verify Go os.File.Read returns 0, io.EOF at end of file.

main.go

package main

import (
	"io"
	"log"
	"os"
)

func main() {
	if err := run(); err != nil {
		log.Fatal(err)
	}
}

func run() error {
	const filename = "hello.txt"
	if err := os.WriteFile(filename, []byte("hello"), os.FileMode(0o600)); err != nil {
		return err
	}
	defer os.Remove(filename)

	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	var buf [4]byte
	for {
		n, err := file.Read(buf[:])
		log.Printf("n=%d, err=%v", n, err)
		if err == io.EOF {
			break
		}
		if err != nil {
			return err
		}
	}

	return nil
}

https://pkg.go.dev/os@go1.20.4#File.Read

$ go version
go version go1.20.4 linux/amd64
$ go run .
2023/05/04 08:05:42 n=4, err=<nil>
2023/05/04 08:05:42 n=1, err=<nil>
2023/05/04 08:05:42 n=0, err=EOF