What is the common way to validate user input in programming?
Answers
Answer:
Input validation is the process of testing input received by the application for compliance against a standard defined within the application. It can be as simple as strictly typing a parameter and as complex as using regular expressions or business logic to validate input. There are two different types of input validation approaches: whitelist validation (sometimes referred to as inclusion or positive validation) and blacklist validation (sometimes known as exclusion or negative validation). These two approaches, and examples of validating input in Java, C#, and PHP to prevent SQL injection, are detailed in the following subsections.
When performing input validation you should always ensure that the input is in its canonical (simplest) form before making any input validation decisions. This may involve decoding the input into a simpler format, or just rejecting input that isn't already in canonical format where non-canonical input isn't expected. We'll cover canonicalization in a separate solution later in this chapter.
Whitelisting
Whitelist validation is the practice of only accepting input that is known to be good. This can involve validating compliance with the expected type, length or size, numeric range, or other format standards before accepting the input for further processing. For example, validating that an input value is a credit card number may involve validating that the input value contains only numbers, is between 13 and 16 digits long, and passes the business logic check of correctly passing the Luhn formula (the formula for calculating the validity of a number based on the last “check” digit of the card).
When using whitelist validation you should consider the following points:
▪
Data type Is the data type correct? If the value is supposed to be numeric, is it numeric? If it is supposed to be a positive number, is it a negative number instead?
▪
Data size If the data is a string, is it of the correct length? Is it less than the expected maximum length? If it is a binary blob, is it less than the maximum expected size? If it is numeric, is it of the correct size or accuracy? (For example, if an integer is expected, is the number that is passed too large to be an integer value?)
▪
Data range If the data is numeric, is it in the expected numeric range for this type of data?
▪
Data content Does the data look like the expected type of data? For example, does it satisfy the expected properties of a ZIP Code if it is supposed to be a ZIP Code? Does it contain only the expected character set for the data type expected? If a name value is submitted, only some punctuation (single quotes and character accents) would normally be expected, and other characters, such as the less than sign (<), would not be expected.
A common method of implementing content validation is to use regular expressions. Following is a simple example of a regular expression for validating a U.S. ZIP Code contained in a string:
^\d{5}(-\d{4})?$
In this case, the regular expression matches both five-digit and five-digit + four-digit ZIP Codes as follows:
▪
^\d{5} Match exactly five numeric digits at the start of the string.
▪
(–\d{4})? Match the dash character plus exactly four digits either once (present) or not at all (not present).
▪
$ This would appear at the end of the string. If there is additional content at the end of the string, the regular expression will not match.
. mark me as brainlist pls pls pls pls pls pls pls pls pls pls pls pls pls pls