use go module for dependencies (#594)

mediaapi/thumbnailer/thumbnailer.go

@@ -0,0 +1,249 @@
+// Copyright 2017 Vector Creations Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package thumbnailer
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/matrix-org/dendrite/common/config"
+	"github.com/matrix-org/dendrite/mediaapi/storage"
+	"github.com/matrix-org/dendrite/mediaapi/types"
+	log "github.com/sirupsen/logrus"
+)
+
+type thumbnailFitness struct {
+	isSmaller      int
+	aspect         float64
+	size           float64
+	methodMismatch int
+	fileSize       types.FileSizeBytes
+}
+
+// thumbnailTemplate is the filename template for thumbnails
+const thumbnailTemplate = "thumbnail-%vx%v-%v"
+
+// GetThumbnailPath returns the path to a thumbnail given the absolute src path and thumbnail size configuration
+func GetThumbnailPath(src types.Path, config types.ThumbnailSize) types.Path {
+	srcDir := filepath.Dir(string(src))
+	return types.Path(filepath.Join(
+		srcDir,
+		fmt.Sprintf(thumbnailTemplate, config.Width, config.Height, config.ResizeMethod),
+	))
+}
+
+// SelectThumbnail compares the (potentially) available thumbnails with the desired thumbnail and returns the best match
+// The algorithm is very similar to what was implemented in Synapse
+// In order of priority unless absolute, the following metrics are compared; the image is:
+// * the same size or larger than requested
+// * if a cropped image is desired, has an aspect ratio close to requested
+// * has a size close to requested
+// * if a cropped image is desired, prefer the same method, if scaled is desired, absolutely require scaled
+// * has a small file size
+// If a pre-generated thumbnail size is the best match, but it has not been generated yet, the caller can use the returned size to generate it.
+// Returns nil if no thumbnail matches the criteria
+func SelectThumbnail(desired types.ThumbnailSize, thumbnails []*types.ThumbnailMetadata, thumbnailSizes []config.ThumbnailSize) (*types.ThumbnailMetadata, *types.ThumbnailSize) {
+	var chosenThumbnail *types.ThumbnailMetadata
+	var chosenThumbnailSize *types.ThumbnailSize
+	bestFit := newThumbnailFitness()
+
+	for _, thumbnail := range thumbnails {
+		if desired.ResizeMethod == types.Scale && thumbnail.ThumbnailSize.ResizeMethod != types.Scale {
+			continue
+		}
+		fitness := calcThumbnailFitness(thumbnail.ThumbnailSize, thumbnail.MediaMetadata, desired)
+		if isBetter := fitness.betterThan(bestFit, desired.ResizeMethod == types.Crop); isBetter {
+			bestFit = fitness
+			chosenThumbnail = thumbnail
+		}
+	}
+
+	for _, thumbnailSize := range thumbnailSizes {
+		if desired.ResizeMethod == types.Scale && thumbnailSize.ResizeMethod != types.Scale {
+			continue
+		}
+		fitness := calcThumbnailFitness(types.ThumbnailSize(thumbnailSize), nil, desired)
+		if isBetter := fitness.betterThan(bestFit, desired.ResizeMethod == types.Crop); isBetter {
+			bestFit = fitness
+			chosenThumbnailSize = (*types.ThumbnailSize)(&thumbnailSize)
+		}
+	}
+
+	return chosenThumbnail, chosenThumbnailSize
+}
+
+// getActiveThumbnailGeneration checks for active thumbnail generation
+func getActiveThumbnailGeneration(dst types.Path, _ types.ThumbnailSize, activeThumbnailGeneration *types.ActiveThumbnailGeneration, maxThumbnailGenerators int, logger *log.Entry) (isActive bool, busy bool, errorReturn error) {
+	// Check if there is active thumbnail generation.
+	activeThumbnailGeneration.Lock()
+	defer activeThumbnailGeneration.Unlock()
+	if activeThumbnailGenerationResult, ok := activeThumbnailGeneration.PathToResult[string(dst)]; ok {
+		logger.Info("Waiting for another goroutine to generate the thumbnail.")
+
+		// NOTE: Wait unlocks and locks again internally. There is still a deferred Unlock() that will unlock this.
+		activeThumbnailGenerationResult.Cond.Wait()
+		// Note: either there is an error or it is nil, either way returning it is correct
+		return false, false, activeThumbnailGenerationResult.Err
+	}
+
+	// Only allow thumbnail generation up to a maximum configured number. Above this we fall back to serving the
+	// original. Or in the case of pre-generation, they maybe get generated on the first request for a thumbnail if
+	// load has subsided.
