Make status code and NGINX error codes on internalError publicly accessible

This will allow users of the plus client to check errors and decide what further action to take. This fix follows the advice of commentators who counsel users of go to assert errors for behavior, not type. https://dave.cheney.net/2014/12/24/inspecting-errors The user would create a simple error interface including Status() and Code() methods and then could use errors.As() to cast the internalError to their own interface type. For example, if the user attempts to delete an upstream server using the client, the user can check the error returned for a http.StatusNotFound code, and if present, can make their application take no further action. If some error status code is returned, then the user can retry the delete. Previously in order to perform this kind of analysis the user would have to resort to string checking on the error: never a good solution.

Author: arussellf5

client/nginx.go

@@ -52,6 +52,15 @@ var (
 	ErrPlusVersionNotFound = errors.New("plus version not found in the input string")
 )
 
+// StatusError is an interface that defines our API with consumers of the plus client errors.
+// The error will return a http status code and an NGINX error code.
+type StatusError interface {
+	Status() int
+	Code() string
+}
+
+var _ StatusError = (*internalError)(nil)
+
 // NginxClient lets you access NGINX Plus API.
 type NginxClient struct {
 	httpClient  *http.Client
@@ -112,8 +121,18 @@ type apiError struct {
 }
 
 type internalError struct {
-	err string
-	apiError
+	err      string
+	apiError apiError
+}
+
+// Status returns the HTTP status code of the error.
+func (internalError *internalError) Status() int {
+	return internalError.apiError.Status
+}
+
+// Status returns the NGINX error code on the response.
+func (internalError *internalError) Code() string {
+	return internalError.apiError.Code
 }
 
 // Error allows internalError to match the Error interface.
@@ -1782,7 +1801,7 @@ func (client *NginxClient) GetStreamServerZones(ctx context.Context) (*StreamSer
 	if err != nil {
 		var ie *internalError
 		if errors.As(err, &ie) {
-			if ie.Code == pathNotFoundCode {
+			if ie.Code() == pathNotFoundCode {
 				return &zones, nil
 			}
 		}
@@ -1808,7 +1827,7 @@ func (client *NginxClient) GetStreamUpstreams(ctx context.Context) (*StreamUpstr
 	if err != nil {
 		var ie *internalError
 		if errors.As(err, &ie) {
-			if ie.Code == pathNotFoundCode {
+			if ie.Code() == pathNotFoundCode {
 				return &upstreams, nil
 			}
 		}
@@ -1824,7 +1843,7 @@ func (client *NginxClient) GetStreamZoneSync(ctx context.Context) (*StreamZoneSy
 	if err != nil {
 		var ie *internalError
 		if errors.As(err, &ie) {
-			if ie.Code == pathNotFoundCode {
+			if ie.Code() == pathNotFoundCode {
 				return nil, nil
 			}
 		}
@@ -2137,7 +2156,7 @@ func (client *NginxClient) GetStreamConnectionsLimit(ctx context.Context) (*Stre
 	if err != nil {
 		var ie *internalError
 		if errors.As(err, &ie) {
-			if ie.Code == pathNotFoundCode {
+			if ie.Code() == pathNotFoundCode {
 				return &limitConns, nil
 			}
 		}

client/nginx_test.go

@@ -3,6 +3,7 @@ package client
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
@@ -1438,6 +1439,62 @@ func TestUpdateStreamServers(t *testing.T) {
 	}
 }
 
+func TestInternalError(t *testing.T) {
+	t.Parallel()
+
+	// mimic a user-defined interface type
+	type TestStatusError interface {
+		Status() int
+		Code() string
+	}
+
+	//nolint
+	anotherErr := errors.New("another error")
+
+	notFoundErr := &internalError{
+		err: "not found error",
+		apiError: apiError{
+			Text:   "not found error",
+			Status: http.StatusNotFound,
+			Code:   "not found code",
+		},
+	}
+
+	testcases := map[string]struct {
+		inputErr       error
+		expectedStatus int
+	}{
+		"simple not found": {
+			inputErr:       notFoundErr,
+			expectedStatus: http.StatusNotFound,
+		},
+		"not found joined with another error": {
+			inputErr:       errors.Join(notFoundErr, anotherErr),
+			expectedStatus: http.StatusNotFound,
+		},
+		"not found wrapped with another error": {
+			inputErr:       notFoundErr.Wrap("some error"),
+			expectedStatus: http.StatusNotFound,
+		},
+	}
+
+	for name, tc := range testcases {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			var se TestStatusError
+			ok := errors.As(tc.inputErr, &se)
+			if !ok {
+				t.Fatalf("could not cast error %v as StatusError", tc.inputErr)
+			}
+
+			if se.Status() != tc.expectedStatus {
+				t.Fatalf("expected status %d, got status %d", tc.expectedStatus, se.Status())
+			}
+		})
+	}
+}
+
 type response struct {
 	servers    interface{}
 	statusCode int