Best Way to Upload Array of Files?

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I have a form that will let a user upload one or more files. The number will always be different because they will be able to add another file input by clicking on a submit button. This will add another input field called "file[]" and will output an array of files. What's the best way to upload an array of files?

PS: A feature should be added to CI that will give the ability to upload an array of files.