util.go

/*
Copyright 2014 The Kubernetes Authors All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package util

import (
	"fmt"
	"os"
	"reflect"
	"regexp"
)

// Takes a list of strings and compiles them into a list of regular expressions
func CompileRegexps(regexpStrings []string) ([]*regexp.Regexp, error) {
	regexps := []*regexp.Regexp{}
	for _, regexpStr := range regexpStrings {
		r, err := regexp.Compile(regexpStr)
		if err != nil {
			return []*regexp.Regexp{}, err
		}
		regexps = append(regexps, r)
	}
	return regexps, nil
}

// Detects if using systemd as the init system
// Please note that simply reading /proc/1/cmdline can be misleading because
// some installation of various init programs can automatically make /sbin/init
// a symlink or even a renamed version of their main program.
// TODO(dchen1107): realiably detects the init system using on the system:
// systemd, upstart, initd, etc.
func UsingSystemdInitSystem() bool {
	if _, err := os.Stat("/run/systemd/system"); err == nil {
		return true
	}

	return false
}

// Tests whether all pointer fields in a struct are nil.  This is useful when,
// for example, an API struct is handled by plugins which need to distinguish
// "no plugin accepted this spec" from "this spec is empty".
//
// This function is only valid for structs and pointers to structs.  Any other
// type will cause a panic.  Passing a typed nil pointer will return true.
func AllPtrFieldsNil(obj interface{}) bool {
	v := reflect.ValueOf(obj)
	if !v.IsValid() {
		panic(fmt.Sprintf("reflect.ValueOf() produced a non-valid Value for %#v", obj))
	}
	if v.Kind() == reflect.Ptr {
		if v.IsNil() {
			return true
		}
		v = v.Elem()
	}
	for i := 0; i < v.NumField(); i++ {
		if v.Field(i).Kind() == reflect.Ptr && !v.Field(i).IsNil() {
			return false
		}
	}
	return true
}

func FileExists(filename string) (bool, error) {
	if _, err := os.Stat(filename); os.IsNotExist(err) {
		return false, nil
	} else if err != nil {
		return false, err
	}
	return true, nil
}

// borrowed from ioutil.ReadDir
// ReadDir reads the directory named by dirname and returns
// a list of directory entries, minus those with lstat errors
func ReadDirNoExit(dirname string) ([]os.FileInfo, []error, error) {
	if dirname == "" {
		dirname = "."
	}

	f, err := os.Open(dirname)
	if err != nil {
		return nil, nil, err
	}
	defer f.Close()

	names, err := f.Readdirnames(-1)
	list := make([]os.FileInfo, 0, len(names))
	errs := make([]error, 0, len(names))
	for _, filename := range names {
		fip, lerr := os.Lstat(dirname + "/" + filename)
		if os.IsNotExist(lerr) {
			// File disappeared between readdir + stat.
			// Just treat it as if it didn't exist.
			continue
		}

		list = append(list, fip)
		errs = append(errs, lerr)
	}

	return list, errs, nil
}

// IntPtr returns a pointer to an int
func IntPtr(i int) *int {
	o := i
	return &o
}

// IntPtrDerefOr dereference the int ptr and returns it i not nil,
// else returns def.
func IntPtrDerefOr(ptr *int, def int) int {
	if ptr != nil {
		return *ptr
	}
	return def
}