Protocol

URI

HTML

HTTP

XML-RPC

Well defined

Complete

Parsable

Available

Protocol Types

Protocol Design Issues

HTTP Message Format

Client Request

Full-Request

Server Response

Request Methods

	CS 580 Client-Server Spring Semester, 2004 Protocols, HTTP & XML-RPC
	Previous Lecture Notes Index Next © 2004, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 09-Mar-04

References
Hypertext Transfer Protocol - HTTP/1.0, Berners-Lee, Fielding, Nielson, rfc1945, http://www.w3.org/Protocols/rfc1945/rfc1945

Hypertext Transfer Protocol -- HTTP/1.1, Fielding, Gettys, Mogul, Masinter, Leach, Berners-Lee, rfc2616, http://www.w3.org/Protocols/rfc2616/rfc2616.html

Uniform Resource Identifiers (URI): Generic Syntax, Berners-Lee, Fielding, Masinter, rfc2396 http://www.ietf.org/rfc/rfc2396.txt

XML-RPC Specification, http://www.xmlrpc.com/spec

Reading
HTTP/1.0 rfc1945, http://ftp.ics.uci.edu/pub/ietf/http/rfc1945.html

Post Office Protocol RFC 1939, http://www.ietf.org/rfc/rfc1939.txt


Doc 18, Protocols, HTTP & XML-RPC Slide # 2

Communication between client and server

Good protocols are hard to design

Requirements for a "good protocol":

Well defined

Complete

Parsable

Extendable

Available protocol document


Doc 18, Protocols, HTTP & XML-RPC Slide # 3

Every bit of data sent in either direction has to have its place in the protocol description.

Protocol is a Language

Common formal description:

BNF and Augmented BNF

Format of the description language needs to be part of the protocol document.

Examples are important


Doc 18, Protocols, HTTP & XML-RPC Slide # 4

The protocol must cover all possible situations.

Garbage data
Old client or server (different protocol versions)
Illegal requests
Boundary conditions
Etc.


Doc 18, Protocols, HTTP & XML-RPC Slide # 5

Both clients and servers are computer programs.

A computer program's IQ is generally 0.

Design goals:

Distinct information packets or messages

Allow parsing independent of semantics

Consistency

Allow for code reuse

Flexibility

For example name-value pairs


Doc 18, Protocols, HTTP & XML-RPC Slide # 6

Different groups may write clients and servers at different times.

Central registry for Internet protocols

Self regulating:

RFC - Request For Comment
IETF - Internet Engineering Task Force

Official:

ISO
ANSI


Doc 18, Protocols, HTTP & XML-RPC Slide # 7

Two basic types

Synchronous
Asynchronous

Typical synchronous

Client sends request to server
Server responds with a reply

Examples

HTTP, POP, SMTP, GOPHER, XMODEM

Typical asynchronous
Client and server both send information to each other concurrently.

Examples

TELNET, RLOGIN, ZMODEM

A hybrid protocol is also possible


Doc 18, Protocols, HTTP & XML-RPC Slide # 8

Protocol design is difficult!

Learn from examples

Some issues

Protocol extendibility and versioning

Byte order used for sending values

ASCII vs. Binary protocol

Easy of debugging
Efficiency

Synchronous vs. Asynchronous

Protocol overhead Roundtrip delays

State

Who is writing, who is reading?

Timeouts

Timeouts vs. Synchronous protocols


Doc 18, Protocols, HTTP & XML-RPC Slide # 9

URI = Uniform Resource Identifiers
URL = Uniform Resource Locator

gopher://gopher.yoyodyne.com/

news:rec.gardening

http://www.yoyodyne.com/pub/foobar.html

http://www.yoyodyne.com/pub/foobar.html?roger

Common Internet Scheme Syntax

URL schemes that involve the direct use of an IP-based protocol to a specified host on the Internet use a common syntax for the scheme-specific data:

//<user>:<password>@<host>:<port>/<url-path>


Doc 18, Protocols, HTTP & XML-RPC Slide # 10

Some Buzz Words
WWW

World Wide Web (or Web, for short)

SGML

Standard Generalized Markup Language
this is a standard for describing markup languages

