chore: vendor

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

@@ -0,0 +1,919 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+// Package retryablehttp 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"
+	"context"
+	"fmt"
+	"io"
+	"log"
+	"math"
+	"math/rand"
+	"net/http"
+	"net/url"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	cleanhttp "github.com/hashicorp/go-cleanhttp"
+)
+
+var (
+	// Default retry configuration
+	defaultRetryWaitMin = 1 * time.Second
+	defaultRetryWaitMax = 30 * time.Second
+	defaultRetryMax     = 4
+
+	// defaultLogger is the logger provided with defaultClient
+	defaultLogger = log.New(os.Stderr, "", log.LstdFlags)
+
+	// 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)
+
+	// timeNow sets the function that returns the current time.
+	// This defaults to time.Now. Changes to this should only be done in tests.
+	timeNow = time.Now
+
+	// A regular expression to match the error returned by net/http when the
+	// configured number of redirects is exhausted. This error isn't typed
+	// specifically so we resort to matching on the error string.
+	redirectsErrorRe = regexp.MustCompile(`stopped after \d+ redirects\z`)
+
+	// A regular expression to match the error returned by net/http when the
+	// scheme specified in the URL is invalid. This error isn't typed
+	// specifically so we resort to matching on the error string.
+	schemeErrorRe = regexp.MustCompile(`unsupported protocol scheme`)
+
+	// A regular expression to match the error returned by net/http when a
+	// request header or value is invalid. This error isn't typed
+	// specifically so we resort to matching on the error string.
+	invalidHeaderErrorRe = regexp.MustCompile(`invalid header`)
+
+	// A regular expression to match the error returned by net/http when the
+	// TLS certificate is not trusted. This error isn't typed
+	// specifically so we resort to matching on the error string.
+	notTrustedErrorRe = regexp.MustCompile(`certificate is not trusted`)
+)
+
+// ReaderFunc is the type of function that can be given natively to NewRequest
+type ReaderFunc func() (io.Reader, error)
+
+// ResponseHandlerFunc is a type of function that takes in a Response, and does something with it.
+// The ResponseHandlerFunc is called when the HTTP client successfully receives a response and the
+// CheckRetry function indicates that a retry of the base request is not necessary.
+// If an error is returned from this function, the CheckRetry policy will be used to determine
+// whether to retry the whole request (including this handler).
+//
+// Make sure to check status codes! Even if the request was completed it may have a non-2xx status code.
+//
+// The response body is not automatically closed. It must be closed either by the ResponseHandlerFunc or
+// by the caller out-of-band. Failure to do so will result in a memory leak.
+type ResponseHandlerFunc func(*http.Response) 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
+
+	responseHandler ResponseHandlerFunc
+
+	// Embed an HTTP request directly. This makes a *Request act exactly
+	// like an *http.Request so that all meta methods are supported.
+	*http.Request
+}
+
+// WithContext returns wrapped Request with a shallow copy of underlying *http.Request
+// with its context changed to ctx. The provided ctx must be non-nil.
+func (r *Request) WithContext(ctx context.Context) *Request {
+	return &Request{
+		body:            r.body,
+		responseHandler: r.responseHandler,
+		Request:         r.Request.WithContext(ctx),
+	}
+}
+
+// SetResponseHandler allows setting the response handler.
+func (r *Request) SetResponseHandler(fn ResponseHandlerFunc) {
+	r.responseHandler = fn
+}
+
+// BodyBytes allows accessing the request body. It is an analogue to
+// http.Request's Body variable, but it returns a copy of the underlying data
+// rather than consuming it.
+//
+// This function is not thread-safe; do not call it at the same time as another
+// call, or at the same time this request is being used with Client.Do.
+func (r *Request) BodyBytes() ([]byte, error) {
+	if r.body == nil {
+		return nil, nil
+	}
+	body, err := r.body()
+	if err != nil {
+		return nil, err
+	}
+	buf := new(bytes.Buffer)
+	_, err = buf.ReadFrom(body)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+// SetBody allows setting the request body.
+//
+// It is useful if a new body needs to be set without constructing a new Request.
