check if a file really is a JPEG or not

check-if-jpeg.go

package main

import (
  "fmt"
  "image"
  "image/jpeg"
  "os"
)

func checkIsJPEG(filename string) error {
  reader, err := os.Open(filename)
  defer reader.Close()
  if err != nil {
    fmt.Printf("file open error - %s\n", err)
    return err
  }
  _, err = jpeg.Decode(reader)
  if err != nil {
    fmt.Printf("file %s likely isnt' a JPEG - %s\n", filename, err)
    return err
  } else {
    fmt.Printf("file %s is a JPEG\n", filename)
    return nil
  }
  return nil
}

func checkJPEGDimensions(filename string) error {
  reader, err := os.Open(filename)
  defer reader.Close()
  if err != nil {
    fmt.Printf("file open error - %s\n", err)
    return err
  }
  im, _, err := image.DecodeConfig(reader)
  if err != nil {
    fmt.Printf("image decode error - %s\n", err)
    return err
  }
  fmt.Printf("JPEG width = %d, height = %d\n", im.Width, im.Height)

  return nil
}

func main() {
  err := checkIsJPEG("/home/rickt/tmp/French-Bronze-Statue-Basset-Hound-Dog-Dogs-Doggy-Casting.jpg")
  if err == nil {
    checkJPEGDimensions("/home/rickt/tmp/French-Bronze-Statue-Basset-Hound-Dog-Dogs-Doggy-Casting.jpg")
  }
}