Go Package 100 Challenges: One Hour Mastery Series 2024 Edition E-Book

Tomoya Kanto

• Herausgeber: tredition
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 107

Veröffentlichungsjahr: 2024

Beschreibung

Unlock the power of Go programming with the "Go Package 100 Challenges: One Hour Mastery Series 2024 Edition" eBook. This comprehensive guide is designed for programmers who want to enhance their skills swiftly and effectively. Dive into 100 diverse challenges that cover essential Go packages, each crafted to be understood and applied within an hour. Whether you're a beginner looking to get a quick start or an intermediate developer aiming to solidify your understanding of Go's standard library, this book is your go-to resource. It provides clear, concise explanations and practical examples to ensure you can integrate these solutions into your own projects seamlessly.

Leseprobe

Index

Chapter 1 Introduction

1. Purpose

Chapter 2 standard library

1. net/http

2. os

3. log

4. html/template

5. crypto/hmac

6. crypto/cipher

7. database/sql

8. net/url

9. regexp

10. flag

11. path

12. expvar

13. bufio.Scanner

14. io.Reader and io.Writer

15. sort

16. image/color

17. math/big

18. math/cmplx

19. encoding/base64

20. encoding/csv

21. context

22. bytes

23. strconv

24. strings

25. unicode/utf8

26. unicode

27. math

28. time

29. bufio

30. encoding/json

31. crypto/rand

32. path/filepath

33. container/list

34. archive/zip

35. sync

36. sync/atomic

37. io/ioutil

38. image

39. fmt

40. reflect

Chapter 3 external library

1. gorilla/mux

2. go-sql-driver/mysql

3. chi

4. go-gorm/gorm

5. Badger

6. Cobra

7. Minio

8. go-ethereum

9. goroutine

10. packr

11. Gin

12. Echo

13. Bleve

14. gopacket

15. gorilla/websocket

16. google.golang.org/grpc

17. gorilla/sessions

18. dgrijalva/jwt-go

19. goleveldb

20. casbin

21. go-cmp

22. testify

23. golang.org/x/crypto/ssh

24. BurntSushi/toml

25. go-github

26. Squirrel

27. gorilla/schema

28. go-toml

29. go-colly

30. pq

31. zerolog

32. govalidator

33. go-pg/pg

34. golang.org/x/oauth2

35. BoltDB

36. Blackfriday

37. gorilla/handlers

38. pgx

39. fasthttp

40. air

41. go-tiedot

42. go-chart

43. urfave/cli

44. fsnotify

45. gocql

46. goquery

47. gorilla/pat

48. GoDotEnv

49. golang.org/x/net/websocket

50. github.com/spf13/viper

51. olivere/elastic

52. fsnotify/fsnotify

53. github.com/Shopify/sarama

54. github.com/lib/pq

55. goroutinepool

56. gota

57. mgo

58. bleve

59. gobuffalo/pop

60. go-redis/redis

Chapter 1 Introduction

1. Purpose

Welcome to an exciting journey through the world of Go programming! This book is designed to offer a comprehensive dive into Go's standard library, showcasing a hundred different packages through practical examples and concise explanations.

Whether you are a beginner looking to get a solid foundation or an intermediate programmer aiming to enhance your Go toolkit, this guide is tailored to help you achieve mastery in just one hour per topic.

Here, you will learn to leverage Go’s robust standard packages to build more efficient and reliable applications. Each chapter focuses on a unique package, exploring its functionalities, common uses, and some tips and tricks to get the most out of it.

Dive in and start enhancing your Go programming skills today!

Chapter 2 standard library

1. net/http

The net/http package in Go provides HTTP client and server implementations.

Ex:net/http

package main

import (

"fmt"

"net/http"

)

func main() {

http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {

fmt.Fprintln(w, "Hello, HTTP!")

})

http.ListenAndServe(":8080", nil)

}

When you run this server and access http://localhost:8080 in your browser, you will see the message: "Hello, HTTP!"

This code snippet demonstrates a basic HTTP server in Go. Here’s a breakdown:Import fmt and net/http packages: fmt for formatting and output, net/http for handling HTTP requests.http.HandleFunc("/") sets up a route handler for the root URL ("/"). Whenever this route is accessed, the function specified as the second argument is called.Inside the function, fmt.Fprintln(w, "Hello, HTTP!") sends a string back to the client. w is an http.ResponseWriter, which is used to write the HTTP response.http.ListenAndServe(":8080", nil) starts the server on port 8080. nil indicates that the default server multiplexer, http.DefaultServeMux, is used for routing.This example creates a very basic web server that can be accessed by visiting localhost:8080 in a web browser, where it simply displays a greeting message.

2. os

The os package in Go provides a platform-independent interface to operating system functionality.

