feat: retry on 5xx (#37)

main.go

@@ -61,8 +61,14 @@ func NewProduct(product string) (Product, error) {
 	}, nil
 }
 
+const maxRetries = 5
+
 // CheckWithContext verifies a license key against a product in Gumroad.
 func (gp Product) VerifyWithContext(ctx context.Context, key string) error {
+	return gp.doVerify(ctx, key, 1)
+}
+
+func (gp Product) doVerify(ctx context.Context, key string, try int) error {
 	// early return if license key is empty
 	if key == "" {
 		return errors.New("license: license key cannot be empty")
@@ -86,6 +92,15 @@ func (gp Product) VerifyWithContext(ctx context.Context, key string) error {
 	}
 	defer resp.Body.Close()
 
+	// something on server side, should probably retry...
+	if resp.StatusCode >= 500 {
+		if try == maxRetries {
+			return fmt.Errorf("license: likely gumroad issue: %s", string(bts))
+		}
+		time.Sleep(time.Duration(try*500) * time.Millisecond)
+		return gp.doVerify(ctx, key, try+1)
+	}
+
 	var gumroad GumroadResponse
 	if err := json.Unmarshal(bts, &gumroad); err != nil {
 		return fmt.Errorf("license: failed check license: %w", err)

main_test.go

@@ -3,6 +3,7 @@ package gumroad
 import (
 	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"net/http"
@@ -14,6 +15,8 @@ import (
 	"time"
 )
 
+const license = "DEADBEEF-CAFE1234-5678DEAD-BEEFCAFE"
+
 func TestIntegrationInvalidLicense(t *testing.T) {
 	t.Parallel()
 	expected := "license: invalid license: That license does not exist for the provided product."
@@ -71,6 +74,47 @@ func TestErrors(t *testing.T) {
 	}
 }
 
+func Test5xx(t *testing.T) {
+	t.Parallel()
+
+	calls := 0
+
+	// server will stand in for GumRoad, and assume that any license it sees is invalid
+	server := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		calls++
+		t.Log("try", calls)
+		if calls == 3 {
+			bts, _ := json.Marshal(GumroadResponse{
+				Success: true,
+				Purchase: Purchase{
+					SaleTimestamp: time.Now(),
+					Email:         "[email protected]",
+				},
+			})
+			_, _ = w.Write(bts)
+			return
+		}
+		w.WriteHeader(http.StatusInternalServerError)
+		_, _ = w.Write([]byte(`some error`))
+	}))
+	t.Cleanup(server.Close)
+
+	p, err := NewProduct("product")
+	if err != nil {
+		t.Errorf("unexpected error %v", err)
+	}
+	p.API = server.URL
+	p.Client = server.Client()
+
+	err = p.Verify(license)
+	if err != nil {
+		t.Fatal("expected no error")
+	}
+	if calls != 3 {
+		t.Errorf("should have called the api 3 times, but called %d", calls)
+	}
+}
+
 func TestMITM(t *testing.T) {
 	t.Parallel()
 	license := "DEADBEEF-CAFE1234-5678DEAD-BEEFCAFE"
@@ -136,7 +180,7 @@ func TestMITM(t *testing.T) {
 	}))
 	t.Cleanup(mitm.Close)
 	// Throw away the log message from http.Server.go complaining about the invalid TLS cert
-	mitm.Config.ErrorLog = log.New(ioutil.Discard, "", 0)
+	mitm.Config.ErrorLog = log.New(io.Discard, "", 0)
 
 	p.API = mitm.URL
 	// Set the client back to the default, which doesn't trust the test certificate used by mitm