plugin/forward: Allow Proxy to be used outside of forward plugin. (#5951)

* plugin/forward: Move Proxy into pkg/plugin/proxy, to allow forward.Proxy to be used outside of forward plugin.

Signed-off-by: Patrick Downey <patrick.downey@dioadconsulting.com>

plugin/pkg/proxy/proxy.go

@@ -0,0 +1,98 @@
+package proxy
+
+import (
+	"crypto/tls"
+	"runtime"
+	"sync/atomic"
+	"time"
+
+	"github.com/coredns/coredns/plugin/pkg/log"
+	"github.com/coredns/coredns/plugin/pkg/up"
+)
+
+// Proxy defines an upstream host.
+type Proxy struct {
+	fails uint32
+	addr  string
+
+	transport *Transport
+
+	readTimeout time.Duration
+
+	// health checking
+	probe  *up.Probe
+	health HealthChecker
+}
+
+// NewProxy returns a new proxy.
+func NewProxy(addr, trans string) *Proxy {
+	p := &Proxy{
+		addr:        addr,
+		fails:       0,
+		probe:       up.New(),
+		readTimeout: 2 * time.Second,
+		transport:   newTransport(addr),
+	}
+	p.health = NewHealthChecker(trans, true, ".")
+	runtime.SetFinalizer(p, (*Proxy).finalizer)
+	return p
+}
+
+func (p *Proxy) Addr() string { return p.addr }
+
+// SetTLSConfig sets the TLS config in the lower p.transport and in the healthchecking client.
+func (p *Proxy) SetTLSConfig(cfg *tls.Config) {
+	p.transport.SetTLSConfig(cfg)
+	p.health.SetTLSConfig(cfg)
+}
+
+// SetExpire sets the expire duration in the lower p.transport.
+func (p *Proxy) SetExpire(expire time.Duration) { p.transport.SetExpire(expire) }
+
+func (p *Proxy) GetHealthchecker() HealthChecker {
+	return p.health
+}
+
+func (p *Proxy) Fails() uint32 {
+	return atomic.LoadUint32(&p.fails)
+}
+
+// Healthcheck kicks of a round of health checks for this proxy.
+func (p *Proxy) Healthcheck() {
+	if p.health == nil {
+		log.Warning("No healthchecker")
+		return
+	}
+
+	p.probe.Do(func() error {
+		return p.health.Check(p)
+	})
+}
+
+// Down returns true if this proxy is down, i.e. has *more* fails than maxfails.
+func (p *Proxy) Down(maxfails uint32) bool {
+	if maxfails == 0 {
+		return false
+	}
+
+	fails := atomic.LoadUint32(&p.fails)
+	return fails > maxfails
+}
+
+// Stop close stops the health checking goroutine.
+func (p *Proxy) Stop()      { p.probe.Stop() }
+func (p *Proxy) finalizer() { p.transport.Stop() }
+
+// Start starts the proxy's healthchecking.
+func (p *Proxy) Start(duration time.Duration) {
+	p.probe.Start(duration)
+	p.transport.Start()
+}
+
+func (p *Proxy) SetReadTimeout(duration time.Duration) {
+	p.readTimeout = duration
+}
+
+const (
+	maxTimeout = 2 * time.Second
+)