+func (r *Request) SetBody(rawBody interface{}) error {
+	bodyReader, contentLength, err := getBodyReaderAndContentLength(rawBody)
+	if err != nil {
+		return err
+	}
+	r.body = bodyReader
+	r.ContentLength = contentLength
+	if bodyReader != nil {
+		r.GetBody = func() (io.ReadCloser, error) {
+			body, err := bodyReader()
+			if err != nil {
+				return nil, err
+			}
+			if rc, ok := body.(io.ReadCloser); ok {
+				return rc, nil
+			}
+			return io.NopCloser(body), nil
+		}
+	} else {
+		r.GetBody = func() (io.ReadCloser, error) { return http.NoBody, nil }
+	}
+	return nil
+}
+
+// WriteTo allows copying the request body into a writer.
+//
+// It writes data to w until there's no more data to write or
+// when an error occurs. The return int64 value is the number of bytes
+// written. Any error encountered during the write is also returned.
+// The signature matches io.WriterTo interface.
+func (r *Request) WriteTo(w io.Writer) (int64, error) {
+	body, err := r.body()
+	if err != nil {
+		return 0, err
+	}
+	if c, ok := body.(io.Closer); ok {
+		defer c.Close()
+	}
+	return io.Copy(w, body)
+}
+
+func getBodyReaderAndContentLength(rawBody interface{}) (ReaderFunc, int64, error) {
+	var bodyReader ReaderFunc
+	var contentLength int64
+
+	switch body := rawBody.(type) {
+	// If they gave us a function already, great! Use it.
+	case ReaderFunc:
+		bodyReader = body
+		tmp, err := body()
+		if err != nil {
+			return nil, 0, 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):
+		bodyReader = body
+		tmp, err := body()
+		if err != nil {
+			return nil, 0, 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 := body
+		bodyReader = 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 := body
+		bodyReader = 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:
+		snapshot := *body
+		bodyReader = func() (io.Reader, error) {
+			r := snapshot
+			return &r, nil
+		}
+		contentLength = int64(body.Len())
+
+	// Compat case
+	case io.ReadSeeker:
+		raw := body
+		bodyReader = func() (io.Reader, error) {
+			_, err := raw.Seek(0, 0)
+			return io.NopCloser(raw), err
+		}
+		if lr, ok := raw.(LenReader); ok {
+			contentLength = int64(lr.Len())
+		}
+
+	// Read all in so we can reset
+	case io.Reader:
+		buf, err := io.ReadAll(body)
+		if err != nil {
+			return nil, 0, err
+		}
+		if len(buf) == 0 {
+			bodyReader = func() (io.Reader, error) {
+				return http.NoBody, nil
+			}
+			contentLength = 0
+		} else {
+			bodyReader = func() (io.Reader, error) {
+				return bytes.NewReader(buf), nil
+			}
+			contentLength = int64(len(buf))
+		}
+
+	// No body provided, nothing to do
+	case nil:
+
+	// Unrecognized type
+	default:
+		return nil, 0, fmt.Errorf("cannot handle type %T", rawBody)
+	}
+	return bodyReader, contentLength, nil
+}
+
+// FromRequest wraps an http.Request in a retryablehttp.Request
+func FromRequest(r *http.Request) (*Request, error) {
+	bodyReader, _, err := getBodyReaderAndContentLength(r.Body)
+	if err != nil {
+		return nil, err
+	}
+	// Could assert contentLength == r.ContentLength
+	return &Request{body: bodyReader, Request: r}, nil
+}
+
+// NewRequest creates a new wrapped request.
+func NewRequest(method, url string, rawBody interface{}) (*Request, error) {
+	return NewRequestWithContext(context.Background(), method, url, rawBody)
+}
+
+// NewRequestWithContext creates a new wrapped request with the provided context.
+//
+// The context controls the entire lifetime of a request and its response:
+// obtaining a connection, sending the request, and reading the response headers and body.
+func NewRequestWithContext(ctx context.Context, method, url string, rawBody interface{}) (*Request, error) {
+	httpReq, err := http.NewRequestWithContext(ctx, method, url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	req := &Request{
+		Request: httpReq,
+	}
+	if err := req.SetBody(rawBody); err != nil {
+		return nil, err
+	}
+
+	return req, nil
+}
+
+// Logger interface allows to use other loggers than
+// standard log.Logger.
+type Logger interface {
+	Printf(string, ...interface{})
+}
+
+// LeveledLogger is an interface that can be implemented by any logger or a
+// logger wrapper to provide leveled logging. The methods accept a message
+// string and a variadic number of key-value pairs. For log.Printf style
+// formatting where message string contains a format specifier, use Logger
+// interface.
