refactor aaparser pkg, add unit tests

Signed-off-by: Jessica Frazelle <acidburn@docker.com>

aaparser/aaparser.go

@@ -1,35 +1,66 @@
+// Package aaparser is a convenience package interacting with `apparmor_parser`.
 package aaparser
 
 import (
 	"fmt"
-	"log"
 	"os/exec"
+	"path/filepath"
 	"strconv"
 	"strings"
 )
 
-// GetVersion returns the major and minor version of apparmor_parser
-func GetVersion() (int, int, error) {
-	// get the apparmor_version version
-	cmd := exec.Command("apparmor_parser", "--version")
+const (
+	binary = "apparmor_parser"
+)
 
-	output, err := cmd.CombinedOutput()
+// GetVersion returns the major and minor version of apparmor_parser.
+func GetVersion() (int, int, error) {
+	output, err := cmd("", "--version")
 	if err != nil {
-		log.Fatalf("getting apparmor_parser version failed: %s (%s)", err, output)
+		return -1, -1, err
 	}
 
-	// parse the version from the output
+	return parseVersion(string(output))
+}
+
+// LoadProfile runs `apparmor_parser -r -W` on a specified apparmor profile to
+// replace and write it to disk.
+func LoadProfile(profilePath string) error {
+	_, err := cmd(filepath.Dir(profilePath), "-r", "-W", filepath.Base(profilePath))
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// cmd runs `apparmor_parser` with the passed arguments.
+func cmd(dir string, arg ...string) (string, error) {
+	c := exec.Command(binary, arg...)
+	c.Dir = dir
+
+	output, err := c.CombinedOutput()
+	if err != nil {
+		return "", fmt.Errorf("running `%s %s` failed with output: %s\nerror: %v", c.Path, strings.Join(c.Args, " "), string(output), err)
+	}
+
+	return string(output), nil
+}
+
+// parseVersion takes the output from `apparmor_parser --version` and returns
+// the major and minor version for `apparor_parser`.
+func parseVersion(output string) (int, int, error) {
 	// output is in the form of the following:
 	// AppArmor parser version 2.9.1
 	// Copyright (C) 1999-2008 Novell Inc.
 	// Copyright 2009-2012 Canonical Ltd.
-	lines := strings.SplitN(string(output), "\n", 2)
+	lines := strings.SplitN(output, "\n", 2)
 	words := strings.Split(lines[0], " ")
 	version := words[len(words)-1]
+
 	// split by major minor version
 	v := strings.Split(version, ".")
 	if len(v) < 2 {
-		return -1, -1, fmt.Errorf("parsing major minor version failed for %q", version)
+		return -1, -1, fmt.Errorf("parsing major minor version failed for output: `%s`", output)
 	}
 
 	majorVersion, err := strconv.Atoi(v[0])