feat: consistent hash balancer support (#5246)

Co-authored-by: 周曙光 <zsg@zhoushuguangdeMacBook-Pro.local>

zrpc/internal/balancer/consistenthash/consistenthash.go

@@ -0,0 +1,97 @@
+package consistenthash
+
+import (
+	"context"
+
+	"github.com/zeromicro/go-zero/core/hash"
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/base"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+const (
+	Name = "consistent_hash"
+
+	defaultReplicaCount = 100
+)
+
+var emptyPickResult balancer.PickResult
+
+func init() {
+	balancer.Register(newBuilder())
+}
+
+type (
+	// hashKey is the key type for consistent hash in context.
+	hashKey struct{}
+	// pickerBuilder is a builder for picker.
+	pickerBuilder struct{}
+	// picker is a picker that uses consistent hash to pick a sub connection.
+	picker struct {
+		hashRing *hash.ConsistentHash
+		conns    map[string]balancer.SubConn
+	}
+)
+
+func (b *pickerBuilder) Build(info base.PickerBuildInfo) balancer.Picker {
+	readySCs := info.ReadySCs
+	if len(readySCs) == 0 {
+		return base.NewErrPicker(balancer.ErrNoSubConnAvailable)
+	}
+
+	conns := make(map[string]balancer.SubConn, len(readySCs))
+	hashRing := hash.NewCustomConsistentHash(defaultReplicaCount, hash.Hash)
+	for conn, connInfo := range readySCs {
+		addr := connInfo.Address.Addr
+		conns[addr] = conn
+		hashRing.Add(addr)
+	}
+
+	return &picker{
+		hashRing: hashRing,
+		conns:    conns,
+	}
+}
+
+func newBuilder() balancer.Builder {
+	return base.NewBalancerBuilder(Name, &pickerBuilder{}, base.Config{HealthCheck: true})
+}
+
+func (p *picker) Pick(info balancer.PickInfo) (balancer.PickResult, error) {
+	hashKey := GetHashKey(info.Ctx)
+	if len(hashKey) == 0 {
+		return emptyPickResult, status.Error(codes.InvalidArgument,
+			"[consistent_hash] missing hash key in context")
+	}
+
+	if addrAny, ok := p.hashRing.Get(hashKey); ok {
+		addr, ok := addrAny.(string)
+		if !ok {
+			return emptyPickResult, status.Error(codes.Internal,
+				"[consistent_hash] invalid addr type in consistent hash")
+		}
+
+		subConn, ok := p.conns[addr]
+		if !ok {
+			return emptyPickResult, status.Errorf(codes.Internal,
+				"[consistent_hash] no subConn for addr: %s", addr)
+		}
+
+		return balancer.PickResult{SubConn: subConn}, nil
+	}
+
+	return emptyPickResult, status.Errorf(codes.Unavailable,
+		"[consistent_hash] no matching conn for hashKey: %s", hashKey)
+}
+
+// SetHashKey sets the hash key into context.
+func SetHashKey(ctx context.Context, key string) context.Context {
+	return context.WithValue(ctx, hashKey{}, key)
+}
+
+// GetHashKey gets the hash key from context.
+func GetHashKey(ctx context.Context) string {
+	v, _ := ctx.Value(hashKey{}).(string)
+	return v
+}