Go: Detect Content Type or MIIME Type

go_detect_content_type.go

package main

import (
	"io"
	"log"
	"net/http"
	"os"
)

func detectContentType(r io.Reader) (string, error) {
	data := make([]byte, 512)
	n, err := r.Read(data)
	// NOTE: io.EOF is normal when len(data) < 512.
	if err != nil && err != io.EOF {
		return "", err
	}
	// NOTE: date[:n] is important when len(data) < 512.
	return http.DetectContentType(data[:n]), nil
}

func main() {
	const filename = "input.file"
	f, err := os.Open(filename)
	if err != nil {
		return log.Fatal(err)
	}
	defer f.Close()
	contentType, err := detectContentType(f)
	if err != nil {
		log.Fatal(err)
	}
	log.Println(contentType)
}