Issue #10733 has been reported by Maarten Claes.

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Bug #10733: Time.httpdate raises ArgumentError when DateTime.now.httpdate is provided as input
https://bugs.ruby-lang.org/issues/10733

* Author: Maarten Claes
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-darwin14]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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An irb session demonstrating the bug:

```
irb(main):001:0> require 'time'
=> true
irb(main):002:0> Time.httpdate("Mon, 12 Jan 2015 12:04:15 GMT")
=> 2015-01-12 12:04:15 UTC
irb(main):003:0> DateTime.now.httpdate.to_s
=> "Mon, 12 Jan 2015 12:04:56 GMT"
irb(main):004:0> Time.httpdate(DateTime.now.httpdate.to_s)
ArgumentError: not RFC 2616 compliant date: "Mon, 12 Jan 2015 12:05:08 GMT"
        from /Users/mcls/.rbenv/versions/2.2.0/lib/ruby/2.2.0/time.rb:544:in `httpdate'
        from (irb):4
        from /Users/mcls/.rbenv/versions/2.2.0/bin/irb:11:in `<main>'
```

To reproduce:
```
require 'time'
Time.httpdate("Mon, 12 Jan 2015 12:04:15 GMT") # works
Time.httpdate(DateTime.now.httpdate.to_s) # => ArgumentError
```

It seems that this only occurs on 2.2.0. (Tested on 2.1.5 and it works fine)



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