URL 与 DNS：从名字到地址

scheme://user:password@host:port/path?query#fragment
  |          |           |    |    |     |      |
 协议     用户信息(罕用)  主机  端口  路径  查询串  片段

https://alice:secret@shop.example.com:8443/list/books?page=2&sort=price#reviews

python3 -c '
from urllib.parse import urlsplit, parse_qs, quote, unquote
 
u = urlsplit("https://shop.example.com:8443/list/books?page=2&sort=price&kw=%E5%9B%BE%E4%B9%A6#reviews")
print("scheme  =", u.scheme)
print("host    =", u.hostname)
print("port    =", u.port)
print("path    =", u.path)
print("query   =", parse_qs(u.query))
print("fragment=", u.fragment)
print()
# 编码与解码
print(quote("北京 hello&world"))
print(unquote("%E5%9B%BE%E4%B9%A6"))
'

浏览器缓存 → 系统缓存 → /etc/hosts → 递归解析器
                                        │ 1. 问根服务器: .com 归谁管？
                                        │ 2. 问 .com 顶级域服务器: example.com 归谁管？
                                        │ 3. 问 example.com 权威服务器: www 的 A 记录？
                                        ▼
                                   93.184.216.34（缓存 TTL 秒）

$ dig +short www.example.com A
93.184.216.34
 
$ dig +trace example.com     # 展示从根开始的完整迭代路径
.               518400  IN  NS  a.root-servers.net.
com.            172800  IN  NS  a.gtld-servers.net.
example.com.    172800  IN  NS  a.iana-servers.net.
example.com.    86400   IN  A   93.184.216.34

# 查看容器的 hosts 文件
cat /etc/hosts
echo "---"
 
# 追加一条自定义映射：myapp.local 指向回环地址
echo "127.0.0.1 myapp.local" >> /etc/hosts
 
# 起服务后，用域名（而非 IP）访问
python3 -m http.server 8000 --bind 127.0.0.1 >/dev/null 2>&1 &
for _i in $(seq 1 50); do (exec 3<>/dev/tcp/127.0.0.1/8000) 2>/dev/null && break; sleep 0.1; done
echo "via-hosts-file" > index.html
 
curl -s http://myapp.local:8000/index.html

python3 -m http.server 8000 --bind 127.0.0.1 >/dev/null 2>&1 &
for _i in $(seq 1 50); do (exec 3<>/dev/tcp/127.0.0.1/8000) 2>/dev/null && break; sleep 0.1; done
echo "hello from fake-example" > index.html
 
# 告诉 curl：api.example.com 的 8000 端口就解析到 127.0.0.1
# 请求里的 Host 头仍然是 api.example.com —— 服务器据此区分虚拟主机
curl -sv --resolve api.example.com:8000:127.0.0.1 \
  http://api.example.com:8000/index.html 2>&1 | grep -E "^(> Host|< HTTP|hello)"