deliveries: implemented client.CancelDelivery

Updates #32

Cancel a delivery by means of the delivery ID.
There are limitations however on when a cancellation
can be made. See more information at
https://developer.uber.com/docs/deliveries/references/api/v1/deliveries-delivery_id-cancel-post

* Exhibit:
```go
func cancelDelivery() {
	client, err := uber.NewClientFromOAuth2File("./testdata/.uber/credentials.json")
	if err != nil {
		log.Fatal(err)
	}

	err := client.CancelDelivery("71a969ca-5359-4334-a7b7-5a1705869c51")
	if err == nil {
		log.Printf("Successfully canceled that delivery!")
	} else {
		log.Printf("Failed to cancel that delivery, err: %v", err)
	}
}
```

Author: odeke-em

README.md

@@ -396,3 +396,20 @@ func requestDelivery() {
 	log.Printf("The confirmation: %+v\n", deliveryConfirmation)
 }
 ```
+
+* Cancel a delivery
+```go
+func cancelDelivery() {
+	client, err := uber.NewClientFromOAuth2File("./testdata/.uber/credentials.json")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err := client.CancelDelivery("71a969ca-5359-4334-a7b7-5a1705869c51")
+	if err == nil {
+		log.Printf("Successfully canceled that delivery!")
+	} else {
+		log.Printf("Failed to cancel that delivery, err: %v", err)
+	}
+}
+```

example_test.go

@@ -419,3 +419,17 @@ func Example_client_RequestDelivery() {
 
 	log.Printf("The confirmation: %+v\n", deliveryConfirmation)
 }
+
+func Example_client_CancelDelivery() {
+	client, err := uber.NewClientFromOAuth2File("./testdata/.uber/credentials.json")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err := client.CancelDelivery("71a969ca-5359-4334-a7b7-5a1705869c51")
+	if err == nil {
+		log.Printf("Successfully canceled that delivery!")
+	} else {
+		log.Printf("Failed to cancel that delivery, err: %v", err)
+	}
+}

v1/deliveries.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"strings"
 
 	"github.com/orijtech/otils"
 )
@@ -210,7 +211,7 @@ func (c *Client) RequestDelivery(req *DeliveryRequest) (*DeliveryResponse, error
 		return nil, err
 	}
 
-	blob, _, err = c.doAuthAndHTTPReq(httpReq)
+	blob, _, err = c.doHTTPReq(httpReq)
 	if err != nil {
 		return nil, err
 	}
@@ -220,3 +221,22 @@ func (c *Client) RequestDelivery(req *DeliveryRequest) (*DeliveryResponse, error
 	}
 	return dRes, nil
 }
+
+var errBlankDeliveryID = errors.New("expecting a non-blank deliveryID")
+
+// CancelDelivery cancels a delivery referenced by its ID. There are
+// potential cancellation fees associated.
+// See https://developer.uber.com/docs/deliveries/faq for more information.
+func (c *Client) CancelDelivery(deliveryID string) error {
+	deliveryID = strings.TrimSpace(deliveryID)
+	if deliveryID == "" {
+		return errBlankDeliveryID
+	}
+	theURL := fmt.Sprintf("%s/deliveries/%s/cancel", c.baseURL(), deliveryID)
+	httpReq, err := http.NewRequest("POST", theURL, nil)
+	if err != nil {
+		return err
+	}
+	_, _, err = c.doHTTPReq(httpReq)
+	return err
+}

v1/rides.go

@@ -158,7 +158,7 @@ func (c *Client) RequestRide(rreq *RideRequest) (*Ride, error) {
 	if err != nil {
 		return nil, err
 	}
-	blob, _, err = c.doAuthAndHTTPReq(req)
