Golang : How to verify uploaded file is image or allowed file types
Problem :
How do I verify if an uploaded file to my server is ... let say I only allow images(JPG, PNG, GIF)... is indeed image file.
Solution :
Use DetectContentType function to detect the uploaded file. Only proceed further if the uploaded file is image or allowed file types.
If not, abort and prompt error message.
The code will assume that the target file is uploaded from client. To see how to upload file in Golang, please visit https://www.socketloop.com/tutorials/golang-upload-file
Codes :
package main
import (
"fmt"
"net/http"
"os"
"runtime"
)
func main() {
// maximize CPU usage for maximum performance
runtime.GOMAXPROCS(runtime.NumCPU())
// open the uploaded file
file, err := os.Open("./img.png")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
buff := make([]byte, 512) // why 512 bytes ? see http://golang.org/pkg/net/http/#DetectContentType
_, err = file.Read(buff)
if err != nil {
fmt.Println(err)
os.Exit(1)
}
filetype := http.DetectContentType(buff)
fmt.Println(filetype)
switch filetype {
case "image/jpeg", "image/jpg":
fmt.Println(filetype)
case "image/gif":
fmt.Println(filetype)
case "image/png":
fmt.Println(filetype)
case "application/pdf": // not image, but application !
fmt.Println(filetype)
default:
fmt.Println("unknown file type uploaded")
}
}
See also : Golang : Upload file from web browser to server
By Adam Ng
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