feat: Support string duration format in config files

[rewenset]

Issue #399

This PR allows setting duration fields, which have time.Duration type, in config files not only in nanoseconds:

reply-timeout: 5000000000

but as a string too

reply-timeout: 5s

[rewenset]

So if I change for example in ETCD config.go this field

cn-infra/db/keyval/etcd/config.go

Line 34 in 9bb0e39

DialTimeout time.Duration `json:"dial-timeout"`

to be not time.Duration, but config.Duration (which is newly created type introduced in this PR)
then I'll need to find all places this field is used and add .Duration, e.g.:

        dialTimeout := defaultDialTimeout
-       if yc.DialTimeout != 0 {
-               dialTimeout = yc.DialTimeout
+       if yc.DialTimeout.Duration != 0 {
+               dialTimeout = yc.DialTimeout.Duration
        }

For now, I didn't find better solution.

@ondrej-fabry please advise

[ondrej-fabry]

Checking by type name is not very certain as it will match for other types named Duration.

However you can compare types directly, because the reflect.Type values are comparable:

reflect.TypeOf(out) == reflect.TypeOf(time.Duration(0))

Play