148 lines
2.6 KiB
Go
148 lines
2.6 KiB
Go
// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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// For more tutorials : https://learngoprogramming.com
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// In-person training : https://www.linkedin.com/in/inancgumus/
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// Follow me on twitter: https://twitter.com/inancgumus
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package main
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import (
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"bytes"
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"fmt"
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"io"
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"os"
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)
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func main() {
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files := []string{
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"pngs/cups-jpg.png",
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"pngs/forest-jpg.png",
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"pngs/golden.png",
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"pngs/work.png",
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"pngs/shakespeare-text.png",
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"pngs/empty.png",
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}
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valids := detect(files)
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fmt.Printf("Correct Files:\n")
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for _, valid := range valids {
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fmt.Printf(" + %s\n", valid)
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}
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}
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func detect(filenames []string) (pngs []string) {
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const pngHeader = "\x89PNG\r\n\x1a\n"
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buf := make([]byte, len(pngHeader))
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for _, filename := range filenames {
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if read(filename, buf) != nil {
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continue
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}
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if bytes.Equal([]byte(pngHeader), buf) {
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pngs = append(pngs, filename)
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}
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}
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return
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}
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// read reads len(buf) bytes to buf from a file
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func read(filename string, buf []byte) error {
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file, err := os.Open(filename)
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if err != nil {
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return err
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}
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defer file.Close()
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fi, err := file.Stat()
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if err != nil {
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return err
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}
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if fi.Size() <= int64(len(buf)) {
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return fmt.Errorf("file size < len(buf)")
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}
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_, err = io.ReadFull(file, buf)
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return err
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}
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func detectPNGUnsafeAndVerbose(filenames []string) (valids []string) {
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const pngHeader = "\x89PNG\r\n\x1a\n"
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buf := make([]byte, len(pngHeader))
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for _, filename := range filenames {
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file, err := os.Open(filename)
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if err != nil {
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continue
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}
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fi, err := file.Stat()
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if err != nil {
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file.Close()
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continue
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}
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if fi.Size() <= int64(len(pngHeader)) {
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file.Close()
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continue
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}
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_, err = io.ReadFull(file, buf)
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file.Close()
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if err != nil {
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continue
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}
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if bytes.Equal([]byte(pngHeader), buf) {
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valids = append(valids, filename)
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}
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}
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return
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}
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// defers don't run when the loop block ends
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func detectPNGWrong(filenames []string) (pngs []string) {
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const pngHeader = "\x89PNG\r\n\x1a\n"
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buf := make([]byte, len(pngHeader))
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for _, filename := range filenames {
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fmt.Printf("processing: %s\n", filename)
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file, err := os.Open(filename)
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if err != nil {
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continue
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}
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defer func() {
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fmt.Printf("closes : %s\n", filename)
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file.Close()
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}()
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fi, err := file.Stat()
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if err != nil {
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continue
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}
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if fi.Size() <= int64(len(pngHeader)) {
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continue
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}
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_, err = io.ReadFull(file, buf)
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if err != nil {
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continue
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}
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if bytes.Equal([]byte(pngHeader), buf) {
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pngs = append(pngs, filename)
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}
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}
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return
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}
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