[#96] Add zip compression

Signed-off-by: Denis Kirillov <denis@nspcc.ru>

README.md

@@ -156,6 +156,10 @@ if needed.
 All timing options accept values with suffixes, so "15s" is 15 seconds and
 "2m" is 2 minutes.
 
+### Zip streaming
+The gateway supports downloading files by common prefix (like dir) in zip format. You can enable compression 
+using config or `HTTP_GW_ZIP_COMPRESSION=true` environment variable.
+
 ### Logging
 
 `--verbose` flag enables gRPC logging and there is a number of environment
@@ -192,6 +196,9 @@ peers:
   0:
     address: grpc://s01.neofs.devenv:8080
     weight: 1
+    
+zip:
+  compression: false 
 ```
 
 To know nesting level of variable you need to cut off the prefix `HTTP_GW` from variable and split the rest parts by `_`.
@@ -311,6 +318,12 @@ $ wget http://localhost:8082/get/Dxhf4PNprrJHWWTG5RGLdfLkJiSQ3AQqit1MSnEPRkDZ/2m
 
 ```
 
+##### Zip
+You can download some dir (files with the same prefix) in zip (it will be compressed if config contains appropriate param):
+```
+$ wget http://localhost:8082/zip/Dxhf4PNprrJHWWTG5RGLdfLkJiSQ3AQqit1MSnEPRkDZ/common/prefix
+```
+
 #### Replies
 
 You get object contents in the reply body (if GET method was used), but at the same time you also get a

app.go

@@ -190,7 +190,7 @@ func (a *app) Serve(ctx context.Context) {
 	}()
 	edts := a.cfg.GetBool(cfgUploaderHeaderEnableDefaultTimestamp)
 	uploader := uploader.New(a.log, a.pool, edts)
-	downloader, err := downloader.New(ctx, a.log, a.pool)
+	downloader, err := downloader.New(a.log, downloader.Settings{ZipCompression: a.cfg.GetBool(cfgZipCompression)}, a.pool)
 	if err != nil {
 		a.log.Fatal("failed to create downloader", zap.Error(err))
 	}

downloader/download.go

@@ -231,12 +231,17 @@ func (o objectIDs) Slice() []string {
 type Downloader struct {
 	log      *zap.Logger
 	pool     pool.Pool
+	settings Settings
+}
+
+type Settings struct {
+	ZipCompression bool
 }
 
 // New creates an instance of Downloader using specified options.
-func New(ctx context.Context, log *zap.Logger, conns pool.Pool) (*Downloader, error) {
+func New(log *zap.Logger, settings Settings, conns pool.Pool) (*Downloader, error) {
 	var err error
-	d := &Downloader{log: log, pool: conns}
+	d := &Downloader{log: log, pool: conns, settings: settings}
 	if err != nil {
 		return nil, fmt.Errorf("failed to get neofs client's reusable artifacts: %w", err)
 	}
@@ -396,6 +401,11 @@ func (d *Downloader) DownloadZipped(c *fasthttp.RequestCtx) {
 
 func (d *Downloader) streamFiles(c *fasthttp.RequestCtx, cid *cid.ID, ids []*object.ID) error {
 	zipWriter := zip.NewWriter(c)
+	compression := zip.Store
+	if d.settings.ZipCompression {
+		compression = zip.Deflate
+	}
+
 	for _, id := range ids {
 		var r io.Reader
 		readerInitCtx, initReader := context.WithCancel(c)
@@ -413,7 +423,7 @@ func (d *Downloader) streamFiles(c *fasthttp.RequestCtx, cid *cid.ID, ids []*obj
 
 		header := &zip.FileHeader{
 			Name:     getFilename(obj),
-			Method:   zip.Store,
+			Method:   compression,
 			Modified: time.Now(),
 		}
 		entryWriter, err := zipWriter.CreateHeader(header)

settings.go

@@ -53,6 +53,9 @@ const (
 	// Peers.
 	cfgPeers = "peers"
 
+	// Zip compression.
+	cfgZipCompression = "zip.compression"
+
 	// Application.
 	cfgApplicationName    = "app.name"
 	cfgApplicationVersion = "app.version"
@@ -134,6 +137,9 @@ func settings() *viper.Viper {
 	// upload header
 	v.SetDefault(cfgUploaderHeaderEnableDefaultTimestamp, false)
 
+	// zip:
+	v.SetDefault(cfgZipCompression, false)
+
 	if err := v.BindPFlags(flags); err != nil {
 		panic(err)
 	}