1 Integration Points: Gateways, Tunnels, and Relays Herng-Yow Chen

2 Outline How gateways interface HTTP with other protocols and applications How application interfaces allow different types of web applications to communicate with one another How tunnels let you send non-HTTP traffic over HTTP connections How relays, a type of simplified HTTP proxy, are used to forward data one hop at a time

3 Why Gateways? client Gateway Database HTTP/ OK NEW product list: … Response message GET /query-db.cgi?newproducts HTTP/1.1 Host: Accept: * Request message Client is requesting:

4 Different types of Gateways Gateway HTTPS client HTTP client Server HTTPFTP HTTPSSL HTTP CGI(or other API) App server Program (c) HTTP/CGI server-side application gateway (b) HTTPS/ HTTP client-side security gateway (A) HTTP/FTP server-side FTP gateway Application server gateway

5 Protocol Gateways (a)MSIE manual proxy settings (b)Navigator manual proxy settings

6 HTTP/*: Server-Side Web Gateways Web server FTP server HTTP client FTP 8080 HTTP/FTP gateway (gw1.joes-hardware.com) GET ftp://ftp.irs.gov/pub/00-index.txt HTTP/1.0 Host: ftp.irs.gov User-agent: SuperBrowser 4.2 HTTP GET HTTP/1.0 Host: User-agent: SuperBrowser 4.2 HTTP ( (ftp.irs.gov)

7 HTTP/*: Server-Side Web Gateways HTTP client HTTP FTP server Port 21 GET ftp://ftp.irs.gov/pub/00-index.txt HTTP/1.0 Host: ftp.irs.gov User-agent: SuperBrowser 4.2 USER anonymous PASS joe CWD /pub TYPE A MDTM 00-index.txt PASV PETR 00-index.txt HTTP/FTP inbound conversion gateway FTP control connection FTP data connection … data … Inbound

8 HTTP/ Security Gateways HTTP client HTTP secure web server HTTP/HTTPS inbound security gateway Port 443 HTTP over SSL(HTTPS) GET HTTP/1.0 Host: User-agent: SuperBrowser 4.2 ……

9 HTTP/ Security Accelerator Gateways Browser HTTP/HTTPS security accelerator gateway …… HTTP over SSL(HTTPS) GET HTTP/1.0 Host: User-agent: SuperBrowser 4.2 HTTP Protected internal LAN

10 Resource Gateways Web camera API E-commerce API Client A Client B $$ $ $ Camera device and software E-commerce application Application server HTTP

11 Common Gateway Interface The first popular API for application gateways was the Common Gateway Interface (CGI). It is a standardized set of interfaces that web servers use to launch programs in response to HTTP requests for special URLs, collect the program output, and send the output back in HTTP response. Over the past years, commercial web servers have provided more sophisticated, efficient interface for the same purpose.

12 CGI Was the first and probably still is the most widely used server extension. Applications Dynamic HTML output, Credit card processing, Query database Can be implemented in almost any language, including Perl, Tcl, C, and various shell languages. Because of its simplicity, almost all HTTP servers support CGI.

13 Server gateway application mechanics Spawned gateway process#1 Spawned gateway process#2 Spawned gateway process#N Request 1 Request 2 Request N Server system Response 1 Response 2 Response N Server process Request Data Response Data Server internal view

14 CGI is wonderful? Yes! It provides a simple, functional form of glue between servers and much type of resource. The interface also is elegant in protecting the server from buggy extensions. NO! This separation incurs a cost in performance. The overhead to spawn a new process for every CGI request is high, limiting the performance of server. New form of CGI- Fast CGI (run as a persistent daemon)

15 Server Extension APIs Allow programmer to graft their own code onto the server, Or completely swap out a component of the server and replace it with their own. Most popular servers provide one or more extension APIs for developers. Most of them are specific to server type, because of its functions tied to server architecture. For example, Microsoft ’ s Frontpage Server Extension (FPSE), which interpret RPC command sent by FrontPage client. Those commands are piggybacked on HTTP (specifically, on POST method).

16 Tunnels Enable access to applications that speak non-HTTP protocols through HTTP applications. Web tunnels are established using HTTP ’ s CONNECT method, which is not part of the core HTTP/1.1, but it is a widely implemented extension.

17 Using CONNECT to establish an SSL tunnel

18 Tunnels let non-HTTP traffic flow through HTTP connections

19 SSL Tunneling

20 Tunnel Authentication

21 Relays client server Blind relay (a)Connection:keep-Alive (b) Server won ’ t close connection when done because It thinks it has been asked to speak keep-alive (c) Connection:Keep Alive (b) Connection:Keep Alive (d) Connection:Keep Alive (c) Relay waits for connection to close ignoring any new requests on the connection (e) Next request (f)Client ’ s second request on the keep-alive connection just hangs because the relay never processes it

22 For More Information RFC 2626 ” Hypertext Transfer Protocol ” by R. Fielding, J. Gettys, J. Mogul,H. Frystyk, L. Masinter, P. Leach, T. Berners- Lee Web Proxy Servers Ari Luotonen,Prentice Hall Computer Books. web-proxy-tunneling-01.txt web-proxy-tunneling-01.txt “ Tunneling TCP based protocols through Web proxy servers ” The Common Gateway Interface-RFC Project Page

23 For More Information W3C-SOAP Version 1.2 Working Draft Programming Web Services with SOAP James Snell,Doug Tidwell,and Pavel Kulchenko,O ’ Reilly & Associates,Inc W3C-Web Services Architecture Requirements Web Services Essentials Ethan Cermai,O ’ Reilly & associates,Inc.