# Golang

## URL


## DNS

### Check <b>hosts</b> file
- `location: C:\windows\system32\drivers\etc\hosts`
### Check local DNS cache
- `ipconfig /displaydns`
### Ask DNS server
- Example:
- HiNet DNS （`168.95.1.1`、`168.95.192.1`）
- google DNS ( `8.8.8.8` )

## HTTP

### GET

GET /path/to/myfile.html?key1=value1 HTTP/1.1        
Host：192.168.100.61:8080               
User-Agent：Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.4 (KHTML, like Gecko) Chrome/22.0.1229.94 Safari/537.4 
Accept：text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding：gzip,deflate,sdch 
Accept-Charset：UTF-8,*;q=0.5

### POST

POST / HTTP/1.1
Host: 127.0.0.1:566
User-Agent: curl/7.74.0
Accept: */*
Content-Length: 34
Content-Type: application/x-www-form-urlencoded

k=v&username=bob&password=p@ssw0rd

## Process

### index.html

<form>
    username: <input type="text" name="username"><br>
    password: <input type="password" name="password"><br>
    <input type="submit" value="submit">
</form>

### main.go

package main

import (
	"fmt"
	"io"
	"net/http"
	"os"
	"regexp"
	"strings"

	"github.com/anaskhan96/soup"
)

func main() {

	// url := "https://www.ptt.cc/bbs/MobileComm/index6505.html"

	// soupExample(url)
	// regExample(url)

	port := "3333"
	if len(os.Args) > 1 {
		port = os.Args[1]
	}
	httpSrvExample(port)
}

func checkErr(err error) {
	if err != nil {
		os.Exit(1)
	}
}

func getRoot(w http.ResponseWriter, request *http.Request) {
	addr := request.RemoteAddr
	remoteIP := strings.Split(addr, ":")[0]
	fmt.Printf("%s: got / request\n", remoteIP)
	io.WriteString(w, "This is my website!\n")
}

func getHello(w http.ResponseWriter, request *http.Request) {
	addr := request.RemoteAddr
	remoteIP := strings.Split(addr, ":")[0]
	fmt.Printf("%s: got /hello request\n", remoteIP)
	io.WriteString(w, "Hello, HTTP!\n")
}

func reqCheck(writer http.ResponseWriter, request *http.Request) {

	addr := request.RemoteAddr
	remoteIP := strings.Split(addr, ":")[0]
	fmt.Printf("%s: got /reqCheck request\n", remoteIP)

	fmt.Fprintln(writer, "Paramaters: ")
	for key, value := range request.URL.Query() {
		fmt.Fprintln(writer, key, "=>", value[0])
	}

	fmt.Fprintln(writer, "\nHeaders: ")
	for key, value := range request.Header {
		fmt.Fprintln(writer, key, "=>", value[0])
	}

	fmt.Fprintln(writer, "\nBody: ")
	bodyBytes, err := io.ReadAll(request.Body)
	checkErr(err)
	bodyString := string(bodyBytes)

	fmt.Fprintln(writer, bodyString)
}

func httpSrvExample(port string) {
	http.HandleFunc("/", getRoot)
	http.HandleFunc("/hello", getHello)
	http.HandleFunc("/reqCheck", reqCheck)

	err := http.ListenAndServe(fmt.Sprintf(":%s", port), nil)
	checkErr(err)
}

func soupExample(url string) {
	resp, err := soup.Get(url)
	checkErr(err)

	doc := soup.HTMLParse(resp)
	divs := doc.FindAll("div", "class", "title")

	for _, div := range divs {
		link := div.Find("a")
		if link.Error != nil {
			continue
		}
		fmt.Println(link.Attrs()["href"], link.Text())
	}
}

func regExample(url string) {
	resp, err := http.Get(url)
	if resp.StatusCode != http.StatusOK {
		println("http request error")
		os.Exit(1)
	}
	defer resp.Body.Close()
	bodyBytes, err := io.ReadAll(resp.Body)
	checkErr(err)
	bodyString := string(bodyBytes)

	r, err := regexp.Compile("href=\"(.*?.html)\">(.*?)</a")
	matches := r.FindAllStringSubmatch(bodyString, -1)

	for _, match := range matches[9:] {
		fmt.Println(match[1], match[2])
	}
}