[MM-57500] Streaming support for importing file attachments (#26629)

* Bulk import: stream file attachments uploads

* Add comment with context on buffer size

* Add file name to logs

* Use sha256 to do checksum

* Fix bad merge

* Fix import file

* Update test

---------

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

server/channels/app/file.go

@@ -633,6 +633,12 @@ func UploadFileSetRaw() func(t *UploadFileTask) {
 	}
 }
 
+func UploadFileSetExtractContent(value bool) func(t *UploadFileTask) {
+	return func(t *UploadFileTask) {
+		t.ExtractContent = value
+	}
+}
+
 type UploadFileTask struct {
 	Logger mlog.LoggerIFace
 
@@ -659,6 +665,10 @@ type UploadFileTask struct {
 	// the file.  Plugins are still invoked.
 	Raw bool
 
+	// Whether or not to extract file attachments content
+	// This is used by the bulk import process.
+	ExtractContent bool
+
 	//=============================================================
 	// Internal state
 
@@ -729,14 +739,15 @@ func (a *App) UploadFileX(c request.CTX, channelID, name string, input io.Reader
 	))
 
 	t := &UploadFileTask{
-		Logger:      c.Logger(),
-		ChannelId:   filepath.Base(channelID),
-		Name:        filepath.Base(name),
-		Input:       input,
-		maxFileSize: *a.Config().FileSettings.MaxFileSize,
-		maxImageRes: *a.Config().FileSettings.MaxImageResolution,
-		imgDecoder:  a.ch.imgDecoder,
-		imgEncoder:  a.ch.imgEncoder,
+		Logger:         c.Logger(),
+		ChannelId:      filepath.Base(channelID),
+		Name:           filepath.Base(name),
+		Input:          input,
+		maxFileSize:    *a.Config().FileSettings.MaxFileSize,
+		maxImageRes:    *a.Config().FileSettings.MaxImageResolution,
+		imgDecoder:     a.ch.imgDecoder,
+		imgEncoder:     a.ch.imgEncoder,
+		ExtractContent: true,
 	}
 	for _, o := range opts {
 		o(t)
@@ -803,7 +814,7 @@ func (a *App) UploadFileX(c request.CTX, channelID, name string, input io.Reader
 		}
 	}
 
-	if *a.Config().FileSettings.ExtractContent {
+	if *a.Config().FileSettings.ExtractContent && t.ExtractContent {
 		infoCopy := *t.fileinfo
 		a.Srv().GoBuffered(func() {
 			err := a.ExtractContentFromFileInfo(c, &infoCopy)
@@ -1264,15 +1275,6 @@ func (a *App) SetFileSearchableContent(rctx request.CTX, fileID string, data str
 	return nil
 }
 
-func (a *App) getFileInfoIgnoreCloudLimit(rctx request.CTX, fileID string) (*model.FileInfo, *model.AppError) {
-	fileInfo, appErr := a.Srv().getFileInfo(fileID)
-	if appErr == nil {
-		a.generateMiniPreview(rctx, fileInfo)
-	}
-
-	return fileInfo, appErr
-}
-
 func (a *App) GetFileInfos(rctx request.CTX, page, perPage int, opt *model.GetFileInfosOptions) ([]*model.FileInfo, *model.AppError) {
 	fileInfos, err := a.Srv().Store().FileInfo().GetWithOptions(page, perPage, opt)
 	if err != nil {
@@ -1317,20 +1319,6 @@ func (a *App) GetFile(rctx request.CTX, fileID string) ([]byte, *model.AppError)
 	return data, nil
 }
 
-func (a *App) getFileIgnoreCloudLimit(rctx request.CTX, fileID string) ([]byte, *model.AppError) {
-	info, err := a.getFileInfoIgnoreCloudLimit(rctx, fileID)
-	if err != nil {
-		return nil, err
-	}
-
-	data, err := a.ReadFile(info.Path)
-	if err != nil {
-		return nil, err
-	}
-
-	return data, nil
-}
-
 func (a *App) CopyFileInfos(rctx request.CTX, userID string, fileIDs []string) ([]string, *model.AppError) {
 	var newFileIds []string
 

server/channels/app/import_functions.go

@@ -6,7 +6,7 @@ package app
 import (
 	"bytes"
 	"context"
-	"crypto/sha1"
+	"crypto/sha256"
 	"errors"
 	"fmt"
 	"io"
@@ -14,6 +14,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"sync"
 
