Advanced Web Programming

1
Advanced Web Programming

• CGI
• Imagemaps
• Frames

2
CGICommon Gateway Interface

• CGI programming allows us to run arbitrary
  programs at the server, with input provided by a
  FORM which is displayed at the client.
• Two Types of FORMs, GET and POST
• GET - parameters sent additions to URL string.
  Each individual parameter separated by
• POST - Data sent in message body. This is
  slightly more general

3
CGI Processing

• Server sends form to client
• Client displays form, and users fills in fields
• Client sends form info to server
• Server runs the CGI program named in the ACTION
  section of the FORM..
• CGI program parses data as input
• Output of CGI program is sent by the server to
  the client (i.e. it should be HTML)

4
CGI Advantages and Disadvantages

• Advantages
• Very general model, easy to do really neat things
  like front end existing applications, databases
  etc.
• Many toolkits available to do common things
• Disadvantages
• All processing is done on server. May overload
  server

5
Writing a CGI Program

• CGI program needs to
• Parse form input
• Process the input
• Generate html output
• Example
• CGI program to collect info and add it to a file
• Password protected

6
CGI Example

• Adds links to a file of students in a class
• Password Protected
• Steps
• Parse data (POST form)
• Check Password
• Add info (in html format) to end of roster

7

• include ltstdio.hgt
• ifndef NO_STDLIB_H
• include ltstdlib.hgt
• else
• char getenv()
• endif
• define MAX_ENTRIES 10000
• typedef struct
• char name
• char val
• entry
• char makeword(char line, char stop)
• char fmakeword(FILE f, char stop, int len)
• char x2c(char what)
• void unescape_url(char url)

8
void unescape_url(char url) void
plustospace(char str) main(int argc, char
argv) entry entriesMAX_ENTRIES
register int x,m0 int cl int PASS
FILE fp printf("Content-type
text/htmlcc",10,10) if(strcmp(getenv("REQU
EST_METHOD"),"POST")) printf("This
script should be referenced with a METHOD of
POST.\n") printf("If you don't
understand this, see this ") printf("ltA
HREF\"http//www.ncsa.uiuc.edu/SDG/Software/Mosai
c/Docs/fil\ l-out-forms/overview.html\"gtforms
overviewlt/Agt.c",10) exit(1)
if(strcmp(getenv("CONTENT_TYPE"),"application/x-ww
w-form-urlencoded")) printf("This
script can only be used to decode form results.
\n")
9
if(strcmp(getenv("CONTENT_TYPE"),"application/x-ww
w-form-urlencoded")) printf("This
script can only be used to decode form results.
\n") exit(1) cl
atoi(getenv("CONTENT_LENGTH")) PASS 0
for(x0cl (!feof(stdin))x) mx
entriesx.val fmakeword(stdin,'',cl)
plustospace(entriesx.val)
unescape_url(entriesx.val)
entriesx.name makeword(entriesx.val,'')
/ Check here for passwd field Z /
if (entriesx.name'p') if
(strcmp(entriesx.val,"MDSS") 0) PASS 1
if (PASS 1) if ((fp
fopen("/class/nwhite/b3146/roster.html","a"))
NULL) PASS3 printf("lth1gt
unable to open output file, tell Professor
Whitelt/h1gt")
10
NULL) PASS3 printf("lth1gt unable
to open output file, tell Professor
Whitelt/h1gt")
else fprintf(fp,"ltA href\"http//www.stern
.nyu.edu/s\" gt Home Page for s \n \ lt/agt",
entries0.val,entries2.val)
fprintf(fp,"ltpgtlth3gtWhy you might want to visit
the homepage for s ... lt/h3\ gt\n ltpgt",
entries2.val) fprintf(fp,"s
ltpgt",entries3.val) fprintf(fp,"ltpgtlthrgtlthrgtlt
pgt") printf(" Link successfully added
\n") printf("lta href\"http//www.stern.nyu.
edu/nwhite/class/b3146/roster.html\ \"gt
ltbgtClick here to see the updated rosterlt/bgt
lt/agt") if (PASS ! 1)
printf("ltH1gt INVALID PASSWORD, See Professor
White lt/H1gt") -----Emacs addlinkm.c
(C)----Bot--------------------------
11
Frames

• Frames are new in Netscape 2.0
• The allow the developer to display multiple
  windows at a time instead of just one. Each
  window will contain a the output from a different
  URL.
• Very powerful if used with JAVA or JavaScript
  (Now can have separate programs running in each
  Window).

12
Spiders and Robots

• Since the HTTP protocol is text based, it is
  relatively easy to write programs that cruise
  the WEB collecting information.
• Examples
• Indexing programs - continually request URLs,
  index the documents, follow the links of the
  indexed documents and index them etc.
• Smartmarks - watches URLs and notifies user
  when they change.