R. David Murray,

You are right it is not specific to the client library. HTTP headers are part of the message (Request/Response) with both the same constraints. Constraints are put on receivers (receiving a message) and senders (sending a message) of the message (which is not specifically related to client or server).

Maybe the way forward in the future is to have a header factory shared by all HTTP libs? I noticed that http.client and http.server had similar issues: 

in http.server
   send_header
in http.client
   putheader

Which are similar features aka constructing headers for sending with the message. 


And what would be the elegant way to solve this current bug?

Ah… before I forget… The WG is having a meeting in 2 weeks. To make a summary of the HTTPBIS work. See the agenda. 
http://tools.ietf.org/wg/httpbis/agenda?item=agenda-86-httpbis.html

The current documents are in Last Call with no issues unresolved.
http://trac.tools.ietf.org/wg/httpbis/trac/report/20

So if R. David is worried that it will change, we can wait a bit more before taking actions, if we are going the way of removing leading/trailing spaces.