feat: add watchdog and monit (#2329)

This PR introduces the `r/gnoland/monit` realm, which can be used by an
external tool to verify if everything is working well, including:
- gnokey compatibility (and all the tx/amino/etc)
- networking (rpc)
- realm state persistency (counter should be higher than the previous
value)

In addition to being a good target for an external monitoring agent, the
realm displays (`Render`) some information, including whether the agent
appears to be missing.

- [x] improve ownable (depends on #2330)
- [x] p/demo/watchdog
- [x] r/gnoland/monit
- [ ] ~update contribs/autocounterd~ -> let's @gnolang/devops tackle
this in another PR. -> #1443

---------

Signed-off-by: moul <94029+moul@users.noreply.github.com>
Co-authored-by: Miloš Živković <milos@zmilos.com>

examples/gno.land/p/demo/watchdog/gno.mod

@@ -0,0 +1,3 @@
+module gno.land/p/demo/watchdog
+
+require gno.land/p/demo/uassert v0.0.0-latest

examples/gno.land/p/demo/watchdog/watchdog.gno

@@ -0,0 +1,39 @@
+package watchdog
+
+import "time"
+
+type Watchdog struct {
+	Duration   time.Duration
+	lastUpdate time.Time
+	lastDown   time.Time
+}
+
+func (w *Watchdog) Alive() {
+	now := time.Now()
+	if !w.IsAlive() {
+		w.lastDown = now
+	}
+	w.lastUpdate = now
+}
+
+func (w Watchdog) Status() string {
+	if w.IsAlive() {
+		return "OK"
+	}
+	return "KO"
+}
+
+func (w Watchdog) IsAlive() bool {
+	return time.Since(w.lastUpdate) < w.Duration
+}
+
+func (w Watchdog) UpSince() time.Time {
+	return w.lastDown
+}
+
+func (w Watchdog) DownSince() time.Time {
+	if !w.IsAlive() {
+		return w.lastUpdate
+	}
+	return time.Time{}
+}

examples/gno.land/p/demo/watchdog/watchdog_test.gno

@@ -0,0 +1,16 @@
+package watchdog
+
+import (
+	"testing"
+	"time"
+
+	"gno.land/p/demo/uassert"
+)
+
+func TestPackage(t *testing.T) {
+	w := Watchdog{Duration: 5 * time.Minute}
+	uassert.False(t, w.IsAlive())
+	w.Alive()
+	uassert.True(t, w.IsAlive())
+	// XXX: add more tests when we'll be able to "skip time".
+}

examples/gno.land/r/gnoland/monit/gno.mod

@@ -0,0 +1,8 @@
+module gno.land/r/gnoland/monit
+
+require (
+	gno.land/p/demo/ownable v0.0.0-latest
+	gno.land/p/demo/uassert v0.0.0-latest
+	gno.land/p/demo/ufmt v0.0.0-latest
+	gno.land/p/demo/watchdog v0.0.0-latest
+)

examples/gno.land/r/gnoland/monit/monit.gno

@@ -0,0 +1,59 @@
+// Package monit links a monitoring system with the chain in both directions.
+//
+// The agent will periodically call Incr() and verify that the value is always
+// higher than the previously known one. The contract will store the last update
+// time and use it to detect whether or not the monitoring agent is functioning
+// correctly.
+package monit
+
+import (
+	"std"
+	"time"
+
+	"gno.land/p/demo/ownable"
+	"gno.land/p/demo/ufmt"
+	"gno.land/p/demo/watchdog"
+)
+
+var (
+	counter          int
+	lastUpdate       time.Time
+	lastCaller       std.Address
+	wd               = watchdog.Watchdog{Duration: 5 * time.Minute}
+	owner            = ownable.New() // TODO: replace with -> ownable.NewWithAddress...
+	watchdogDuration = 5 * time.Minute
+)
+
+// Incr increments the counter and informs the watchdog that we're alive.
+// This function can be called by anyone.
+func Incr() int {
+	counter++
+	lastUpdate = time.Now()
+	lastCaller = std.PrevRealm().Addr()
+	wd.Alive()
+	return counter
+}
+
+// Reset resets the realm state.
+// This function can only be called by the admin.
+func Reset() {
+	if owner.CallerIsOwner() != nil { // TODO: replace with owner.AssertCallerIsOwner
+		panic("unauthorized")
+	}
+	counter = 0
+	lastCaller = std.PrevRealm().Addr()
+	lastUpdate = time.Now()
+	wd = watchdog.Watchdog{Duration: 5 * time.Minute}
+}
+
+func Render(_ string) string {
+	status := wd.Status()
+	return ufmt.Sprintf(
+		"counter=%d\nlast update=%s\nlast caller=%s\nstatus=%s",
+		counter, lastUpdate, lastCaller, status,
+	)
+}
+
+// TransferOwnership transfers ownership to a new owner. This is a proxy to
+// ownable.Ownable.TransferOwnership.
+func TransferOwnership(newOwner std.Address) { owner.TransferOwnership(newOwner) }

examples/gno.land/r/gnoland/monit/monit_test.gno

@@ -0,0 +1,56 @@
+package monit
+
+import (
+	"testing"
+
+	"gno.land/p/demo/uassert"
+)
+
+func TestPackage(t *testing.T) {
+	// initial state, watchdog is KO.
+	{
+		expected := `counter=0
+last update=0001-01-01 00:00:00 +0000 UTC
+last caller=
+status=KO`
+		got := Render("")
+		uassert.Equal(t, expected, got)
+	}
+
+	// call Incr(), watchdog is OK.
+	Incr()
+	Incr()
+	Incr()
+	{
+		expected := `counter=3
+last update=2009-02-13 23:31:30 +0000 UTC m=+1234567890.000000001
+last caller=g1wymu47drhr0kuq2098m792lytgtj2nyx77yrsm
+status=OK`
+		got := Render("")
+		uassert.Equal(t, expected, got)
+	}
+
+	/* XXX: improve tests once we've the missing std.TestSkipTime feature
+		// wait 1h, watchdog is KO.
+		use std.TestSkipTime(time.Hour)
+		{
+			expected := `counter=3
+	last update=2009-02-13 22:31:30 +0000 UTC m=+1234564290.000000001
+	last caller=g1wymu47drhr0kuq2098m792lytgtj2nyx77yrsm
+	status=KO`
+			got := Render("")
+			uassert.Equal(t, expected, got)
+		}
+
+		// call Incr(), watchdog is OK.
+		Incr()
+		{
+			expected := `counter=4
+	last update=2009-02-13 23:31:30 +0000 UTC m=+1234567890.000000001
+	last caller=g1wymu47drhr0kuq2098m792lytgtj2nyx77yrsm
+	status=OK`
+			got := Render("")
+			uassert.Equal(t, expected, got)
+		}
+	*/
+}