 	"github.com/mattermost/mattermost/server/public/model"
 	"github.com/mattermost/mattermost/server/public/shared/mlog"
@@ -1272,10 +1273,65 @@ func (a *App) importReplies(rctx request.CTX, data []imports.ReplyImportData, po
 	return nil
 }
 
+func compareFilesContent(fileA, fileB io.Reader, bufSize int64) (bool, error) {
+	aHash := sha256.New()
+	bHash := sha256.New()
+
+	if bufSize == 0 {
+		// This buffer size was selected after some extensive benchmarking
+		// (BenchmarkCompareFilesContent) and it showed to provide
+		// a good compromise between processing speed and allocated memory,
+		// especially in the common case of the readers being part of an S3 stored ZIP file.
+		// See https://github.com/mattermost/mattermost/pull/26629 for full context.
+		bufSize = 1024 * 1024 * 2 // 2MB
+	}
+
+	var nA, nB int64
+	var errA, errB error
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		var buf []byte
+		// If the reader has a WriteTo method (e.g. *os.File)
+		// we can avoid the buffer allocation.
+		if _, ok := fileA.(io.WriterTo); !ok {
+			buf = make([]byte, bufSize)
+		}
+		nA, errA = io.CopyBuffer(aHash, fileA, buf)
+	}()
+	go func() {
+		defer wg.Done()
+		var buf []byte
+		// If the reader has a WriteTo method (e.g. *os.File)
+		// we can avoid the buffer allocation.
+		if _, ok := fileA.(io.WriterTo); !ok {
+			buf = make([]byte, bufSize)
+		}
+		nB, errB = io.CopyBuffer(bHash, fileB, buf)
+	}()
+	wg.Wait()
+
+	if errA != nil {
+		return false, fmt.Errorf("failed to compare files: %w", errA)
+	}
+
+	if errB != nil {
+		return false, fmt.Errorf("failed to compare files: %w", errB)
+	}
+
+	if nA != nB {
+		return false, fmt.Errorf("size mismatch: %d != %d", nA, nB)
+	}
+
+	return bytes.Equal(aHash.Sum(nil), bHash.Sum(nil)), nil
+}
+
 func (a *App) importAttachment(rctx request.CTX, data *imports.AttachmentImportData, post *model.Post, teamID string, extractContent bool) (*model.FileInfo, *model.AppError) {
 	var (
-		name string
-		file io.Reader
+		name     string
+		file     io.ReadCloser
+		fileSize int64
 	)
 	if data.Data != nil {
 		zipFile, err := data.Data.Open()
@@ -1284,7 +1340,8 @@ func (a *App) importAttachment(rctx request.CTX, data *imports.AttachmentImportD
 		}
 		defer zipFile.Close()
 		name = data.Data.Name
-		file = zipFile.(io.Reader)
+		fileSize = int64(data.Data.UncompressedSize64)
+		file = zipFile
 
 		rctx.Logger().Info("Preparing file upload from ZIP", mlog.String("file_name", name), mlog.Uint("file_size", data.Data.UncompressedSize64))
 	} else {
@@ -1296,58 +1353,81 @@ func (a *App) importAttachment(rctx request.CTX, data *imports.AttachmentImportD
 		name = realFile.Name()
 		file = realFile
 
-		fields := []mlog.Field{mlog.String("file_name", name)}
-		if info, err := realFile.Stat(); err != nil {
-			fields = append(fields, mlog.Int("file_size", info.Size()))
+		info, err := realFile.Stat()
+		if err != nil {
+			return nil, model.NewAppError("BulkImport", "app.import.attachment.file_stat.error", map[string]any{"FilePath": *data.Path}, "", http.StatusBadRequest).Wrap(err)
 		}
-		rctx.Logger().Info("Preparing file upload from file system", fields...)
+		fileSize = info.Size()
+
+		rctx.Logger().Info("Preparing file upload from file system", mlog.String("file_name", name), mlog.Int("file_size", info.Size()))
 	}
 
 	timestamp := utils.TimeFromMillis(post.CreateAt)
 
