web programming basics(Web programming basics).ppt

23-Jul-24 Advanced Programming
Spring 2002
Web programming
Henning Schulzrinne
Dept. of Computer Science
Columbia University

Spring 2002
2
Web programming
 Web services vs. "classical" web
programming
 Client vs. server programming
 client: JavaScript, Java
 HTML-centric vs. program-centric
 HTML-centric: PHP, ASP
 cgi, fast-cgi
 (Java) servlet
 data model: Java servlet, database

Spring 2002
3
Web services vs. web
programming
 web services = remote procedure call
 we saw SOAP
 structured data (XML)
 methods and responses
 generally, for machine consumption
 web programming  generate HTML pages
 for humans
 often, database-driven
 replacement for IBM 3270 terminals ...

Spring 2002
4
Client vs. server
programming
 Execute code on client:
 download Java applet  self-contained
programming environment
 JavaScript (aka ECMAscript):
 modify and get values from HTML ("document
object model" – DOM)
 Execute code on server  generate
document
 state maintenance (HTTP stateless)
 login, shopping cart, preferences

Spring 2002
5
Taxonomy
embedded in HTML separate
server SSI, ASP, PHP, JSP,
CFM
server API (NSAPI),
cgi, servlets
client JavaScript Java applets, plug-in

Spring 2002
6
Example: JavaScript –
cookies
var expires = new Date()
var today = new Date()
function setCookie(name, value, hours) {
var expire = new Date();
expire.setTime (expire.getTime() + (1000 * 60 * 60 *
hours));
document.cookie = name + "=" + escape(value)
+ ((expire == null) ? "" : ("; expires=" +
expire.toGMTString()))
}
function unsetCookie(name) {
var exp = new Date();
exp.setTime(today.getTime() - 10);
document.cookie = name + "=" + "; expires=" +
exp.toGMTString()
}
expires.setTime(today.getTime() + 86400*365)

Spring 2002
7
JavaScript – DOM
function tz (f,v) {
var t = -1;
switch (f[v].value) {
case "US": t=128; break;
case "CI": t=0; break;
case "GH": t=1; break;
..
}
if (t != -1) {
f.form.timezone.options[t].selected = true
}
}

Spring 2002
8
Web as RPC
 request = HTTP GET, PUT
 response (result): headers + body
 object identifier ~ URL
 typed data (XML) vs. HTML
 from constant  mostly constant 
completely on-demand

Spring 2002
9
Server-side include
 .shtml documents (or configured by default
for all .html documents)
 include in HMTL/XML comments
<!-- #element attribute=value
attribute=value ... -- >
 limited scripting: if/else, include, exec,
variables
 primarily for conditional inclusion, boilerplate
 security issues: exec

Spring 2002
10
SSI example
 Columbia CS home page
<html>
<head><TITLE>Computer Science: Welcome </TITLE>
<script language=javascript>
var section = "home";
var subsection = "home";
var subsectionID = "-1";
</script>
</head>



</tr> </table>

</html>

Spring 2002
11
SSI Example
<body>
<h1>SSI Test</h1>
The document was last modified on
<!-- #flastmod file="$DOCUMENT_NAME" 
and has <!-- #fsize
file="$DOCUMENT_NAME" -- > bytes.
<h2>Environment</h2>
<!-- #printenv 
</pre>

Spring 2002
12
Common gateway interface
(cgi)
 Earliest attempt at dynamic web content
 language-independent
 passes HTTP request information via
 command line (ISINDEX) – rarely used
 environment variables: system info + query string
(GET)
 request body (POST)  standard input
 return HTML or XML via standard output
 non-parsed headers (NPH) return complete
response

Spring 2002
13
cgi arguments
 application/x-www-form-urlencoded
format
 space characters  "+"
 escape (%xx) reserved characters
 name=value pairs separated by &
 GET:
foo.cgi?name=John+Doe&gender=male&family=5&city=kent
&city=miami&other=abc%0D%0Adef&nickname=J%26D
 POST: include in body of message

Spring 2002
14
cgi forms
 single form per submission
<form action=scripturi method=GET|POST>
form fields:
<input type="text" name="text1" size=10
maxlength=15 value="Initial text">
<input type="hidden" name="state"
value="secret">
<input type=radio name=radio value=WNYC
checked>
<input type=radio name=radio value=KQED>
<input type=submit value="Submit">

Spring 2002
15
Web state
 State:
 stateless
 state completely stored on client
 state referenced by client, stored on server
(most common)
 Mechanisms:
 hidden form fields
 URL parameters
 cookies (HTTP headers)

Spring 2002
16
cgi mechanics
 either called .cgi in HTML directory or
stored in cgi-bin
 in CS, both /home/alice/html/foo.cgi or
/home/alice/secure_html/foo.cgi work
 executable (script file)
 runs as nobody or as owning user
(~user/mycgi.cgi)
 store secret data off the document tree!

Spring 2002
17
SQL interface
 Most common web model:
 cgi script (or Java servlet) accesses
database
 database via TCP connection (ODBC, JDBC,
script)
 n-tier model:
 delegate "business logic" to RPC-based
server
 XML-based model:
 generate XML, render via XSLT

Spring 2002
18
Tcl cgi example
set env(LD_LIBRARY_PATH) /home/hgs/sun5/lib
load $env(LD_LIBRARY_PATH)/libfbsql.so
lappend auto_path /home/hgs/html/edas3
lappend auto_path /home/hgs/lib
package require cgi
cgi_debug –on
cgi_eval {
sql connect dbhost.columbia.edu dbuser secret
cgi_body {
...
}
sql disconnect
}

web programming basics(Web programming basics).ppt

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