Add images and binary content on gist preview (#615)

internal/db/gist.go

@@ -73,6 +73,7 @@ type Gist struct {
 	URL             string
 	Preview         string
 	PreviewFilename string
+	PreviewMimeType string
 	Description     string
 	Private         Visibility // 0: public, 1: unlisted, 2: private
 	UserID          uint
@@ -551,6 +552,7 @@ func (gist *Gist) UpdatePreviewAndCount(withTimestampUpdate bool) error {
 	if len(filesStr) == 0 {
 		gist.Preview = ""
 		gist.PreviewFilename = ""
+		gist.PreviewMimeType = ""
 	} else {
 		for _, fileStr := range filesStr {
 			file, err := gist.File("HEAD", fileStr, true)
@@ -562,6 +564,7 @@ func (gist *Gist) UpdatePreviewAndCount(withTimestampUpdate bool) error {
 			}
 			gist.Preview = ""
 			gist.PreviewFilename = file.Filename
+			gist.PreviewMimeType = file.MimeType.ContentType
 
 			if !file.MimeType.CanBeEdited() {
 				continue

internal/render/highlight.go

@@ -27,8 +27,9 @@ func (r HighlightedFile) InternalType() string {
 
 type RenderedGist struct {
 	*db.Gist
-	Lines []string
-	HTML  string
+	Lines           []string
+	HTML            string
+	PreviewMimeType *git.MimeType
 }
 
 func highlightFile(file *git.File) (HighlightedFile, error) {
@@ -76,6 +77,18 @@ func HighlightGistPreview(gist *db.Gist) (RenderedGist, error) {
 		Gist: gist,
 	}
 
+	if gist.PreviewMimeType != "" {
+		mt := &git.MimeType{ContentType: gist.PreviewMimeType}
+		if mt.CanBeEmbedded() {
+			rendered.PreviewMimeType = mt
+			return rendered, nil
+		}
+	}
+
+	if gist.Preview == "" {
+		return rendered, nil
+	}
+
 	style := newStyle()
 	lexer := newLexer(gist.PreviewFilename)
 	if lexer.Config().Name == "markdown" {