returns a list of encodings in Content-Encoding field as an Array of String. The
encodings are downcased for canonicalization.
# File lib/open-uri.rb, line 514
def content_encoding
v = @meta['content-encoding']
if v && %{\A#{RE_LWS}?#{RE_TOKEN}#{RE_LWS}?(?:,#{RE_LWS}?#{RE_TOKEN}#{RE_LWS}?)*} =~ v
v.scan(RE_TOKEN).map {|content_coding| content_coding.downcase}
else
[]
end
end