Example stringsvc updated to reflect gokit.io (#638)

* Example/stringsvc1 updated file flow to mimic tutorial on gokit.io

Change the order of the code in the example/stringsvc1 so that it flows
with the tutorial on gokit.io

* Stringsvc1 is missing Context in StringService interface

StringService interface should have a Context in its service
definition. File does not match the tutorial on gokit.io

examples/stringsvc1/main.go

@@ -14,47 +14,50 @@ import (
 
 // StringService provides operations on strings.
 type StringService interface {
-	Uppercase(string) (string, error)
-	Count(string) int
+	Uppercase(context.Context, string) (string, error)
+	Count(context.Context, string) int
 }
 
+// stringService is a concrete implementation of StringService
 type stringService struct{}
 
-func (stringService) Uppercase(s string) (string, error) {
+func (stringService) Uppercase(_ context.Context, s string) (string, error) {
 	if s == "" {
 		return "", ErrEmpty
 	}
 	return strings.ToUpper(s), nil
 }
 
-func (stringService) Count(s string) int {
+func (stringService) Count(_ context.Context, s string) int {
 	return len(s)
 }
 
-func main() {
-	svc := stringService{}
+// ErrEmpty is returned when an input string is empty.
+var ErrEmpty = errors.New("empty string")
 
-	uppercaseHandler := httptransport.NewServer(
-		makeUppercaseEndpoint(svc),
-		decodeUppercaseRequest,
-		encodeResponse,
-	)
+// For each method, we define request and response structs
+type uppercaseRequest struct {
+	S string `json:"s"`
+}
 
-	countHandler := httptransport.NewServer(
-		makeCountEndpoint(svc),
-		decodeCountRequest,
-		encodeResponse,
-	)
+type uppercaseResponse struct {
+	V   string `json:"v"`
+	Err string `json:"err,omitempty"` // errors don't define JSON marshaling
+}
 
-	http.Handle("/uppercase", uppercaseHandler)
-	http.Handle("/count", countHandler)
-	log.Fatal(http.ListenAndServe(":8080", nil))
+type countRequest struct {
+	S string `json:"s"`
 }
 
+type countResponse struct {
+	V int `json:"v"`
+}
+
+// Endpoints are a primary abstraction in go-kit. An endpoint represents a single RPC (method in our service interface)
 func makeUppercaseEndpoint(svc StringService) endpoint.Endpoint {
 	return func(ctx context.Context, request interface{}) (interface{}, error) {
 		req := request.(uppercaseRequest)
-		v, err := svc.Uppercase(req.S)
+		v, err := svc.Uppercase(ctx, req.S)
 		if err != nil {
 			return uppercaseResponse{v, err.Error()}, nil
 		}
@@ -65,11 +68,32 @@ func makeUppercaseEndpoint(svc StringService) endpoint.Endpoint {
 func makeCountEndpoint(svc StringService) endpoint.Endpoint {
 	return func(ctx context.Context, request interface{}) (interface{}, error) {
 		req := request.(countRequest)
-		v := svc.Count(req.S)
+		v := svc.Count(ctx, req.S)
 		return countResponse{v}, nil
 	}
 }
 
+// Transports expose the service to the network. In this first example we utilize JSON over HTTP.
+func main() {
+	svc := stringService{}
+
+	uppercaseHandler := httptransport.NewServer(
+		makeUppercaseEndpoint(svc),
+		decodeUppercaseRequest,
+		encodeResponse,
+	)
+
+	countHandler := httptransport.NewServer(
+		makeCountEndpoint(svc),
+		decodeCountRequest,
+		encodeResponse,
+	)
+
+	http.Handle("/uppercase", uppercaseHandler)
+	http.Handle("/count", countHandler)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}
+
 func decodeUppercaseRequest(_ context.Context, r *http.Request) (interface{}, error) {
 	var request uppercaseRequest
 	if err := json.NewDecoder(r.Body).Decode(&request); err != nil {
@@ -89,23 +113,3 @@ func decodeCountRequest(_ context.Context, r *http.Request) (interface{}, error)
 func encodeResponse(_ context.Context, w http.ResponseWriter, response interface{}) error {
 	return json.NewEncoder(w).Encode(response)
 }
-
-type uppercaseRequest struct {
-	S string `json:"s"`
-}
-
-type uppercaseResponse struct {
-	V   string `json:"v"`
-	Err string `json:"err,omitempty"` // errors don't define JSON marshaling
-}
-
-type countRequest struct {
-	S string `json:"s"`
-}
-
-type countResponse struct {
-	V int `json:"v"`
-}
-
-// ErrEmpty is returned when an input string is empty.
-var ErrEmpty = errors.New("empty string")