From aeac6398f8f020762f2234e581a328aaa4dfd236 Mon Sep 17 00:00:00 2001
From: Tim Vaillancourt <tim@timvaillancourt.com>
Date: Thu, 23 Jan 2025 18:18:58 +0100
Subject: [PATCH] primary pinger

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>
---
 go/vt/vttablet/tabletserver/health_pinger.go  | 137 ++++++++++++++++++
 .../tabletserver/health_pinger_test.go        |  27 ++++
 2 files changed, 164 insertions(+)
 create mode 100644 go/vt/vttablet/tabletserver/health_pinger.go
 create mode 100644 go/vt/vttablet/tabletserver/health_pinger_test.go

diff --git a/go/vt/vttablet/tabletserver/health_pinger.go b/go/vt/vttablet/tabletserver/health_pinger.go
new file mode 100644
index 00000000000..cc45a5e2d05
--- /dev/null
+++ b/go/vt/vttablet/tabletserver/health_pinger.go
@@ -0,0 +1,137 @@
+/*
+Copyright 2025 The Vitess Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package tabletserver
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"vitess.io/vitess/go/vt/log"
+	topodatapb "vitess.io/vitess/go/vt/proto/topodata"
+	vtrpcpb "vitess.io/vitess/go/vt/proto/vtrpc"
+	"vitess.io/vitess/go/vt/topo/topoproto"
+	"vitess.io/vitess/go/vt/vterrors"
+	"vitess.io/vitess/go/vt/vttablet/grpctmclient"
+)
+
+var (
+	ErrPrimaryHealthPingerOpen = vterrors.New(vtrpcpb.Code_FAILED_PRECONDITION,
+		"primary health pinger is already open")
+	ErrPrimaryUnreachable = vterrors.New(vtrpcpb.Code_UNAVAILABLE,
+		"primary is unreachable")
+	PrimaryPingTimeout = time.Second * 5
+)
+
+type PrimaryHealthPinger interface {
+	Open() error
+	Close()
+	IsReachable() error
+	SetPrimary(*topodatapb.Tablet)
+}
+
+func NewPrimaryHealthPinger(interval time.Duration) PrimaryHealthPinger {
+	return &tmPrimaryHealthPinger{
+		interval: interval,
+	}
+}
+
+type tmPrimaryHealthPinger struct {
+	cancel    context.CancelFunc
+	ctx       context.Context
+	interval  time.Duration
+	mu        sync.Mutex
+	opened    bool
+	primary   *topodatapb.Tablet
+	reachable uint32
+}
+
+func (php *tmPrimaryHealthPinger) getPrimary() *topodatapb.Tablet {
+	php.mu.Lock()
+	defer php.mu.Unlock()
+	return php.primary
+}
+
+func (php *tmPrimaryHealthPinger) SetPrimary(primary *topodatapb.Tablet) {
+	php.mu.Lock()
+	defer php.mu.Unlock()
+	php.primary = primary
+}
+
+func (php *tmPrimaryHealthPinger) ping(tmc *grpctmclient.Client) {
+	primary := php.getPrimary()
+	if primary == nil {
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(php.ctx, PrimaryPingTimeout)
+	defer cancel()
+	if err := tmc.Ping(ctx, primary); err != nil {
+		log.Errorf("Failed to ping primary %s: %+v", topoproto.TabletAliasString(primary.Alias), err)
+		return
+	}
+	atomic.StoreUint32(&php.reachable, 1)
+}
+
+func (php *tmPrimaryHealthPinger) Open() error {
+	php.mu.Lock()
+	defer php.mu.Unlock()
+
+	if php.opened {
+		return ErrPrimaryHealthPingerOpen
+	}
+
+	php.ctx, php.cancel = context.WithCancel(context.Background())
+	go func() {
+		tmc := grpctmclient.NewClient()
+		defer tmc.Close()
+
+		// initial ping
+		php.ping(tmc)
+
+		// periodic ping
+		ticker := time.NewTicker(php.interval)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-php.ctx.Done():
+				return
+			case <-ticker.C:
+				php.ping(tmc)
+			}
+		}
+	}()
+	return nil
+}
+
+func (php *tmPrimaryHealthPinger) Close() {
+	php.mu.Lock()
+	defer php.mu.Unlock()
+	if php.cancel != nil {
+		php.cancel()
+	}
+	atomic.StoreUint32(&php.reachable, 0)
+	php.opened = false
+}
+
+func (php *tmPrimaryHealthPinger) IsReachable() error {
+	if atomic.LoadUint32(&php.reachable) != 1 {
+		return ErrPrimaryUnreachable
+	}
+	return nil
+}
diff --git a/go/vt/vttablet/tabletserver/health_pinger_test.go b/go/vt/vttablet/tabletserver/health_pinger_test.go
new file mode 100644
index 00000000000..f652af982ad
--- /dev/null
+++ b/go/vt/vttablet/tabletserver/health_pinger_test.go
@@ -0,0 +1,27 @@
+/*
+Copyright 2025 The Vitess Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package tabletserver
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPrimaryHealthPinger(t *testing.T) {
+	require.True(t, true)
+}