Added reader seek start for multipart files on request retry

go.mod

@@ -1,5 +1,5 @@
 module github.com/go-resty/resty/v2
 
-require golang.org/x/net v0.0.0-20211029224645-99673261e6eb
+require golang.org/x/net v0.0.0-20220325170049-de3da57026de
 
 go 1.11

go.sum

@@ -1,7 +1,2 @@
-golang.org/x/net v0.0.0-20211029224645-99673261e6eb h1:pirldcYWx7rx7kE5r+9WsOXPXK0+WH5+uZ7uPmJ44uM=
-golang.org/x/net v0.0.0-20211029224645-99673261e6eb/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
-golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/net v0.0.0-20220325170049-de3da57026de h1:pZB1TWnKi+o4bENlbzAgLrEbY4RMYmUIRobMcSmfeYc=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=

retry.go

@@ -6,6 +6,7 @@ package resty
 
 import (
 	"context"
+	"io"
 	"math"
 	"math/rand"
 	"sync"
@@ -125,6 +126,14 @@ func Backoff(operation func() (*Response, error), options ...Option) error {
 			return err
 		}
 
+		for _, f := range resp.Request.multipartFiles {
+			if rs, ok := f.Reader.(io.ReadSeeker); ok {
+				if _, err := rs.Seek(0, io.SeekStart); err != nil {
+					return err
+				}
+			}
+		}
+
 		for _, hook := range opts.retryHooks {
 			hook(resp, err)
 		}