path: root/vendor/google.golang.org/api/gensupport/retry.go

// Copyright 2017 Google LLC
//
// 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 gensupport

import (
    "context"
    "io"
    "net"
    "net/http"
    "time"
)

// Retry invokes the given function, retrying it multiple times if the connection failed or
// the HTTP status response indicates the request should be attempted again. ctx may be nil.
func Retry(ctx context.Context, f func() (*http.Response, error), backoff BackoffStrategy) (*http.Response, error) {
    for {
        resp, err := f()

        var status int
        if resp != nil {
            status = resp.StatusCode
        }

        // Return if we shouldn't retry.
        pause, retry := backoff.Pause()
        if !shouldRetry(status, err) || !retry {
            return resp, err
        }

        // Ensure the response body is closed, if any.
        if resp != nil && resp.Body != nil {
            resp.Body.Close()
        }

        // Pause, but still listen to ctx.Done if context is not nil.
        var done <-chan struct{}
        if ctx != nil {
            done = ctx.Done()
        }
        select {
        case <-done:
            return nil, ctx.Err()
        case <-time.After(pause):
        }
    }
}

// DefaultBackoffStrategy returns a default strategy to use for retrying failed upload requests.
func DefaultBackoffStrategy() BackoffStrategy {
    return &ExponentialBackoff{
        Base: 250 * time.Millisecond,
        Max:  16 * time.Second,
    }
}

// shouldRetry returns true if the HTTP response / error indicates that the
// request should be attempted again.
func shouldRetry(status int, err error) bool {
    if 500 <= status && status <= 599 {
        return true
    }
    if status == statusTooManyRequests {
        return true
    }
    if err == io.ErrUnexpectedEOF {
        return true
    }
    if err, ok := err.(net.Error); ok {
        return err.Temporary()
    }
    return false
}