http-retry-after

http-retry-after is a Ruby gem for parsing HTTP Retry-After header values and converting them into Ruby Time instances, so clients can respect server retry policies defined in RFC 9110 without reimplementing parsing logic.

The HTTP Retry-After response header, defined in RFC 9110, Section 10.2.2, tells a client when it may retry a request after receiving a response such as 503 Service Unavailable or 429 Too Many Requests. The value can be either an HTTP-date, indicating the time after which the retry is safe, or a delta-seconds value that expresses the remaining seconds until the retry should be attempted. Servers may also include additional hints (for example Retry-After: 120 for two minutes) so clients can implement a backoff strategy.

Require the gem and call HTTP::RetryAfter.parse with either a delta-seconds value or an HTTP-date string:

require "http/retry-after"

# Delta-seconds value (interpreted as seconds from now)
HTTP::RetryAfter.parse("120")

# HTTP-date value
HTTP::RetryAfter.parse("Wed, 21 Oct 2015 07:28:00 GMT")

When parse receives a string it first attempts to interpret it as delta seconds and, if that fails, falls back to parsing an HTTP-date. You can also call the lower-level helpers directly when you already know which format you are dealing with:

HTTP::RetryAfter.parse_seconds("30")
HTTP::RetryAfter.parse_http_date("Wed, 21 Oct 2015 07:28:00 GMT")

Working with Net::HTTP:

require "net/http"
require "uri"
require "http/retry-after"

uri = URI("https://httpbin.org/response-headers?Retry-After=120")
response = Net::HTTP.get_response(uri)

retry_after_header = response["Retry-After"]
retry_at = HTTP::RetryAfter.parse(retry_after_header)

Errors:

• HTTP::RetryAfter::NegativeRetryAfterError is raised when a negative delta-seconds value is provided.
• HTTP::RetryAfter::InvalidFormatError is raised when the value cannot be interpreted as seconds or an HTTP-date (including nil values or malformed strings).

Both helpers return a Time object. parse_seconds uses Time.now + seconds, so the result is in the current system timezone, whereas parse_http_date uses Time.httpdate and returns a UTC timestamp.

Add this line to your application's Gemfile:

gem "http-retry-after"

And then execute:

bundle install

After checking out the repository, install dependencies and run the test suite:

bundle install
bundle exec rake test

Bug reports and pull requests are welcome on GitHub at https://github.com/kudoas/http-retry-after. This project is intended to be a safe, welcoming space for collaboration.

The gem is available as open source under the terms of the MIT License.