Convert .tgs with go libraries (and cgo) (telegram) (#1569)

This commit adds support for go/cgo tgs conversion when building with the -tags `cgo`
The default binaries are still "pure" go and uses the old way of converting.

* Move lottie_convert.py conversion code to its own file

* Add optional libtgsconverter

* Update vendor

* Apply suggestions from code review

* Update bridge/helper/libtgsconverter.go

Co-authored-by: Wim <wim@42.be>

2 files changed, 7 insertions, 19 deletions

diff --git a/bridge/telegram/handlers.go b/bridge/telegram/handlers.go
index a93c71bb..84881f7f 100644
--- a/bridge/telegram/handlers.go
+++ b/bridge/telegram/handlers.go
@@ -220,20 +220,10 @@ func (b *Btelegram) handleDownloadAvatar(userid int, channel string) {
 }
 
 func (b *Btelegram) maybeConvertTgs(name *string, data *[]byte) {
-	var format string
-	switch b.GetString("MediaConvertTgs") {
-	case FormatWebp:
-		b.Log.Debugf("Tgs to WebP conversion enabled, converting %v", name)
-		format = FormatWebp
-	case FormatPng:
-		// The WebP to PNG converter can't handle animated webp files yet,
-		// and I'm not going to write a path for x/image/webp.
-		// The error message would be:
-		//     conversion failed: webp: non-Alpha VP8X is not implemented
-		// So instead, we tell lottie to directly go to PNG.
-		b.Log.Debugf("Tgs to PNG conversion enabled, converting %v", name)
-		format = FormatPng
-	default:
+	format := b.GetString("MediaConvertTgs")
+	if helper.SupportsFormat(format) {
+		b.Log.Debugf("Format supported by %s, converting %v", helper.LottieBackend(), name)
+	} else {
 		// Otherwise, no conversion was requested. Trying to run the usual webp
 		// converter would fail, because '.tgs.webp' is actually a gzipped JSON
 		// file, and has nothing to do with WebP.
diff --git a/bridge/telegram/telegram.go b/bridge/telegram/telegram.go
index 0f08a45b..199a76ab 100644
--- a/bridge/telegram/telegram.go
+++ b/bridge/telegram/telegram.go
@@ -17,8 +17,6 @@ const (
 	HTMLFormat  = "HTML"
 	HTMLNick    = "htmlnick"
 	MarkdownV2  = "MarkdownV2"
-	FormatPng   = "png"
-	FormatWebp  = "webp"
 )
 
 type Btelegram struct {
@@ -32,10 +30,10 @@ func New(cfg *bridge.Config) bridge.Bridger {
 	if tgsConvertFormat != "" {
 		err := helper.CanConvertTgsToX()
 		if err != nil {
-			log.Fatalf("Telegram bridge configured to convert .tgs files to '%s', but lottie does not appear to work:\n%#v", tgsConvertFormat, err)
+			log.Fatalf("Telegram bridge configured to convert .tgs files to '%s', but %s does not appear to work:\n%#v", tgsConvertFormat, helper.LottieBackend(), err)
 		}
-		if tgsConvertFormat != FormatPng && tgsConvertFormat != FormatWebp {
-			log.Fatalf("Telegram bridge configured to convert .tgs files to '%s', but only '%s' and '%s' are supported.", FormatPng, FormatWebp, tgsConvertFormat)
+		if !helper.SupportsFormat(tgsConvertFormat) {
+			log.Fatalf("Telegram bridge configured to convert .tgs files to '%s', but %s doesn't support it.", tgsConvertFormat, helper.LottieBackend())
 		}
 	}
 	return &Btelegram{Config: cfg, avatarMap: make(map[string]string)}