Golang : Find out mime type from bytes in buffer

Problem :

You are building an application that need to detect the MIME type of an object. Such as an email application that handles file attachment. How to find out the MIME type of an object or file ?

Solution :

Use net/http.DetectContentType() function to detect the file or object MIME type. For example :

 package main

 import (
 "fmt"
 "net/http"
 "os"
 )

 func main() {
 filename := os.Args[1]

 if len(os.Args) != 2 {
 fmt.Println("Missing filename argument")
 fmt.Printf("Usage : %s filename\n", os.Args[0])
 os.Exit(0)
 }

 fmt.Println(filename)

 file, err := os.Open(filename)

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

 buff := make([]byte, 512)

 _, err = file.Read(buff)

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

 filetype := http.DetectContentType(buff)
 fmt.Println("File type or MIME type : ", filetype)

 }

Sample output :

img.gif

File type or MIME type : image/gif

img.pdf

File type or MIME type : application/pdf

Reference :

https://www.socketloop.com/tutorials/golang-how-to-verify-uploaded-file-is-image-or-allowed-file-types