[#38] service/object: Implement simplified object Head service

Implement Head service w/o linking object processing and restoration from
split-chain.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/object/head/distributed.go

@@ -0,0 +1,138 @@
+package headsvc
+
+import (
+	"context"
+	"sync"
+
+	"github.com/nspcc-dev/neofs-node/pkg/core/netmap"
+	"github.com/nspcc-dev/neofs-node/pkg/core/object"
+	"github.com/nspcc-dev/neofs-node/pkg/network"
+	"github.com/nspcc-dev/neofs-node/pkg/services/object/util"
+	"github.com/nspcc-dev/neofs-node/pkg/services/object_manager/placement"
+	"github.com/pkg/errors"
+)
+
+type distributedHeader struct {
+	*cfg
+
+	w *onceHeaderWriter
+
+	traverser *placement.Traverser
+}
+
+func (h *distributedHeader) head(ctx context.Context, prm *Prm) (*Response, error) {
+	if err := h.prepare(ctx, prm); err != nil {
+		return nil, errors.Wrapf(err, "(%T) could not prepare parameters", h)
+	}
+
+	return h.finish(ctx, prm)
+}
+
+func (h *distributedHeader) prepare(ctx context.Context, prm *Prm) error {
+	var err error
+
+	// get latest network map
+	nm, err := netmap.GetLatestNetworkMap(h.netMapSrc)
+	if err != nil {
+		return errors.Wrapf(err, "(%T) could not get latest network map", h)
+	}
+
+	// get container to store the object
+	cnr, err := h.cnrSrc.Get(prm.addr.GetContainerID())
+	if err != nil {
+		return errors.Wrapf(err, "(%T) could not get container by ID", h)
+	}
+
+	// allocate placement traverser options
+	traverseOpts := make([]placement.Option, 0, 4)
+
+	// add common options
+	traverseOpts = append(traverseOpts,
+		// set processing container
+		placement.ForContainer(cnr),
+		// set success count (1st incoming header)
+		placement.SuccessAfter(1),
+	)
+
+	// create placement builder from network map
+	builder := placement.NewNetworkMapBuilder(nm)
+
+	if prm.local {
+		// use local-only placement builder
+		builder = util.NewLocalPlacement(placement.NewNetworkMapBuilder(nm), h.localAddrSrc)
+	}
+
+	// set placement builder
+	traverseOpts = append(traverseOpts, placement.UseBuilder(builder))
+
+	// build placement traverser
+	if h.traverser, err = placement.NewTraverser(traverseOpts...); err != nil {
+		return errors.Wrapf(err, "(%T) could not build placement traverser", h)
+	}
+
+	return nil
+}
+
+func (h *distributedHeader) finish(ctx context.Context, prm *Prm) (*Response, error) {
+	resp := new(Response)
+
+	h.w = &onceHeaderWriter{
+		once:      new(sync.Once),
+		traverser: h.traverser,
+		resp:      resp,
+	}
+
+	ctx, h.w.cancel = context.WithCancel(ctx)
+
+loop:
+	for {
+		addrs := h.traverser.Next()
+		if len(addrs) == 0 {
+			break
+		}
+
+		wg := new(sync.WaitGroup)
+
+		for i := range addrs {
+			wg.Add(1)
+
+			addr := addrs[i]
+
+			if err := h.workerPool.Submit(func() {
+				defer wg.Done()
+
+				var header interface {
+					head(context.Context, *Prm, func(*object.Object)) error
+				}
+
+				if network.IsLocalAddress(h.localAddrSrc, addr) {
+					header = &localHeader{
+						storage: h.localStore,
+					}
+				} else {
+					header = &remoteHeader{
+						key:  h.key,
+						node: addr,
+					}
+				}
+
+				if err := header.head(ctx, prm, h.w.write); err != nil {
+					// TODO: log error
+					return
+				}
+			}); err != nil {
+				wg.Done()
+				// TODO: log error
+				break loop
+			}
+		}
+
+		wg.Wait()
+	}
+
+	if !h.traverser.Success() {
+		return nil, errors.Errorf("(%T) incomplete object Head operation", h)
+	}
+
+	return resp, nil
+}