github.com/rudderlabs/rudder-go-kit@v0.30.0/testhelper/rand/rand.go (about)

     1  package rand
     2  
     3  import (
     4  	"math/rand"
     5  	"sync"
     6  	"time"
     7  	"unsafe"
     8  )
     9  
    10  const (
    11  	letterBytes   = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
    12  	letterIdxBits = 6                    // 6 bits to represent a letter index
    13  	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
    14  	letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
    15  )
    16  
    17  var (
    18  	src                   = rand.NewSource(time.Now().UnixNano())
    19  	uniqueRandomStrings   = make(map[string]struct{})
    20  	uniqueRandomStringsMu sync.Mutex
    21  )
    22  
    23  // String returns a random string
    24  // Credits to https://stackoverflow.com/a/31832326/828366
    25  func String(n int) string {
    26  	b := make([]byte, n)
    27  	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
    28  	for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
    29  		if remain == 0 {
    30  			cache, remain = src.Int63(), letterIdxMax
    31  		}
    32  		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
    33  			b[i] = letterBytes[idx]
    34  			i--
    35  		}
    36  		cache >>= letterIdxBits
    37  		remain--
    38  	}
    39  
    40  	return *(*string)(unsafe.Pointer(&b)) // skipcq: GSC-G103
    41  }
    42  
    43  // UniqueString returns a random string that is unique
    44  func UniqueString(n int) string {
    45  	str := String(n)
    46  
    47  	uniqueRandomStringsMu.Lock()
    48  	defer uniqueRandomStringsMu.Unlock()
    49  
    50  	for {
    51  		if _, ok := uniqueRandomStrings[str]; !ok {
    52  			uniqueRandomStrings[str] = struct{}{}
    53  			return str
    54  		}
    55  		str = String(n)
    56  	}
    57  }