refactor: move from io/ioutil to io and os package

[Juneezee]

Overview

The io/ioutil package has been deprecated in Go 1.16 (See https://golang.org/doc/go1.16#ioutil). This PR replaces the existing io/ioutil functions with their new definitions in io and os packages.

What this PR does / why we need it

The io/ioutil package has turned out to be a poorly defined and hard to understand collection of things. -- https://golang.org/doc/go1.16#ioutil

Avoid meaningless package names. Packages named util, common, or misc provide clients with no sense of what the package contains. -- https://go.dev/blog/package-names

The Golang team has decided to deprecate the io/ioutil package and recommends new code to use the new definitions. To avoid inconsistency in the future, it is a good idea to move all current usage of io/ioutil functions to the new definitions.

Special notes for your reviewer

No breaking changes.

Does this PR introduce a user-facing change?

NONE

[nabokihms]

Good catch, thanks!

I think that to consolidate what you have done there, we need to setup a depguard linter to prevent others from using the ioutil package.

It is possible by adding the following block to the .golangci.yml in the repo root:

linters-settings:
  depguard:
    list-type: blacklist
    include-go-root: true
    packages:
    - io/ioutil
    packages-with-error-message:
    - io/ioutil: "The 'io/ioutil' package is deprecated. Use corresponding 'os' or 'io' functions instead."

and enabling the depguard linter.

[Juneezee]

@nabokihms Hi! Thanks for reviewing the pull request. I have added the depguard linter. Please take a look again. Thanks

[nabokihms]

You should also enable the depguard linter in the linters.enable section (it is commented right now).

[Juneezee]

@nabokihms Sorry, my bad. depguard should be enabled now.

[sagikazarmark]

LGTM, thanks!