-	fileData, err := io.ReadAll(file)
-	if err != nil {
-		return nil, model.NewAppError("BulkImport", "app.import.attachment.read_file_data.error", map[string]any{"FilePath": *data.Path}, "", http.StatusBadRequest)
-	}
-
 	// Go over existing files in the post and see if there already exists a file with the same name, size and hash. If so - skip it
 	if post.Id != "" {
-		oldFiles, err := a.getFileInfosForPostIgnoreCloudLimit(rctx, post.Id, true, false)
+		oldFiles, err := a.Srv().Store().FileInfo().GetForPost(post.Id, true, false, true)
 		if err != nil {
 			return nil, model.NewAppError("BulkImport", "app.import.attachment.file_upload.error", map[string]any{"FilePath": *data.Path}, "", http.StatusBadRequest)
 		}
 		for _, oldFile := range oldFiles {
-			if oldFile.Name != path.Base(name) || oldFile.Size != int64(len(fileData)) {
+			if oldFile.Name != path.Base(name) || oldFile.Size != fileSize {
 				continue
 			}
 
-			// check sha1
-			newHash := sha1.Sum(fileData)
-			oldFileData, err := a.getFileIgnoreCloudLimit(rctx, oldFile.Id)
-			if err != nil {
+			oldFileReader, appErr := a.FileReader(oldFile.Path)
+			if appErr != nil {
 				return nil, model.NewAppError("BulkImport", "app.import.attachment.file_upload.error", map[string]any{"FilePath": *data.Path}, "", http.StatusBadRequest)
 			}
-			oldHash := sha1.Sum(oldFileData)
+			defer oldFileReader.Close()
 
-			if bytes.Equal(oldHash[:], newHash[:]) {
-				rctx.Logger().Info("Skipping uploading of file because name already exists", mlog.String("file_name", name))
+			if ok, err := compareFilesContent(oldFileReader, file, 0); err != nil {
+				rctx.Logger().Error("Failed to compare files content", mlog.String("file_name", name), mlog.Err(err))
+			} else if ok {
+				rctx.Logger().Info("Skipping uploading of file because name already exists and content matches", mlog.String("file_name", name))
 				return oldFile, nil
 			}
+
+			rctx.Logger().Info("File contents don't match, will re-upload", mlog.String("file_name", name))
+
+			// Since compareFilesContent needs to read the whole file we need to
+			// either seek back (local file) or re-open it (zip file).
+			if f, ok := file.(*os.File); ok {
+				rctx.Logger().Info("File is *os.File, can seek", mlog.String("file_name", name))
+				if _, err := f.Seek(0, io.SeekStart); err != nil {
+					return nil, model.NewAppError("BulkImport", "app.import.attachment.seek_file.error", map[string]any{"FilePath": *data.Path}, "", http.StatusBadRequest).Wrap(err)
+				}
+			} else if data.Data != nil {
+				rctx.Logger().Info("File is from ZIP, can't seek, opening again", mlog.String("file_name", name))
+				file.Close()
+
+				f, err := data.Data.Open()
+				if err != nil {
+					return nil, model.NewAppError("BulkImport", "app.import.attachment.bad_file.error", map[string]any{"FilePath": *data.Path}, "", http.StatusBadRequest).Wrap(err)
+				}
+				defer f.Close()
+
+				file = f
+			}
+
+			break
 		}
 	}
 
 	rctx.Logger().Info("Uploading file with name", mlog.String("file_name", name))
 
-	fileInfo, appErr := a.DoUploadFile(rctx, timestamp, teamID, post.ChannelId, post.UserId, name, fileData, extractContent)
+	fileInfo, appErr := a.UploadFileX(rctx, post.ChannelId, name, file,
+		UploadFileSetTeamId(teamID),
+		UploadFileSetUserId(post.UserId),
+		UploadFileSetTimestamp(timestamp),
+		UploadFileSetContentLength(fileSize),
+		UploadFileSetExtractContent(extractContent),
+	)
 	if appErr != nil {
 		rctx.Logger().Error("Failed to upload file", mlog.Err(appErr), mlog.String("file_name", name))
 		return nil, appErr
 	}
 
