open-consul/vendor/github.com/hashicorp/go-retryablehttp/client.go

488 lines
16 KiB
Go

// The retryablehttp package provides a familiar HTTP client interface with
// automatic retries and exponential backoff. It is a thin wrapper over the
// standard net/http client library and exposes nearly the same public API.
// This makes retryablehttp very easy to drop into existing programs.
//
// retryablehttp performs automatic retries under certain conditions. Mainly, if
// an error is returned by the client (connection errors etc), or if a 500-range
// response is received, then a retry is invoked. Otherwise, the response is
// returned and left to the caller to interpret.
//
// Requests which take a request body should provide a non-nil function
// parameter. The best choice is to provide either a function satisfying
// ReaderFunc which provides multiple io.Readers in an efficient manner, a
// *bytes.Buffer (the underlying raw byte slice will be used) or a raw byte
// slice. As it is a reference type, and we will wrap it as needed by readers,
// we can efficiently re-use the request body without needing to copy it. If an
// io.Reader (such as a *bytes.Reader) is provided, the full body will be read
// prior to the first request, and will be efficiently re-used for any retries.
// ReadSeeker can be used, but some users have observed occasional data races
// between the net/http library and the Seek functionality of some
// implementations of ReadSeeker, so should be avoided if possible.
package retryablehttp
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"log"
"math"
"math/rand"
"net/http"
"net/url"
"os"
"strings"
"time"
"github.com/hashicorp/go-cleanhttp"
)
var (
// Default retry configuration
defaultRetryWaitMin = 1 * time.Second
defaultRetryWaitMax = 30 * time.Second
defaultRetryMax = 4
// defaultClient is used for performing requests without explicitly making
// a new client. It is purposely private to avoid modifications.
defaultClient = NewClient()
// We need to consume response bodies to maintain http connections, but
// limit the size we consume to respReadLimit.
respReadLimit = int64(4096)
)
// ReaderFunc is the type of function that can be given natively to NewRequest
type ReaderFunc func() (io.Reader, error)
// LenReader is an interface implemented by many in-memory io.Reader's. Used
// for automatically sending the right Content-Length header when possible.
type LenReader interface {
Len() int
}
// Request wraps the metadata needed to create HTTP requests.
type Request struct {
// body is a seekable reader over the request body payload. This is
// used to rewind the request data in between retries.
body ReaderFunc
// Embed an HTTP request directly. This makes a *Request act exactly
// like an *http.Request so that all meta methods are supported.
*http.Request
}
// NewRequest creates a new wrapped request.
func NewRequest(method, url string, rawBody interface{}) (*Request, error) {
var err error
var body ReaderFunc
var contentLength int64
if rawBody != nil {
switch rawBody.(type) {
// If they gave us a function already, great! Use it.
case ReaderFunc:
body = rawBody.(ReaderFunc)
tmp, err := body()
if err != nil {
return nil, err
}
if lr, ok := tmp.(LenReader); ok {
contentLength = int64(lr.Len())
}
if c, ok := tmp.(io.Closer); ok {
c.Close()
}
case func() (io.Reader, error):
body = rawBody.(func() (io.Reader, error))
tmp, err := body()
if err != nil {
return nil, err
}
if lr, ok := tmp.(LenReader); ok {
contentLength = int64(lr.Len())
}
if c, ok := tmp.(io.Closer); ok {
c.Close()
}
// If a regular byte slice, we can read it over and over via new
// readers
case []byte:
buf := rawBody.([]byte)
body = func() (io.Reader, error) {
return bytes.NewReader(buf), nil
}
contentLength = int64(len(buf))
// If a bytes.Buffer we can read the underlying byte slice over and
// over
case *bytes.Buffer:
buf := rawBody.(*bytes.Buffer)
body = func() (io.Reader, error) {
return bytes.NewReader(buf.Bytes()), nil
}
contentLength = int64(buf.Len())
// We prioritize *bytes.Reader here because we don't really want to
// deal with it seeking so want it to match here instead of the
// io.ReadSeeker case.
case *bytes.Reader:
buf, err := ioutil.ReadAll(rawBody.(*bytes.Reader))
if err != nil {
return nil, err
}
body = func() (io.Reader, error) {
return bytes.NewReader(buf), nil
}
contentLength = int64(len(buf))
// Compat case
case io.ReadSeeker:
raw := rawBody.(io.ReadSeeker)
body = func() (io.Reader, error) {
raw.Seek(0, 0)
return ioutil.NopCloser(raw), nil
}
if lr, ok := raw.(LenReader); ok {
contentLength = int64(lr.Len())
}
// Read all in so we can reset
case io.Reader:
buf, err := ioutil.ReadAll(rawBody.(io.Reader))
if err != nil {
return nil, err
}
body = func() (io.Reader, error) {
return bytes.NewReader(buf), nil
}
contentLength = int64(len(buf))
default:
return nil, fmt.Errorf("cannot handle type %T", rawBody)
}
}
httpReq, err := http.NewRequest(method, url, nil)
if err != nil {
return nil, err
}
httpReq.ContentLength = contentLength
return &Request{body, httpReq}, nil
}
// RequestLogHook allows a function to run before each retry. The HTTP
// request which will be made, and the retry number (0 for the initial
// request) are available to users. The internal logger is exposed to
// consumers.
