How to remove redundant spaces/whitespace from a string in Golang?

You can get quite far just using the strings package as strings.Fields does most of the work for you:

package main

import (
    "fmt"
    "strings"
)

func standardizeSpaces(s string) string {
    return strings.Join(strings.Fields(s), " ")
}

func main() {
    tests := []string{" Hello,   World  ! ", "Hello,\tWorld ! ", " \t\n\t Hello,\tWorld\n!\n\t"}
    for _, test := range tests {
        fmt.Println(standardizeSpaces(test))
    }
}
// "Hello, World !"
// "Hello, World !"
// "Hello, World !"