download.go

package main
 
import (
    "fmt"
    "io"
    "net/http"
    "os"
    "strconv"
)
 
func main() {
    fmt.Println("Starting http file sever")
    http.HandleFunc("/", HandleClient)
    err := http.ListenAndServe(":80", nil)
    if err != nil {
        fmt.Println(err)
    }
}
func HandleClient(writer http.ResponseWriter, request *http.Request) {
    //First of check if Get is set in the URL
    Filename := request.URL.Query().Get("file")
    if Filename == "" {
        //Get not set, send a 400 bad request
        http.Error(writer, "Get 'file' not specified in url.", 400)
        return
    }
    fmt.Println("Client requests: " + Filename)
 
    //Check if file exists and open
    Openfile, err := os.Open(Filename)
    defer Openfile.Close() //Close after function return
    if err != nil {
        //File not found, send 404
        http.Error(writer, "File not found.", 404)
        return
    }
 
    //File is found, create and send the correct headers
 
    //Get the Content-Type of the file
    //Create a buffer to store the header of the file in
    FileHeader := make([]byte, 512)
    //Copy the headers into the FileHeader buffer
    Openfile.Read(FileHeader)
    //Get content type of file
    FileContentType := http.DetectContentType(FileHeader)
 
    //Get the file size
    FileStat, _ := Openfile.Stat()                     //Get info from file
    FileSize := strconv.FormatInt(FileStat.Size(), 10) //Get file size as a string
 
    //Send the headers
    writer.Header().Set("Content-Disposition", "attachment; filename="+Filename)
    writer.Header().Set("Content-Type", FileContentType)
    writer.Header().Set("Content-Length", FileSize)
 
    //Send the file
    //We read 512 bytes from the file already so we reset the offset back to 0
    Openfile.Seek(0, 0)
    io.Copy(writer, Openfile) //'Copy' the file to the client
    return
}