Golang Request.CreateReply方法代碼示例

// MaybeWrap wraps the given argument in a batch, unless it is already one.
func maybeWrap(args proto.Request) (*proto.BatchRequest, func(*proto.BatchResponse) proto.Response) {
	if ba, ok := args.(*proto.BatchRequest); ok {
		return ba, func(br *proto.BatchResponse) proto.Response { return br }
	}
	ba := &proto.BatchRequest{}
	ba.RequestHeader = *(gogoproto.Clone(args.Header()).(*proto.RequestHeader))
	ba.Add(args)
	return ba, func(br *proto.BatchResponse) proto.Response {
		var unwrappedReply proto.Response
		if len(br.Responses) == 0 {
			unwrappedReply = args.CreateReply()
		} else {
			unwrappedReply = br.Responses[0].GetInner()
		}
		// The ReplyTxn is propagated from one response to the next request,
		// and we adopt the mechanism that whenever the Txn changes, it needs
		// to be set in the reply, for example to ratched up the transaction
		// timestamp on writes when necessary.
		// This is internally necessary to sequentially execute the batch,
		// so it makes some sense to take the burden of updating the Txn
		// from TxnCoordSender - it will only need to act on retries/aborts
		// in the future.
		unwrappedReply.Header().Txn = br.Txn
		if unwrappedReply.Header().Error == nil {
			unwrappedReply.Header().Error = br.Error
		}
		return unwrappedReply
	}
}

// sendRPC sends one or more RPCs to replicas from the supplied proto.Replica
// slice. First, replicas which have gossiped addresses are corralled (and
// rearranged depending on proximity and whether the request needs to go to a
// leader) and then sent via rpc.Send, with requirement that one RPC to a
// server must succeed. Returns an RPC error if the request could not be sent.
// Note that the reply may contain a higher level error and must be checked in
// addition to the RPC error.
func (ds *DistSender) sendRPC(raftID proto.RaftID, replicas replicaSlice, order rpc.OrderingPolicy,
	args proto.Request, reply proto.Response) error {
	if len(replicas) == 0 {
		return util.Errorf("%s: replicas set is empty", args.Method())
	}

	// Build a slice of replica addresses (if gossiped).
	var addrs []net.Addr
	replicaMap := map[string]*proto.Replica{}
	for i := range replicas {
		nd := &replicas[i].NodeDesc
		addr := util.MakeUnresolvedAddr(nd.Address.Network, nd.Address.Address)
		addrs = append(addrs, addr)
		replicaMap[addr.String()] = &replicas[i].Replica
	}
	if len(addrs) == 0 {
		return noNodeAddrsAvailError{}
	}

	// TODO(pmattis): This needs to be tested. If it isn't set we'll
	// still route the request appropriately by key, but won't receive
	// RangeNotFoundErrors.
	args.Header().RaftID = raftID

	// Set RPC opts with stipulation that one of N RPCs must succeed.
	rpcOpts := rpc.Options{
		N:               1,
		Ordering:        order,
		SendNextTimeout: defaultSendNextTimeout,
		Timeout:         defaultRPCTimeout,
	}
	// getArgs clones the arguments on demand for all but the first replica.
	firstArgs := true
	getArgs := func(addr net.Addr) interface{} {
		var a proto.Request
		// Use the supplied args proto if this is our first address.
		if firstArgs {
			firstArgs = false
			a = args
		} else {
			// Otherwise, copy the args value and set the replica in the header.
			a = gogoproto.Clone(args).(proto.Request)
		}
		a.Header().Replica = *replicaMap[addr.String()]
		return a
	}
	// RPCs are sent asynchronously and there is no synchronized access to
	// the reply object, so we don't pass itself to rpcSend.
	// Otherwise there maybe a race case:
	// If the RPC call times out using our original reply object,
	// we must not use it any more; the rpc call might still return
	// and just write to it at any time.
	// args.CreateReply() should be cheaper than gogoproto.Clone which use reflect.
	getReply := func() interface{} {
		return args.CreateReply()
	}

	replies, err := ds.rpcSend(rpcOpts, "Node."+args.Method().String(),
		addrs, getArgs, getReply, ds.gossip.RPCContext)
	if err == nil {
		// Set content of replies[0] back to reply
		dst := reflect.ValueOf(reply).Elem()
		dst.Set(reflect.ValueOf(replies[0]).Elem())
	}

	return err
}

// applyRaftCommandInBatch executes the command in a batch engine and
// returns the batch containing the results. The caller is responsible
// for committing the batch, even on error.
func (r *Range) applyRaftCommandInBatch(ctx context.Context, index uint64, originNode proto.RaftNodeID,
	args proto.Request, ms *engine.MVCCStats) (engine.Engine, proto.Response, error) {
	// Create a new batch for the command to ensure all or nothing semantics.
	batch := r.rm.Engine().NewBatch()

	if lease := r.getLease(); args.Method() != proto.InternalLeaderLease &&
		(!lease.OwnedBy(originNode) || !lease.Covers(args.Header().Timestamp)) {
		// Verify the leader lease is held, unless this command is trying to
		// obtain it. Any other Raft command has had the leader lease held
		// by the replica at proposal time, but this may no longer be the case.
		// Corruption aside, the most likely reason is a leadership change (the
		// most recent leader assumes responsibility for all past timestamps as
		// well). In that case, it's not valid to go ahead with the execution:
		// Writes must be aware of the last time the mutated key was read, and
		// since reads are served locally by the lease holder without going
		// through Raft, a read which was not taken into account may have been
		// served. Hence, we must retry at the current leader.
		//
		// It's crucial that we don't update the response cache for the error
		// returned below since the request is going to be retried with the
		// same ClientCmdID and would get the distributed sender stuck in an
		// infinite loop, retrieving a stale NotLeaderError over and over
		// again, even when proposing at the correct replica.
		return batch, nil, r.newNotLeaderError(lease, originNode)
	}