-	if fileInfo.IsImage() && !fileInfo.IsSvg() {
-		a.HandleImages(rctx, []string{fileInfo.PreviewPath}, []string{fileInfo.ThumbnailPath}, [][]byte{fileData})
-	}
-
 	return fileInfo, nil
 }
 

server/channels/app/import_functions_test.go

@@ -6,6 +6,7 @@ package app
 import (
 	"archive/zip"
 	"context"
+	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -21,6 +22,7 @@ import (
 	"github.com/mattermost/mattermost/server/v8/channels/testlib"
 	"github.com/mattermost/mattermost/server/v8/channels/utils"
 	"github.com/mattermost/mattermost/server/v8/channels/utils/fileutils"
+	"github.com/mattermost/mattermost/server/v8/platform/shared/filestore"
 )
 
 func TestImportImportScheme(t *testing.T) {
@@ -4383,6 +4385,85 @@ func TestImportPostAndRepliesWithAttachments(t *testing.T) {
 		assert.Contains(t, attachments[0].Path, "noteam")
 		AssertFileIdsInPost(attachments, th, t)
 	})
+
+	t.Run("import existing post with different attachment's content", func(t *testing.T) {
+		tmpDir := os.TempDir()
+		filePath := filepath.Join(tmpDir, "test_diff.png")
+
+		t.Run("different size", func(t *testing.T) {
+			testImage := filepath.Join(testsDir, "test.png")
+			imageData, err := os.ReadFile(testImage)
+			require.NoError(t, err)
+			err = os.WriteFile(filePath, imageData, 0644)
+			require.NoError(t, err)
+
+			data.Post.Attachments = &[]imports.AttachmentImportData{{Path: &filePath}}
+			data.Post.Replies = nil
+			data.Post.Message = model.NewString("new post")
+			errLine, appErr := th.App.importMultiplePostLines(th.Context, []imports.LineImportWorkerData{data}, false, true)
+			require.Nil(t, appErr)
+			require.Equal(t, 0, errLine)
+
+			attachments := GetAttachments(user3.Id, th, t)
+			require.Len(t, attachments, 2)
+			assert.Contains(t, attachments[1].Path, team.Id)
+			AssertFileIdsInPost(attachments[1:], th, t)
+
+			testImage = filepath.Join(testsDir, "test-data-graph.png")
+			imageData, err = os.ReadFile(testImage)
+			require.NoError(t, err)
+			err = os.WriteFile(filePath, imageData, 0644)
+			require.NoError(t, err)
+
+			data.Post.Attachments = &[]imports.AttachmentImportData{{Path: &filePath}}
+			data.Post.Replies = nil
+			errLine, appErr = th.App.importMultiplePostLines(th.Context, []imports.LineImportWorkerData{data}, false, true)
+			require.Nil(t, appErr)
+			require.Equal(t, 0, errLine)
+
+			attachments2 := GetAttachments(user3.Id, th, t)
+			require.NotEqual(t, attachments, attachments2)
+			require.Len(t, attachments2, 2)
+			assert.Contains(t, attachments2[1].Path, team.Id)
+			AssertFileIdsInPost(attachments2[1:], th, t)
+		})
+
+		t.Run("same size", func(t *testing.T) {
+			imageData, err := os.ReadFile(filepath.Join(testsDir, "test_img_diff_A.png"))
+			require.NoError(t, err)
+			err = os.WriteFile(filePath, imageData, 0644)
+			require.NoError(t, err)
+
+			data.Post.Attachments = &[]imports.AttachmentImportData{{Path: &filePath}}
+			data.Post.Replies = nil
+			data.Post.Message = model.NewString("new post2")
+			errLine, appErr := th.App.importMultiplePostLines(th.Context, []imports.LineImportWorkerData{data}, false, true)
+			require.Nil(t, appErr)
+			require.Equal(t, 0, errLine)
+
+			attachments := GetAttachments(user3.Id, th, t)
+			require.Len(t, attachments, 3)
+			assert.Contains(t, attachments[2].Path, team.Id)
+			AssertFileIdsInPost(attachments[2:], th, t)
+
+			imageData, err = os.ReadFile(filepath.Join(testsDir, "test_img_diff_B.png"))
+			require.NoError(t, err)
+			err = os.WriteFile(filePath, imageData, 0644)
+			require.NoError(t, err)
+
+			data.Post.Attachments = &[]imports.AttachmentImportData{{Path: &filePath}}
+			data.Post.Replies = nil
+			errLine, appErr = th.App.importMultiplePostLines(th.Context, []imports.LineImportWorkerData{data}, false, true)
+			require.Nil(t, appErr)
+			require.Equal(t, 0, errLine)
+
+			attachments2 := GetAttachments(user3.Id, th, t)
+			require.NotEqual(t, attachments, attachments2)
+			require.Len(t, attachments2, 3)
+			assert.Contains(t, attachments2[2].Path, team.Id)
+			AssertFileIdsInPost(attachments2[2:], th, t)
+		})
+	})
 }
 