DTD

Document Type Definition
this is a specific markup language, written using SGML

HTML

HyperText Markup Language
HTML is a SGML DTD.
HTML uses markup tags to tell the Web browser how to display the text

XML

Extensible Markup Language

XHTML

XML + HTML 4.0


Doc 18, Protocols, HTTP & XML-RPC Slide # 11

What is HTML?
HTML is a language for describing structured documents

HTML does not describe page layout

Web browsers use HTML to render & display a document

HTML is content sent by HTTP

<HTML>
<HEAD>
<TITLE>Sample HTML Document</TITLE>
</HEAD>
<BODY>
This is a document
</BODY>
</HTML>
Doc 18, Protocols, HTTP & XML-RPC Slide # 12

Stateless (http 1.0)
Object-oriented protocol

The typing and negotiation of data representation, allows systems to be built independently of the data being transferred

Assigned port 80

Basic Server-Client Interaction (http 1.0)
Client: Open connection

Server: Accept/Reject connection

Client: Send request

Server: Send response to request

Connection closed


Doc 18, Protocols, HTTP & XML-RPC Slide # 13

HTTP-message   =   Simple-Request       (HTTP/0.9 messages)
   | Simple-Response
   | Full-Request               (HTTP/1.0 messages)
   | Full-Response
   
   
Full-Request   =   Request-Line 
   *( General-Header   | Request-Header  | Entity-Header ) 
   CRLF
   [ Entity-Body ]
   
   
Full-Response  =    Status-Line      
   *( General-Header   | Request-Header   | Entity-Header ) 
   CRLF
   [ Entity-Body ]
   
   
HTTP-header   = field-name ":" [ field-value ] CRLF
   
Entity-Body   = *OCTET


Doc 18, Protocols, HTTP & XML-RPC Slide # 14

Request    = Simple-Request | Full-Request
Simple-Request = "GET" SP Request-URI CRLF

Simple-Request Example

rohan 11-> telnet www.eli.sdsu.edu 80
Trying 130.191.226.80...
Connected to www.eli.sdsu.edu.
Escape character is '^]'.
GET /courses/fall00/cs580/index.html
<HTML>
<HEAD>
<TITLE>CS 580: Course Web Site</TITLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF">
<TABLE BORDER=0 WIDTH="100%">
...stuff removed...
</sub>Visitors since 21-Aug-00
</center>
</BODY>
</HTML>
Connection closed by foreign host.


Doc 18, Protocols, HTTP & XML-RPC Slide # 15

Full-Request   =   Request-Line 
   *( General-Header   | Request-Header   | Entity-Header ) 
   CRLF
   [ Entity-Body ]

Request-Line   = Method SP URI SP HTTP-Version CRLF

rohan 13-> telnet www.eli.sdsu.edu 80
Trying 130.191.226.80...
Connected to www.eli.sdsu.edu.
Escape character is '^]'.
GET /courses/fall00/cs580/index.html HTTP/1.0
HTTP/1.1 200 OK
Date: Tue, 05 Sep 2000 19:31:14 GMT
Server: Apache/1.3.9 (Unix) PHP/3.0.12
Last-Modified: Mon, 04 Sep 2000 21:03:56 GMT
ETag: "14c199-7e8-39b40e3c"
Accept-Ranges: bytes
Content-Length: 2024
Connection: close
Content-Type: text/html
X-Pad: avoid browser bug
<HTML>
<HEAD>
<TITLE>CS 580: Course Web Site</TITLE>
</HTML>
... stuff removed here...
Connection closed by foreign host.

Note 2 CRLF are needed to end the full request


Doc 18, Protocols, HTTP & XML-RPC Slide # 16

HTTP 1.1 Example

rohan 14-> telnet www.eli.sdsu.edu 80
Trying 130.191.226.80...
Connected to www.eli.sdsu.edu.
Escape character is '^]'.
GET /courses/fall00/cs580/index.html HTTP/1.1
Connection: close
Host: www.eli.sdsu.edu
HTTP/1.1 200 OK
Date: Tue, 05 Sep 2000 22:41:26 GMT
Server: Apache/1.3.9 (Unix) PHP/3.0.12
Last-Modified: Mon, 04 Sep 2000 21:03:56 GMT
ETag: "14c199-7e8-39b40e3c"
Accept-Ranges: bytes
Content-Length: 2024
Connection: close
Content-Type: text/html
X-Pad: avoid browser bug
<HTML>
<HEAD>
<TITLE>CS 580: Course Web Site</TITLE>
</HEAD>
...stuff removed here...
</BODY>
</HTML>
Connection closed by foreign host.


