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// Package main provides simple consistenthash commandline utility.
/*
Demo:
$ seq -f node-%.f 1 100 > /tmp/nodes
$ consistenthash < /tmp/nodes apple
node-42
$ consistenthash < /tmp/nodes banana
node-48
$ consistenthash < /tmp/nodes chocolate
node-2
Modify /tmp/nodes and confirm that the result rarely changes.
*/
package main
import (
"fmt"
"io"
"os"
"strings"
"github.com/pkg/errors"
"github.com/serialx/hashring"
"github.com/sirupsen/logrus"
)
func main() {
if err := xmain(); err != nil {
logrus.Fatal(err)
}
}
func xmain() error {
if len(os.Args) != 2 {
fmt.Fprintf(os.Stderr, "Usage: %s KEY\nNode list needs to be provided via stdin\n", os.Args[0])
os.Exit(1)
return errors.New("should not reach here")
}
key := os.Args[1]
stdin, err := io.ReadAll(os.Stdin)
if err != nil {
return err
}
var nodes []string
for _, s := range strings.Split(string(stdin), "\n") {
s = strings.TrimSpace(s)
if s != "" {
nodes = append(nodes, s)
}
}
chosen, err := doConsistentHash(nodes, key)
if err != nil {
return err
}
fmt.Println(chosen)
return nil
}
func doConsistentHash(nodes []string, key string) (string, error) {
ring := hashring.New(nodes)
x, ok := ring.GetNode(key)
if !ok {
return "", errors.Errorf("no node found for key %q", key)
}
return x, nil
}
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