Ex:os

The file "example.txt" is created in the current directory with the text "Hello, file handling!" inside it.

This code snippet demonstrates basic file handling using the os package:Import fmt and os: fmt for output and error handling, os for interacting with the operating system.os.Create("example.txt") attempts to create a file named "example.txt". It returns a file handle and an error. If an error occurs, the error handling block will print it and stop further execution.defer file.Close() schedules the file.Close() method to be called when the main function completes, ensuring that the file handle is properly closed after the operations are done.file.WriteString("Hello, file handling!") writes a string to the file. It returns the number of bytes written and an error if any.Error handling is present to manage potential issues during file creation and writing.This example provides a simple demonstration of creating and writing to a file, showcasing basic error handling and file operations.

3. log

The "log" package in Go provides a simple logging facility, allowing you to output formatted and timestamped log entries.

Ex:log

package main

import (

"log"

"os"

)

func main() {

// Creating a log file

file, err := os.Create("example.log")

if err != nil {

log.Fatal(err) // Logs a message and then calls os.Exit(1)

}

defer file.Close()

// Setting the output of the logger to the file

log.SetOutput(file)

// Print info log with date and time

log.Println("This is an informational message")

}

The log file example.log will contain a timestamped entry like:csharpCopy code2009/11/10 23:00:00 This is an informational message

(Note: Timestamp will vary based on when the code is run.)

In the code above, we start by importing the necessary packages. The log package is used for logging, and os is used for file handling operations such as creating a file. Here’s what happens in the code:File Creation: We attempt to create a file named "example.log". If an error occurs during file creation (e.g., due to permission issues), log.Fatal(err) will log the error and then terminate the program with an exit code of 1.Set Logger Output: By default, the log package writes to standard error (stderr). We change this behavior by setting the logger's output destination to the file we just created.Logging a Message: We then log an informational message. This message is automatically prefixed with the current date and time, thanks to the default logger setup.This basic setup is very useful for adding logs to your application which can help in debugging or monitoring the software behavior over time.

4. html/template

The "html/template" package in Go is used for data-driven templates that generate HTML output safe against code injection.

Ex:html/template

package main

import (

"html/template"

"os"

)

func main() {

// Define a template with a placeholder

tmpl := `<!DOCTYPE html>

<html>

<head>

<title>{{.Title}}</title>

</head>

<body>

<h1>{{.Header}}</h1>

<p>{{.Message}}</p>

</body>

</html>`

// Parse the template string

t, err := template.New("webpage").Parse(tmpl)

if err != nil {

panic(err)

}

// Data to fill the template

data := struct {

Title string

Header string

Message string

}{

Title: "Test Page",

Header: "Welcome to the Test Page",

Message: "This is a test message.",

}

// Execute the template and output to os.Stdout

t.Execute(os.Stdout, data)

}

<!DOCTYPE html>

<html>

<head>

<title>Test Page</title>

</head>

<body>

<h1>Welcome to the Test Page</h1>

<p>This is a test message.</p>

</body>

</html>

This example demonstrates how to use the html/template package to create and execute HTML templates. Here’s a breakdown:Template Definition: We start by defining a string that acts as our HTML template. It includes placeholders ({{.Title}}, {{.Header}}, {{.Message}}) that will be replaced by actual values.Parsing the Template: The template string is then parsed into a template object. Errors in parsing (such as syntax errors in the template) would cause the program to panic, though in a production setting, you'd likely handle this more gracefully.Data Structure: We define a data structure that matches the placeholders in our template. This data is passed to the template during execution.Executing the Template: Finally, the template is executed with the provided data, and the output is sent directly to os.Stdout (standard output), but it could also be written to a file or an HTTP response body.This process ensures that any data used in the template is appropriately escaped, preventing Cross-Site Scripting (XSS) attacks, making it a safer choice for generating dynamic HTML content.

5. crypto/hmac

This package implements key-hashed message authentication code (HMAC) support. HMAC is a mechanism for message authentication using cryptographic hash functions.

Ex:crypto/hmac

package main

import (

"crypto/hmac"

"crypto/sha256"

"encoding/hex"

"fmt"

)

func main() {

key := []byte("secret")

message := []byte("Message to hash")

hash := hmac.New(sha256.New, key)

hash.Write(message)

signature := hash.Sum(nil)

fmt.Println(hex.EncodeToString(signature))

}

9a0d60c9b4f4b04e97f616157069c47b227a1f03124a000747b6ef805fd5d1bb

In the provided Go code, we first import necessary packages for HMAC with SHA256 hashing. We define a 'key' and a 'message' that we want to secure. The hmac.New(sha256.New, key) function initializes a new HMAC object using SHA256 for hashing and the secret key. The Write method is used to input the message into the hash object, and Sum(nil) calculates the HMAC value. Finally, we convert the HMAC byte slice to a hex string to make it readable, which is printed as the output.

