proxy_pass: allow filtering or overriding response headers

We shouldn't blindly pass the "Server" tag through, since we may
be proxying Apache instances and we don't want to misadvertise,
either.

IMHO, it is best to say nothing at all to save bandwidth and
reduce the potential for attackers in case a vulnerability is
discovered in yahns.

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/yahns/proxy_http_response.rb b/lib/yahns/proxy_http_response.rb
index 90a9395..cbdce6f 100644
--- a/lib/yahns/proxy_http_response.rb
+++ b/lib/yahns/proxy_http_response.rb
@@ -66,6 +66,7 @@ module Yahns::HttpResponse # :nodoc:
                 env[REQUEST_METHOD] != HEAD
     flags = MSG_DONTWAIT
     alive = @hs.next? && self.class.persistent_connections
+    response_headers = env['yahns.proxy_pass.response_headers']
 
     res = "HTTP/1.1 #{status}\r\n"
     headers.each do |key,value| # n.b.: headers is an Array of 2-element Arrays
@@ -76,6 +77,14 @@ module Yahns::HttpResponse # :nodoc:
         flags |= MSG_MORE if have_body && value.to_i > 0
       end
 
+      # response header mapping
+      case val = response_headers[key]
+      when :ignore
+        next
+      when String
+        value = val
+      end
+
       res << "#{key}: #{value}\r\n"
     end