[#73] Uploader, downloader structures refactoring

Signed-off-by: Marina Biryukova <m.biryukova@yadro.com>

internal/handler/multipart.go

@@ -0,0 +1,47 @@
+package handler
+
+import (
+	"io"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-http-gw/internal/handler/multipart"
+	"git.frostfs.info/TrueCloudLab/frostfs-http-gw/internal/logs"
+	"go.uber.org/zap"
+)
+
+// MultipartFile provides standard ReadCloser interface and also allows one to
+// get file name, it's used for multipart uploads.
+type MultipartFile interface {
+	io.ReadCloser
+	FileName() string
+}
+
+func fetchMultipartFile(l *zap.Logger, r io.Reader, boundary string) (MultipartFile, error) {
+	// To have a custom buffer (3mb) the custom multipart reader is used.
+	// Default reader uses 4KiB chunks, which slow down upload speed up to 400%
+	// https://github.com/golang/go/blob/91b9915d3f6f8cd2e9e9fda63f67772803adfa03/src/mime/multipart/multipart.go#L32
+	reader := multipart.NewReader(r, boundary)
+
+	for {
+		part, err := reader.NextPart()
+		if err != nil {
+			return nil, err
+		}
+
+		name := part.FormName()
+		if name == "" {
+			l.Debug(logs.IgnorePartEmptyFormName)
+			continue
+		}
+
+		filename := part.FileName()
+
+		// ignore multipart/form-data values
+		if filename == "" {
+			l.Debug(logs.IgnorePartEmptyFilename, zap.String("form", name))
+
+			continue
+		}
+
+		return part, nil
+	}
+}