Allow VIES Service timeout to be editable (#7)

* Allow VIES Service timeout to be editable

* Set timeout via a function rather than editing an exported global

* Accept a duration rather than a number of seconds for service timeout

rates.go

@@ -83,7 +83,7 @@ func GetRates() ([]CountryRates, error) {
 // FetchRates fetches the latest VAT rates from ibericode/vat-rates and updates the in-memory rates
 func FetchRates() ([]CountryRates, error) {
 	client := http.Client{
-		Timeout: time.Duration(ViesServiceTimeout) * time.Second,
+		Timeout: serviceTimeout,
 	}
 	r, err := client.Get("https://raw.githubusercontent.com/ibericode/vat-rates/master/vat-rates.json")
 	if err != nil {

uk_vat_service.go

@@ -19,7 +19,10 @@ func (s *ukVATService) Validate(vatNumber string) error {
 		return ErrInvalidCountryCode
 	}
 
-	response, err := http.Get(fmt.Sprintf(ukVATServiceURL, vatNumber[2:]))
+	client := http.Client{
+		Timeout: serviceTimeout,
+	}
+	response, err := client.Get(fmt.Sprintf(ukVATServiceURL, vatNumber[2:]))
 	if err != nil {
 		return ErrServiceUnavailable{Err: err}
 	}

vat.go

@@ -15,8 +15,17 @@ Get VAT rate that is currently in effect for a given country
 */
 package vat
 
+import "time"
+
 // ViesLookupService is the interface for the VIES VAT number validation service
 var ViesLookupService LookupServiceInterface = &viesService{}
 
 // UKVATLookupService is the interface for the UK VAT number validation service
 var UKVATLookupService LookupServiceInterface = &ukVATService{}
+
+var serviceTimeout = time.Second * 60
+
+// SetServiceTimeout sets the timeout for the external VAT lookup services.
+func SetServiceTimeout(timeout time.Duration) {
+	serviceTimeout = timeout
+}

vies_service.go

@@ -6,7 +6,6 @@ import (
 	"io"
 	"net/http"
 	"strings"
-	"time"
 )
 
 // LookupServiceInterface is an interface for the service that calls external services to validate VATs.
@@ -106,16 +105,13 @@ func (s *viesService) getEnvelope(n string) string {
 func (s *viesService) lookup(envelope string) (*http.Response, error) {
 	envelopeBuffer := bytes.NewBufferString(envelope)
 	client := http.Client{
-		Timeout: time.Duration(ViesServiceTimeout) * time.Second,
+		Timeout: serviceTimeout,
 	}
 	return client.Post(viesServiceURL, "text/xml;charset=UTF-8", envelopeBuffer)
 }
 
 const viesServiceURL = "https://ec.europa.eu/taxation_customs/vies/services/checkVatService"
 
-// ViesServiceTimeout is the timeout for the VIES service
-const ViesServiceTimeout = 10
-
 // viesResponse holds the response data from the Vies call
 type viesResponse struct {
 	CountryCode string