debian-forge-composer/vendor/github.com/hashicorp/go-retryablehttp

go-retryablehttp

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 code is received (except 501), then a retry is invoked after a wait period. Otherwise, the response is returned and left to the caller to interpret.

The main difference from net/http is that requests which take a request body (POST/PUT et. al) can have the body provided in a number of ways (some more or less efficient) that allow "rewinding" the request body if the initial request fails so that the full request can be attempted again. See the godoc for more details.

Version 0.6.0 and before are compatible with Go prior to 1.12. From 0.6.1 onward, Go 1.12+ is required. From 0.6.7 onward, Go 1.13+ is required.

Example Use

Using this library should look almost identical to what you would do with net/http. The most simple example of a GET request is shown below:

resp, err := retryablehttp.Get("/foo")
if err != nil {
    panic(err)
}

The returned response object is an *http.Response, the same thing you would usually get from net/http. Had the request failed one or more times, the above call would block and retry with exponential backoff.

Retrying cases that fail after a seeming success

It's possible for a request to succeed in the sense that the expected response headers are received, but then to encounter network-level errors while reading the response body. In go-retryablehttp's most basic usage, this error would not be retryable, due to the out-of-band handling of the response body. In some cases it may be desirable to handle the response body as part of the retryable operation.

A toy example (which will retry the full request and succeed on the second attempt) is shown below:

c := retryablehttp.NewClient()
r := retryablehttp.NewRequest("GET", "://foo", nil)
handlerShouldRetry := true
r.SetResponseHandler(func(*http.Response) error {
    if !handlerShouldRetry {
        return nil
    }
    handlerShouldRetry = false
    return errors.New("retryable error")
})

Getting a stdlib *http.Client with retries

It's possible to convert a *retryablehttp.Client directly to a *http.Client. This makes use of retryablehttp broadly applicable with minimal effort. Simply configure a *retryablehttp.Client as you wish, and then call StandardClient():

retryClient := retryablehttp.NewClient()
retryClient.RetryMax = 10

standardClient := retryClient.StandardClient() // *http.Client

For more usage and examples see the godoc.