 func TestImportDirectPostWithAttachments(t *testing.T) {
@@ -4574,7 +4655,6 @@ func TestZippedImportPostAndRepliesWithAttachments(t *testing.T) {
 
 	require.NotEmpty(t, testZipReader.File)
 	imageData := testZipReader.File[0]
-	require.NoError(t, err, "failed to copy test Image file into zip")
 
 	testMarkDown := filepath.Join(testsDir, "test-attachments.md")
 	data := imports.LineImportWorkerData{
@@ -4662,4 +4742,327 @@ func TestZippedImportPostAndRepliesWithAttachments(t *testing.T) {
 		assert.Contains(t, attachments[0].Path, "noteam")
 		AssertFileIdsInPost(attachments, th, t)
 	})
+
+	t.Run("import existing post with different attachment's content", func(t *testing.T) {
+		var fileA, fileB *zip.File
+		for _, f := range testZipReader.File {
+			if f.Name == "data/test_img_diff_A.png" {
+				fileA = f
+			} else if f.Name == "data/test_img_diff_B.png" {
+				fileB = f
+			}
+		}
+
+		require.NotNil(t, fileA)
+		require.NotNil(t, fileB)
+
+		data.Post.Attachments = &[]imports.AttachmentImportData{{Path: &fileA.Name, Data: fileA}}
+		data.Post.Message = model.NewString("new post")
+		data.Post.Replies = nil
+		errLine, err := th.App.importMultiplePostLines(th.Context, []imports.LineImportWorkerData{data}, false, true)
+		require.Nil(t, err)
+		require.Equal(t, 0, errLine)
+
+		attachments := GetAttachments(user3.Id, th, t)
+		require.Len(t, attachments, 2)
+		assert.Contains(t, attachments[1].Path, team.Id)
+		AssertFileIdsInPost(attachments[1:], th, t)
+
+		fileB.Name = fileA.Name
+		data.Post.Attachments = &[]imports.AttachmentImportData{{Path: &fileA.Name, Data: fileB}}
+		errLine, err = th.App.importMultiplePostLines(th.Context, []imports.LineImportWorkerData{data}, false, true)
+		require.Nil(t, err)
+		require.Equal(t, 0, errLine)
+
+		attachments = GetAttachments(user3.Id, th, t)
+		require.Len(t, attachments, 2)
+		assert.Contains(t, attachments[1].Path, team.Id)
+		AssertFileIdsInPost(attachments[1:], th, t)
+	})
+}
+
+func TestCompareFilesContent(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		ok, err := compareFilesContent(strings.NewReader(""), strings.NewReader(""), 0)
+		require.NoError(t, err)
+		require.True(t, ok)
+	})
+
+	t.Run("no match", func(t *testing.T) {
+		ok, err := compareFilesContent(strings.NewReader("fileA"), strings.NewReader("fileB"), 0)
+		require.NoError(t, err)
+		require.False(t, ok)
+	})
+
+	t.Run("match", func(t *testing.T) {
+		ok, err := compareFilesContent(strings.NewReader("fileA"), strings.NewReader("fileA"), 0)
+		require.NoError(t, err)
+		require.True(t, ok)
+	})
+}
+
+func BenchmarkCompareFilesContent(b *testing.B) {
+	tmpDir := os.TempDir()
+	fileAPath := filepath.Join(tmpDir, "fileA")
+	fileBPath := filepath.Join(tmpDir, "fileB")
+
+	fileA, err := os.Create(fileAPath)
+	require.NoError(b, err)
+	defer fileA.Close()
+	defer os.Remove(fileAPath)
+
+	fileB, err := os.Create(fileBPath)
+	require.NoError(b, err)
+	defer fileB.Close()
+	defer os.Remove(fileBPath)
+
+	fileSize := int64(1024 * 1024 * 1024) // 1GB
+
+	err = fileA.Truncate(fileSize)
+	require.NoError(b, err)
+	err = fileB.Truncate(fileSize)
+	require.NoError(b, err)
+
+	bufSizesMap := map[string]int64{
+		"32KB":  1024 * 32, // current default of io.Copy
+		"128KB": 1024 * 128,
+		"1MB":   1024 * 1024,
+		"2MB":   1024 * 1024 * 2,
+		"4MB":   1024 * 1024 * 4,
+		"8MB":   1024 * 1024 * 8,
+	}
+
+	fileSizesMap := map[string]int64{
+		"512KB": 1024 * 512,
+		"1MB":   1024 * 1024,
+		"10MB":  1024 * 1024 * 10,
+		"100MB": 1024 * 1024 * 100,
