Switch KapacitorRulesGet to use Pagination

Kapacitor responses are paginated, and sometimes users have more than
the default 100 tasks that are returned from Kapacitor. This replaces
the previous Kapa client with one that automatically follows paginated
responses from Kapacitor's ListTasks endpoint and returns the full
response.

Tests for the KapacitorRulesGet endpoint had to be updated because they
did not account for "limit" and "offset", and so led to an infinite
loop with the paginated client. A correct kapacitor backend will not
have this behavior

kapacitor/client.go

@@ -12,6 +12,10 @@ import (
 const (
 	// Prefix is prepended to the ID of all alerts
 	Prefix = "chronograf-v1-"
+
+	// DefaultFetchRate is the rate at which paginated responses will be consumed
+	// from a Kapacitor
+	FetchRate = 100
 )
 
 // Client communicates to kapacitor
@@ -325,8 +329,14 @@ func NewKapaClient(url, username, password string) (KapaClient, error) {
 		}
 	}
 
-	return client.New(client.Config{
+	clnt, err := client.New(client.Config{
 		URL:         url,
 		Credentials: creds,
 	})
+
+	if err != nil {
+		return clnt, err
+	}
+
+	return &PaginatingKapaClient{clnt, FetchRate}, nil
 }

kapacitor/kapa_client.go

@@ -1,6 +1,8 @@
 package kapacitor
 
-import client "github.com/influxdata/kapacitor/client/v1"
+import (
+	client "github.com/influxdata/kapacitor/client/v1"
+)
 
 // ensure PaginatingKapaClient is a KapaClient
 var _ KapaClient = &PaginatingKapaClient{}

kapacitor/kapa_client_test.go

@@ -9,7 +9,7 @@ import (
 )
 
 func Test_Kapacitor_PaginatingKapaClient(t *testing.T) {
-	const lenAllTasks = 200
+	const lenAllTasks = 227 // prime, to stress odd result sets
 
 	// create a mock client that will return a huge response from ListTasks
 	mockClient := &mocks.KapaClient{
@@ -30,7 +30,7 @@ func Test_Kapacitor_PaginatingKapaClient(t *testing.T) {
 		},
 	}
 
-	pkap := kapacitor.PaginatingKapaClient{mockClient, 100}
+	pkap := kapacitor.PaginatingKapaClient{mockClient, 50}
 
 	opts := &client.ListTasksOptions{
 		Limit:  100,

server/kapacitors_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -106,6 +107,18 @@ func Test_KapacitorRulesGet(t *testing.T) {
 
 			// setup mock kapa API
 			kapaSrv := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+				params := r.URL.Query()
+				limit, err := strconv.Atoi(params.Get("limit"))
+				if err != nil {
+					rw.WriteHeader(http.StatusBadRequest)
+					return
+				}
+				offset, err := strconv.Atoi(params.Get("offset"))
+				if err != nil {
+					rw.WriteHeader(http.StatusBadRequest)
+					return
+				}
+
 				tsks := []map[string]interface{}{}
 				for _, task := range test.mockAlerts {
 					tsks = append(tsks, map[string]interface{}{
@@ -119,11 +132,23 @@ func Test_KapacitorRulesGet(t *testing.T) {
 					})
 				}
 
-				tasks := map[string]interface{}{
-					"tasks": tsks,
+				var tasks map[string]interface{}
+
+				if offset >= len(tsks) {
+					tasks = map[string]interface{}{
+						"tasks": []map[string]interface{}{},
+					}
+				} else if limit+offset > len(tsks) {
+					tasks = map[string]interface{}{
+						"tasks": tsks[offset:],
+					}
+				} else {
+					tasks = map[string]interface{}{
+						"tasks": tsks[offset : offset+limit],
+					}
 				}
 
-				err := json.NewEncoder(rw).Encode(&tasks)
+				err = json.NewEncoder(rw).Encode(&tasks)
 				if err != nil {
 					t.Error("Failed to encode JSON. err:", err)
 				}