util: file copy and exec.LookPath wrapper

Add convenience functions for copying files to owner readable targets and LookPath comma ok wrapper.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

util.go

@@ -3,8 +3,10 @@ package main
 import (
 	"errors"
 	"fmt"
+	"io"
 	"io/fs"
 	"os"
+	"os/exec"
 )
 
 const (
@@ -26,3 +28,35 @@ func sdBooted() bool {
 	}
 	return true
 }
+
+func which(file string) (string, bool) {
+	path, err := exec.LookPath(file)
+	return path, err == nil
+}
+
+func copyFile(dst, src string) error {
+	srcD, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if srcD.Close() != nil {
+			// unreachable
+			panic("src file closed prematurely")
+		}
+	}()
+
+	dstD, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if dstD.Close() != nil {
+			// unreachable
+			panic("dst file closed prematurely")
+		}
+	}()
+
+	_, err = io.Copy(dstD, srcD)
+	return err
+}