add: error handling

28-error-handling/02-png-detector/main.go

@@ -14,25 +14,6 @@ import (
 	"os"
 )
 
-/*
-	// Most other languages do this:
-	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
-*/
-
 func main() {
 	files := []string{
 		"pngs/cups-jpg.png",
@@ -43,11 +24,11 @@ func main() {
 		"pngs/empty.png",
 	}
 
-	pngs := detect(files)
+	valids := detect(files)
 
 	fmt.Printf("Correct Files:\n")
-	for _, png := range pngs {
+	for _, valid := range valids {
-		fmt.Printf(" + %s\n", png)
+		fmt.Printf(" + %s\n", valid)
 	}
 }
 
@@ -89,7 +70,7 @@ func read(filename string, buf []byte) error {
 	return err
 }
 
-func detectPNGUnsafeAndVerbose(filenames []string) (pngs []string) {
+func detectPNGUnsafeAndVerbose(filenames []string) (valids []string) {
 	const pngHeader = "\x89PNG\r\n\x1a\n"
 
 	buf := make([]byte, len(pngHeader))
@@ -118,7 +99,7 @@ func detectPNGUnsafeAndVerbose(filenames []string) (pngs []string) {
 		}
 
 		if bytes.Equal([]byte(pngHeader), buf) {
-			pngs = append(pngs, filename)
+			valids = append(valids, filename)
 		}
 	}
 	return

28-error-handling/03-png-detector-with-panic/main.go

@@ -0,0 +1,111 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+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
+}

28-error-handling/03-png-detector-with-panic/pngs/shakespeare-text.png

@@ -0,0 +1,12 @@
+come night come romeo come thou day in night
+for thou wilt lie upon the wings of night
+whiter than new snow on a raven's back
+come gentle night come loving black-browed night
+give me my romeo and when he shall die
+take him and cut him out in little stars
+and he will make the face of heaven so fine
+that all the world will be in love with night
+and pay no worship to the garish sun
+oh i have bought the mansion of love
+but not possessed it and though i am sold
+not yet enjoyed

28-error-handling/04-image-detector-recover/main.go

@@ -0,0 +1,99 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+func main() {
+	defer func() {
+		if rerr := recover(); rerr != nil {
+			fmt.Println("panicked:", rerr)
+		}
+	}()
+
+	files := []string{
+		"pngs/cups-jpg.png",
+		"pngs/forest-jpg.png",
+		"pngs/golden.png",
+		"pngs/work.png",
+		"pngs/shakespeare-text.png",
+		"pngs/empty.png",
+	}
+
+	args := os.Args[1:]
+	if len(args) != 1 {
+		fmt.Println("png or jpg?")
+		return
+	}
+
+	list(args[0], 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) (pngs []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) {
+			pngs = append(pngs, filename)
+		}
+	}
+	return
+}
+
+func headerOf(format string) string {
+	switch format {
+	case "png":
+		return "\x89PNG\r\n\x1a\n"
+	case "jpg":
+		return "\xff\xd8\xff"
+	}
+	// this should never occur
+	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
+}

28-error-handling/04-image-detector-recover/pngs/shakespeare-text.png

@@ -0,0 +1,12 @@
+come night come romeo come thou day in night
+for thou wilt lie upon the wings of night
+whiter than new snow on a raven's back
+come gentle night come loving black-browed night
+give me my romeo and when he shall die
+take him and cut him out in little stars
+and he will make the face of heaven so fine
+that all the world will be in love with night
+and pay no worship to the garish sun
+oh i have bought the mansion of love
+but not possessed it and though i am sold
+not yet enjoyed

28-error-handling/04-image-detector-recoverxxx/main.go

@@ -0,0 +1,49 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/inancgumus/learngo/internal/magic"
+)
+
+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",
+	}
+
+	args := os.Args[1:]
+	if len(args) != 1 {
+		fmt.Println("png or jpg?")
+		return
+	}
+
+	list(args[0], files)
+
+	// fmt.Println("catch me if you can!")
+}
+
+func list(format string, files []string) {
+	valids, err := magic.Detect(format, files)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	fmt.Printf("Correct Files:\n")
+	for _, valid := range valids {
+		fmt.Printf(" + %s\n", valid)
+	}
+}

28-error-handling/04-image-detector-recoverxxx/pngs/shakespeare-text.png

@@ -0,0 +1,12 @@
+come night come romeo come thou day in night
+for thou wilt lie upon the wings of night
+whiter than new snow on a raven's back
+come gentle night come loving black-browed night
+give me my romeo and when he shall die
+take him and cut him out in little stars
+and he will make the face of heaven so fine
+that all the world will be in love with night
+and pay no worship to the garish sun
+oh i have bought the mansion of love
+but not possessed it and though i am sold
+not yet enjoyed

internal/magic/detect.go

@@ -0,0 +1,74 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package magic
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+// Detect returns only the valid filenames that match to a header of the given format.
+func Detect(format string, filenames []string) (valids []string, err error) {
+	defer func() {
+		if rerr := recover(); rerr != nil {
+			err = fmt.Errorf("cannot detect: %v", rerr)
+		}
+	}()
+
+	return detect(format, filenames), nil
+}
+
+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"
+	}
+	// this should never occur
+	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
+}