fix(host): PickHost 改为加权随机

Author: yokowu

backend/biz/host/usecase/publichost.go

@@ -2,8 +2,9 @@ package usecase
 
 import (
 	"context"
+	"crypto/rand"
+	"encoding/binary"
 	"fmt"
-	"sync/atomic"
 
 	"github.com/samber/do"
 
@@ -17,9 +18,10 @@ import (
 type PublicHostUsecase struct {
 	repo     domain.PublicHostRepo
 	taskflow taskflow.Clienter
-	rr       uint64
 }
 
+var randUint64n = randomUint64n
+
 func NewPublicHostUsecase(i *do.Injector) (domain.PublicHostUsecase, error) {
 	return &PublicHostUsecase{
 		repo:     do.MustInvoke[domain.PublicHostRepo](i),
@@ -52,9 +54,18 @@ func (p *PublicHostUsecase) PickHost(ctx context.Context) (*domain.Host, error)
 		return nil, errcode.ErrPublicHostNotFound.Wrap(fmt.Errorf("no online public hosts found"))
 	}
 
-	weights := make([]uint64, len(onlines))
+	selected, err := pickWeightedHost(onlines)
+	if err != nil {
+		return nil, err
+	}
+
+	return cvt.From(selected, &domain.Host{}), nil
+}
+
+func pickWeightedHost(hosts []*db.Host) (*db.Host, error) {
+	weights := make([]uint64, len(hosts))
 	var totalWeight uint64
-	for i, h := range onlines {
+	for i, h := range hosts {
 		w := h.Weight
 		if w <= 0 {
 			w = 1
@@ -66,19 +77,34 @@ func (p *PublicHostUsecase) PickHost(ctx context.Context) (*domain.Host, error)
 		return nil, errcode.ErrPublicHostNotFound.Wrap(fmt.Errorf("no valid weights found"))
 	}
 
-	idx := atomic.AddUint64(&p.rr, 1) - 1
-	offset := idx % totalWeight
-	var selected *db.Host
+	offset, err := randUint64n(totalWeight)
+	if err != nil {
+		return nil, err
+	}
 	for i, w := range weights {
 		if offset < w {
-			selected = onlines[i]
-			break
+			return hosts[i], nil
 		}
 		offset -= w
 	}
-	if selected == nil {
-		return nil, errcode.ErrPublicHostNotFound.Wrap(fmt.Errorf("failed to select public host"))
+
+	return nil, errcode.ErrPublicHostNotFound.Wrap(fmt.Errorf("failed to select public host"))
+}
+
+func randomUint64n(n uint64) (uint64, error) {
+	if n == 0 {
+		return 0, fmt.Errorf("random upper bound must be positive")
 	}
 
-	return cvt.From(selected, &domain.Host{}), nil
+	limit := ^uint64(0) - (^uint64(0) % n)
+	var buf [8]byte
+	for {
+		if _, err := rand.Read(buf[:]); err != nil {
+			return 0, err
+		}
+		v := binary.BigEndian.Uint64(buf[:])
+		if v < limit {
+			return v % n, nil
+		}
+	}
 }

