Let Resolver#send_tcp take a block

This solves the looping problem. Since the TCP connection wouldn't
necessarily close, we couldn't count on a 0-length recv, and the
connection was timing out. Changed it so send_tcp can take a block, in
which we do parsing. AXFR responses are sandwiched between SOA answers,
so when the second one is reached, the transfer is done.

This is also cleaner for existing code that uses send_tcp, since if no
block is passed, it just returns the first response and tears down the
connection, just like it used to.

lib/net/dns/resolver.rb

@@ -1019,27 +1019,29 @@ module Net # :nodoc:
 		  method = :send_tcp
 		end
 
-        ans = self.old_send(method, packet, packet_data)
+        answers = []
+        soa = 0
+        self.old_send(method, packet, packet_data) do |ans|
+          @logger.info "Received #{ans[0].size} bytes from #{ans[1][2]+":"+ans[1][1].to_s}"
 
-        unless ans
+          begin
+            response = Net::DNS::Packet.parse(ans[0],ans[1])
+            if response.answer[0].type == "SOA"
+              soa += 1
+              if soa >= 2
+                break
+              end
+            end
+            answers << response
+          rescue NameError => e
+            @logger.warn "Error parsing axfr response: #{e.message}"
+          end
+        end
+        if answers.empty?
           @logger.fatal "No response from nameservers list: aborting"
           raise NoResponseError
         end
 
-        @logger.info "Received #{ans[0].size} bytes from #{ans[1][2]+":"+ans[1][1].to_s}"
-
-        pos = 0
-        begin
-          while pos < buffer.size
-            len = buffer.unpack("n")[0]
-            response = Net::DNS::Packet.parse(ans[0][pos,len],ans[1])
-            pos += len
-            answers << response
-          end
-        rescue NameError => e
-          @logger.warn "Error parsing axfr response: #{e.message}"
-        end
-
         return answers
       end
 
@@ -1166,21 +1168,22 @@ module Net # :nodoc:
 
             @config[:tcp_timeout].timeout do
               catch "next nameserver" do
-                buffer = ""
                 socket.connect(sockaddr)
                 @logger.info "Contacting nameserver #{ns} port #{@config[:port]}"
                 socket.write(length+packet_data)
+                got_something = false
                 loop do
-                  ansbuf = ""
+                  buffer = ""
                   ans = socket.recv(Net::DNS::INT16SZ)
                   if ans.size == 0
-                    if buffer.size > 0
+                    if got_something
                       break #Proper exit from loop
                     else
-                      @logger.warn "Connection reset to namserver #{ns}, trying next."
+                      @logger.warn "Connection reset to nameserver #{ns}, trying next."
                       throw "next nameserver"
                     end
                   end
+                  got_something = true
                   len = ans.unpack("n")[0]
 
                   @logger.info "Receiving #{len} bytes..."
@@ -1190,20 +1193,23 @@ module Net # :nodoc:
                     throw "next nameserver"
                   end
 
-                  while (ansbuf.size < len)
-                    left = len - ansbuf.size
+                  while (buffer.size < len)
+                    left = len - buffer.size
                     temp,from = socket.recvfrom(left)
-                    ansbuf += temp
+                    buffer += temp
                   end
 
-                  unless ansbuf.size == len
+                  unless buffer.size == len
                     @logger.warn "Malformed packet from nameserver #{ns}, trying next."
                     throw "next nameserver"
                   end
-                  buffer += ansbuf
+                  if block_given?
+                    yield [buffer,["",@config[:port],ns.to_s,ns.to_s]]
+                  else
+                    return [buffer,["",@config[:port],ns.to_s,ns.to_s]]
+                  end
                 end
               end
-              return [buffer,["",@config[:port],ns.to_s,ns.to_s]]
             end
           rescue Timeout::Error
             @logger.warn "Nameserver #{ns} not responding within TCP timeout, trying next one"
@@ -1212,6 +1218,7 @@ module Net # :nodoc:
             socket.close
           end
         end
+        return nil
       end
 
       def send_udp(packet,packet_data)