serving up pdfs using golang

just wondering if you guys can help with some code.

It works serving up images but not a pdf brochure.
Thanks in advance

func main(){
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request){
    	filename 	:= "/var/www/filedipenser/brochure.pdf"
    	
    	streamPDFbytes, err := ioutil.ReadFile( filename )

    	if err != nil {
			fmt.Println(err)
			os.Exit(1)
		}

		b := bytes.NewBuffer(streamPDFbytes)

		w.Header().Set("Content-type", "application/pdf")

		if _, err := b.WriteTo(w); err != nil {
			fmt.Fprintf(w, "%s", err)
		}

		w.Write([]byte("PDF Generated"))
    })

    err := http.ListenAndServe(":4111", nil)
    if err != nil {
        log.Fatal("ListenAndServe: ", err)
        fmt.Println(err)
    }
}

The code is a bit inefficient but it appears to be working. However, some PDF viewers might be sensitive to the extraneous output you are adding to the end of the HTTP response stream. Remove w.Write([]byte("PDF Generated")) as this will be corrupting the output. You could change this to a fmt.Println if you wanted for debugging purposes.

The inefficiency is because you are loading the entire PDF file into memory to then send to the client. For large files this will waste memory. You would be better to open the file and stream directly from the file (an io.Reader) to the response (an io.Writer) using io.Copy. Something like:

    // Open file
	f, err := os.Open(filename)
	if err != nil {
		fmt.Println(err)
		w.WriteHeader(500)
		return
	}
	defer f.Close()

	//Set header
	w.Header().Set("Content-type", "application/pdf")

	//Stream to response
	if _, err := io.Copy(w, f); err != nil {
		fmt.Println(err)
		w.WriteHeader(500)
	}

You would obviously want to handle errors better, this is just an example. However, it is important the client is provided an HTTP error response when you encounter an error so it is aware that the request failed.