snapper: support custom timestamp format

fixes https://github.com/zrepl/zrepl/issues/465
closes https://github.com/zrepl/zrepl/pull/639

config/config.go

@@ -232,6 +232,7 @@ type SnapshottingPeriodic struct {
 	Prefix          string        `yaml:"prefix"`
 	Interval        time.Duration `yaml:"interval,positive"`
 	Hooks           HookList      `yaml:"hooks,optional"`
+	TimestampFormat string        `yaml:"timestamp_format,optional,default=dense"`
 }
 
 type CronSpec struct {
@@ -264,6 +265,7 @@ type SnapshottingCron struct {
 	Prefix          string   `yaml:"prefix"`
 	Cron            CronSpec `yaml:"cron"`
 	Hooks           HookList `yaml:"hooks,optional"`
+	TimestampFormat string   `yaml:"timestamp_format,optional,default=dense"`
 }
 
 type SnapshottingManual struct {

config/config_snapshotting_test.go

@@ -35,8 +35,16 @@ jobs:
   snapshotting:
     type: periodic
     prefix: zrepl_
+    timestamp_format: dense
     interval: 10m
 `
+	cron := `
+  snapshotting:
+    type: cron
+    prefix: zrepl_
+    timestamp_format: human
+    cron: "10 * * * *"
+`
 
 	hooks := `
   snapshotting:
@@ -76,6 +84,15 @@ jobs:
 		assert.Equal(t, "periodic", snp.Type)
 		assert.Equal(t, 10*time.Minute, snp.Interval)
 		assert.Equal(t, "zrepl_", snp.Prefix)
+		assert.Equal(t, "dense", snp.TimestampFormat)
+	})
+
+	t.Run("cron", func(t *testing.T) {
+		c = testValidConfig(t, fillSnapshotting(cron))
+		snp := c.Jobs[0].Ret.(*PushJob).Snapshotting.Ret.(*SnapshottingCron)
+		assert.Equal(t, "cron", snp.Type)
+		assert.Equal(t, "zrepl_", snp.Prefix)
+		assert.Equal(t, "human", snp.TimestampFormat)
 	})
 
 	t.Run("hooks", func(t *testing.T) {
@@ -88,3 +105,57 @@ jobs:
 	})
 
 }
+
+func TestSnapshottingTimestampDefaults(t *testing.T) {
+	tmpl := `
+jobs:
+- name: foo
+  type: push
+  connect:
+    type: local
+    listener_name: foo
+    client_identity: bar
+  filesystems: {"<": true}
+  %s
+  pruning:
+    keep_sender:
+    - type: last_n
+      count: 10
+    keep_receiver:
+    - type: last_n
+      count: 10
+`
+
+	periodic := `
+  snapshotting:
+    type: periodic
+    prefix: zrepl_
+    interval: 10m
+`
+	cron := `
+  snapshotting:
+    type: cron
+    prefix: zrepl_
+    cron: "10 * * * *"
+`
+
+	fillSnapshotting := func(s string) string { return fmt.Sprintf(tmpl, s) }
+	var c *Config
+
+	t.Run("periodic", func(t *testing.T) {
+		c = testValidConfig(t, fillSnapshotting(periodic))
+		snp := c.Jobs[0].Ret.(*PushJob).Snapshotting.Ret.(*SnapshottingPeriodic)
+		assert.Equal(t, "periodic", snp.Type)
+		assert.Equal(t, 10*time.Minute, snp.Interval)
+		assert.Equal(t, "zrepl_", snp.Prefix)
+		assert.Equal(t, "dense", snp.TimestampFormat) // default was set correctly
+	})
+
+	t.Run("cron", func(t *testing.T) {
+		c = testValidConfig(t, fillSnapshotting(cron))
+		snp := c.Jobs[0].Ret.(*PushJob).Snapshotting.Ret.(*SnapshottingCron)
+		assert.Equal(t, "cron", snp.Type)
+		assert.Equal(t, "zrepl_", snp.Prefix)
+		assert.Equal(t, "dense", snp.TimestampFormat) // default was set correctly
+	})
+}

daemon/snapper/cron.go

@@ -21,6 +21,7 @@ func cronFromConfig(fsf zfs.DatasetFilter, in config.SnapshottingCron) (*Cron, e
 	}
 	planArgs := planArgs{
 		prefix:          in.Prefix,
+		timestampFormat: in.TimestampFormat,
 		hooks:           hooksList,
 	}
 	return &Cron{config: in, fsf: fsf, planArgs: planArgs}, nil

daemon/snapper/impl.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -15,6 +16,7 @@ import (
 
 type planArgs struct {
 	prefix          string
+	timestampFormat string
 	hooks           *hooks.List
 }
 
