[tor-bugs] #22865 [Obfuscation/meek]: Explicitly set Content-Length to zero when there is no data to send

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#22865: Explicitly set Content-Length to zero when there is no data to send
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     Reporter:  twim              |      Owner:  dcf
         Type:  defect            |     Status:  new
     Priority:  Medium            |  Milestone:
    Component:  Obfuscation/meek  |    Version:
     Severity:  Normal            |   Keywords:
Actual Points:                    |  Parent ID:
       Points:                    |   Reviewer:
      Sponsor:                    |
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 Since Go 1.8 http.Transport does not set Content-Length header if body
 contains no bytes.
 https://golang.org/doc/go1.8#net_http
 https://go-review.googlesource.com/c/31445/

 However some of domain fronts do inspect Content-Length header and return
 411 error when it is not set. This breaks connection entierly since these
 packets do not travel beyond a frontend to a meek server.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/22865>
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