Remove the word middleware (#1067)

* Rename middleware to plugin

first pass; mostly used 'sed', few spots where I manually changed
text.

This still builds a coredns binary.

* fmt error

* Rename AddMiddleware to AddPlugin

* Readd AddMiddleware to remain backwards compat

plugin/proxy/proxy_test.go

@@ -0,0 +1,87 @@
+package proxy
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/mholt/caddy/caddyfile"
+)
+
+func TestStop(t *testing.T) {
+	config := "proxy . %s {\n health_check /healthcheck:%s %dms \n}"
+	tests := []struct {
+		name                    string
+		intervalInMilliseconds  int
+		numHealthcheckIntervals int
+	}{
+		{
+			"No Healthchecks After Stop - 5ms, 1 intervals",
+			5,
+			1,
+		},
+		{
+			"No Healthchecks After Stop - 5ms, 2 intervals",
+			5,
+			2,
+		},
+		{
+			"No Healthchecks After Stop - 5ms, 3 intervals",
+			5,
+			3,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+
+			// Set up proxy.
+			var counter int64
+			backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				r.Body.Close()
+				atomic.AddInt64(&counter, 1)
+			}))
+
+			defer backend.Close()
+
+			port := backend.URL[17:] // Remove all crap up to the port
+			back := backend.URL[7:]  // Remove http://
+			c := caddyfile.NewDispenser("Testfile", strings.NewReader(fmt.Sprintf(config, back, port, test.intervalInMilliseconds)))
+			upstreams, err := NewStaticUpstreams(&c)
+			if err != nil {
+				t.Error("Expected no error. Got:", err.Error())
+			}
+
+			// Give some time for healthchecks to hit the server.
+			time.Sleep(time.Duration(test.intervalInMilliseconds*test.numHealthcheckIntervals) * time.Millisecond)
+
+			for _, upstream := range upstreams {
+				if err := upstream.Stop(); err != nil {
+					t.Error("Expected no error stopping upstream. Got: ", err.Error())
+				}
+			}
+
+			counterValueAfterShutdown := atomic.LoadInt64(&counter)
+
+			// Give some time to see if healthchecks are still hitting the server.
+			time.Sleep(time.Duration(test.intervalInMilliseconds*test.numHealthcheckIntervals) * time.Millisecond)
+
+			if counterValueAfterShutdown == 0 {
+				t.Error("Expected healthchecks to hit test server. Got no healthchecks.")
+			}
+
+			// health checks are in a go routine now, so one may well occur after we shutdown,
+			// but we only ever expect one more
+			counterValueAfterWaiting := atomic.LoadInt64(&counter)
+			if counterValueAfterWaiting > (counterValueAfterShutdown + 1) {
+				t.Errorf("Expected no more healthchecks after shutdown. Got: %d healthchecks after shutdown", counterValueAfterWaiting-counterValueAfterShutdown)
+			}
+
+		})
+
+	}
+}