drone-yaml/yaml/compiler/internal/rand/rand.go

// Copyright 2019 Drone IO, Inc.
//
// 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 rand

import (
	"crypto/rand"
)

var chars = []byte("abcdefghijklmnopqrstuvwxyz0123456789")

// random string length
const length = 32

// String returns a string value.
func String() string {
	clen := len(chars)
	maxrb := 255 - (256 % clen)
	b := make([]byte, length)
	r := make([]byte, length+(length/4)) // storage for random bytes.
	i := 0
	for {
		if _, err := rand.Read(r); err != nil {
			panic("rand: error reading random bytes")
		}
		for _, rb := range r {
			c := int(rb)
			if c > maxrb {
				// Skip this number to avoid modulo bias.
				continue
			}
			b[i] = chars[c%clen]
			i++
			if i == length {
				return string(b)
			}
		}
	}
}