fix machine id to 48 bits, add test (#877)

another bone head fail here. hopefully can leave this alone meow...

newID does not get inlined, but doesn't allocate to trigger any stack
expansion either. net perf hit on my laptop is 5ns, and we get a test out of
it. it will push a new stack, so it's not negligible overhead and we could
avoid it. we could keep the logic in both places just to have a test for it
separate instead of re-using the function in the hot path. up to us.

api/id/id.go

@@ -11,7 +11,7 @@ type Id [16]byte
 
 var (
 	machineID uint64
-	counter   uint64
+	counter   uint32
 )
 
 // SetMachineId may only be called by one thread before any id generation
@@ -45,11 +45,15 @@ func SetMachineIdHost(addr net.IP, port uint16) {
 // Ids are sortable within (not between, thanks to clocks) each machine, with
 // a modified base32 encoding exposed for convenience in API usage.
 func New() Id {
-	var id Id
 	t := time.Now()
 	// NOTE compiler optimizes out division by constant for us
 	ms := uint64(t.Unix())*1000 + uint64(t.Nanosecond()/int(time.Millisecond))
-	count := atomic.AddUint64(&counter, 1)
+	count := atomic.AddUint32(&counter, 1)
+	return newID(ms, machineID, count)
+}
+
+func newID(ms, machineID uint64, count uint32) Id {
+	var id Id
 
 	id[0] = byte(ms >> 40)
 	id[1] = byte(ms >> 32)
@@ -58,14 +62,13 @@ func New() Id {
 	id[4] = byte(ms >> 8)
 	id[5] = byte(ms)
 
-	id[6] = byte(machineID >> 12)
+	id[6] = byte(machineID >> 40)
-	id[7] = byte(machineID >> 4)
+	id[7] = byte(machineID >> 32)
+	id[8] = byte(machineID >> 24)
+	id[9] = byte(machineID >> 16)
+	id[10] = byte(machineID >> 8)
+	id[11] = byte(machineID)
 
-	id[8] = byte(machineID<<4) | byte((count<<4)>>60)
-
-	id[9] = byte(count >> 48)
-	id[10] = byte(count >> 40)
-	id[11] = byte(count >> 32)
 	id[12] = byte(count >> 24)
 	id[13] = byte(count >> 16)
 	id[14] = byte(count >> 8)

api/id/id_test.go

@@ -1,7 +1,12 @@
 package id
 
 import (
+	"encoding/binary"
+	"fmt"
+	"math"
+	"net"
 	"testing"
+	"time"
 )
 
 func BenchmarkGen(b *testing.B) {
@@ -28,3 +33,31 @@ func BenchmarkUnmarshalText(b *testing.B) {
 		_ = id
 	}
 }
+
+func TestIdRaw(t *testing.T) {
+	SetMachineIdHost(net.IP{127, 0, 0, 1}, 8080)
+
+	ts := time.Now()
+	ms := uint64(ts.Unix())*1000 + uint64(ts.Nanosecond()/int(time.Millisecond))
+	count := uint32(math.MaxUint32)
+	id := newID(ms, machineID, count)
+	fmt.Println(len(id), id)
+
+	var buf [8]byte
+	copy(buf[2:], id[:6])
+	idTime := binary.BigEndian.Uint64(buf[:])
+	if ms != idTime {
+		t.Fatal("id time doesn't not match time given", ms, idTime)
+	}
+
+	copy(buf[2:], id[6:12])
+	idMid := binary.BigEndian.Uint64(buf[:])
+	if idMid != machineID {
+		t.Fatal("machine id mismatch", idMid, machineID)
+	}
+
+	idCount := binary.BigEndian.Uint32(id[12:16])
+	if idCount != count {
+		t.Fatal("count mismatch", idCount, count)
+	}
+}