server side scripting - homepages.math.uic.eduhomepages.math.uic.edu/~jan/mcs275/servscript.pdf ·...

Server Side Scripting

1 a simple Web Calculator

the web interface

html form and Python script

2 A Login Form

the web interface


3 Passing Text and Code

textarea element

running given Python code

MCS 275 Lecture 22

Programming Tools and File Management

Jan Verschelde, 1 March 2017

Programming Tools (MCS 275) server side scripting L-22 1 March 2017 1 / 30

Server-Side Scripting


the web interface


2 A Login Form

the web interface



textarea element



The Web Interfacefor a simple calculator

1 two input elements for two operands

2 select element for the operator

3 checkbox for converting operands to float

4 submit and reset buttons


Result of the Calculationoutput of Python script

Python script writes result inside an h1 header.




the web interface


2 A Login Form

the web interface



textarea element



html form for calculator

<html>

<head>

<title> MCS 275 : a calculator </title>

</head>

<body>

<form method="post"

action="http://localhost/cgi-bin/calculate.py">

<table width = "100%" border = "3">

<tr>

<th> 1st operand </th>

<th> operator </th>

<th> 2nd operand </th>

</tr>

...


html form continued

the table continued:

<tr>

<td><input type = "text"

name = "operand1" size="45%"></td>

<td><select name = "operator">

<option value = "+">+

<option value = "-">-

<option value = "*">*<option value = "/">/

</td>

<td><input type = "text"

name = "operand2" size="45%"></td>

</table>


a Checkbox – html form continued

<p>

<input name = "convert" type = checkbox

value = True>

convert operands to floats

<input type="submit"

value = "submit calculation">

<input type="reset"

value = "reset the form">

</p>

</form>

</body>

</html>


Python script calculate.py

#!/usr/bin/python

import cgi

FORM = cgi.FieldStorage()

print("Content-Type: text/html\n")

ERROR = False

try:

XVAL = FORM[’operand1’].value

except KeyError:

print("please enter first operand")

ERROR = True

try:

YVAL = FORM[’operand2’].value

except KeyError:

print("please enter second operand")

ERROR = True


the script continued

if not ERROR:

try:

CONV = eval(FORM[’convert’].value)

except:

CONV = False

OPER = FORM[’operator’].value

if not CONV:

EXPR = XVAL + ’ ’ + OPER + ’ ’ + YVAL

else:

EXPR = str(float(XVAL)) + ’ ’ + OPER \

+ ’ ’ + str(float(YVAL))

RESULT = EXPR + ’ = ’ + str(eval(EXPR))

print("<html><body>")

print("<h1>%s</h1>" % RESULT)

print("</body></html>")




the web interface


2 A Login Form

the web interface



textarea element



The Web Interface

1 two input elements for name and password2 radio button for new or returning user


Result of the Submitaction by Python script login_form.py

Python script checks whether new or returning user

and confirms the name.




the web interface


2 A Login Form

the web interface



textarea element



html form in the file login_form.html

<html>

<head>

<title> MCS 275 : login form </title>

</head>

<body>

<h1> please register </h1>

<form

action="http://localhost/cgi-bin/login_form.py">

<p>

enter your name:

<input type="text" name="login" size ="20">

</p>


a radio button – html continued

<input type="radio" name="new"

value = True checked> new user

<input type="radio" name="new"

value = False> returning user

<p> enter your password:

<input type="password"

name="password" size ="16">

</p>

<p> <input type="submit">

<input type="reset">

</p>

</body>

</html>


the Python script in the file login_form.py

#!/usr/bin/python

"""

Gets login name and password.

"""

from ast import literal_eval

import cgi


print("Content-Type: text/plain\n")

ERROR = False

try:

NAME = FORM[’login’].value

except KeyError:

print("please enter your name")

ERROR = True


script continued

try:

WORD = FORM[’password’].value

except KeyError:

print("please enter a password")

ERROR = True

if not ERROR:

if literal_eval(FORM[’new’].value):

print(’welcome new user ’ + NAME)

else:

print(’welcome back ’ + NAME)

For new user, check if name does not already exist.

If okay, add to name and password file.

For returning user, check if name already exists on file.

If okay, check if password matches.




the web interface


2 A Login Form

the web interface



textarea element



The Web Interfacefor submitting a text paragraph


Result of the Submitoutput of Python script


the element textarea in give_words.html

<html>

<head>

<title> MCS 275 : enter some text </title>

</head>

<body>

<h1> write a paragraph </h1>

<form method="post"

action="http://localhost/cgi-bin/give_words.py">

<p>

<textarea name = "sometext"

rows = 4 cols = 20></textarea>

</p>

<p>

<input type="submit"> <input type="reset">

</p>

</form>

</body>

</html>


getting the textarea in give_words.py

#!/usr/bin/python

"""

Illustration of processing a textarea.

"""

import cgi



try:

TEXT = FORM[’sometext’].value

print("your paragraph is \n" + TEXT)

except KeyError:

print("please enter some words")




the web interface


2 A Login Form

the web interface



textarea element



The Web Interfacefor submitting Python code


Result of the Submitoutput of Python script


accepting Python code in run_python.html

<html>

<head>

<title> MCS 275 : run python </title>

</head>

<body>

<h1> run python </h1>

<form method="post"

action="http://localhost/cgi-bin/run_python.py">

give some Python code below:

<p>

<textarea name = "code"

rows = 4 cols = 20></textarea>

</p>

<p> <input type="submit"> <input type="reset">

</p>

</form> </body> </html>


getting the Python code in run_python.py

#!/usr/bin/python

"""

Takes the textarea from run_python.html

and runs the code in that element.

"""

import cgi

from os import system



ERROR = False

try:

CODE = FORM[’code’].value

print("your code is \n\n" + CODE)

except KeyError:

print("please enter code")

ERROR = True


running the Python code – script continued

if not ERROR:

FILE = open(’/tmp/code.py’, ’w’)

FILE.write(CODE)

FILE.close()

print("\n... running the code ...\n")

CMD = ’python /tmp/code.py > /tmp/out’

RETVAL = system(CMD)

if RETVAL != 0:

print("the code has an error")

else:

FILE = open(’/tmp/out’, ’r’)

OUTP = FILE.readlines()

print("the output is \n\n", OUTP[0])


Summary and Exercises

Because of security issues, keep working offline.

1 Modify the script give_words.py so it writes the words typed in

the textarea in reverse order.

2 Replace the radio buttons in login_form.html by one

CheckBox "new user".

3 Add to login_form.html a select element offering the options:

instructor, student, and staff.

4 Extend the script login_form.py so it maintains a password

file. For every user there is one line: two strings (name and

password) separated by a colon.


server side scripting - homepages.math.uic.eduhomepages.math.uic.edu/~jan/mcs275/servscript.pdf ·...

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