backend/biz/host/usecase/publichost_test.go

@@ -0,0 +1,144 @@
+package usecase
+
+import (
+	"context"
+	"testing"
+
+	"github.com/chaitin/MonkeyCode/backend/db"
+	"github.com/chaitin/MonkeyCode/backend/pkg/taskflow"
+)
+
+func TestPickHostSelectsHostByRandomOffset(t *testing.T) {
+	repo := &publicHostRepoStub{
+		hosts: []*db.Host{
+			{ID: "host-a", Hostname: "a", Weight: 1},
+			{ID: "host-b", Hostname: "b", Weight: 3},
+			{ID: "host-c", Hostname: "c", Weight: 1},
+		},
+	}
+	hoster := &publicHosterStub{
+		onlineMap: map[string]bool{
+			"host-a": true,
+			"host-b": true,
+			"host-c": true,
+		},
+	}
+	u := &PublicHostUsecase{
+		repo:     repo,
+		taskflow: &taskflowClientStub{hoster: hoster},
+	}
+
+	offsets := []uint64{0, 1, 3, 4}
+	limits := make([]uint64, 0, len(offsets))
+	prevRandUint64n := randUint64n
+	randUint64n = func(n uint64) (uint64, error) {
+		limits = append(limits, n)
+		v := offsets[0]
+		offsets = offsets[1:]
+		return v, nil
+	}
+	t.Cleanup(func() {
+		randUint64n = prevRandUint64n
+	})
+
+	got := make([]string, 0, 4)
+	for range 4 {
+		host, err := u.PickHost(context.Background())
+		if err != nil {
+			t.Fatalf("PickHost() error = %v", err)
+		}
+		got = append(got, host.ID)
+	}
+
+	want := []string{"host-a", "host-b", "host-b", "host-c"}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("PickHost() at %d = %q, want %q", i, got[i], want[i])
+		}
+	}
+
+	for _, limit := range limits {
+		if limit != 5 {
+			t.Fatalf("rand limit = %d, want 5", limit)
+		}
+	}
+}
+
+func TestPickHostTreatsNonPositiveWeightsAsOne(t *testing.T) {
+	u := &PublicHostUsecase{
+		repo: &publicHostRepoStub{
+			hosts: []*db.Host{
+				{ID: "host-a", Hostname: "a", Weight: 0},
+				{ID: "host-b", Hostname: "b", Weight: -2},
+			},
+		},
+		taskflow: &taskflowClientStub{
+			hoster: &publicHosterStub{
+				onlineMap: map[string]bool{
+					"host-a": true,
+					"host-b": true,
+				},
+			},
+		},
+	}
+
+	prevRandUint64n := randUint64n
+	randUint64n = func(n uint64) (uint64, error) {
+		if n != 2 {
+			t.Fatalf("rand limit = %d, want 2", n)
+		}
+		return 1, nil
+	}
+	t.Cleanup(func() {
+		randUint64n = prevRandUint64n
+	})
+
+	host, err := u.PickHost(context.Background())
+	if err != nil {
+		t.Fatalf("PickHost() error = %v", err)
+	}
+	if host.ID != "host-b" {
+		t.Fatalf("PickHost() = %q, want %q", host.ID, "host-b")
+	}
+}
+
+type publicHostRepoStub struct {
+	hosts []*db.Host
+	err   error
+}
+
+func (s *publicHostRepoStub) All(context.Context) ([]*db.Host, error) {
+	return s.hosts, s.err
+}
+
+type publicHosterStub struct {
+	onlineMap map[string]bool
+	err       error
+}
+
+func (s *publicHosterStub) List(context.Context, string) (map[string]*taskflow.Host, error) {
+	return nil, nil
+}
+
+func (s *publicHosterStub) IsOnline(context.Context, *taskflow.IsOnlineReq[string]) (*taskflow.IsOnlineResp, error) {
+	if s.err != nil {
+		return nil, s.err
+	}
+	return &taskflow.IsOnlineResp{OnlineMap: s.onlineMap}, nil
+}
+
+type taskflowClientStub struct {
+	hoster taskflow.Hoster
+}
+
+func (s *taskflowClientStub) VirtualMachiner() taskflow.VirtualMachiner { return nil }
+func (s *taskflowClientStub) Host() taskflow.Hoster                     { return s.hoster }
+func (s *taskflowClientStub) FileManager() taskflow.FileManager         { return nil }
+func (s *taskflowClientStub) TaskManager() taskflow.TaskManager         { return nil }
+func (s *taskflowClientStub) PortForwarder() taskflow.PortForwarder     { return nil }
+func (s *taskflowClientStub) Stats(context.Context) (*taskflow.Stats, error) {
+	return nil, nil
+}
+func (s *taskflowClientStub) TaskLive(context.Context, string, bool, func(*taskflow.TaskChunk) error) error {
+	return nil
+}