Implement header_parser_block option

README.md

@@ -111,13 +111,14 @@ retry_options = {
 }
 ```
 
-If you are working with an API which does not comply with the Rate Limit RFC you can specify custom headers to be used for retry and reset.
+If you are working with an API which does not comply with the Rate Limit RFC you can specify custom headers to be used for retry and reset, as well as a block to parse the headers:
 
 ```ruby
 retry_options = {
   retry_statuses: [429],
   rate_limit_retry_header: 'x-rate-limit-retry-after',
-  rate_limit_reset_header: 'x-rate-limit-reset'
+  rate_limit_reset_header: 'x-rate-limit-reset',
+  header_parser_block: ->(value) { Time.at(value.to_i).utc - Time.now.utc }
 }
 ```
 

lib/faraday/retry/middleware.rb

@@ -27,7 +27,7 @@ class Options < Faraday::Options.new(:max, :interval, :max_interval,
                                            :backoff_factor, :exceptions,
                                            :methods, :retry_if, :retry_block,
                                            :retry_statuses, :rate_limit_retry_header,
-                                           :rate_limit_reset_header)
+                                           :rate_limit_reset_header, :header_parser_block)
 
         DEFAULT_CHECK = ->(_env, _exception) { false }
 
@@ -120,6 +120,10 @@ def retry_statuses
       #   codes or a single Integer value that determines whether to raise
       #   a Faraday::RetriableResponse exception based on the HTTP status code
       #   of an HTTP response.
+      # @option options [Block] :header_parser_block block that will receive
+      #   the the value of the retry header and should return the number of
+      #   seconds to wait before retrying the request. This is useful if the
+      #   value of the header is not a number of seconds or a RFC 2822 formatted date.
       def initialize(app, options = nil)
         super(app)
         @options = Options.from(options)
@@ -244,12 +248,16 @@ def parse_retry_header(env, header)
 
         retry_after_value = env[:response_headers][header]
 
-        # Try to parse date from the header value
-        begin
-          datetime = DateTime.rfc2822(retry_after_value)
-          datetime.to_time - Time.now.utc
-        rescue ArgumentError
-          retry_after_value.to_f
+        if @options.header_parser_block
+          @options.header_parser_block.call(retry_after_value)
+        else
+          # Try to parse date from the header value
+          begin
+            datetime = DateTime.rfc2822(retry_after_value)
+            datetime.to_time - Time.now.utc
+          rescue ArgumentError
+            retry_after_value.to_f
+          end
         end
       end
     end

spec/faraday/retry/middleware_spec.rb

@@ -294,6 +294,13 @@
       it { expect(elapsed).to be > 1 }
     end
 
+    context 'when custom header_parser_block is set' do
+      let(:headers) { { 'Retry-After' => '0.1', 'RateLimit-Reset' => (Time.now.utc + 2).to_i.to_s } }
+      let(:options) { [{ max: 1, interval: 0.1, retry_statuses: 504, header_parser_block: ->(value) { Time.at(value.to_i).utc - Time.now.utc } }] }
+
+      it { expect(elapsed).to be > 1 }
+    end
+
     context 'when retry_after is bigger than max_interval' do
       let(:headers) { { 'Retry-After' => (Time.now.utc + 20).strftime('%a, %d %b %Y %H:%M:%S GMT') } }
       let(:options) { [{ max: 2, interval: 0.1, max_interval: 5, retry_statuses: 504 }] }