Doc 18, Protocols, HTTP & XML-RPC Slide # 17

Example Full-response

HTTP/1.0 200 Document follows
MIME-Version: 1.0
Server: CERN/3.0
Date: Thursday, 21-Mar-96 17:00:45 GMT
Content-Type: text/html
Content-Length: 2686
Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

field-name

field-value

MIME-Version:

1.0

Server:

CERN/3.0

Date:

Thursday, 21-Mar-96 17:00:45 GMT

Content-Type:

text/html

Content-Length:

2686

Last-Modified:

Tuesday, 27-Feb-96 05:34:12 GMT


Doc 18, Protocols, HTTP & XML-RPC Slide # 18

What is the big Deal?

What are the data fields in this?

1.0; CERN/3.0; Thursday, 21-Mar-96 17:00:45 GMT; text/html; 2686; Tuesday, 27-Feb-96 05:34:12 GMT

What are the data fields in this?

MIME-Version: 1.0
Server: CERN/3.0
Date: Thursday, 21-Mar-96 17:00:45 GMT
Content-Type: text/html
Content-Length: 2686
Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

Which is Safer?
Which is Easier to Parse?


Doc 18, Protocols, HTTP & XML-RPC Slide # 19

Name -Value Pairs are GoodDoes Order Matter?

MIME-Version: 1.0
Server: CERN/3.0
Date: Thursday, 21-Mar-96 17:00:45 GMT
Content-Type: text/html
Content-Length: 2686
Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

Server: CERN/3.0
Content-Type: text/html
MIME-Version: 1.0
Content-Length: 2686
Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT
Date: Thursday, 21-Mar-96 17:00:45 GMT


Doc 18, Protocols, HTTP & XML-RPC Slide # 20

Extending Protocols

MIME-Version: 1.0
Server: CERN/3.0
Date: Thursday, 21-Mar-96 17:00:45 GMT
Content-Type: text/html
Forwarded: by http://rohan.sdsu.edu/ for cs.sdsu.edu
Content-Length: 2686
WhitneyInfo: Hi Mom
Last-Modified: Tuesday, 27-Feb-96 05:34:12 GMT

Cookies were added to HTTP by adding a new name-value pair

Clients/servers that were not programmed for cookies ignored the new name-value pair


Doc 18, Protocols, HTTP & XML-RPC Slide # 21

Name -Value Pairs are Everywhere
Data Files Which is easier for a program to parse?Which is safer

name

course

hwork

exam1

exam2

final

as1

Allen, Sally

Battista, Joe

Biag, Sam

Chen, Pete

Chen, Roger

lastName:Allen, lastName:Sally, course:87, hwork:92, exam1:85, exam2:55, final:74, as1:10
lastName:Battista, lastName:Joe, course:92, hwork:98, exam1:98, exam2:55, final:78, as1:10
lastName:Baig, lastName:Sam, course:83, hwork:91, exam1:78, exam2:51, final:72, as1:8
lastName:Chen, lastName:Pete, course:89, hwork:92, exam1:89, exam2:57, final:79, as1:10
lastName:Chen, lastName:Roger, course:74, hwork:68, exam1:59, exam2:61, final:55, as1:10


Doc 18, Protocols, HTTP & XML-RPC Slide # 22

Name-Value Pairs and Parameters
Most languages use positional matching for parameters

“The cat in the hat came back”.substring( 2, 6);

Smallktalk uses name-value pairs

 ‘The cat in the hat came back’ copyFrom: 2 to: 6

copyFrom:to: is on method

Keyword (name)	Parameter (value)
copyFrom:	2
to:	6


Doc 18, Protocols, HTTP & XML-RPC Slide # 23

Name -Value Pairs are Your Friends
Don't program without them


Doc 18, Protocols, HTTP & XML-RPC Slide # 24

Big Issue: In-line data
If we send binary data or data of unknown format how does receiver know when the data ends?

