distribution/vendor/github.com/denverdino/aliyungo/cdn/auth/random_uuid.go
Shawn Chen 3390f32aec fix Context issue
Signed-off-by: Shawn Chen <chen8132@gmail.com>
2019-03-04 17:48:32 +08:00

97 lines
2.3 KiB
Go

package auth
import (
"crypto/rand"
"fmt"
"io"
"os"
"syscall"
"time"
)
const (
// Bits is the number of bits in a UUID
Bits = 128
// Size is the number of bytes in a UUID
Size = Bits / 8
format = "%08x%04x%04x%04x%012x"
)
var (
// Loggerf can be used to override the default logging destination. Such
// log messages in this library should be logged at warning or higher.
Loggerf = func(format string, args ...interface{}) {}
)
// UUID represents a UUID value. UUIDs can be compared and set to other values
// and accessed by byte.
type UUID [Size]byte
// GenerateUUID creates a new, version 4 uuid.
func GenerateUUID() (u UUID) {
const (
// ensures we backoff for less than 450ms total. Use the following to
// select new value, in units of 10ms:
// n*(n+1)/2 = d -> n^2 + n - 2d -> n = (sqrt(8d + 1) - 1)/2
maxretries = 9
backoff = time.Millisecond * 10
)
var (
totalBackoff time.Duration
count int
retries int
)
for {
// This should never block but the read may fail. Because of this,
// we just try to read the random number generator until we get
// something. This is a very rare condition but may happen.
b := time.Duration(retries) * backoff
time.Sleep(b)
totalBackoff += b
n, err := io.ReadFull(rand.Reader, u[count:])
if err != nil {
if retryOnError(err) && retries < maxretries {
count += n
retries++
Loggerf("error generating version 4 uuid, retrying: %v", err)
continue
}
// Any other errors represent a system problem. What did someone
// do to /dev/urandom?
panic(fmt.Errorf("error reading random number generator, retried for %v: %v", totalBackoff.String(), err))
}
break
}
u[6] = (u[6] & 0x0f) | 0x40 // set version byte
u[8] = (u[8] & 0x3f) | 0x80 // set high order byte 0b10{8,9,a,b}
return u
}
func (u UUID) String() string {
return fmt.Sprintf(format, u[:4], u[4:6], u[6:8], u[8:10], u[10:])
}
// retryOnError tries to detect whether or not retrying would be fruitful.
func retryOnError(err error) bool {
switch err := err.(type) {
case *os.PathError:
return retryOnError(err.Err) // unpack the target error
case syscall.Errno:
if err == syscall.EPERM {
// EPERM represents an entropy pool exhaustion, a condition under
// which we backoff and retry.
return true
}
}
return false
}