refactor: migrate error to a method parameter, not part of ErrorHandlerOpts

While writing the documentation for this, it didn't feel quite right to
note that the `error` wasn't part of the method signature, despite it
being very important for the actual handling of errors.

Author: jamietanna

oapi_validate.go

@@ -30,25 +30,22 @@ type ErrorHandler func(w http.ResponseWriter, message string, statusCode int)
 
 // ErrorHandlerWithOpts is called when there is an error in validation, with more information about the `error` that occurred and which request is currently being processed.
 //
+// There are a number of known types that the `error` can be:
+//
+// - `*openapi3filter.SecurityRequirementsError` - if the `AuthenticationFunc` has failed to authenticate the request
+// - `*openapi3filter.RequestError` - if a bad request has been made
+//
+// Additionally, if you have set `openapi3filter.Options#MultiError`:
+//
+// - `openapi3.MultiError` (https://pkg.go.dev/github.com/getkin/kin-openapi/openapi3#MultiError)
+//
 // If both an `ErrorHandlerWithOpts` and `ErrorHandler` are set, the `ErrorHandlerWithOpts` takes precedence.
 //
 // NOTE that this should ideally be used instead of ErrorHandler
-type ErrorHandlerWithOpts func(ctx context.Context, w http.ResponseWriter, r *http.Request, opts ErrorHandlerOpts)
+type ErrorHandlerWithOpts func(ctx context.Context, err error, w http.ResponseWriter, r *http.Request, opts ErrorHandlerOpts)
 
 // ErrorHandlerOpts contains additional options that are passed to the `ErrorHandlerWithOpts` function in the case of an error being returned by the middleware
 type ErrorHandlerOpts struct {
-	// Error is the underlying error that triggered this error handler to be executed.
-	//
-	// Known error types:
-	//
-	// - `*openapi3filter.SecurityRequirementsError` - if the `AuthenticationFunc` has failed to authenticate the request
-	// - `*openapi3filter.RequestError` - if a bad request has been made
-	//
-	// Additionally, if you have set `openapi3filter.Options#MultiError`:
-	//
-	// - `openapi3.MultiError` (https://pkg.go.dev/github.com/getkin/kin-openapi/openapi3#MultiError)
-	Error error
-
 	// StatusCode indicates the HTTP Status Code that the OpenAPI validation middleware _suggests_ is returned to the user.
 	//
 	// NOTE that this is very much a suggestion, and can be overridden if you believe you have a better approach.
@@ -163,11 +160,10 @@ func performRequestValidationForErrorHandlerWithOpts(next http.Handler, w http.R
 	if err != nil {
 		errOpts := ErrorHandlerOpts{
 			// MatchedRoute will be nil, as we've not matched a route we know about
-			Error:      err,
 			StatusCode: http.StatusNotFound,
 		}
 
-		options.ErrorHandlerWithOpts(r.Context(), w, r, errOpts)
+		options.ErrorHandlerWithOpts(r.Context(), err, w, r, errOpts)
 		return
 	}
 
@@ -197,26 +193,28 @@ func performRequestValidationForErrorHandlerWithOpts(next http.Handler, w http.R
 		return
 	}
 
+	var theErr error
+
 	switch e := err.(type) {
 	case openapi3.MultiError:
-		errOpts.Error = e
+		theErr = e
 		errOpts.StatusCode = determineStatusCodeForMultiError(e)
 	case *openapi3filter.RequestError:
 		// We've got a bad request
-		errOpts.Error = e
+		theErr = e
 		errOpts.StatusCode = http.StatusBadRequest
 	case *openapi3filter.SecurityRequirementsError:
-		errOpts.Error = e
+		theErr = e
 		errOpts.StatusCode = http.StatusUnauthorized
 	default:
 		// This should never happen today, but if our upstream code changes,
 		// we don't want to crash the server, so handle the unexpected error.
 		// return http.StatusInternalServerError,
-		errOpts.Error = fmt.Errorf("error validating route: %w", e)
+		theErr = fmt.Errorf("error validating route: %w", e)
 		errOpts.StatusCode = http.StatusUnauthorized
 	}
 
-	options.ErrorHandlerWithOpts(r.Context(), w, r, errOpts)
+	options.ErrorHandlerWithOpts(r.Context(), theErr, w, r, errOpts)
 }
 
 // validateRequest is called from the middleware above and actually does the work

oapi_validate_example_test.go

@@ -469,9 +469,7 @@ components:
 		return fmt.Errorf("this check always fails - don't let anyone in!")
 	}
 
-	errorHandlerFunc := func(ctx context.Context, w http.ResponseWriter, r *http.Request, opts middleware.ErrorHandlerOpts) {
-		err := opts.Error
-
+	errorHandlerFunc := func(ctx context.Context, err error, w http.ResponseWriter, r *http.Request, opts middleware.ErrorHandlerOpts) {
 		if opts.MatchedRoute == nil {
 			fmt.Printf("ErrorHandlerWithOpts: An HTTP %d was returned by the middleware with error message: %s\n", opts.StatusCode, err.Error())
 
@@ -716,9 +714,7 @@ paths:
 		w.WriteHeader(http.StatusMethodNotAllowed)
 	})
 
-	errorHandlerFunc := func(ctx context.Context, w http.ResponseWriter, r *http.Request, opts middleware.ErrorHandlerOpts) {
-		err := opts.Error
-
+	errorHandlerFunc := func(ctx context.Context, err error, w http.ResponseWriter, r *http.Request, opts middleware.ErrorHandlerOpts) {
 		if opts.MatchedRoute == nil {
 			fmt.Printf("ErrorHandlerWithOpts: An HTTP %d was returned by the middleware with error message: %s\n", opts.StatusCode, err.Error())