4 User form

A user form is something that is very commonly used when developing web applications. It provides the ability to communicate between clients and servers. You must be very familiar with forms if you are a web developer; if you are a C/C++ programmer, you may want to ask: what is a user form?

A form is an area that contains form elements. Users can input information into form elements like text boxes, drop down lists, radio buttons, check boxes, etc. We use the form tag <form> to define forms.

<form>
...
input elements
...
</form>

Go already has many convenient functions to deal with user forms. You can easily get form data in HTTP requests, and they are easy to integrate into your own web applications. In section 4.1, we are going to talk about how to handle form data in Go. Also, since you cannot trust any data coming from the client side, you must first validate the data before using it. We'll go through some examples about how to validate form data in section 4.2.

We say that HTTP is stateless. How can we identify that certain forms are from the same user? And how do we make sure that one form can only be submitted once? We'll look at some details concerning cookies (a cookie is information that can be saved on the client side and added to the request header when the request is sent to the server) in both sections 4.3 and 4.4.

Another common use-case for forms is uploading files. In section 4.5, you will learn how to do this as well as controlling the file upload size before it begins uploading, in Go.

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