[MM-54770] Add ability to export profile pictures and fix importing them (#25042)

* add ability to export pp and fix import

* remove unused nopSeeker

* remove debug log

* fix shadow vars

* generate a warning instead of an error when unable to export profile picture

* fix merge conflicts

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/import_functions.go

@@ -619,18 +619,34 @@ func (a *App) importUser(rctx request.CTX, data *imports.UserImportData, dryRun
 	}
 
 	if data.ProfileImage != nil {
-		var file io.ReadCloser
+		var file io.ReadSeeker
 		var err error
 		if data.ProfileImageData != nil {
-			file, err = data.ProfileImageData.Open()
+			// *zip.File does not support Seek, and we need a seeker to reset the cursor position after checking the picture dimension
+			var f io.ReadCloser
+			f, err = data.ProfileImageData.Open()
+			if err != nil {
+				rctx.Logger().Warn("Unable to open the profile image data.", mlog.Err(err))
+			} else {
+				limitedReader := io.LimitReader(f, *a.Config().FileSettings.MaxFileSize)
+				var b []byte
+				b, err = io.ReadAll(limitedReader)
+				if err != nil {
+					rctx.Logger().Warn("Unable to read all bytes from profile picture.", mlog.Err(err))
+				} else {
+					file = bytes.NewReader(b)
+				}
+			}
 		} else {
 			file, err = os.Open(*data.ProfileImage)
+			if err != nil {
+				rctx.Logger().Warn("Unable to open the profile image.", mlog.Err(err))
+			} else {
+				defer file.(*os.File).Close()
+			}
 		}
 
-		if err != nil {
-			rctx.Logger().Warn("Unable to open the profile image.", mlog.Err(err))
-		} else {
-			defer file.Close()
+		if file != nil {
 			if limitErr := checkImageLimits(file, *a.Config().FileSettings.MaxImageResolution); limitErr != nil {
 				return model.NewAppError("SetProfileImage", "api.user.upload_profile_user.check_image_limits.app_error", nil, "", http.StatusBadRequest)
 			}