@@ -58,6 +60,21 @@ type snapProgress struct {
 	runResults hooks.PlanReport
 }
 
+func (plan *plan) formatNow(format string) string {
+	now := time.Now().UTC()
+	switch strings.ToLower(format) {
+	case "dense":
+		format = "20060102_150405_000"
+	case "human":
+		format = "2006-01-02_15:04:05"
+	case "iso-8601":
+		format = "2006-01-02T15:04:05.000Z"
+	case "unix-seconds":
+		return strconv.FormatInt(now.Unix(), 10)
+	}
+	return now.Format(format)
+}
+
 func (plan *plan) execute(ctx context.Context, dryRun bool) (ok bool) {
 
 	hookMatchCount := make(map[hooks.Hook]int, len(*plan.args.hooks))
@@ -68,7 +85,7 @@ func (plan *plan) execute(ctx context.Context, dryRun bool) (ok bool) {
 	anyFsHadErr := false
 	// TODO channel programs -> allow a little jitter?
 	for fs, progress := range plan.snaps {
-		suffix := time.Now().In(time.UTC).Format("20060102_150405_000")
+		suffix := plan.formatNow(plan.args.timestampFormat)
 		snapname := fmt.Sprintf("%s%s", plan.args.prefix, suffix)
 
 		ctx := logging.WithInjectedField(ctx, "fs", fs.ToString())

daemon/snapper/periodic.go

@@ -36,6 +36,7 @@ func periodicFromConfig(g *config.Global, fsf zfs.DatasetFilter, in *config.Snap
 		fsf:      fsf,
 		planArgs: planArgs{
 			prefix:          in.Prefix,
+			timestampFormat: in.TimestampFormat,
 			hooks:           hookList,
 		},
 		// ctx and log is set in Run()

docs/changelog.rst

@@ -22,6 +22,7 @@ Developers should consult the git commit log or GitHub issue tracker.
 * `Feature Wishlist on GitHub <https://github.com/zrepl/zrepl/discussions/547>`_
 
 * |feature| :ref:`Schedule-based snapshotting<job-snapshotting--cron>` using ``cron`` syntax instead of an interval.
+* |feature| Configurable timestamp format for snapshot names via :ref:`timestamp_format<job-snapshotting-timestamp_format>`.
 * |feature| Add ``ZREPL_DESTROY_MAX_BATCH_SIZE`` env var (default 0=unlimited).
 * |bugfix| Fix resuming from interrupted replications that use ``send.raw`` on unencrypted datasets.
 

docs/configuration/snapshotting.rst

@@ -62,6 +62,9 @@ The ``periodic`` and ``cron`` snapshotting types share some common options and b
        type: periodic
        prefix: zrepl_
        interval: 10m
+       # Timestamp format that is used as snapshot suffix.
+       # Can be any of "dense" (default), "human", "iso-8601", "unix-seconds" or a custom Go time format (see https://go.dev/src/time/format.go)
+       timestamp_format: dense
        hooks: ...
     pruning: ...
 
@@ -91,6 +94,9 @@ The snapshotter uses the ``prefix`` to identify which snapshots it created.
        # (second, optional) minute hour day-of-month month day-of-week
        # This example takes snapshots daily at 3:00.
        cron: "0 3 * * *"
+       # Timestamp format that is used as snapshot suffix.
+       # Can be any of "dense" (default), "human", "iso-8601", "unix-seconds" or a custom Go time format (see https://go.dev/src/time/format.go)
+       timestamp_format: dense
      pruning: ...
 
 In ``cron`` mode, the snapshotter takes snaphots at fixed points in time.
@@ -98,6 +104,21 @@ See https://en.wikipedia.org/wiki/Cron for details on the syntax.
 zrepl uses the ``the github.com/robfig/cron/v3`` Go package for parsing.
 An optional field for "seconds" is supported to take snapshots at sub-minute frequencies.
 
+.. _job-snapshotting-timestamp_format:
+
+Timestamp Format
+~~~~~~~~~~~~~~~~
+
+The ``cron`` and ``periodic`` snapshotter support configuring a custom timestamp format that is used as suffix for the snapshot name.
+It can be used by setting ``timestamp_format`` to any of the following values:
+
+* ``dense`` (default) looks like ``20060102_150405_000``
+* ``human`` looks like ``2006-01-02_15:04:05``
+* ``iso-8601`` looks like ``2006-01-02T15:04:05.000Z``
+* ``unix-seconds`` looks like ``1136214245``
+* Any custom Go time format accepted by `time.Time#Format <https://go.dev/src/time/format.go>`_.
+
+
 ``manual`` Snapshotting
 -----------------------