are all exactly equivalent. (source)
If the input contains more than 9 fractional digits, Go 1.19 and below return an error, while Go 1.20 ignores any fractional digits beyond the 9th ("truncate[s] to nanosecond precision"). (source)
Playground samples: https://go.dev/play/p/-aE8T9DchlQ