What is client-side validation
Which is better for client-side or server-side validation?
In our situation we use
- jQuery and MVC.
- JSON data to be transferred between our view and the controller.
A lot of my validation consists of validating data as users enter it. For example, I use the event to prevent letters in a text field, to set a maximum number of characters, and to have a number in a range.
I think the better question would be: are there any advantages to server-side validation over client-side?
As others have said, you should do both. Here's why:
You want to check the input on the client side first because you have better feedback for the average user can give. For example, if you enter an invalid email address and move to the next field, you can immediately see an error message. In this way the user can correct any field, before he submits the form.
If you are only validating on the server, you will have to submit the form, get an error message and try to fix the problem.
(This pain can be alleviated by having the server re-render the form using the user's original input, but client-side validation is still faster.)
( This is not theoretical. For example, I've worked on a travel search engine where the user's search was re-sent to many partner airlines, bus companies, etc., sending requests as if the user had filled out each company's search form, then collecting and sorting all the results. These companies' Form JS never ran, and it was vital for us that they provide error messages in the returned HTML. Of course an API would have been nice, but we had to do that. )
Not taking this into account is not only naive for security reasons, it is also not standardized: a client should be allowed to send HTTP by any means desired, and you should react correctly. That includes validation.
Addendum - December 2016
There are some checks which cannot even be done properly in server-side application code and cannot even be done in client-side code as they depend on the current state of the database. For example, “Nobody registered this username” or “The blog post you are commenting on still exists” or “No existing reservation overlaps the details you requested” or “You have enough balance on your account to cover this purchase . " Only the database can reliably validate data that depends on related data. Developers screw this up on a regular basis, but PostgreSQL has some good solutions.
Yes, client-side validation can always be bypassed completely. You need to do both client side for a better user experience and server side to make sure that the input you get is actually validated, not just supposedly validated by the client.
I'll only repeat it because it's pretty important:
Always check on the server
The advantage of server-side validation over client-side validation is that client-side validation can be bypassed / manipulated:
- The data can be sent directly to your server by someone who doesn't even use your website with a custom app designed for it
In short - always validate server-side and then consider client-side validation as an extra "extra" to improve the end-user experience.
you always have to validate on the server.
Validation on the client is also helpful for users, but extremely insecure.
Well I still find room to answer.
In addition to Rob and Nathan's responses, I'd like to add that having client-side validations is important. When applying validations to your web forms, be sure to follow these guidelines:
- Client-side validations must be used to filter real requests from real users on your website.
- Client-side validation should be used to reduce the errors that can occur during server-side processing.
- Client-side validation should be used to minimize server-side round trips so that you save bandwidth and requirements per user.
- You should NOT assume that the validation performed successfully on the client side is 100% perfect. It doesn't matter, even if it serves less than 50 users. You never know which of your users / employees will turn into "evil" and perform malicious activities if you know they don't have the correct validations.
- Even if it's perfect for checking email addresses, phone numbers, or valid entries, it can contain very harmful data. What needs to be filtered on the server side, whether it's right or wrong.
- If client-side validation is bypassed, your server-side validations will save you from possible damage to your server-side processing. We've heard many stories lately about SQL injections and other techniques that could be used to get some nasty benefits.
The client side should use basic validation over HTML5 input types and pattern attributes as these are only used for progressive improvements for better user experience (although not supported in IE9 and Safari but we do not rely on them). However, the main validation should be done on the server side.
I propose a pattern where a validation structure is created on the server and shared with the client.
You need separate validation logic at both ends, e.g.
However, using the same validation specification avoids redundancies (and errors) in mirror validation at both ends.
Client-side data validation can be helpful for a better user experience: for example, a user who types their email address incorrectly shouldn't wait for their request to be processed by a remote server to learn more about the typo they made committed.
Since an attacker can bypass client-side validation (and may not use the browser at all), server-side validation is required and must be the real gateway to protecting your backend from nefarious users.
I came across an interesting connection, the one between differentiates between gross, systematic and random errors.
is perfect for avoiding gross and accidental mistakes. Usually a maximum length for texture and input. Do not imitate the server-side validation rule. Provide your own gross rule of thumb validation rule (e.g. 200 characters on the client side. On the server side dictated by a strong business rule).
is perfect for avoiding systematic errors; it will enforce business rules.
In a project I'm involved in, validation is done on the server using Ajax requests. On the client, I display error messages accordingly.
Further reading: gross, systematic, random errors:
If you are doing light validation, it is best to do it on the client. This will save network traffic, which will help your server perform better. If validation makes it difficult to get data from a database or something like passwords, it is best to do so on the server where the data can be securely verified.
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