refactor: DNS

dns/transport/hosts/hosts_file.go

@@ -0,0 +1,102 @@
+package hosts
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"net/netip"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+const cacheMaxAge = 5 * time.Second
+
+type File struct {
+	path    string
+	access  sync.Mutex
+	byName  map[string][]netip.Addr
+	expire  time.Time
+	modTime time.Time
+	size    int64
+}
+
+func NewFile(path string) *File {
+	return &File{
+		path: path,
+	}
+}
+
+func (f *File) Lookup(name string) []netip.Addr {
+	f.access.Lock()
+	defer f.access.Unlock()
+	f.update()
+	return f.byName[name]
+}
+
+func (f *File) update() {
+	now := time.Now()
+	if now.Before(f.expire) && len(f.byName) > 0 {
+		return
+	}
+	stat, err := os.Stat(f.path)
+	if err != nil {
+		return
+	}
+	if f.modTime.Equal(stat.ModTime()) && f.size == stat.Size() {
+		f.expire = now.Add(cacheMaxAge)
+		return
+	}
+	byName := make(map[string][]netip.Addr)
+	file, err := os.Open(f.path)
+	if err != nil {
+		return
+	}
+	defer file.Close()
+	reader := bufio.NewReader(file)
+	var (
+		prefix   []byte
+		line     []byte
+		isPrefix bool
+	)
+	for {
+		line, isPrefix, err = reader.ReadLine()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			return
+		}
+		if isPrefix {
+			prefix = append(prefix, line...)
+			continue
+		} else if len(prefix) > 0 {
+			line = append(prefix, line...)
+			prefix = nil
+		}
+		commentIndex := strings.IndexRune(string(line), '#')
+		if commentIndex != -1 {
+			line = line[:commentIndex]
+		}
+		fields := strings.Fields(string(line))
+		if len(fields) < 2 {
+			continue
+		}
+		var addr netip.Addr
+		addr, err = netip.ParseAddr(fields[0])
+		if err != nil {
+			continue
+		}
+		for index := 1; index < len(fields); index++ {
+			canonicalName := dns.CanonicalName(fields[index])
+			byName[canonicalName] = append(byName[canonicalName], addr)
+		}
+	}
+	f.expire = now.Add(cacheMaxAge)
+	f.modTime = stat.ModTime()
+	f.size = stat.Size()
+	f.byName = byName
+}