+		"1GB":   1024 * 1024 * 1000,
+	}
+
+	// To force order
+	bufSizeLabels := []string{"32KB", "128KB", "1MB", "2MB", "4MB", "8MB"}
+	fileSizeLabels := []string{"512KB", "1MB", "10MB", "100MB", "1GB"}
+
+	b.Run("plain", func(b *testing.B) {
+		b.Run("local", func(b *testing.B) {
+			b.ReportAllocs()
+			b.ResetTimer()
+			b.StopTimer()
+
+			for i := 0; i < b.N; i++ {
+				_, err := fileA.Seek(0, io.SeekStart)
+				require.NoError(b, err)
+				_, err = fileB.Seek(0, io.SeekStart)
+				require.NoError(b, err)
+
+				b.StartTimer()
+				ok, err := compareFilesContent(fileA, fileB, 0)
+				b.StopTimer()
+				require.NoError(b, err)
+				require.True(b, ok)
+			}
+		})
+
+		b.Run("s3", func(b *testing.B) {
+			th := SetupConfig(b, func(cfg *model.Config) {
+				cfg.FileSettings = model.FileSettings{
+					DriverName:                         model.NewString(model.ImageDriverS3),
+					AmazonS3AccessKeyId:                model.NewString(model.MinioAccessKey),
+					AmazonS3SecretAccessKey:            model.NewString(model.MinioSecretKey),
+					AmazonS3Bucket:                     model.NewString("comparefilescontentbucket"),
+					AmazonS3Endpoint:                   model.NewString("localhost:9000"),
+					AmazonS3Region:                     model.NewString(""),
+					AmazonS3PathPrefix:                 model.NewString(""),
+					AmazonS3SSL:                        model.NewBool(false),
+					AmazonS3RequestTimeoutMilliseconds: model.NewInt64(300 * 1000),
+				}
+			})
+			defer th.TearDown()
+
+			err := th.App.Srv().FileBackend().(*filestore.S3FileBackend).TestConnection()
+			require.NoError(b, err)
+
+			_, err = fileA.Seek(0, io.SeekStart)
+			require.NoError(b, err)
+			_, err = fileB.Seek(0, io.SeekStart)
+			require.NoError(b, err)
+
+			_, appErr := th.App.WriteFile(fileA, "compareFileA")
+			require.Nil(b, appErr)
+			defer th.App.RemoveFile("compareFileA")
+
+			_, appErr = th.App.WriteFile(fileB, "compareFileB")
+			require.Nil(b, appErr)
+			defer th.App.RemoveFile("compareFileB")
+
+			rdA, appErr := th.App.FileReader("compareFileA")
+			require.Nil(b, appErr)
+			defer rdA.Close()
+
+			rdB, appErr := th.App.FileReader("compareFileB")
+			require.Nil(b, appErr)
+			defer rdB.Close()
+
+			b.ResetTimer()
+
+			for _, fileSizeLabel := range fileSizeLabels {
+				fileSize := fileSizesMap[fileSizeLabel]
+				for _, bufSizeLabel := range bufSizeLabels {
+					bufSize := bufSizesMap[bufSizeLabel]
+					b.Run("bufSize-fileSize"+fileSizeLabel+"-bufSize"+bufSizeLabel, func(b *testing.B) {
+						b.ReportAllocs()
+						b.StopTimer()
+						for i := 0; i < b.N; i++ {
+							_, err := rdA.Seek(0, io.SeekStart)
+							require.NoError(b, err)
+							_, err = rdB.Seek(0, io.SeekStart)
+							require.NoError(b, err)
+
+							b.StartTimer()
+							ok, err := compareFilesContent(&io.LimitedReader{
+								R: rdA,
+								N: fileSize,
+							}, &io.LimitedReader{
+								R: rdB,
+								N: fileSize,
+							}, bufSize)
+							b.StopTimer()
+							require.NoError(b, err)
+							require.True(b, ok)
+						}
+					})
+				}
+			}
+		})
+	})
+
+	b.Run("zip", func(b *testing.B) {
+		zipFilePath := filepath.Join(tmpDir, "compareFiles.zip")
+		zipFile, err := os.Create(zipFilePath)
+		require.NoError(b, err)
+		defer zipFile.Close()
+		defer os.Remove(zipFilePath)
+
+		zipWr := zip.NewWriter(zipFile)
+
+		fileAZipWr, err := zipWr.CreateHeader(&zip.FileHeader{
+			Name:   "compareFileA",
+			Method: zip.Store,
+		})
+		require.NoError(b, err)