type RequestLogHook func(*log.Logger, *http.Request, int)
// ResponseLogHook is like RequestLogHook, but allows running a function
// on each HTTP response. This function will be invoked at the end of
// every HTTP request executed, regardless of whether a subsequent retry
// needs to be performed or not. If the response body is read or closed
// from this method, this will affect the response returned from Do().
type ResponseLogHook func(*log.Logger, *http.Response)
// CheckRetry specifies a policy for handling retries. It is called
// following each request with the response and error values returned by
// the http.Client. If CheckRetry returns false, the Client stops retrying
// and returns the response to the caller. If CheckRetry returns an error,
// that error value is returned in lieu of the error from the request. The
// Client will close any response body when retrying, but if the retry is
// aborted it is up to the CheckResponse callback to properly close any
// response body before returning.
type CheckRetry func(resp *http.Response, err error) (bool, error)
// Backoff specifies a policy for how long to wait between retries.
// It is called after a failing request to determine the amount of time
// that should pass before trying again.
type Backoff func(min, max time.Duration, attemptNum int, resp *http.Response) time.Duration
// ErrorHandler is called if retries are expired, containing the last status
// from the http library. If not specified, default behavior for the library is
// to close the body and return an error indicating how many tries were
// attempted. If overriding this, be sure to close the body if needed.
type ErrorHandler func(resp *http.Response, err error, numTries int) (*http.Response, error)
// Client is used to make HTTP requests. It adds additional functionality
// like automatic retries to tolerate minor outages.
type Client struct {
HTTPClient *http.Client // Internal HTTP client.
Logger *log.Logger // Customer logger instance.
RetryWaitMin time.Duration // Minimum time to wait
RetryWaitMax time.Duration // Maximum time to wait
RetryMax int // Maximum number of retries
// RequestLogHook allows a user-supplied function to be called
// before each retry.
RequestLogHook RequestLogHook
// ResponseLogHook allows a user-supplied function to be called
// with the response from each HTTP request executed.
ResponseLogHook ResponseLogHook
// CheckRetry specifies the policy for handling retries, and is called
// after each request. The default policy is DefaultRetryPolicy.
CheckRetry CheckRetry
// Backoff specifies the policy for how long to wait between retries
Backoff Backoff
// ErrorHandler specifies the custom error handler to use, if any
ErrorHandler ErrorHandler
}
// NewClient creates a new Client with default settings.
func NewClient() *Client {
return &Client{
HTTPClient: cleanhttp.DefaultClient(),
Logger: log.New(os.Stderr, "", log.LstdFlags),
RetryWaitMin: defaultRetryWaitMin,
RetryWaitMax: defaultRetryWaitMax,
RetryMax: defaultRetryMax,
CheckRetry: DefaultRetryPolicy,
Backoff: DefaultBackoff,
}
}
// DefaultRetryPolicy provides a default callback for Client.CheckRetry, which
// will retry on connection errors and server errors.
func DefaultRetryPolicy(resp *http.Response, err error) (bool, error) {
if err != nil {
return true, err
}
// Check the response code. We retry on 500-range responses to allow
// the server time to recover, as 500's are typically not permanent
// errors and may relate to outages on the server side. This will catch
// invalid response codes as well, like 0 and 999.
if resp.StatusCode == 0 || (resp.StatusCode >= 500 && resp.StatusCode != 501) {
return true, nil
}
return false, nil
}
// DefaultBackoff provides a default callback for Client.Backoff which
// will perform exponential backoff based on the attempt number and limited
// by the provided minimum and maximum durations.
func DefaultBackoff(min, max time.Duration, attemptNum int, resp *http.Response) time.Duration {
mult := math.Pow(2, float64(attemptNum)) * float64(min)
sleep := time.Duration(mult)
if float64(sleep) != mult || sleep > max {
sleep = max
}
return sleep
}
// LinearJitterBackoff provides a callback for Client.Backoff which will
// perform linear backoff based on the attempt number and with jitter to
// prevent a thundering herd.
//
// min and max here are *not* absolute values. The number to be multipled by
// the attempt number will be chosen at random from between them, thus they are
// bounding the jitter.
//
// For instance:
// * To get strictly linear backoff of one second increasing each retry, set
// both to one second (1s, 2s, 3s, 4s, ...)
// * To get a small amount of jitter centered around one second increasing each
// retry, set to around one second, such as a min of 800ms and max of 1200ms
// (892ms, 2102ms, 2945ms, 4312ms, ...)
