I think I found the cause of the error; the error was in
declare-uri-header! That was not a encoding problem.

http://www.gnu.org/home.html will send Content-Location header and it is
home.en.html if your Accept-Language is en-US. Yes!! This is a relativeURI.

Location is absolute URI but Content-Location and Referer may be relative
URI or absolute URI. Current declare-uri-header! can do only absolute URI
because string->uri returns false value whenever not absolute URI!!

2012/4/26 Sunjoong Lee <sunjoong@gmail.com>
>
> (use-modules ((srfi srfi-11) #:select (let-values))
>              ((web uri)      #:select (string->uri))
>              ((web client)   #:select (http-get)))
> (let-values (((res-headers res-body)
>               (http-get (string->uri "http://www.gnu.org/home.html")
>                         #:extra-headers
>                         (acons 'Accept "text/html"
>                                (acons 'Accept-Charset "ISO-8859-1"
>                                       (acons 'Accept-Language "en-US"
>                                              '()))))))
>   (display res-body)
>   (newline))
>
> Above code makes an error:
>   ...
>   In web/response.scm:
>    187: 2 [read-response #<input-output: socket 5>]
>   In web/http.scm:
>    218: 1 [lp ((server . "Apache/2.2.14") (date . #))]
>    184: 0 [read-header #<input-output: socket 5>]
>