+		_, err = io.Copy(fileAZipWr, fileA)
+		require.NoError(b, err)
+
+		fileBZipWr, err := zipWr.CreateHeader(&zip.FileHeader{
+			Name:   "compareFileB",
+			Method: zip.Store,
+		})
+		require.NoError(b, err)
+		_, err = io.Copy(fileBZipWr, fileB)
+		require.NoError(b, err)
+
+		err = zipWr.Close()
+		require.NoError(b, err)
+
+		info, err := zipFile.Stat()
+		require.NoError(b, err)
+
+		zipFileSize := info.Size()
+
+		b.Run("local", func(b *testing.B) {
+			b.ResetTimer()
+
+			for _, label := range bufSizeLabels {
+				bufSize := bufSizesMap[label]
+				b.Run("bufSize-"+label, func(b *testing.B) {
+					b.ReportAllocs()
+					b.StopTimer()
+					for i := 0; i < b.N; i++ {
+						_, err := zipFile.Seek(0, io.SeekStart)
+						require.NoError(b, err)
+						zipRd, err := zip.NewReader(zipFile, zipFileSize)
+						require.NoError(b, err)
+
+						zipFileA, err := zipRd.Open("compareFileA")
+						require.NoError(b, err)
+
+						zipFileB, err := zipRd.Open("compareFileB")
+						require.NoError(b, err)
+
+						b.StartTimer()
+						ok, err := compareFilesContent(zipFileA, zipFileB, bufSize)
+						b.StopTimer()
+						require.NoError(b, err)
+						require.True(b, ok)
+					}
+				})
+			}
+		})
+
+		b.Run("s3", func(b *testing.B) {
+			th := SetupConfig(b, func(cfg *model.Config) {
+				cfg.FileSettings = model.FileSettings{
+					DriverName:                         model.NewString(model.ImageDriverS3),
+					AmazonS3AccessKeyId:                model.NewString(model.MinioAccessKey),
+					AmazonS3SecretAccessKey:            model.NewString(model.MinioSecretKey),
+					AmazonS3Bucket:                     model.NewString("comparefilescontentbucket"),
+					AmazonS3Endpoint:                   model.NewString("localhost:9000"),
+					AmazonS3Region:                     model.NewString(""),
+					AmazonS3PathPrefix:                 model.NewString(""),
+					AmazonS3SSL:                        model.NewBool(false),
+					AmazonS3RequestTimeoutMilliseconds: model.NewInt64(300 * 1000),
+				}
+			})
+			defer th.TearDown()
+
+			err := th.App.Srv().FileBackend().(*filestore.S3FileBackend).TestConnection()
+			require.NoError(b, err)
+
+			_, appErr := th.App.WriteFile(zipFile, "compareFiles.zip")
+			require.Nil(b, appErr)
+			defer th.App.RemoveFile("compareFiles.zip")
+
+			zipFileRd, appErr := th.App.FileReader("compareFiles.zip")
+			require.Nil(b, appErr)
+			defer zipFileRd.Close()
+
+			b.ResetTimer()
+
+			for _, fileSizeLabel := range fileSizeLabels {
+				fileSize := fileSizesMap[fileSizeLabel]
+				for _, bufSizeLabel := range bufSizeLabels {
+					bufSize := bufSizesMap[bufSizeLabel]
+					b.Run("bufSize-fileSize"+fileSizeLabel+"-bufSize"+bufSizeLabel, func(b *testing.B) {
+						b.ReportAllocs()
+						b.StopTimer()
+						for i := 0; i < b.N; i++ {
+							_, err := zipFileRd.Seek(0, io.SeekStart)
+							require.NoError(b, err)
+							zipRd, err := zip.NewReader(zipFileRd.(io.ReaderAt), zipFileSize)
+							require.NoError(b, err)
+
+							zipFileA, err := zipRd.Open("compareFileA")
+							require.NoError(b, err)
+
+							zipFileB, err := zipRd.Open("compareFileB")
+							require.NoError(b, err)
+
+							b.StartTimer()
+							ok, err := compareFilesContent(&io.LimitedReader{
+								R: zipFileA,
+								N: fileSize,
+							}, &io.LimitedReader{
+								R: zipFileB,
+								N: fileSize,
+							}, bufSize)
+							b.StopTimer()
+							require.NoError(b, err)
+							require.True(b, ok)
+						}
+					})
+				}
+			}
+		})
+	})
 }

