[MM-29241] Image logic refactor (#17702)

* Image logic refactor

* Add missing translations

* Improve prepareImage

* Use iota

* Limit image encoder concurrency

* Unexport validation methods

* Avoid shortening on exported names

* Remove unnecessary complexity

app/server.go

@@ -38,6 +38,7 @@ import (
 	"golang.org/x/crypto/acme/autocert"
 
 	"github.com/mattermost/mattermost-server/v5/app/featureflag"
+	"github.com/mattermost/mattermost-server/v5/app/imaging"
 	"github.com/mattermost/mattermost-server/v5/app/request"
 	"github.com/mattermost/mattermost-server/v5/audit"
 	"github.com/mattermost/mattermost-server/v5/config"
@@ -207,6 +208,9 @@ type Server struct {
 	featureFlagStop              chan struct{}
 	featureFlagStopped           chan struct{}
 	featureFlagSynchronizerMutex sync.Mutex
+
+	imgDecoder *imaging.Decoder
+	imgEncoder *imaging.Encoder
 }
 
 func NewServer(options ...Option) (*Server, error) {
@@ -245,6 +249,20 @@ func NewServer(options ...Option) (*Server, error) {
 		mlog.Error("Could not initiate logging", mlog.Err(err))
 	}
 
+	var imgErr error
+	s.imgDecoder, imgErr = imaging.NewDecoder(imaging.DecoderOptions{
+		ConcurrencyLevel: runtime.NumCPU(),
+	})
+	if imgErr != nil {
+		return nil, errors.Wrap(imgErr, "failed to create image decoder")
+	}
+	s.imgEncoder, imgErr = imaging.NewEncoder(imaging.EncoderOptions{
+		ConcurrencyLevel: runtime.NumCPU(),
+	})
+	if imgErr != nil {
+		return nil, errors.Wrap(imgErr, "failed to create image encoder")
+	}
+
 	// This is called after initLogging() to avoid a race condition.
 	mlog.Info("Server is initializing...", mlog.String("go_version", runtime.Version()))