@@ -0,0 +1,93 @@
1+package timestamp
2+3+import (
4+"fmt"
5+"strconv"
6+"strings"
7+"time"
8+9+"github.com/pkg/errors"
10+)
11+12+type Formatter struct {
13+format func(time.Time) string
14+location *time.Location
15+}
16+17+func New(formatString string, locationString string) (*Formatter, error) {
18+location, err := time.LoadLocation(locationString) // no shadow
19+if err != nil {
20+return nil, errors.Wrapf(err, "load location from string %q", locationString)
21+ }
22+makeFormatFunc := func(formatString string) (func(time.Time) string, error) {
23+// NB: we use zfs.EntityNamecheck in higher-level code to filter out all invalid characters.
24+// This check here is specifically so that we know for sure that the `+`=>`_` replacement
25+// that we do in the returned func replaces exactly the timezone offset `+` and not some other `+`.
26+if strings.Contains(formatString, "+") {
27+return nil, fmt.Errorf("character '+' is not allowed in ZFS snapshot names and has special handling")
28+ }
29+return func(t time.Time) string {
30+res := t.Format(formatString)
31+// if the formatString contains a time zone specifier
32+// and the location would result in a positive offset to UTC
33+// then the result of t.Format would contain a '+' sign.
34+if isLocationPositiveOffsetToUTC(location) {
35+// the only source of `+` can be the positive time zone offset because we disallowed `+` as a character in the format string
36+res = strings.Replace(res, "+", "_", 1)
37+ }
38+if strings.Contains(res, "+") {
39+panic(fmt.Sprintf("format produced a string containing illegal character '+' that wasn't the expected case of positive time zone offset: format=%q location=%q unix=%q result=%q", formatString, location, t.Unix(), res))
40+ }
41+return res
42+ }, nil
43+ }
44+var formatFunc func(time.Time) string
45+mustUseUtcError := func() error {
46+return fmt.Errorf("format string requires UTC location")
47+ }
48+switch strings.ToLower(formatString) {
49+case "dense":
50+if location != time.UTC {
51+err = mustUseUtcError()
52+ } else {
53+formatFunc, err = makeFormatFunc("20060102_150405_000")
54+ }
55+case "human":
56+if location != time.UTC {
57+err = mustUseUtcError()
58+ } else {
59+formatFunc, err = makeFormatFunc("2006-01-02_15:04:05")
60+ }
61+case "iso-8601":
62+formatFunc, err = makeFormatFunc("2006-01-02T15:04:05.000Z0700")
63+case "unix-seconds":
64+if location != time.UTC {
65+// Technically not required because unix time is by definition in UTC
66+// but let's make that clear to confused users...
67+err = mustUseUtcError()
68+ } else {
69+formatFunc = func(t time.Time) string {
70+return strconv.FormatInt(t.Unix(), 10)
71+ }
72+ }
73+default:
74+formatFunc, err = makeFormatFunc(formatString)
75+ }
76+if err != nil {
77+return nil, errors.Wrapf(err, "invalid format string %q or location %q", formatString, locationString)
78+ }
79+return &Formatter{
80+format: formatFunc,
81+location: location,
82+ }, nil
83+}
84+85+func isLocationPositiveOffsetToUTC(location *time.Location) bool {
86+_, offsetSeconds := time.Now().In(location).Zone()
87+return offsetSeconds > 0
88+}
89+90+func (f *Formatter) Format(t time.Time) string {
91+t = t.In(f.location)
92+return f.format(t)
93+}