How to server a file from a handler in golang

Question

I was wondering how to serve a file from a handler. I'm using go and gin and I've tried to do.

func DownloadHandler(c *gin.Context) {
   c.File("./downloads/file.zip")
}

and

func DownloadConfigs(c *gin.Context) {
   http.ServeFile(c.Writer, c.Request, "./downloads/file.zip")
}

and both of those solutions without the dot as well.

I'm open to any solution and because gin is compatible with the standard http lib, I can use non-gin specific solutions as well

Answer 1

Here is a complete working example using the standard http package. Please note, that the filename or path you use is relative to your current working directory.

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request)     {
        http.ServeFile(w, r, "file")
    })

    err := http.ListenAndServe(":8080", nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
    }
}

Answer 2

Just use this function from gin.Context: https://godoc.org/github.com/gin-gonic/gin#Context.File

Something like this:

const DOWNLOADS_PATH = "downloads/"

ginRouter.GET("/download-user-file/:filename", func (ctx *gin.Context) {
    fileName := ctx.Param("filename")
    targetPath := filepath.Join(DOWNLOADS_PATH, fileName)
    //This ckeck is for example, I not sure is it can prevent all possible filename attacks - will be much better if real filename will not come from user side. I not even tryed this code
    if !strings.HasPrefix(filepath.Clean(targetPath), DOWNLOADS_PATH) {
        ctx.String(403, "Look like you attacking me")
        return
    }
    //Seems this headers needed for some browsers (for example without this headers Chrome will download files as txt)
    ctx.Header("Content-Description", "File Transfer")
    ctx.Header("Content-Transfer-Encoding", "binary")
    ctx.Header("Content-Disposition", "attachment; filename="+fileName )
    ctx.Header("Content-Type", "application/octet-stream")
    ctx.File(targetPath)
})