v2: take only 'bitsMachine' least significant bits from generated machine IDs so it doesn't corrupt the other ID parts (#72)

Co-authored-by: ok32 <[email protected]>
Co-authored-by: Yoshiyuki Mineo <[email protected]>

Author: 3 people

v2/sonyflake.go

@@ -213,7 +213,7 @@ func (sf *Sonyflake) toID() (int64, error) {
 
 	return sf.elapsedTime<<(sf.bitsSequence+sf.bitsMachine) |
 		int64(sf.sequence)<<sf.bitsMachine |
-		int64(sf.machine), nil
+		(int64(sf.machine) & ((1 << sf.bitsMachine) - 1)), nil
 }
 
 func privateIPv4(interfaceAddrs types.InterfaceAddrs) (net.IP, error) {
@@ -264,7 +264,7 @@ func (sf *Sonyflake) Compose(t time.Time, sequence, machineID int) int64 {
 	elapsedTime := sf.toInternalTime(t.UTC()) - sf.startTime
 	return elapsedTime<<(sf.bitsSequence+sf.bitsMachine) |
 		int64(sequence)<<sf.bitsMachine |
-		int64(machineID)
+		(int64(machineID) & ((1 << sf.bitsMachine) - 1))
 }
 
 // Decompose returns a set of Sonyflake ID parts.

v2/sonyflake_test.go

@@ -3,6 +3,7 @@ package sonyflake
 import (
 	"errors"
 	"fmt"
+	"math"
 	"net"
 	"runtime"
 	"testing"
@@ -437,3 +438,28 @@ func TestComposeAndDecompose(t *testing.T) {
 		})
 	}
 }
+
+func TestBigMachineDoesntBreakID(t *testing.T) {
+	start := time.Now()
+	sf := newSonyflake(t, Settings{
+		TimeUnit:  time.Millisecond,
+		StartTime: start,
+		MachineID: func() (int, error) {
+			return math.MaxInt, nil
+		},
+	})
+
+	id := nextID(t, sf)
+	parts := sf.Decompose(id)
+
+	if parts["sequence"] != 0 {
+		t.Errorf("next id sequence mismatch: got %d, want %d", parts["sequence"], 0)
+	}
+
+	id = sf.Compose(time.Now(), 0, math.MaxInt)
+	parts = sf.Decompose(id)
+
+	if parts["sequence"] != 0 {
+		t.Errorf("decompose sequence mismatch: got %d, want %d", parts["sequence"], 0)
+	}
+}