package main
import (
	"net/http"
)
func main() {
	http.HandleFunc("/", handler)
	http.ListenAndServe(":8080", nil)
}
func handler(w http.ResponseWriter, r *http.Request) {
	// 设置允许跨域请求
	w.Header().Set("Access-Control-Allow-Origin", "http://example.com") // 替换成实际允许的源
	// 设置 Cookie
	cookie := http.Cookie{
		Name:     "my-cookie",
		Value:    "cookie-value",
		Path:     "/",
		Domain:   ".example.com", // 替换成实际的共享父级域名
		HttpOnly: true,
	}
	http.SetCookie(w, &cookie)
	w.Write([]byte("Cookie set successfully"))
}

// SetCookie adds a Set-Cookie header to the provided ResponseWriter's headers.
// The provided cookie must have a valid Name. Invalid cookies may be
// silently dropped.
func SetCookie(w ResponseWriter, cookie *Cookie) {
	if v := cookie.String(); v != "" {
		w.Header().Add("Set-Cookie", v)
	}
}

// String returns the serialization of the cookie for use in a Cookie
// header (if only Name and Value are set) or a Set-Cookie response
// header (if other fields are set).
// If c is nil or c.Name is invalid, the empty string is returned.
func (c *Cookie) String() string {
	if c == nil || !isCookieNameValid(c.Name) {
		return ""
	}
	// extraCookieLength derived from typical length of cookie attributes
	// see RFC 6265 Sec 4.1.
	const extraCookieLength = 110
	var b strings.Builder
	b.Grow(len(c.Name) + len(c.Value) + len(c.Domain) + len(c.Path) + extraCookieLength)
	b.WriteString(c.Name)
	b.WriteRune('=')
	b.WriteString(sanitizeCookieValue(c.Value))

	if len(c.Path) > 0 {
		b.WriteString("; Path=")
		b.WriteString(sanitizeCookiePath(c.Path))
	}
	if len(c.Domain) > 0 {
		if validCookieDomain(c.Domain) {
			// A c.Domain containing illegal characters is not
			// sanitized but simply dropped which turns the cookie
			// into a host-only cookie. A leading dot is okay
			// but won't be sent.
			d := c.Domain
			if d[0] == '.' {
				d = d[1:]
			}
			b.WriteString("; Domain=")
			b.WriteString(d)
		} else {
			log.Printf("net/http: invalid Cookie.Domain %q; dropping domain attribute", c.Domain)
		}
	}
}

// validCookieDomain reports whether v is a valid cookie domain-value.
func validCookieDomain(v string) bool {
	if isCookieDomainName(v) {
		return true
	}
	if net.ParseIP(v) != nil && !strings.Contains(v, ":") {
		return true
	}
	return false
}

// isCookieDomainName reports whether s is a valid domain name or a valid
// domain name with a leading dot '.'.  It is almost a direct copy of
// package net's isDomainName.
func isCookieDomainName(s string) bool {
	if len(s) == 0 {
		return false
	}
	if len(s) > 255 {
		return false
	}

	if s[0] == '.' {
		// A cookie a domain attribute may start with a leading dot.
		s = s[1:]
	}
	last := byte('.')
	ok := false // Ok once we've seen a letter.
	partlen := 0
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		default:
			return false
		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
			// No '_' allowed here (in contrast to package net).
			ok = true
			partlen++
		case '0' <= c && c <= '9':
			// fine
			partlen++
		case c == '-':
			// Byte before dash cannot be dot.
			if last == '.' {
				return false
			}
			partlen++
		case c == '.':
			// Byte before dot cannot be dot, dash.
			if last == '.' || last == '-' {
				return false
			}
			if partlen > 63 || partlen == 0 {
				return false
			}
			partlen = 0
		}
		last = c
	}
	if last == '-' || partlen > 63 {
		return false
	}

	return ok
}

package main

import (
	"fmt"
	"net"
)

func isCookieDomainName(s string) bool {
	if len(s) == 0 {
		return false
	}
	if len(s) > 255 {
		return false
	}

	if s[0] == '.' {
		// A cookie a domain attribute may start with a leading dot.
		s = s[1:]
	}
	last := byte('.')
	ok := false // Ok once we've seen a letter.
	partlen := 0
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		default:
			return false
		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
			// No '_' allowed here (in contrast to package net).
			ok = true
			partlen++
		case '0' <= c && c <= '9':
			// fine
			partlen++
		case c == '-':
			// Byte before dash cannot be dot.
			if last == '.' {
				return false
			}
			partlen++
		case c == '.':
			// Byte before dot cannot be dot, dash.
			if last == '.' || last == '-' {
				return false
			}
			if partlen > 63 || partlen == 0 {
				return false
			}
			partlen = 0
		}
		last = c
	}
	if last == '-' || partlen > 63 {
		return false
	}

	return ok
}

func main() {
	fmt.Println(isCookieDomainName(".wldev.com"))
	fmt.Println(isCookieDomainName(".wl119.com"))
	fmt.Println(isCookieDomainName(".wl_dev.com"))
	fmt.Println(net.ParseIP("wl_dev.com"))
	fmt.Println(net.ParseIP("wl119.club"))
}

true
true
false
<nil>
<nil>