refactor: DNS

dns/transport/local/local_linkname.go

@@ -0,0 +1,44 @@
+package local
+
+import (
+	"sync/atomic"
+	"time"
+	_ "unsafe"
+)
+
+const (
+	// net.maxDNSPacketSize
+	maxDNSPacketSize = 1232
+)
+
+type dnsConfig struct {
+	servers       []string      // server addresses (in host:port form) to use
+	search        []string      // rooted suffixes to append to local name
+	ndots         int           // number of dots in name to trigger absolute lookup
+	timeout       time.Duration // wait before giving up on a query, including retries
+	attempts      int           // lost packets before giving up on server
+	rotate        bool          // round robin among servers
+	unknownOpt    bool          // anything unknown was encountered
+	lookup        []string      // OpenBSD top-level database "lookup" order
+	err           error         // any error that occurs during open of resolv.conf
+	mtime         time.Time     // time of resolv.conf modification
+	soffset       uint32        // used by serverOffset
+	singleRequest bool          // use sequential A and AAAA queries instead of parallel queries
+	useTCP        bool          // force usage of TCP for DNS resolutions
+	trustAD       bool          // add AD flag to queries
+	noReload      bool          // do not check for config file updates
+}
+
+func (c *dnsConfig) serverOffset() uint32 {
+	if c.rotate {
+		return atomic.AddUint32(&c.soffset, 1) - 1 // return 0 to start
+	}
+	return 0
+}
+
+//go:linkname runtime_rand runtime.rand
+func runtime_rand() uint64
+
+func randInt() int {
+	return int(uint(runtime_rand()) >> 1) // clear sign bit
+}