6. crypto/cipher

The package provides interfaces to generic block cipher implementations. This package is typically used to implement encryption and decryption of data using various symmetric key algorithms.

Ex:crypto/cipher

package main

import (

"crypto/aes"

"crypto/cipher"

"crypto/rand"

"fmt"

"io"

)

func main() {

key := []byte("examplekey123456") // 16 bytes for AES-128

block, err := aes.NewCipher(key)

if err != nil {

panic(err)

}

plaintext := []byte("This is some text that needs encryption")

ciphertext := make([]byte, aes.BlockSize+len(plaintext))

iv := ciphertext[:aes.BlockSize] // initialization vector

if _, err := io.ReadFull(rand.Reader, iv); err != nil {

panic(err)

}

stream := cipher.NewCFBEncrypter(block, iv)

stream.XORKeyStream(ciphertext[aes.BlockSize:], plaintext)

fmt.Printf("Encrypted: %x\n", ciphertext)

}

Encrypted: 16byteIVfollowedbyencrypteddata

This code demonstrates the usage of the crypto/cipher package to encrypt plaintext using the AES algorithm in CFB mode. Initially, we generate a new AES cipher block with a 16-byte key suitable for AES-128. The aes.NewCipher function initializes the AES cipher with the provided key. The ciphertext slice is prepared to include space for the initialization vector (IV) and the actual ciphertext. We then populate the IV with random bytes, ensuring that each encryption session is unique. The cipher.NewCFBEncrypter creates a stream cipher from the AES block cipher in CFB mode, and XORKeyStream encrypts the plaintext by XORing it with the keyed pseudo-random stream generated from the IV and key. The resulting encrypted data is printed in a hexadecimal format.

7. database/sql

The database/sql package provides a generic interface around SQL (or SQL-like) databases. This package includes the ability to connect to a database, execute queries, and retrieve results.

Ex:database/sql

package main

import (

"database/sql"

"fmt"

_ "github.com/mattn/go-sqlite3"

)

func main() {

db, err := sql.Open("sqlite3", "file:locked.sqlite?cache=shared")

if err != nil {

fmt.Println("Error opening database: ", err)

return

}

defer db.Close()

result, err := db.Exec("CREATE TABLE IF NOT EXISTS hello (id integer not null primary key, name text)")

if err != nil {

fmt.Println("Error creating table: ", err)

return

}

fmt.Println(result)

}

<Output depends on database state, typically will be nil or an SQL result object>

In the above code:We import the database/sql package along with a driver for SQLite (github.com/mattn/go-sqlite3), which is a popular lightweight database.We open a database using sql.Open which establishes a connection to our specified database, here a SQLite database.db.Exec is used to execute SQL statements that do not return rows, such as CREATE, INSERT, UPDATE. In this example, we're creating a table named 'hello'.It’s crucial to handle errors in real applications, to ensure that the database operations do not fail silently.defer db.Close() ensures that the database connection is closed when the surrounding function exits, preventing resource leaks.

8. net/url

The net/url package provides functions to parse URLs and implement URL encoding and decoding. This package handles the encoding and decoding of URLs according to the rules defined in standards.

Ex:net/url

package main

import (

"fmt"

"net/url"

)

func main() {

parsedUrl, err := url.Parse("https://www.example.com/search?q=golang")

if err != nil {

fmt.Println("Error parsing URL: ", err)

return

}

fmt.Println("Scheme:", parsedUrl.Scheme)

fmt.Println("Host:", parsedUrl.Host)

fmt.Println("Path:", parsedUrl.Path)

fmt.Println("Query:", parsedUrl.Query())

}

Scheme: https

Host: www.example.com

Path: /search

Query: map[q:[golang]]

In this example:We use the net/url package to parse a given URL.url.Parse takes a string and returns a URL structure if the URL is valid. Here, "https://www.example.com/search?q=golang" is successfully parsed.parsedUrl.Scheme retrieves the protocol ('https').parsedUrl.Host gets the domain name along with the port if specified ('www.example.com').parsedUrl.Path provides the path section of the URL ('/search').parsedUrl.Query() returns a map containing the query parameters; here, the key is "q" with the value "golang".Proper URL parsing is essential for applications that need to manipulate or analyze web addresses, ensuring they handle web data correctly and safely.

9. regexp

The "regexp" package in Go is used for parsing and matching regular expressions. It provides functions to compile and execute regular expressions that can be used to search, match, or replace substrings in text.

Ex:regexp

package main

import (

"fmt"

"regexp"

)

func main() {

regex, err := regexp.Compile("hello")

if err != nil {

fmt.Println("Invalid regex pattern")

return

}

fmt.Println(regex.MatchString("hello world"))

}

true