Preliminary model for URL preview cache

src/github.com/turt2live/matrix-media-repo/types/url_preview.go

+package types
+
+import "github.com/turt2live/matrix-media-repo/client/r0"
+
+type UrlPreview struct {
+	Url string
+	SiteName string
+	Type string
+	Description string
+	Title string
+	ImageMxc string
+	ImageType string
+	ImageSize int64
+	ImageWidth int
+	ImageHeight int
+}
+
+func (p *UrlPreview) ToOpenGraphResponse() r0.MatrixOpenGraph {
+	return r0.MatrixOpenGraph{
+		Url: p.Url,
+		SiteName: p.SiteName,
+		Type: p.Type,
+		Description: p.Description,
+		Title: p.Title,
+		ImageMxc: p.ImageMxc,
+		ImageType: p.ImageType,
+		ImageSize: p.ImageSize,
+		ImageWidth: p.ImageWidth,
+		ImageHeight: p.ImageHeight,
+	}
+}
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