How to copy a directory tree (preserving permissions) in Go.

copytree.go

package main

import "fmt"
import "os"
import "io"
import "io/ioutil"
import "log"

// Copies file source to destination dest.
func CopyFile(source string, dest string) (err error) {
    sf, err := os.Open(source)
    if err != nil {
        return err
    }
    defer sf.Close()
    df, err := os.Create(dest)
    if err != nil {
        return err
    }
    defer df.Close()
    _, err = io.Copy(df, sf)
    if err == nil {
        si, err := os.Stat(source)
        if err != nil {
            err = os.Chmod(dest, si.Mode())
        }

    }

    return
}

// Recursively copies a directory tree, attempting to preserve permissions. 
// Source directory must exist, destination directory must *not* exist. 
func CopyDir(source string, dest string) (err error) {

    // get properties of source dir
    fi, err := os.Stat(source)
    if err != nil {
        return err
    }

    if !fi.IsDir() {
        return &CustomError{"Source is not a directory"}
    }

    // ensure dest dir does not already exist

    _, err = os.Open(dest)
    if !os.IsNotExist(err) {
        return &CustomError{"Destination already exists"}
    }

    // create dest dir

    err = os.MkdirAll(dest, fi.Mode())
    if err != nil {
        return err
    }

    entries, err := ioutil.ReadDir(source)

    for _, entry := range entries {

        sfp := source + "/" + entry.Name()
        dfp := dest + "/" + entry.Name()
        if entry.IsDir() {
            err = CopyDir(sfp, dfp)
            if err != nil {
                log.Println(err)
            }
        } else {
            // perform copy         
            err = CopyFile(sfp, dfp)
            if err != nil {
                log.Println(err)
            }
        }

    }
    return
}

// A struct for returning custom error messages
type CustomError struct {
    What string
}

// Returns the error message defined in What as a string
func (e *CustomError) Error() string {
    return e.What
}

func main() {
    err = CopyDir("/home/jaybill/data", "/home/jaybill/backup")
    if err != nil {
        log.Fatal(err)
    } else {
        log.Print("Files copied.")
    }
}

There is an error:

    if err == nil {
        si, err := os.Stat(source)
        if err != nil {
            err = os.Chmod(dest, si.Mode())
        }
    }

should be

    if err == nil {
        si, err := os.Stat(source)
        if err == nil {
            err = os.Chmod(dest, si.Mode())
        }
    }

However still one error is not handled right...

And you didn't handle the error case here:

    entries, err := ioutil.ReadDir(source)

    for _, entry := range entries {

And don't use log.Println! Return the error instead!

sfp := source + "/" + entry.Name()
dfp := dest + "/" + entry.Name()
if entry.IsDir() {
    err = CopyDir(sfp, dfp)
    if err != nil {
        log.Println(err)
    }
} else {
    // perform copy         
    err = CopyFile(sfp, dfp)
    if err != nil {
        log.Println(err)
    }
}

Here is a clean implementation: https://gist.github.com/m4ng0squ4sh/92462b38df26839a3ca324697c8cba04

This seems useful, but the link to the @r0l1 clean implementation seems to be broken unfortunately, and I think it should be here: https://gist.github.com/r0l1/92462b38df26839a3ca324697c8cba04