+type LeveledLogger interface {
+	Error(msg string, keysAndValues ...interface{})
+	Info(msg string, keysAndValues ...interface{})
+	Debug(msg string, keysAndValues ...interface{})
+	Warn(msg string, keysAndValues ...interface{})
+}
+
+// hookLogger adapts an LeveledLogger to Logger for use by the existing hook functions
+// without changing the API.
+type hookLogger struct {
+	LeveledLogger
+}
+
+func (h hookLogger) Printf(s string, args ...interface{}) {
+	h.Info(fmt.Sprintf(s, args...))
+}
+
+// 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(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(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 CheckRetry callback to properly close any
+// response body before returning.
+type CheckRetry func(ctx context.Context, 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)
+
+// PrepareRetry is called before retry operation. It can be used for example to re-sign the request
+type PrepareRetry func(req *http.Request) 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     interface{}  // Customer logger instance. Can be either Logger or LeveledLogger
+
+	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
+
+	// PrepareRetry can prepare the request for retry operation, for example re-sign it
+	PrepareRetry PrepareRetry
+
+	loggerInit sync.Once
+	clientInit sync.Once
+}
+
+// NewClient creates a new Client with default settings.
+func NewClient() *Client {
+	return &Client{
+		HTTPClient:   cleanhttp.DefaultPooledClient(),
+		Logger:       defaultLogger,
+		RetryWaitMin: defaultRetryWaitMin,
+		RetryWaitMax: defaultRetryWaitMax,
+		RetryMax:     defaultRetryMax,
+		CheckRetry:   DefaultRetryPolicy,
+		Backoff:      DefaultBackoff,
+	}
+}
+
+func (c *Client) logger() interface{} {
+	c.loggerInit.Do(func() {
+		if c.Logger == nil {
+			return
+		}
+
+		switch c.Logger.(type) {
+		case Logger, LeveledLogger:
+			// ok
+		default:
+			// This should happen in dev when they are setting Logger and work on code, not in prod.
+			panic(fmt.Sprintf("invalid logger type passed, must be Logger or LeveledLogger, was %T", c.Logger))
+		}
+	})
+
+	return c.Logger
+}
+
+// DefaultRetryPolicy provides a default callback for Client.CheckRetry, which
+// will retry on connection errors and server errors.
+func DefaultRetryPolicy(ctx context.Context, resp *http.Response, err error) (bool, error) {
+	// do not retry on context.Canceled or context.DeadlineExceeded
+	if ctx.Err() != nil {
+		return false, ctx.Err()
+	}
+
+	// don't propagate other errors
+	shouldRetry, _ := baseRetryPolicy(resp, err)
+	return shouldRetry, nil
+}
+
+// ErrorPropagatedRetryPolicy is the same as DefaultRetryPolicy, except it
+// propagates errors back instead of returning nil. This allows you to inspect
+// why it decided to retry or not.
+func ErrorPropagatedRetryPolicy(ctx context.Context, resp *http.Response, err error) (bool, error) {
+	// do not retry on context.Canceled or context.DeadlineExceeded
+	if ctx.Err() != nil {
+		return false, ctx.Err()
+	}
+
+	return baseRetryPolicy(resp, err)
+}
+
+func baseRetryPolicy(resp *http.Response, err error) (bool, error) {
+	if err != nil {
+		if v, ok := err.(*url.Error); ok {
+			// Don't retry if the error was due to too many redirects.
+			if redirectsErrorRe.MatchString(v.Error()) {
+				return false, v
+			}
+
+			// Don't retry if the error was due to an invalid protocol scheme.
+			if schemeErrorRe.MatchString(v.Error()) {
+				return false, v
+			}
+
+			// Don't retry if the error was due to an invalid header.
+			if invalidHeaderErrorRe.MatchString(v.Error()) {
+				return false, v
+			}
+
+			// Don't retry if the error was due to TLS cert verification failure.
+			if notTrustedErrorRe.MatchString(v.Error()) {
+				return false, v
+			}
+			if isCertError(v.Err) {
+				return false, v
+			}
+		}
+
+		// The error is likely recoverable so retry.
+		return true, nil
+	}
+
+	// 429 Too Many Requests is recoverable. Sometimes the server puts
+	// a Retry-After response header to indicate when the server is
+	// available to start processing request from client.
