serve s3: fixes before merge

- add context to log and fallthrough to error log level
- test: use rclone random lib to generate random strings
- calculate hash from vfs cache if file is uploading
- add server started log with server url
- remove md5 hasher

cmd/serve/s3/utils.go

@@ -4,11 +4,14 @@ import (
 	"context"
 	"encoding/hex"
 	"fmt"
+	"io"
+	"os"
 	"path"
 	"strings"
 
 	"github.com/Mikubill/gofakes3"
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/hash"
 	"github.com/rclone/rclone/vfs"
 )
 
@@ -47,9 +50,29 @@ func getFileHash(node interface{}) string {
 
 	switch b := node.(type) {
 	case vfs.Node:
-		o = b.DirEntry().(fs.Object)
-	case fs.DirEntry:
-		o = b.(fs.Object)
+		fsObj, ok := b.DirEntry().(fs.Object)
+		if !ok {
+			fs.Debugf("serve s3", "File uploading - reading hash from VFS cache")
+			in, err := b.Open(os.O_RDONLY)
+			if err != nil {
+				return ""
+			}
+			defer func() {
+				_ = in.Close()
+			}()
+			h, err := hash.NewMultiHasherTypes(hash.NewHashSet(Opt.hashType))
+			if err != nil {
+				return ""
+			}
+			_, err = io.Copy(h, in)
+			if err != nil {
+				return ""
+			}
+			return h.Sums()[Opt.hashType]
+		}
+		o = fsObj
+	case fs.Object:
+		o = b
 	}
 
 	hash, err := o.Hash(context.Background(), Opt.hashType)