fix(files): update all callers to provide seekable readers for S3 uploads

Update all code paths that pass file content to the storage layer to
provide io.ReadSeeker instead of io.Reader:

- Avatar upload: use bytes.NewReader instead of bytes.Buffer
- Background upload handler: use bytes.NewReader instead of bytes.Buffer
- Unsplash background: buffer response body into bytes.NewReader
- Dump restore: buffer zip entry into bytes.NewReader
- Migration structure: pass bytes.NewReader directly instead of wrapping
  in io.NopCloser
- Task attachment: change NewAttachment parameter from io.ReadCloser to
  io.ReadSeeker

pkg/models/task_attachment.go

@@ -58,8 +58,7 @@ func (*TaskAttachment) TableName() string {
 }
 
 // NewAttachment creates a new task attachment
-// Note: I'm not sure if only accepting an io.ReadCloser and not an afero.File or os.File instead is a good way of doing things.
-func (ta *TaskAttachment) NewAttachment(s *xorm.Session, f io.ReadCloser, realname string, realsize uint64, a web.Auth) error {
+func (ta *TaskAttachment) NewAttachment(s *xorm.Session, f io.ReadSeeker, realname string, realsize uint64, a web.Auth) error {
 
 	// Store the file
 	file, err := files.Create(f, realname, realsize, a)

pkg/modules/avatar/upload/upload.go

@@ -171,7 +171,7 @@ func StoreAvatarFile(s *xorm.Session, u *user.User, src io.Reader) (err error) {
 	}
 
 	// Save the file
-	f, err := files.CreateWithMime(buf, "avatar.png", uint64(buf.Len()), u, "image/png")
+	f, err := files.CreateWithMime(bytes.NewReader(buf.Bytes()), "avatar.png", uint64(buf.Len()), u, "image/png")
 	if err != nil {
 		return err
 	}

pkg/modules/background/handler/background.go

@@ -278,7 +278,7 @@ func SaveBackgroundFile(s *xorm.Session, auth web.Auth, project *models.Project,
 		return err
 	}
 
-	f, err := files.Create(&buf, filename, filesize, auth)
+	f, err := files.Create(bytes.NewReader(buf.Bytes()), filename, filesize, auth)
 	if err != nil {
 		return err
 	}

pkg/modules/background/unsplash/unsplash.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"io"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -279,8 +280,14 @@ func (p *Provider) Set(s *xorm.Session, image *background.Image, project *models
 	}
 	log.Debugf("Pinged unsplash download endpoint for photo %s", image.ID)
 
+	// Buffer the response body so we have a seekable reader for S3 uploads
+	bodyBytes, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return err
+	}
+
 	// Save it as a file in vikunja
-	file, err := files.Create(resp.Body, "", 0, auth)
+	file, err := files.Create(bytes.NewReader(bodyBytes), "", uint64(len(bodyBytes)), auth)
 	if err != nil {
 		return
 	}

pkg/modules/dump/restore.go

@@ -181,11 +181,15 @@ func Restore(filename string, overrideConfig bool) error {
 			return fmt.Errorf("could not open file %s: %w", i, err)
 		}
 
-		if err := f.Save(fc); err != nil {
-			return fmt.Errorf("could not save file: %w", err)
+		content, err := io.ReadAll(fc)
+		_ = fc.Close()
+		if err != nil {
+			return fmt.Errorf("could not read file %s: %w", i, err)
 		}
 
-		_ = fc.Close()
+		if err := f.Save(bytes.NewReader(content)); err != nil {
+			return fmt.Errorf("could not save file: %w", err)
+		}
 		log.Infof("Restored file %s", i)
 	}
 	log.Infof("Restored %d files.", len(filesFiles))

pkg/modules/migration/create_from_structure.go

@@ -18,7 +18,6 @@ package migration
 
 import (
 	"bytes"
-	"io"
 
 	"xorm.io/xorm"
 
@@ -395,8 +394,7 @@ func createProjectWithEverything(s *xorm.Session, project *models.ProjectWithTas
 				oldID := a.ID
 				a.ID = 0
 				a.TaskID = t.ID
-				fr := io.NopCloser(bytes.NewReader(a.File.FileContent))
-				err = a.NewAttachment(s, fr, a.File.Name, a.File.Size, user)
+				err = a.NewAttachment(s, bytes.NewReader(a.File.FileContent), a.File.Name, a.File.Size, user)
 				if err != nil {
 					if models.IsErrTaskAttachmentIsTooLarge(err) {
 						log.Warningf("[creating structure] Attachment %s is too large (%d bytes), skipping: %v", a.File.Name, a.File.Size, err)