+	if resp.StatusCode == http.StatusTooManyRequests {
+		return true, nil
+	}
+
+	// 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 != http.StatusNotImplemented) {
+		return true, fmt.Errorf("unexpected HTTP status %s", resp.Status)
+	}
+
+	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.
+//
+// It also tries to parse Retry-After response header when a http.StatusTooManyRequests
+// (HTTP Code 429) is found in the resp parameter. Hence it will return the number of
+// seconds the server states it may be ready to process more requests from this client.
+func DefaultBackoff(min, max time.Duration, attemptNum int, resp *http.Response) time.Duration {
+	if resp != nil {
+		if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode == http.StatusServiceUnavailable {
+			if sleep, ok := parseRetryAfterHeader(resp.Header["Retry-After"]); ok {
+				return sleep
+			}
+		}
+	}
+
+	mult := math.Pow(2, float64(attemptNum)) * float64(min)
+	sleep := time.Duration(mult)
+	if float64(sleep) != mult || sleep > max {
+		sleep = max
+	}
+	return sleep
+}
+
+// parseRetryAfterHeader parses the Retry-After header and returns the
+// delay duration according to the spec: https://httpwg.org/specs/rfc7231.html#header.retry-after
+// The bool returned will be true if the header was successfully parsed.
+// Otherwise, the header was either not present, or was not parseable according to the spec.
+//
+// Retry-After headers come in two flavors: Seconds or HTTP-Date
+//
+// Examples:
+// * Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
+// * Retry-After: 120
+func parseRetryAfterHeader(headers []string) (time.Duration, bool) {
+	if len(headers) == 0 || headers[0] == "" {
+		return 0, false
+	}
+	header := headers[0]
+	// Retry-After: 120
+	if sleep, err := strconv.ParseInt(header, 10, 64); err == nil {
+		if sleep < 0 { // a negative sleep doesn't make sense
+			return 0, false
+		}
+		return time.Second * time.Duration(sleep), true
+	}
+
+	// Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
+	retryTime, err := time.Parse(time.RFC1123, header)
+	if err != nil {
+		return 0, false
+	}
+	if until := retryTime.Sub(timeNow()); until > 0 {
+		return until, true
+	}
+	// date is in the past
+	return 0, true
+}
+
+// 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 multiplied 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
+	source := 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 := source.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) {
+	c.clientInit.Do(func() {
+		if c.HTTPClient == nil {
+			c.HTTPClient = cleanhttp.DefaultPooledClient()
+		}
+	})
+
+	logger := c.logger()
+
+	if logger != nil {
+		switch v := logger.(type) {
+		case LeveledLogger:
+			v.Debug("performing request", "method", req.Method, "url", redactURL(req.URL))
+		case Logger:
+			v.Printf("[DEBUG] %s %s", req.Method, redactURL(req.URL))
+		}
+	}
+
+	var resp *http.Response
+	var attempt int
+	var shouldRetry bool
+	var doErr, respErr, checkErr, prepareErr error
+
+	for i := 0; ; i++ {
+		doErr, respErr, prepareErr = nil, nil, nil
+		attempt++
+
+		// Always rewind the request body when non-nil.
+		if req.body != nil {
+			body, err := req.body()
+			if err != nil {
+				c.HTTPClient.CloseIdleConnections()
+				return resp, err
+			}
+			if c, ok := body.(io.ReadCloser); ok {
+				req.Body = c
+			} else {
+				req.Body = io.NopCloser(body)
+			}
+		}
+
+		if c.RequestLogHook != nil {
+			switch v := logger.(type) {
+			case LeveledLogger:
+				c.RequestLogHook(hookLogger{v}, req.Request, i)
+			case Logger:
+				c.RequestLogHook(v, req.Request, i)
+			default:
+				c.RequestLogHook(nil, req.Request, i)
+			}
+		}
+
+		// Attempt the request
+		resp, doErr = c.HTTPClient.Do(req.Request)
+
+		// Check if we should continue with retries.
