[ruby/open-uri] Set default for max_redirects and add exception class

https://github.com/ruby/open-uri/commit/dcdcb885cc

lib/open-uri.rb

@@ -108,7 +108,7 @@ module OpenURI
     :ftp_active_mode => false,
     :redirect => true,
     :encoding => nil,
-    :max_redirects => nil,
+    :max_redirects => 64,
   }
 
   def OpenURI.check_options(options) # :nodoc:
@@ -240,7 +240,7 @@ module OpenURI
         uri = redirect
         raise "HTTP redirection loop: #{uri}" if uri_set.include? uri.to_s
         uri_set[uri.to_s] = true
-        raise "Too many redirects" if max_redirects && uri_set.size > max_redirects
+        raise TooManyRedirects.new("Too many redirects", buf.io) if max_redirects && uri_set.size > max_redirects
       else
         break
       end
@@ -395,6 +395,9 @@ module OpenURI
     attr_reader :uri
   end
 
+  class TooManyRedirects < HTTPError
+  end
+
   class Buffer # :nodoc: all
     def initialize
       @io = StringIO.new

test/open-uri/test_open-uri.rb

@@ -572,7 +572,7 @@ class TestOpenURI < Test::Unit::TestCase
       srv.mount_proc("/r1/") {|req, res| res.status = 301; res["location"] = "#{url}/r2"; res.body = "r1" }
       srv.mount_proc("/r2/") {|req, res| res.status = 301; res["location"] = "#{url}/r3"; res.body = "r2" }
       srv.mount_proc("/r3/") {|req, res| res.body = "r3" }
-      exc = assert_raise(RuntimeError) { URI.open("#{url}/r1/", max_redirects: 1) {} }
+      exc = assert_raise(OpenURI::TooManyRedirects) { URI.open("#{url}/r1/", max_redirects: 1) {} }
       assert_equal("Too many redirects", exc.message)
     }
   end