11:55 AM $ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/dave/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/dave/go"
GORACE=""
GOROOT="/usr/lib/go-1.10"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.10/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build611611681=/tmp/go-build -gno-record-gcc-switches"

func Current() (*User, error)
    Current returns the current user.

11:53 AM $ cat main.go 
package main

import "runtime"
import "syscall"
import "os"
import "os/user"
import "log"
import "fmt"

func main() {

	runtime.LockOSThread()

	u, _ := user.Current()
	fmt.Printf("user.Current before priv drop: %v\n", u.Name)

	if os.Getuid() == 0 {
		if err := syscall.Setresuid(1000, 1000, 0); err != nil {
			log.Fatalf("failed to set user identity: %v", err)
		}

		u, _ = user.Current()
		fmt.Printf("user.Current after priv drop: %v\n", u.Name)

	}
}
dave@piran:~/currentuser_test.go
11:53 AM $ sudo go run main.go 
user.Current before priv drop: root
user.Current after priv drop: root

func Current() (*User, error)
    Current returns the current user.
    Note - the current user is cached at first call to Current().
    Subsequent calls will return the cached value and will not reflect changes
    to the EUID.