dendrite/mediaapi/thumbnailer/thumbnailer.go
2019-05-21 21:56:55 +01:00

250 lines
8.7 KiB
Go

// 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
}