github.com/emc-cmd/terraform@v0.7.8-0.20161101145618-f16309630e7c/helper/resource/id.go (about)

     1  package resource
     2  
     3  import (
     4  	"crypto/rand"
     5  	"encoding/base32"
     6  	"fmt"
     7  	"strings"
     8  	"time"
     9  )
    10  
    11  const UniqueIdPrefix = `terraform-`
    12  
    13  // Helper for a resource to generate a unique identifier w/ default prefix
    14  func UniqueId() string {
    15  	return PrefixedUniqueId(UniqueIdPrefix)
    16  }
    17  
    18  // Helper for a resource to generate a unique identifier w/ given prefix
    19  //
    20  // After the prefix, the ID consists of a timestamp and 12 random base32
    21  // characters.  The timestamp means that multiple IDs created with the same
    22  // prefix will sort in the order of their creation.
    23  func PrefixedUniqueId(prefix string) string {
    24  	// Be precise to the level nanoseconds, but remove the dot before the
    25  	// nanosecond. We assume that the randomCharacters call takes at least a
    26  	// nanosecond, so that multiple calls to this function from the same goroutine
    27  	// will have distinct ordered timestamps.
    28  	timestamp := strings.Replace(
    29  		time.Now().UTC().Format("20060102150405.000000000"),
    30  		".",
    31  		"", 1)
    32  	// This uses 3 characters, so that the length of the unique ID is the same as
    33  	// it was before we added the timestamp prefix, which happened to be 23
    34  	// characters.
    35  	return fmt.Sprintf("%s%s%s", prefix, timestamp, randomCharacters(3))
    36  }
    37  
    38  func randomCharacters(n int) string {
    39  	// Base32 has 5 bits of information per character.
    40  	b := randomBytes(n * 8 / 5)
    41  	chars := strings.ToLower(
    42  		strings.Replace(
    43  			base32.StdEncoding.EncodeToString(b),
    44  			"=", "", -1))
    45  	// Trim extra characters.
    46  	return chars[:n]
    47  }
    48  
    49  func randomBytes(n int) []byte {
    50  	b := make([]byte, n)
    51  	rand.Read(b)
    52  	return b
    53  }