PLT-7407: Back-end plugins (#7409)

* tie back-end plugins together

* fix comment typo

* add tests and a bit of polish

* tests and polish

* add test, don't let backend executable paths escape the plugin directory

plugin/rpcplugin/hooks_test.go

@@ -6,10 +6,12 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
 
 	"github.com/mattermost/mattermost-server/plugin"
 	"github.com/mattermost/mattermost-server/plugin/plugintest"
@@ -50,6 +52,9 @@ func TestHooks(t *testing.T) {
 		hooks.On("OnDeactivate").Return(nil)
 		assert.NoError(t, remote.OnDeactivate())
 
+		hooks.On("OnConfigurationChange").Return(nil)
+		assert.NoError(t, remote.OnConfigurationChange())
+
 		hooks.On("ServeHTTP", mock.AnythingOfType("*rpcplugin.RemoteHTTPResponseWriter"), mock.AnythingOfType("*http.Request")).Run(func(args mock.Arguments) {
 			w := args.Get(0).(http.ResponseWriter)
 			r := args.Get(1).(*http.Request)
@@ -77,6 +82,45 @@ func TestHooks(t *testing.T) {
 	}))
 }
 
+func TestHooks_Concurrency(t *testing.T) {
+	var hooks plugintest.Hooks
+	defer hooks.AssertExpectations(t)
+
+	assert.NoError(t, testHooksRPC(&hooks, func(remote *RemoteHooks) {
+		ch := make(chan bool)
+
+		hooks.On("ServeHTTP", mock.AnythingOfType("*rpcplugin.RemoteHTTPResponseWriter"), mock.AnythingOfType("*http.Request")).Run(func(args mock.Arguments) {
+			r := args.Get(1).(*http.Request)
+			if r.URL.Path == "/1" {
+				<-ch
+			} else {
+				ch <- true
+			}
+		})
+
+		rec := httptest.NewRecorder()
+
+		wg := sync.WaitGroup{}
+		wg.Add(2)
+
+		go func() {
+			req, err := http.NewRequest("GET", "/1", nil)
+			require.NoError(t, err)
+			remote.ServeHTTP(rec, req)
+			wg.Done()
+		}()
+
+		go func() {
+			req, err := http.NewRequest("GET", "/2", nil)
+			require.NoError(t, err)
+			remote.ServeHTTP(rec, req)
+			wg.Done()
+		}()
+
+		wg.Wait()
+	}))
+}
+
 type testHooks struct {
 	mock.Mock
 }