syncthing/vendor/github.com/dustin/go-humanize/si.go
Jakob Borg 916ec63af6 cmd/stdiscosrv: New discovery server (fixes #4618)
This is a new revision of the discovery server. Relevant changes and
non-changes:

- Protocol towards clients is unchanged.

- Recommended large scale design is still to be deployed nehind nginx (I
  tested, and it's still a lot faster at terminating TLS).

- Database backend is leveldb again, only. It scales enough, is easy to
  setup, and we don't need any backend to take care of.

- Server supports replication. This is a simple TCP channel - protect it
  with a firewall when deploying over the internet. (We deploy this within
  the same datacenter, and with firewall.) Any incoming client announces
  are sent over the replication channel(s) to other peer discosrvs.
  Incoming replication changes are applied to the database as if they came
  from clients, but without the TLS/certificate overhead.

- Metrics are exposed using the prometheus library, when enabled.

- The database values and replication protocol is protobuf, because JSON
  was quite CPU intensive when I tried that and benchmarked it.

- The "Retry-After" value for failed lookups gets slowly increased from
  a default of 120 seconds, by 5 seconds for each failed lookup,
  independently by each discosrv. This lowers the query load over time for
  clients that are never seen. The Retry-After maxes out at 3600 after a
  couple of weeks of this increase. The number of failed lookups is
  stored in the database, now and then (avoiding making each lookup a
  database put).

All in all this means clients can be pointed towards a cluster using
just multiple A / AAAA records to gain both load sharing and redundancy
(if one is down, clients will talk to the remaining ones).

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4648
2018-01-14 08:52:31 +00:00

114 lines
2.4 KiB
Go

package humanize
import (
"errors"
"math"
"regexp"
"strconv"
)
var siPrefixTable = map[float64]string{
-24: "y", // yocto
-21: "z", // zepto
-18: "a", // atto
-15: "f", // femto
-12: "p", // pico
-9: "n", // nano
-6: "µ", // micro
-3: "m", // milli
0: "",
3: "k", // kilo
6: "M", // mega
9: "G", // giga
12: "T", // tera
15: "P", // peta
18: "E", // exa
21: "Z", // zetta
24: "Y", // yotta
}
var revSIPrefixTable = revfmap(siPrefixTable)
// revfmap reverses the map and precomputes the power multiplier
func revfmap(in map[float64]string) map[string]float64 {
rv := map[string]float64{}
for k, v := range in {
rv[v] = math.Pow(10, k)
}
return rv
}
var riParseRegex *regexp.Regexp
func init() {
ri := `^([\-0-9.]+)\s?([`
for _, v := range siPrefixTable {
ri += v
}
ri += `]?)(.*)`
riParseRegex = regexp.MustCompile(ri)
}
// ComputeSI finds the most appropriate SI prefix for the given number
// and returns the prefix along with the value adjusted to be within
// that prefix.
//
// See also: SI, ParseSI.
//
// e.g. ComputeSI(2.2345e-12) -> (2.2345, "p")
func ComputeSI(input float64) (float64, string) {
if input == 0 {
return 0, ""
}
mag := math.Abs(input)
exponent := math.Floor(logn(mag, 10))
exponent = math.Floor(exponent/3) * 3
value := mag / math.Pow(10, exponent)
// Handle special case where value is exactly 1000.0
// Should return 1 M instead of 1000 k
if value == 1000.0 {
exponent += 3
value = mag / math.Pow(10, exponent)
}
value = math.Copysign(value, input)
prefix := siPrefixTable[exponent]
return value, prefix
}
// SI returns a string with default formatting.
//
// SI uses Ftoa to format float value, removing trailing zeros.
//
// See also: ComputeSI, ParseSI.
//
// e.g. SI(1000000, "B") -> 1 MB
// e.g. SI(2.2345e-12, "F") -> 2.2345 pF
func SI(input float64, unit string) string {
value, prefix := ComputeSI(input)
return Ftoa(value) + " " + prefix + unit
}
var errInvalid = errors.New("invalid input")
// ParseSI parses an SI string back into the number and unit.
//
// See also: SI, ComputeSI.
//
// e.g. ParseSI("2.2345 pF") -> (2.2345e-12, "F", nil)
func ParseSI(input string) (float64, string, error) {
found := riParseRegex.FindStringSubmatch(input)
if len(found) != 4 {
return 0, "", errInvalid
}
mag := revSIPrefixTable[found[2]]
unit := found[3]
base, err := strconv.ParseFloat(found[1], 64)
return base * mag, unit, err
}