server/channels/app/import_test.go

@@ -267,12 +267,16 @@ func TestImportProcessImportDataFileVersionLine(t *testing.T) {
 }
 
 func GetAttachments(userID string, th *TestHelper, t *testing.T) []*model.FileInfo {
+	t.Helper()
+
 	fileInfos, err := th.App.Srv().Store().FileInfo().GetForUser(userID)
 	require.NoError(t, err)
 	return fileInfos
 }
 
 func AssertFileIdsInPost(files []*model.FileInfo, th *TestHelper, t *testing.T) {
+	t.Helper()
+
 	postID := files[0].PostId
 	require.NotNil(t, postID)
 

server/channels/app/post.go

@@ -1782,17 +1782,6 @@ func (a *App) GetFileInfosForPost(rctx request.CTX, postID string, fromMaster bo
 	return fileInfos, firstInaccessibleFileTime, nil
 }
 
-func (a *App) getFileInfosForPostIgnoreCloudLimit(rctx request.CTX, postID string, fromMaster bool, includeDeleted bool) ([]*model.FileInfo, *model.AppError) {
-	fileInfos, err := a.Srv().Store().FileInfo().GetForPost(postID, fromMaster, includeDeleted, true)
-	if err != nil {
-		return nil, model.NewAppError("getFileInfosForPostIgnoreCloudLimit", "app.file_info.get_for_post.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
-	}
-
-	a.generateMiniPreviewForInfos(rctx, fileInfos)
-
-	return fileInfos, nil
-}
-
 func (a *App) PostWithProxyAddedToImageURLs(post *model.Post) *model.Post {
 	if f := a.ImageProxyAdder(); f != nil {
 		return post.WithRewrittenImageURLs(f)

server/cmd/mmctl/commands/import_e2e_test.go

@@ -401,7 +401,7 @@ func (s *MmctlE2ETestSuite) TestImportValidateCmdF() {
 		s.Require().Equal(struct {
 			UnusedAttachments []string `json:"unused_attachments"`
 		}{
-			UnusedAttachments: []string{"data/test2.png"},
+			UnusedAttachments: []string{"data/test2.png", "data/test_img_diff_A.png", "data/test_img_diff_B.png"},
 		}, printer.GetLines()[1].(struct {
 			UnusedAttachments []string `json:"unused_attachments"`
 		}))

server/i18n/en.json

@@ -5410,13 +5410,17 @@
     "id": "app.import.attachment.bad_file.error",
     "translation": "Error reading the file at: \"{{.FilePath}}\""
   },
+  {
+    "id": "app.import.attachment.file_stat.error",
+    "translation": "Error reading the file status: \"{{.FilePath}}\""
+  },
   {
     "id": "app.import.attachment.file_upload.error",
     "translation": "Error uploading the file: \"{{.FilePath}}\""
   },
   {
-    "id": "app.import.attachment.read_file_data.error",
-    "translation": "Failed to read file attachment during import."
+    "id": "app.import.attachment.seek_file.error",
+    "translation": "Error seeking the file: \"{{.FilePath}}\""
   },
   {
     "id": "app.import.bulk_import.file_scan.error",