4 files changed, 110 insertions, 9 deletions
diff --git a/bridge/config/config.go b/bridge/config/config.go
index 6e99066c..f34da511 100644
--- a/bridge/config/config.go
+++ b/bridge/config/config.go
@@ -100,6 +100,7 @@ type Protocol struct {
 	MediaDownloadSize      int    // all protocols
 	MediaServerDownload    string
 	MediaServerUpload      string
+	MediaConvertTgs        string     // telegram
 	MediaConvertWebPToPNG  bool       // telegram
 	MessageDelay           int        // IRC, time in millisecond to wait between messages
 	MessageFormat          string     // telegram
diff --git a/bridge/helper/helper.go b/bridge/helper/helper.go
index 41244766..2b449e14 100644
--- a/bridge/helper/helper.go
+++ b/bridge/helper/helper.go
@@ -5,7 +5,10 @@ import (
 	"fmt"
 	"image/png"
 	"io"
+	"io/ioutil"
 	"net/http"
+	"os"
+	"os/exec"
 	"regexp"
 	"strings"
 	"time"
@@ -192,7 +195,7 @@ func ParseMarkdown(input string) string {
 	return res
 }
 
-// ConvertWebPToPNG convert input data (which should be WebP format to PNG format)
+// ConvertWebPToPNG converts input data (which should be WebP format) to PNG format
 func ConvertWebPToPNG(data *[]byte) error {
 	r := bytes.NewReader(*data)
 	m, err := webp.Decode(r)
@@ -207,3 +210,49 @@ func ConvertWebPToPNG(data *[]byte) error {
 	*data = w.Bytes()
 	return nil
 }
+
+// CanConvertTgsToX Checks whether the external command necessary for ConvertTgsToX works.
+func CanConvertTgsToX() error {
+	// We depend on the fact that `lottie_convert.py --help` has exit status 0.
+	// Hyrum's Law predicted this, and Murphy's Law predicts that this will break eventually.
+	// However, there is no alternative like `lottie_convert.py --is-properly-installed`
+	cmd := exec.Command("lottie_convert.py", "--help")
+	return cmd.Run()
+}
+
+// ConvertTgsToWebP convert input data (which should be tgs format) to WebP format
+// This relies on an external command, which is ugly, but works.
+func ConvertTgsToX(data *[]byte, outputFormat string, logger *logrus.Entry) error {
+	// lottie can't handle input from a pipe, so write to a temporary file:
+	tmpFile, err := ioutil.TempFile(os.TempDir(), "matterbridge-lottie-*.tgs")
+	if err != nil {
+		return err
+	}
+	tmpFileName := tmpFile.Name()
+	defer func() {
+		if removeErr := os.Remove(tmpFileName); removeErr != nil {
+			logger.Errorf("Could not delete temporary file %s: %v", tmpFileName, removeErr)
+		}
+	}()
+
+	if _, writeErr := tmpFile.Write(*data); writeErr != nil {
+		return writeErr
+	}
+	// Must close before calling lottie to avoid data races:
+	if closeErr := tmpFile.Close(); closeErr != nil {
+		return closeErr
+	}
+
+	// Call lottie to transform:
+	cmd := exec.Command("lottie_convert.py", "--input-format", "lottie", "--output-format", outputFormat, tmpFileName, "/dev/stdout")
+	cmd.Stderr = nil
+	// NB: lottie writes progress into to stderr in all cases.
+	stdout, stderr := cmd.Output()
+	if stderr != nil {
+		// 'stderr' already contains some parts of Stderr, because it was set to 'nil'.
+		return stderr
+	}
+
+	*data = stdout
+	return nil
+}
diff --git a/bridge/telegram/handlers.go b/bridge/telegram/handlers.go
index 5c60f74b..ee087524 100644
--- a/bridge/telegram/handlers.go
+++ b/bridge/telegram/handlers.go
@@ -217,6 +217,46 @@ 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:
+		// 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.
+		return
+	}
+	err := helper.ConvertTgsToX(data, format, b.Log)
+	if err != nil {
+		b.Log.Errorf("conversion failed: %v", err)
+	} else {
+		*name = strings.Replace(*name, "tgs.webp", format, 1)
+	}
+}
+
+func (b *Btelegram) maybeConvertWebp(name *string, data *[]byte) {
+	if b.GetBool("MediaConvertWebPToPNG") {
+		b.Log.Debugf("WebP to PNG conversion enabled, converting %v", name)
+		err := helper.ConvertWebPToPNG(data)
+		if err != nil {
+			b.Log.Errorf("conversion failed: %v", err)
+		} else {
+			*name = strings.Replace(*name, ".webp", ".png", 1)
+		}
+	}
+}
+
 // handleDownloadFile handles file download
 func (b *Btelegram) handleDownload(rmsg *config.Message, message *tgbotapi.Message) error {
 	size := 0
@@ -264,15 +304,13 @@ func (b *Btelegram) handleDownload(rmsg *config.Message, message *tgbotapi.Messa
 	if err != nil {
 		return err
 	}
-	if strings.HasSuffix(name, ".webp") && b.GetBool("MediaConvertWebPToPNG") {
-		b.Log.Debugf("WebP to PNG conversion enabled, converting %s", name)
-		err := helper.ConvertWebPToPNG(data)
-		if err != nil {
-			b.Log.Errorf("conversion failed: %s", err)
-		} else {
-			name = strings.Replace(name, ".webp", ".png", 1)
-		}
+
+	if strings.HasSuffix(name, ".tgs.webp") {
+		b.maybeConvertTgs(&name, data)
+	} else if strings.HasSuffix(name, ".webp") {
+		b.maybeConvertWebp(&name, data)
 	}
+
 	helper.HandleDownloadData(b.Log, rmsg, name, message.Caption, "", data, b.General)
 	return nil
 }
diff --git a/bridge/telegram/telegram.go b/bridge/telegram/telegram.go
index 29f2f291..f1c7168c 100644
--- a/bridge/telegram/telegram.go
+++ b/bridge/telegram/telegram.go
@@ -2,6 +2,7 @@ package btelegram
 
 import (
 	"html"
+	"log"
 	"strconv"
 	"strings"
 
@@ -16,6 +17,8 @@ const (
 	HTMLFormat  = "HTML"
 	HTMLNick    = "htmlnick"
 	MarkdownV2  = "MarkdownV2"
+	FormatPng   = "png"
+	FormatWebp  = "webp"
 )
 
 type Btelegram struct {
@@ -25,6 +28,16 @@ type Btelegram struct {
 }
 
 func New(cfg *bridge.Config) bridge.Bridger {
+	tgsConvertFormat := cfg.GetString("MediaConvertTgs")
+	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)
+		}
+		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)
+		}
+	}
 	return &Btelegram{Config: cfg, avatarMap: make(map[string]string)}
 }