util.go

/*
Copyright 2014 Google Inc. 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 (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"reflect"
	"regexp"
	"runtime"
	"strconv"
	"time"

	"github.com/golang/glog"
)

// For testing, bypass HandleCrash.
var ReallyCrash bool

// HandleCrash simply catches a crash and logs an error. Meant to be called via defer.
func HandleCrash() {
	if ReallyCrash {
		return
	}

	r := recover()
	if r != nil {
		callers := ""
		for i := 0; true; i++ {
			_, file, line, ok := runtime.Caller(i)
			if !ok {
				break
			}
			callers = callers + fmt.Sprintf("%v:%v\n", file, line)
		}
		glog.Infof("Recovered from panic: %#v (%v)\n%v", r, r, callers)
	}
}

// Forever loops forever running f every period.  Catches any panics, and keeps going.
func Forever(f func(), period time.Duration) {
	Until(f, period, nil)
}

// Until loops until stop channel is closed, running f every period.
// Catches any panics, and keeps going. f may not be invoked if
// stop channel is already closed.
func Until(f func(), period time.Duration, stopCh <-chan struct{}) {
	for {
		select {
		case <-stopCh:
			return
		default:
		}
		func() {
			defer HandleCrash()
			f()
		}()
		time.Sleep(period)
	}
}

// IntOrString is a type that can hold an int or a string.  When used in
// JSON or YAML marshalling and unmarshalling, it produces or consumes the
// inner type.  This allows you to have, for example, a JSON field that can
// accept a name or number.
type IntOrString struct {
	Kind   IntstrKind
	IntVal int
	StrVal string
}

// IntstrKind represents the stored type of IntOrString.
type IntstrKind int

const (
	IntstrInt    IntstrKind = iota // The IntOrString holds an int.
	IntstrString                   // The IntOrString holds a string.
)

// NewIntOrStringFromInt creates an IntOrString object with an int value.
func NewIntOrStringFromInt(val int) IntOrString {
	return IntOrString{Kind: IntstrInt, IntVal: val}
}

// NewIntOrStringFromString creates an IntOrString object with a string value.
func NewIntOrStringFromString(val string) IntOrString {
	return IntOrString{Kind: IntstrString, StrVal: val}
}

// UnmarshalJSON implements the json.Unmarshaller interface.
func (intstr *IntOrString) UnmarshalJSON(value []byte) error {
	if value[0] == '"' {
		intstr.Kind = IntstrString
		return json.Unmarshal(value, &intstr.StrVal)
	}
	intstr.Kind = IntstrInt
	return json.Unmarshal(value, &intstr.IntVal)
}

// String returns the string value, or Itoa's the int value.
func (intstr *IntOrString) String() string {
	if intstr.Kind == IntstrString {
		return intstr.StrVal
	}
	return strconv.Itoa(intstr.IntVal)
}

// MarshalJSON implements the json.Marshaller interface.
func (intstr IntOrString) MarshalJSON() ([]byte, error) {
	switch intstr.Kind {
	case IntstrInt:
		return json.Marshal(intstr.IntVal)
	case IntstrString:
		return json.Marshal(intstr.StrVal)
	default:
		return []byte{}, fmt.Errorf("impossible IntOrString.Kind")
	}
}

// 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
}

// Writes 'value' to /proc/self/oom_score_adj.
func ApplyOomScoreAdj(value int) error {
	if value < -1000 || value > 1000 {
		return fmt.Errorf("invalid value(%d) specified for oom_score_adj. Values must be within the range [-1000, 1000]", value)
	}

	if err := ioutil.WriteFile("/proc/self/oom_score_adj", []byte(strconv.Itoa(value)), 0700); err != nil {
		fmt.Errorf("failed to set oom_score_adj to %d - %q", value, err)
	}

	return nil
}

// 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
}