main.go 源码
// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
// For more tutorials : https://learngoprogramming.com
// In-person training : https://www.linkedin.com/in/inancgumus/
// Follow me on twitter: https://twitter.com/inancgumus
package main
import (
"bytes"
"fmt"
"io"
"os"
)
/*
// ~~~ THE CLASSIC WAY ~~~
try {
// open a file
// throws an exception
} catch (ExceptionType name) {
// handle the error
} finally {
// close the file
}
// ~~~ GO WAY ~~~
file, err := // open the file
if err != nil {
// handle the error
}
// close the file
// really really exceptional problem occurs
// mostly due to a programmer
// panic("PANIC PANIC")
*/
func main() {
files := []string{
"pngs/cups-jpg.png",
"pngs/forest-jpg.png",
"pngs/golden.png",
"pngs/work.png",
"pngs/shakespeare-text.png",
"pngs/empty.png",
}
list("png", files)
// fmt.Println("catch me if you can!")
}
func list(format string, files []string) {
valids := detect(format, files)
fmt.Printf("Correct Files:\n")
for _, valid := range valids {
fmt.Printf(" + %s\n", valid)
}
}
func detect(format string, filenames []string) (valids []string) {
header := headerOf(format)
buf := make([]byte, len(header))
for _, filename := range filenames {
if read(filename, buf) != nil {
continue
}
if bytes.Equal([]byte(header), buf) {
valids = append(valids, filename)
}
}
return
}
func headerOf(format string) string {
switch format {
case "png":
return "\x89PNG\r\n\x1a\n"
case "jpg":
return "\xff\xd8\xff"
}
panic("unknown format: " + format)
}
// read reads len(buf) bytes to buf from a file
func read(filename string, buf []byte) error {
file, err := os.Open(filename)
if err != nil {
return err
}
defer file.Close()
fi, err := file.Stat()
if err != nil {
return err
}
if fi.Size() <= int64(len(buf)) {
return fmt.Errorf("file size < len(buf)")
}
_, err = io.ReadFull(file, buf)
return err
}
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