+	if len(activeThumbnailGeneration.PathToResult) >= maxThumbnailGenerators {
+		return false, true, nil
+	}
+
+	// No active thumbnail generation so create one
+	activeThumbnailGeneration.PathToResult[string(dst)] = &types.ThumbnailGenerationResult{
+		Cond: &sync.Cond{L: activeThumbnailGeneration},
+	}
+
+	return true, false, nil
+}
+
+// broadcastGeneration broadcasts that thumbnail generation completed and the error to all waiting goroutines
+// Note: This should only be called by the owner of the activeThumbnailGenerationResult
+func broadcastGeneration(dst types.Path, activeThumbnailGeneration *types.ActiveThumbnailGeneration, _ types.ThumbnailSize, errorReturn error, logger *log.Entry) {
+	activeThumbnailGeneration.Lock()
+	defer activeThumbnailGeneration.Unlock()
+	if activeThumbnailGenerationResult, ok := activeThumbnailGeneration.PathToResult[string(dst)]; ok {
+		logger.Info("Signalling other goroutines waiting for this goroutine to generate the thumbnail.")
+		// Note: errorReturn is a named return value error that is signalled from here to waiting goroutines
+		activeThumbnailGenerationResult.Err = errorReturn
+		activeThumbnailGenerationResult.Cond.Broadcast()
+	}
+	delete(activeThumbnailGeneration.PathToResult, string(dst))
+}
+
+func isThumbnailExists(
+	ctx context.Context,
+	dst types.Path,
+	config types.ThumbnailSize,
+	mediaMetadata *types.MediaMetadata,
+	db *storage.Database,
+	logger *log.Entry,
+) (bool, error) {
+	thumbnailMetadata, err := db.GetThumbnail(
+		ctx, mediaMetadata.MediaID, mediaMetadata.Origin,
+		config.Width, config.Height, config.ResizeMethod,
+	)
+	if err != nil {
+		logger.Error("Failed to query database for thumbnail.")
+		return false, err
+	}
+	if thumbnailMetadata != nil {
+		return true, nil
+	}
+	// Note: The double-negative is intentional as os.IsExist(err) != !os.IsNotExist(err).
+	// The functions are error checkers to be used in different cases.
+	if _, err = os.Stat(string(dst)); !os.IsNotExist(err) {
+		// Thumbnail exists
+		return true, nil
+	}
+	return false, nil
+}
+
+// init with worst values
+func newThumbnailFitness() thumbnailFitness {
+	return thumbnailFitness{
+		isSmaller:      1,
+		aspect:         math.Inf(1),
+		size:           math.Inf(1),
+		methodMismatch: 0,
+		fileSize:       types.FileSizeBytes(math.MaxInt64),
+	}
+}
+
+func calcThumbnailFitness(size types.ThumbnailSize, metadata *types.MediaMetadata, desired types.ThumbnailSize) thumbnailFitness {
+	dW := desired.Width
+	dH := desired.Height
+	tW := size.Width
+	tH := size.Height
+
+	fitness := newThumbnailFitness()
+	// In all cases, a larger metric value is a worse fit.
+	// compare size: thumbnail smaller is true and gives 1, larger is false and gives 0
+	fitness.isSmaller = boolToInt(tW < dW || tH < dH)
+	// comparison of aspect ratios only makes sense for a request for desired cropped
+	fitness.aspect = math.Abs(float64(dW*tH - dH*tW))
+	// compare sizes
+	fitness.size = math.Abs(float64((dW - tW) * (dH - tH)))
+	// compare resize method
+	fitness.methodMismatch = boolToInt(size.ResizeMethod != desired.ResizeMethod)
+	if metadata != nil {
+		// file size
+		fitness.fileSize = metadata.FileSizeBytes
+	}
+
+	return fitness
+}
+
+func boolToInt(b bool) int {
+	if b {
+		return 1
+	}
+	return 0
+}
+
+func (a thumbnailFitness) betterThan(b thumbnailFitness, desiredCrop bool) bool {
+	// preference means returning -1
+
+	// prefer images that are not smaller
+	// e.g. isSmallerDiff > 0 means b is smaller than desired and a is not smaller
+	if a.isSmaller > b.isSmaller {
+		return false
+	} else if a.isSmaller < b.isSmaller {
+		return true
+	}
+
+	// prefer aspect ratios closer to desired only if desired cropped
+	// only cropped images have differing aspect ratios
+	// desired scaled only accepts scaled images
+	if desiredCrop {
+		if a.aspect > b.aspect {
+			return false
+		} else if a.aspect < b.aspect {
+			return true
+		}
+	}
+
+	// prefer closer in size
+	if a.size > b.size {
+		return false
+	} else if a.size < b.size {
+		return true
+	}
+
+	// prefer images using the same method
+	// e.g. methodMismatchDiff > 0 means b's method is different from desired and a's matches the desired method
+	if a.methodMismatch > b.methodMismatch {
+		return false
+	} else if a.methodMismatch < b.methodMismatch {
+		return true
+	}
+
+	// prefer smaller files
+	if a.fileSize > b.fileSize {
+		return false
+	} else if a.fileSize < b.fileSize {
+		return true
+	}
+
+	return false
+}