235 lines
7.2 KiB
Go
235 lines
7.2 KiB
Go
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// The retryablehttp package provides a familiar HTTP client interface with
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// automatic retries and exponential backoff. It is a thin wrapper over the
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// standard net/http client library and exposes nearly the same public API.
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// This makes retryablehttp very easy to drop into existing programs.
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//
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// retryablehttp performs automatic retries under certain conditions. Mainly, if
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// an error is returned by the client (connection errors etc), or if a 500-range
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// response is received, then a retry is invoked. Otherwise, the response is
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// returned and left to the caller to interpret.
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//
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// The main difference from net/http is that requests which take a request body
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// (POST/PUT et. al) require an io.ReadSeeker to be provided. This enables the
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// request body to be "rewound" if the initial request fails so that the full
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// request can be attempted again.
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package retryablehttp
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import (
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"fmt"
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"io"
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"io/ioutil"
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"log"
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"math"
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"net/http"
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"net/url"
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"os"
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"strings"
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"time"
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"github.com/hashicorp/go-cleanhttp"
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)
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var (
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// Default retry configuration
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defaultRetryWaitMin = 1 * time.Second
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defaultRetryWaitMax = 5 * time.Minute
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defaultRetryMax = 32
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// defaultClient is used for performing requests without explicitly making
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// a new client. It is purposely private to avoid modifications.
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defaultClient = NewClient()
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)
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// LenReader is an interface implemented by many in-memory io.Reader's. Used
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// for automatically sending the right Content-Length header when possible.
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type LenReader interface {
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Len() int
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}
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// Request wraps the metadata needed to create HTTP requests.
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type Request struct {
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// body is a seekable reader over the request body payload. This is
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// used to rewind the request data in between retries.
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body io.ReadSeeker
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// Embed an HTTP request directly. This makes a *Request act exactly
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// like an *http.Request so that all meta methods are supported.
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*http.Request
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}
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// NewRequest creates a new wrapped request.
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func NewRequest(method, url string, body io.ReadSeeker) (*Request, error) {
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// Wrap the body in a noop ReadCloser if non-nil. This prevents the
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// reader from being closed by the HTTP client.
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var rcBody io.ReadCloser
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if body != nil {
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rcBody = ioutil.NopCloser(body)
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}
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// Make the request with the noop-closer for the body.
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httpReq, err := http.NewRequest(method, url, rcBody)
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if err != nil {
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return nil, err
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}
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// Check if we can set the Content-Length automatically.
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if lr, ok := body.(LenReader); ok {
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httpReq.ContentLength = int64(lr.Len())
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}
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return &Request{body, httpReq}, nil
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}
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// RequestLogHook allows a function to run before each retry. The HTTP
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// request which will be made, and the retry number (0 for the initial
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// request) are available to users. The internal logger is exposed to
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// consumers.
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type RequestLogHook func(*log.Logger, *http.Request, int)
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// Client is used to make HTTP requests. It adds additional functionality
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// like automatic retries to tolerate minor outages.
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type Client struct {
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HTTPClient *http.Client // Internal HTTP client.
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Logger *log.Logger // Customer logger instance.
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RetryWaitMin time.Duration // Minimum time to wait
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RetryWaitMax time.Duration // Maximum time to wait
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RetryMax int // Maximum number of retries
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// RequestLogHook allows a user-supplied function to be called
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// before each retry.
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RequestLogHook RequestLogHook
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}
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// NewClient creates a new Client with default settings.
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func NewClient() *Client {
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return &Client{
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HTTPClient: cleanhttp.DefaultClient(),
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Logger: log.New(os.Stderr, "", log.LstdFlags),
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RetryWaitMin: defaultRetryWaitMin,
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RetryWaitMax: defaultRetryWaitMax,
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RetryMax: defaultRetryMax,
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}
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}
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// Do wraps calling an HTTP method with retries.