POP solution
Use termination sequence

Insure that termination sequence does not occur in data

HTTP Solution

Full-Response  = Status-Line
   *General-Header         
   *Response-Header      
   *Entity-Header      
   CRLF
   [ Entity-Body ]

Send length of data to be sent in header


Doc 18, Protocols, HTTP & XML-RPC Slide # 25

Method         = "GET" | "HEAD" | "PUT" | "POST"
   | "DELETE" | "LINK" | "UNLINK"
   | extension-method

All HTTP/1.0 servers must support GET and HEAD

Servers should return the Status-Code

"501 Not Implemented"

if the method is unknown.

GET
Retrieves whatever item is identified by the URI.

The URI can refer to a data-producing process, or a script

The produced data which shall be returned as the Entity-Body

HEAD
Identical to GET except that the server must not return any Entity-Body in the response


Doc 18, Protocols, HTTP & XML-RPC Slide # 26

POST

Request that the origin server accept the item enclosed in the request as a new subordinate of the resource identified by the URI

Allows a uniform function to:

Annotation of existing documents;

Posting a message to a bulletin board topic, newsgroup, mailing list, or similar group of articles;

Providing a block of data (usually a form) to a data-handling process, or a script, which can be run by such a process;

Extending a document during authorship


Doc 18, Protocols, HTTP & XML-RPC Slide # 27

These are not always supported
Why?

PUT
The enclosed item in the request is to be stored under the supplied URI
DELETE
Requests that the server delete the resource identified by the given URI

LINK
Establishes one or more Link relationships between the existing resource identified by the URI and other existing resources

UNLINK
UNLINK method removes one or more Link relationships from the existing resource identified by the URI


Doc 18, Protocols, HTTP & XML-RPC Slide # 28

Allen, Sally

Battista, Joe

Chen, Pete

Chen, Roger

Requests
Send via HTTP post

User-Agent & Host must be specified

Content-Type is text/xml

Content-Length must be specified and be correct in bytes

Content is in XML and contains single <methodCall>

Example

POST /cs580 HTTP/1.1
Host: rugby.sdsu.edu:8008
Content-length: 158
Content-type: text/xml;charset=iso-8859-1
User-Agent: Smalltalk XMLRPC version 0.5 (VisualWorksÆ NonCommercial, Release 7 of June 14, 2002)
Connection: keep-alive
 
<?xml version="1.0"?><methodCall><methodName>officeDataFor</methodName><params>
   <param><value><string>Whitney</string></value></param>
</params></methodCall>


Doc 18, Protocols, HTTP & XML-RPC Slide # 29

XML in Requests

<methodCall>
   <methodName>[Character]*</methodName>
   <params>
      <param><value>[Legal type]</value></param>*
   </params>
</methodCall>

Characters – string of characters

Legal types

<i4> or <int>
<boolean>
<string>
<double>
<dateTime.iso86021>
<base64>

<struct>
   <member>
      <name>[Character]*</name>
      <value>[Legal type]</value>
   </member>*
</struct>
<array>
   <data>
      <value>[Legal type]</value>
   </data>*
</array>


Doc 18, Protocols, HTTP & XML-RPC Slide # 30

Response
Unless lower-level error always return 200 OK

Content type is text/xml

Content-length must be present and be correct

Body contains on XML structure <methodResponse>

Example

HTTP/1.0 200 OK
Date: Tue, 8 Oct 2002 23:27:43 -0700
Server: VisualWave TinyHTTP/1.0
Mime-version: 1.0
Content-type: text/xml;
Content-length: 252
   
<?xml version="1.0"?><methodResponse><params><param><value><array><data>
   <value><string>Whitney</string></value>
   <value><string>P-243</string></value>
   <value><string>594-3535</string></value>
</data></array></value></param></params></methodResponse>
Doc 18, Protocols, HTTP & XML-RPC Slide # 31

Response XML
Response contains one <methodReponse> tag

The <methodReponse> tag can contain either

<params>
<fault>

<params> tag can only contain one <param>

methodReponse Structure

<?xml version="1.0"?>
<methodResponse>
   <params>
      <param>
         <value>[Legal type]</value>
      </param>
   </params>
</methodResponse>

<?xml version="1.0"?>
<methodResponse>
   <fault>
      <value>[Legal type]</value>
   </fault>
</methodResponse>

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