	// Check the response cache to ensure idempotency.
	if proto.IsWrite(args) {
		if reply, err := r.respCache.GetResponse(batch, args.Header().CmdID); err != nil {
			// Any error encountered while fetching the response cache entry means corruption.
			return batch, reply, newReplicaCorruptionError(util.Errorf("could not read from response cache"), err)
		} else if reply != nil {
			if log.V(1) {
				log.Infoc(ctx, "found response cache entry for %+v", args.Header().CmdID)
			}
			// TODO(tamird): move this into the response cache itself
			defer func() { reply.Header().Error = nil }()
			// We successfully read from the response cache, so return whatever error
			// was present in the cached entry (if any).
			return batch, reply, reply.Header().GoError()
		}
	}

	// Execute the command.
	reply, intents, rErr := r.executeCmd(batch, ms, args)
	// Regardless of error, add result to the response cache if this is
	// a write method. This must be done as part of the execution of
	// raft commands so that every replica maintains the same responses
	// to continue request idempotence, even if leadership changes.
	if proto.IsWrite(args) {
		if rErr == nil {
			// If command was successful, flush the MVCC stats to the batch.
			if err := r.stats.MergeMVCCStats(batch, ms, args.Header().Timestamp.WallTime); err != nil {
				log.Fatalc(ctx, "setting mvcc stats in a batch should never fail: %s", err)
			}
		} else {
			// Otherwise, reset the batch to clear out partial execution and
			// prepare for the failed response cache entry.
			batch.Close()
			batch = r.rm.Engine().NewBatch()
		}
		// TODO(tamird): move this into the response cache itself
		if reply == nil {
			reply = args.CreateReply()
		}
		if reply.Header().Error != nil {
			panic("the world is on fire")
		}
		reply.Header().SetGoError(rErr)
		if err := r.respCache.PutResponse(batch, args.Header().CmdID, reply); err != nil {
			log.Fatalc(ctx, "putting a response cache entry in a batch should never fail: %s", err)
		}
		reply.Header().Error = nil
	}

	// If the execution of the command wasn't successful, stop here.
	if rErr != nil {
		return batch, reply, rErr
	}

	// On success and only on the replica on which this command originated,
	// resolve skipped intents asynchronously.
	if originNode == r.rm.RaftNodeID() {
		r.handleSkippedIntents(args, intents)
	}

	return batch, reply, nil
}

// sendRPC sends one or more RPCs to replicas from the supplied proto.Replica
// slice. First, replicas which have gossiped addresses are corralled (and
// rearranged depending on proximity and whether the request needs to go to a
// leader) and then sent via rpc.Send, with requirement that one RPC to a
// server must succeed. Returns an RPC error if the request could not be sent.
// Note that the reply may contain a higher level error and must be checked in
// addition to the RPC error.
func (ds *DistSender) sendRPC(trace *tracer.Trace, rangeID proto.RangeID, replicas replicaSlice, order rpc.OrderingPolicy,
	args proto.Request) (proto.Response, error) {
	if len(replicas) == 0 {
		// TODO(tschottdorf): this gets in the way of some tests. Consider
		// refactoring so that gossip is mocked out more easily. Provisional
		// code. return nil, util.Errorf("%s: replicas set is empty",
		// args.Method())
	}

	// Build a slice of replica addresses (if gossiped).
	var addrs []net.Addr
	replicaMap := map[string]*proto.Replica{}
	for i := range replicas {
		addr := replicas[i].NodeDesc.Address
		addrs = append(addrs, addr)
		replicaMap[addr.String()] = &replicas[i].Replica
	}
	if len(addrs) == 0 {
		// TODO(tschottdorf): see len(replicas) above.
		// return nil, noNodeAddrsAvailError{}
	}

	// TODO(pmattis): This needs to be tested. If it isn't set we'll
	// still route the request appropriately by key, but won't receive
	// RangeNotFoundErrors.
	args.Header().RangeID = rangeID

	// Set RPC opts with stipulation that one of N RPCs must succeed.
	rpcOpts := rpc.Options{
		N:               1,
		Ordering:        order,
		SendNextTimeout: defaultSendNextTimeout,
		Timeout:         defaultRPCTimeout,
		Trace:           trace,
	}
	// getArgs clones the arguments on demand for all but the first replica.
	firstArgs := true
	getArgs := func(addr net.Addr) gogoproto.Message {
		var a proto.Request
		// Use the supplied args proto if this is our first address.
		if firstArgs {
			firstArgs = false
			a = args
		} else {
			// Otherwise, copy the args value and set the replica in the header.
			a = gogoproto.Clone(args).(proto.Request)
		}
		if addr != nil {
			// TODO(tschottdorf): see len(replicas) above.
			a.Header().Replica = *replicaMap[addr.String()]
		}
		return a
	}
	// RPCs are sent asynchronously and there is no synchronized access to
	// the reply object, so we don't pass itself to RPCSend.
	// Otherwise there maybe a race case:
	// If the RPC call times out using our original reply object,
	// we must not use it any more; the rpc call might still return
	// and just write to it at any time.
	// args.CreateReply() should be cheaper than gogoproto.Clone which use reflect.
	getReply := func() gogoproto.Message {
		return args.CreateReply()
	}

	replies, err := ds.rpcSend(rpcOpts, "Node."+args.Method().String(),
		addrs, getArgs, getReply, ds.gossip.RPCContext)
	if err != nil {
		return nil, err
	}
	return replies[0].(proto.Response), nil
}