How to read a file character by character in Go

Just read each rune one by one in the loop... See example

package main

import (
    "bufio"
    "fmt"
    "io"
    "log"
    "strings"
)

var text = `
The quick brown fox jumps over the lazy dog #1.
Быстрая коричневая лиса перепрыгнула через ленивую собаку.
`

func main() {
    r := bufio.NewReader(strings.NewReader(text))
    for {
        if c, sz, err := r.ReadRune(); err != nil {
            if err == io.EOF {
                break
            } else {
                log.Fatal(err)
            }
        } else {
            fmt.Printf("%q [%d]\n", string(c), sz)
        }
    }
}

This code reads runes from the input. No cast is necessary, and it is iterator-like:

package main

import (
    "bufio"
    "fmt"
    "strings"
)

func main() {
    in := `{"sample":"json string"}`

    s := bufio.NewScanner(strings.NewReader(in))
    s.Split(bufio.ScanRunes)

    for s.Scan() {
        fmt.Println(s.Text())
    }
}