// * To get extreme jitter, set to a very wide spread, such as a min of 100ms
// and a max of 20s (15382ms, 292ms, 51321ms, 35234ms, ...)
func LinearJitterBackoff(min, max time.Duration, attemptNum int, resp *http.Response) time.Duration {
// attemptNum always starts at zero but we want to start at 1 for multiplication
attemptNum++
if max <= min {
// Unclear what to do here, or they are the same, so return min *
// attemptNum
return min * time.Duration(attemptNum)
}
// Seed rand; doing this every time is fine
rand := rand.New(rand.NewSource(int64(time.Now().Nanosecond())))
// Pick a random number that lies somewhere between the min and max and
// multiply by the attemptNum. attemptNum starts at zero so we always
// increment here. We first get a random percentage, then apply that to the
// difference between min and max, and add to min.
jitter := rand.Float64() * float64(max-min)
jitterMin := int64(jitter) + int64(min)
return time.Duration(jitterMin * int64(attemptNum))
}
// PassthroughErrorHandler is an ErrorHandler that directly passes through the
// values from the net/http library for the final request. The body is not
// closed.
func PassthroughErrorHandler(resp *http.Response, err error, _ int) (*http.Response, error) {
return resp, err
}
// Do wraps calling an HTTP method with retries.
func (c *Client) Do(req *Request) (*http.Response, error) {
if c.Logger != nil {
c.Logger.Printf("[DEBUG] %s %s", req.Method, req.URL)
}
var resp *http.Response
var err error
for i := 0; ; i++ {
var code int // HTTP response code
// Always rewind the request body when non-nil.
if req.body != nil {
body, err := req.body()
if err != nil {
return resp, err
}
if c, ok := body.(io.ReadCloser); ok {
req.Request.Body = c
} else {
req.Request.Body = ioutil.NopCloser(body)
}
}
if c.RequestLogHook != nil {
c.RequestLogHook(c.Logger, req.Request, i)
}
// Attempt the request
resp, err = c.HTTPClient.Do(req.Request)
if resp != nil {
code = resp.StatusCode
}
// Check if we should continue with retries.
checkOK, checkErr := c.CheckRetry(resp, err)
if err != nil {
if c.Logger != nil {
c.Logger.Printf("[ERR] %s %s request failed: %v", req.Method, req.URL, err)
}
} else {
// Call this here to maintain the behavior of logging all requests,
// even if CheckRetry signals to stop.
if c.ResponseLogHook != nil {
// Call the response logger function if provided.
c.ResponseLogHook(c.Logger, resp)
}
}
// Now decide if we should continue.
if !checkOK {
if checkErr != nil {
err = checkErr
}
return resp, err
}
// We do this before drainBody beause there's no need for the I/O if
// we're breaking out
remain := c.RetryMax - i
if remain <= 0 {
break
}
// We're going to retry, consume any response to reuse the connection.
if err == nil && resp != nil {
c.drainBody(resp.Body)
}
wait := c.Backoff(c.RetryWaitMin, c.RetryWaitMax, i, resp)
desc := fmt.Sprintf("%s %s", req.Method, req.URL)
if code > 0 {
desc = fmt.Sprintf("%s (status: %d)", desc, code)
}
if c.Logger != nil {
c.Logger.Printf("[DEBUG] %s: retrying in %s (%d left)", desc, wait, remain)
}
time.Sleep(wait)
}
if c.ErrorHandler != nil {
return c.ErrorHandler(resp, err, c.RetryMax+1)
}
// By default, we close the response body and return an error without
// returning the response
if resp != nil {
resp.Body.Close()
}
return nil, fmt.Errorf("%s %s giving up after %d attempts",
req.Method, req.URL, c.RetryMax+1)
}
// Try to read the response body so we can reuse this connection.
func (c *Client) drainBody(body io.ReadCloser) {
defer body.Close()
_, err := io.Copy(ioutil.Discard, io.LimitReader(body, respReadLimit))
if err != nil {
if c.Logger != nil {
c.Logger.Printf("[ERR] error reading response body: %v", err)
}
}
}
// Get is a shortcut for doing a GET request without making a new client.
func Get(url string) (*http.Response, error) {
return defaultClient.Get(url)
}
// Get is a convenience helper for doing simple GET requests.
func (c *Client) Get(url string) (*http.Response, error) {
req, err := NewRequest("GET", url, nil)
if err != nil {
return nil, err
}
return c.Do(req)
}
// Head is a shortcut for doing a HEAD request without making a new client.
func Head(url string) (*http.Response, error) {
return defaultClient.Head(url)
}
// Head is a convenience method for doing simple HEAD requests.
func (c *Client) Head(url string) (*http.Response, error) {
req, err := NewRequest("HEAD", url, nil)
if err != nil {
return nil, err
}
return c.Do(req)
}
// Post is a shortcut for doing a POST request without making a new client.
func Post(url, bodyType string, body interface{}) (*http.Response, error) {
return defaultClient.Post(url, bodyType, body)
}
// Post is a convenience method for doing simple POST requests.
func (c *Client) Post(url, bodyType string, body interface{}) (*http.Response, error) {
req, err := NewRequest("POST", url, body)
if err != nil {
return nil, err
}
req.Header.Set("Content-Type", bodyType)
return c.Do(req)
}
// PostForm is a shortcut to perform a POST with form data without creating
// a new client.
func PostForm(url string, data url.Values) (*http.Response, error) {
return defaultClient.PostForm(url, data)
}
// PostForm is a convenience method for doing simple POST operations using
// pre-filled url.Values form data.
func (c *Client) PostForm(url string, data url.Values) (*http.Response, error) {
return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
}