+		shouldRetry, checkErr = c.CheckRetry(req.Context(), resp, doErr)
+		if !shouldRetry && doErr == nil && req.responseHandler != nil {
+			respErr = req.responseHandler(resp)
+			shouldRetry, checkErr = c.CheckRetry(req.Context(), resp, respErr)
+		}
+
+		err := doErr
+		if respErr != nil {
+			err = respErr
+		}
+		if err != nil {
+			switch v := logger.(type) {
+			case LeveledLogger:
+				v.Error("request failed", "error", err, "method", req.Method, "url", redactURL(req.URL))
+			case Logger:
+				v.Printf("[ERR] %s %s request failed: %v", req.Method, redactURL(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.
+				switch v := logger.(type) {
+				case LeveledLogger:
+					c.ResponseLogHook(hookLogger{v}, resp)
+				case Logger:
+					c.ResponseLogHook(v, resp)
+				default:
+					c.ResponseLogHook(nil, resp)
+				}
+			}
+		}
+
+		if !shouldRetry {
+			break
+		}
+
+		// We do this before drainBody because 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 doErr == nil {
+			c.drainBody(resp.Body)
+		}
+
+		wait := c.Backoff(c.RetryWaitMin, c.RetryWaitMax, i, resp)
+		if logger != nil {
+			desc := fmt.Sprintf("%s %s", req.Method, redactURL(req.URL))
+			if resp != nil {
+				desc = fmt.Sprintf("%s (status: %d)", desc, resp.StatusCode)
+			}
+			switch v := logger.(type) {
+			case LeveledLogger:
+				v.Debug("retrying request", "request", desc, "timeout", wait, "remaining", remain)
+			case Logger:
+				v.Printf("[DEBUG] %s: retrying in %s (%d left)", desc, wait, remain)
+			}
+		}
+		timer := time.NewTimer(wait)
+		select {
+		case <-req.Context().Done():
+			timer.Stop()
+			c.HTTPClient.CloseIdleConnections()
+			return nil, req.Context().Err()
+		case <-timer.C:
+		}
+
+		// Make shallow copy of http Request so that we can modify its body
+		// without racing against the closeBody call in persistConn.writeLoop.
+		httpreq := *req.Request
+		req.Request = &httpreq
+
+		if c.PrepareRetry != nil {
+			if err := c.PrepareRetry(req.Request); err != nil {
+				prepareErr = err
+				break
+			}
+		}
+	}
+
+	// this is the closest we have to success criteria
+	if doErr == nil && respErr == nil && checkErr == nil && prepareErr == nil && !shouldRetry {
+		return resp, nil
+	}
+
+	defer c.HTTPClient.CloseIdleConnections()
+
+	var err error
+	if prepareErr != nil {
+		err = prepareErr
+	} else if checkErr != nil {
+		err = checkErr
+	} else if respErr != nil {
+		err = respErr
+	} else {
+		err = doErr
+	}
+
+	if c.ErrorHandler != nil {
+		return c.ErrorHandler(resp, err, attempt)
+	}
+
+	// By default, we close the response body and return an error without
+	// returning the response
+	if resp != nil {
+		c.drainBody(resp.Body)
+	}
+
+	// this means CheckRetry thought the request was a failure, but didn't
+	// communicate why
+	if err == nil {
+		return nil, fmt.Errorf("%s %s giving up after %d attempt(s)",
+			req.Method, redactURL(req.URL), attempt)
+	}
+
+	return nil, fmt.Errorf("%s %s giving up after %d attempt(s): %w",
+		req.Method, redactURL(req.URL), attempt, err)
+}
+
+// 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(io.Discard, io.LimitReader(body, respReadLimit))
+	if err != nil {
+		if c.logger() != nil {
+			switch v := c.logger().(type) {
+			case LeveledLogger:
+				v.Error("error reading response body", "error", err)
+			case Logger:
+				v.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()))
+}
+
+// StandardClient returns a stdlib *http.Client with a custom Transport, which
+// shims in a *retryablehttp.Client for added retries.
+func (c *Client) StandardClient() *http.Client {
+	return &http.Client{
+		Transport: &RoundTripper{Client: c},
+	}
+}
+
+// Taken from url.URL#Redacted() which was introduced in go 1.15.
+// We can switch to using it directly if we'll bump the minimum required go version.
+func redactURL(u *url.URL) string {
+	if u == nil {
+		return ""
+	}
+
+	ru := *u
+	if _, has := ru.User.Password(); has {
+		ru.User = url.UserPassword(ru.User.Username(), "xxxxx")
+	}
+	return ru.String()
+}