Initial commit

Author: tmatias

README.md

@@ -0,0 +1,14 @@
+# perm
+
+Print human-friendly descriptions of a file's permissions
+
+## Usage:
+
+```
+$ ls perm/perm.go
+-rw-r--r-- 1 tiago tiago 906 ago 24 22:29 perm/perm.go
+$ go run main.go --file perm/perm.go
+owner can read and write to it
+group members can read from it
+others can read from it
+```

main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/tmatias/perm/perm"
+)
+
+func main() {
+	f := flag.String("file", "", "file for which to describe permissions")
+	flag.Parse()
+
+	fi, err := os.Stat(*f)
+	if err != nil {
+		log.Fatal(err)
+	}
+	bits := fi.Mode().Perm()
+	owner, group, other := perm.Permissions(int(bits))
+
+	printPerm("owner", owner)
+	printPerm("group members", group)
+	printPerm("others", other)
+}
+
+func printPerm(who string, bits int) {
+	what, err := perm.Description(bits)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s %s\n", who, what)
+}

perm/perm.go

@@ -0,0 +1,38 @@
+package perm
+
+import (
+	"fmt"
+)
+
+// Description returns an human-friendly description of unix file permission bits
+func Description(bits int) (string, error) {
+	switch bits {
+	case 0:
+		return "cannot do anything", nil
+	case 1:
+		return "can execute it", nil
+	case 2:
+		return "can write to it", nil
+	case 3:
+		return "can execute and write to it", nil
+	case 4:
+		return "can read from it", nil
+	case 5:
+		return "can read and execute it", nil
+	case 6:
+		return "can read and write to it", nil
+	case 7:
+		return "can read, write and execute it", nil
+	default:
+		return "", fmt.Errorf("Invalid bits %d", bits)
+	}
+}
+
+// Permissions return three integers containing permissions for the owner, group and everyone else
+// from an int representing unix file permissions bits
+func Permissions(bits int) (owner int, group int, other int) {
+	owner = bits >> 6 & 7
+	group = bits >> 3 & 7
+	other = bits & 7
+	return
+}

perm/perm_test.go

@@ -0,0 +1,62 @@
+package perm
+
+import (
+	"testing"
+)
+
+func TestPermDescription(t *testing.T) {
+	tt := []struct {
+		name string
+		bits int
+		desc string
+	}{
+		{"no permission", 0, "cannot do anything"},
+		{"execute permission", 1, "can execute it"},
+		{"write permission", 2, "can write to it"},
+		{"execute and write permission", 3, "can execute and write to it"},
+		{"read permission", 4, "can read from it"},
+		{"read and execute permission", 5, "can read and execute it"},
+		{"write permission", 6, "can read and write to it"},
+		{"read, write and execute permission", 7, "can read, write and execute it"},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			desc, err := Description(tc.bits)
+			if err != nil {
+				t.Error(err)
+			}
+			if desc != tc.desc {
+				t.Errorf("expected description of %d to be '%s'; got '%s'", tc.bits, tc.desc, desc)
+			}
+		})
+	}
+}
+
+func TestPermissions(t *testing.T) {
+	tt := []struct {
+		name  string
+		bits  int
+		owner int
+		group int
+		other int
+	}{
+		{"world readable and writable", 0777, 7, 7, 7},
+		{"readable only by the owner", 0400, 4, 0, 0},
+	}
+
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			owner, group, other := Permissions(tc.bits)
+			if owner != tc.owner {
+				t.Errorf("expected owner permission for %d to be %d; got %d", tc.bits, tc.owner, owner)
+			}
+			if group != tc.group {
+				t.Errorf("expected group permission for %d to be %d; got %d", tc.bits, tc.group, owner)
+			}
+			if other != tc.other {
+				t.Errorf("expected other permission for %d to be %d; got %d", tc.bits, tc.other, owner)
+			}
+		})
+	}
+}