A) validating username in php
as part of a registration form a user fills there desired username and this
is stored in a mysql. there are certain conditions for the username.
a) the username should only begin either letters or numbers, and Underscore
character
example = user123, 123user, u_ser123, user_123 = completely case insensitive
b) a user may choose not to have an underscore or numbers sometimes. example
= username
presently my validation for username is
$username = $_POST["username"];
if( $username == "" || !eregi("^[a-zA-Z0-9_]+$", $username) )
{
$error.="User name cannot be blank or has special characters";
}
Question = how can i rewrite this php validation for username to meet the
above criteria or is my validation correct
B) preventing sql injection
till now i have been capturing the form values and directly inserting into
the table without considering sql injection however for this project as it
is for a forum i would like to implement prevention of sql injection. from
what i have read about preventing sql injection there are several steps that
need to be followed,
htmlentities
addslashes
trim
mysql-real-escape-string
magic_quotes_gpc is ON
magic_quotes_runtime is OFF
magic_quotes_sybase is OFF
as i have not done preventing sql injection i am not sure what is the
correct process.
Question =
a) please advice a step by step process of how to go about avoiding the sql
injection before the insert sql query is executed starting from
$username = $_POST["username"]; till the
insert into tablename(field1, field2) values($value1, $value2) SQL query is
executed which will prevent sql injection even if the user enters any
special characters while filling the form.
b) should i consider the setting of magic quotes as in should it be ON or
OFF or should i ignore it if so should it be
ON or OFF
c) also with the prevention methods if a user types a special character in
the data will that character be written in the table as a escaped character
or how does it store those special characters
d) a very important point here, i have a feature where a user can check if a
username is available or not. so while storing a username if the username is
stored as john\smith in mysql and if the user is searching for johnsmith
this would not match, so even in the table the username should be stored
without slashes as i have to read the username and compare with what the
user has typed to see if they both are same or different.
please advice if i have missed any other steps to prevent sql injection.
thanks a lot for your help.
