retry.go

/*
Copyright (c) 2015 VMware, Inc. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package vim25

import (
	"context"
	"time"

	"github.com/vmware/govmomi/vim25/soap"
)

type RetryFunc func(err error) (retry bool, delay time.Duration)

// TemporaryNetworkError is deprecated. Use Retry() with RetryTemporaryNetworkError and retryAttempts instead.
func TemporaryNetworkError(n int) RetryFunc {
	return func(err error) (bool, time.Duration) {
		if IsTemporaryNetworkError(err) {
			// Don't retry if we're out of tries.
			if n--; n <= 0 {
				return false, 0
			}
			return true, 0
		}
		return false, 0
	}
}

// RetryTemporaryNetworkError returns a RetryFunc that returns IsTemporaryNetworkError(err)
func RetryTemporaryNetworkError(err error) (bool, time.Duration) {
	return IsTemporaryNetworkError(err), 0
}

// IsTemporaryNetworkError returns false unless the error implements
// a Temporary() bool method such as url.Error and net.Error.
// Otherwise, returns the value of the Temporary() method.
func IsTemporaryNetworkError(err error) bool {
	t, ok := err.(interface {
		// Temporary is implemented by url.Error and net.Error
		Temporary() bool
	})

	if !ok {
		// Not a Temporary error.
		return false
	}

	return t.Temporary()
}

type retry struct {
	roundTripper soap.RoundTripper

	// fn is a custom function that is called when an error occurs.
	// It returns whether or not to retry, and if so, how long to
	// delay before retrying.
	fn               RetryFunc
	maxRetryAttempts int
}

// Retry wraps the specified soap.RoundTripper and invokes the
// specified RetryFunc. The RetryFunc returns whether or not to
// retry the call, and if so, how long to wait before retrying. If
// the result of this function is to not retry, the original error
// is returned from the RoundTrip function.
// The soap.RoundTripper will return the original error if retryAttempts is specified and reached.
func Retry(roundTripper soap.RoundTripper, fn RetryFunc, retryAttempts ...int) soap.RoundTripper {
	r := &retry{
		roundTripper:     roundTripper,
		fn:               fn,
		maxRetryAttempts: 1,
	}

	if len(retryAttempts) == 1 {
		r.maxRetryAttempts = retryAttempts[0]
	}

	return r
}

func (r *retry) RoundTrip(ctx context.Context, req, res soap.HasFault) error {
	var err error

	for attempt := 0; attempt < r.maxRetryAttempts; attempt++ {
		err = r.roundTripper.RoundTrip(ctx, req, res)
		if err == nil {
			break
		}

		// Invoke retry function to see if another attempt should be made.
		if retry, delay := r.fn(err); retry {
			time.Sleep(delay)
			continue
		}

		break
	}

	return err
}