Adding Amazon IAP to the go-iap library

Fix the README by updating the amazon example

amazon/validator.go

@@ -0,0 +1,106 @@
+package amazon
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/parnurzeal/gorequest"
+)
+
+const (
+	SandboxURL    string = "http://localhost:8080/RVSSandbox"
+	ProductionURL string = "https://appstore-sdk.amazon.com"
+)
+
+// Config is a configuration to initialize client
+type Config struct {
+	IsProduction bool
+	Secret       string
+	TimeOut      time.Duration
+}
+
+// The IAPResponse type has the response properties
+type IAPResponse struct {
+	ReceiptID       string `json:"receiptId"`
+	ProductType     string `json:"productType"`
+	ProductID       string `json:"productId"`
+	PurchaseDate    int64  `json:"purchaseDate"`
+	CancelDate      int64  `json:"cancelDate"`
+	TestTransaction bool   `json:"testTransaction"`
+}
+
+type IAPResponseError struct {
+	Message string `json:"message"`
+	Status  bool   `json:"status"`
+}
+
+// IAPClient is an interface to call validation API in Amazon App Store
+type IAPClient interface {
+	Verify(string, string) (IAPResponse, error)
+}
+
+// Client implements IAPClient
+type Client struct {
+	URL     string
+	Secret  string
+	TimeOut time.Duration
+}
+
+// New creates a client object
+func New(secret string) IAPClient {
+	client := Client{
+		URL:     SandboxURL,
+		Secret:  secret,
+		TimeOut: time.Second * 5,
+	}
+	if os.Getenv("IAP_ENVIRONMENT") == "production" {
+		client.URL = ProductionURL
+	}
+	return client
+}
+
+// NewWithConfig creates a client with configuration
+func NewWithConfig(config Config) Client {
+	if config.TimeOut == 0 {
+		config.TimeOut = time.Second * 5
+	}
+
+	client := Client{
+		URL:     SandboxURL,
+		Secret:  config.Secret,
+		TimeOut: config.TimeOut,
+	}
+	if config.IsProduction {
+		client.URL = ProductionURL
+	}
+
+	return client
+}
+
+// Verify sends receipts and gets validation result
+func (c Client) Verify(userID string, receiptID string) (IAPResponse, error) {
+	result := IAPResponse{}
+	url := fmt.Sprintf("%v/version/1.0/verifyReceiptId/developer/%v/user/%v/receiptId/%v", c.URL, c.Secret, userID, receiptID)
+	res, body, errs := gorequest.New().
+		Get(url).
+		Timeout(c.TimeOut).
+		End()
+
+	if errs != nil {
+		return result, fmt.Errorf("%v", errs)
+	}
+
+	if res.StatusCode < 200 || res.StatusCode >= 300 {
+		responseError := IAPResponseError{}
+		json.NewDecoder(strings.NewReader(body)).Decode(&responseError)
+		return result, errors.New(responseError.Message)
+	}
+
+	err := json.NewDecoder(strings.NewReader(body)).Decode(&result)
+
+	return result, err
+}