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func (c *Client) Do(req *Request) (*http.Response, error) {
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c.Logger.Printf("[DEBUG] %s %s", req.Method, req.URL)
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for i := 0; ; i++ {
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var code int // HTTP response code
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// Always rewind the request body when non-nil.
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if req.body != nil {
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if _, err := req.body.Seek(0, 0); err != nil {
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return nil, fmt.Errorf("failed to seek body: %v", err)
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}
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}
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if c.RequestLogHook != nil {
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c.RequestLogHook(c.Logger, req.Request, i)
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}
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// Attempt the request
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resp, err := c.HTTPClient.Do(req.Request)
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if err != nil {
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c.Logger.Printf("[ERR] %s %s request failed: %v", req.Method, req.URL, err)
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goto RETRY
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}
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code = resp.StatusCode
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// Check the response code. We retry on 500-range responses to allow
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// the server time to recover, as 500's are typically not permanent
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// errors and may relate to outages on the server side.
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if code%500 < 100 {
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resp.Body.Close()
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goto RETRY
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}
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return resp, nil
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RETRY:
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remain := c.RetryMax - i
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if remain == 0 {
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break
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}
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wait := backoff(c.RetryWaitMin, c.RetryWaitMax, i)
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desc := fmt.Sprintf("%s %s", req.Method, req.URL)
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if code > 0 {
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desc = fmt.Sprintf("%s (status: %d)", desc, code)
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}
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c.Logger.Printf("[DEBUG] %s: retrying in %s (%d left)", desc, wait, remain)
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time.Sleep(wait)
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}
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// Return an error if we fall out of the retry loop
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return nil, fmt.Errorf("%s %s giving up after %d attempts",
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req.Method, req.URL, c.RetryMax+1)
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}
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// Get is a shortcut for doing a GET request without making a new client.
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func Get(url string) (*http.Response, error) {
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return defaultClient.Get(url)
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}
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// Get is a convenience helper for doing simple GET requests.
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func (c *Client) Get(url string) (*http.Response, error) {
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req, err := NewRequest("GET", url, nil)
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if err != nil {
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return nil, err
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}
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return c.Do(req)
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}
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// Head is a shortcut for doing a HEAD request without making a new client.
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func Head(url string) (*http.Response, error) {
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return defaultClient.Head(url)
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}
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// Head is a convenience method for doing simple HEAD requests.
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func (c *Client) Head(url string) (*http.Response, error) {
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req, err := NewRequest("HEAD", url, nil)
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if err != nil {
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return nil, err
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}
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return c.Do(req)
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}
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// Post is a shortcut for doing a POST request without making a new client.
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func Post(url, bodyType string, body io.ReadSeeker) (*http.Response, error) {
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return defaultClient.Post(url, bodyType, body)
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}
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// Post is a convenience method for doing simple POST requests.
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func (c *Client) Post(url, bodyType string, body io.ReadSeeker) (*http.Response, error) {
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req, err := NewRequest("POST", url, body)
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if err != nil {
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return nil, err
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}
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req.Header.Set("Content-Type", bodyType)
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return c.Do(req)
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}
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// PostForm is a shortcut to perform a POST with form data without creating
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// a new client.
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func PostForm(url string, data url.Values) (*http.Response, error) {
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return defaultClient.PostForm(url, data)
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}
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// PostForm is a convenience method for doing simple POST operations using
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// pre-filled url.Values form data.
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func (c *Client) PostForm(url string, data url.Values) (*http.Response, error) {
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return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
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}
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// backoff is used to calculate how long to sleep before retrying
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// after observing failures. It takes the minimum/maximum wait time and
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// iteration, and returns the duration to wait.
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func backoff(min, max time.Duration, iter int) time.Duration {
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mult := math.Pow(2, float64(iter)) * float64(min)
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sleep := time.Duration(mult)
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if float64(sleep) != mult || sleep > max {
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sleep = max
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}
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return sleep
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}
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