rename backend to pkg

pkg/api/api_render.go

@@ -0,0 +1,20 @@
+package api
+
+import "github.com/gin-gonic/gin"
+
+func init() {
+	addRoutes(func(self *HttpServer) {
+		self.router.GET("/api/render", self.renderToPng)
+	})
+}
+
+func (self *HttpServer) renderToPng(c *gin.Context) {
+	qs := c.Request.URL.Query()
+	url := qs["url"][0]
+	pngPath, err := self.renderer.RenderToPng(url)
+	if err != nil {
+		c.HTML(500, "error.html", nil)
+	}
+
+	c.File(pngPath)
+}