+	blob, _, err = c.doHTTPReq(req)
 	if err != nil {
 		return nil, err
 	}

v1/uber_test.go

@@ -73,14 +73,43 @@ func TestListPaymentMethods(t *testing.T) {
 	}
 }
 
-func TestDeliveryRequest(t *testing.T) {
+func TestCancelDelivery(t *testing.T) {
+	client, err := uber.NewClient(testToken1)
+	if err != nil {
+		t.Fatalf("initializing client; %v", err)
+	}
+
+	backend := &tRoundTripper{route: cancelDeliveryRoute}
+	transport := uberOAuth2.TransportWithBase(testOAuth2Token1, backend)
+	client.SetHTTPRoundTripper(transport)
+
+	tests := [...]struct {
+		reqID   string
+		wantErr bool
+	}{
+		0: {"", true},
+		1: {"     ", true},
+		2: {reqID: deliveryID1},
+	}
+
+	for i, tt := range tests {
+		err := client.CancelDelivery(tt.reqID)
+		gotErr := err != nil
+		if gotErr != tt.wantErr {
+			t.Errorf("#%d: gotErr=(%v) wantErr=(%v) err=(%v)", i, gotErr, tt.wantErr, err)
+		}
+	}
+}
+
+func TestRequestDelivery(t *testing.T) {
 	client, err := uber.NewClient(testToken1)
 	if err != nil {
 		t.Fatalf("initializing client; %v", err)
 	}
 
 	backend := &tRoundTripper{route: deliveryRoute}
-	client.SetHTTPRoundTripper(backend)
+	transport := uberOAuth2.TransportWithBase(testOAuth2Token1, backend)
+	client.SetHTTPRoundTripper(transport)
 
 	tests := [...]struct {
 		req     *uber.DeliveryRequest
@@ -918,6 +947,8 @@ func (trt *tRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
 		return trt.upfrontFareRoundTrip(req)
 	case deliveryRoute:
 		return trt.deliveryRoundTrip(req)
+	case cancelDeliveryRoute:
+		return trt.cancelDeliveryRoundTrip(req)
 	default:
 		return makeResp("Not Found", http.StatusNotFound), nil
 	}
@@ -1099,8 +1130,36 @@ func deliveryResponsePath(id string) string {
 
 const (
 	deliveryResponseID1 = "gizmo"
+
+	deliveryID1 = "4536381f-2e29-40bb-88eb-004682aa332e"
+	deliveryID2 = "6ef419ce-1003-456c-8884-836f4d669093"
 )
 
+func knownDeliveryID(deliveryID string) bool {
+	switch deliveryID {
+	case deliveryID1, deliveryID2:
+		return true
+	default:
+		return false
+	}
+}
+
+func (trt *tRoundTripper) cancelDeliveryRoundTrip(req *http.Request) (*http.Response, error) {
+	if badAuthResp, _, err := prescreenAuthAndMethod(req, "POST"); badAuthResp != nil || err != nil {
+		return badAuthResp, err
+	}
+	splits := strings.Split(req.URL.Path, "/")
+	if len(splits) != 5 || (splits[2] != "deliveries" || splits[4] != "cancel") {
+		resp := makeResp("expecting a path of form: /v1.2/deliveries/<deliveryRequestID>/cancel", http.StatusBadRequest)
+		return resp, nil
+	}
+	deliveryID := splits[3]
+	if !knownDeliveryID(deliveryID) {
+		return makeResp("unknown deliveryID", http.StatusBadRequest), nil
+	}
+	return makeResp("204 No content", http.StatusNoContent), nil
+}
+
 func (trt *tRoundTripper) deliveryRoundTrip(req *http.Request) (*http.Response, error) {
 	if badAuthResp, _, err := prescreenAuthAndMethod(req, "POST"); badAuthResp != nil || err != nil {
 		return badAuthResp, err
@@ -1370,4 +1429,5 @@ const (
 	upfrontFareRoute     = "upfront-fare"
 	deliveryRoute        = "delivery"
 	sandboxTesterRoute   = "sandbox-test"
+	cancelDeliveryRoute  = "cancel-delivery"
 )