refactor: drop custom dns cache, use net.Dialer directly

pkg/net/proxytransport.go

@@ -1,29 +1,14 @@
 package netutil
 
 import (
-	"context"
-	"fmt"
 	"net"
 	"net/http"
-	"sync"
 	"time"
 )
 
-var dnsCache sync.Map
-
-func init() {
-	go func() {
-		for {
-			time.Sleep(5 * time.Minute)
-			dnsCache.Range(func(key, _ any) bool {
-				dnsCache.Delete(key)
-				return true
-			})
-		}
-	}()
-}
-
 func newTransport(dialTimeout, tlsTimeout, headerTimeout time.Duration) *http.Transport {
+	dialer := &net.Dialer{Timeout: dialTimeout}
+
 	return &http.Transport{
 		MaxIdleConns:          100,
 		MaxIdleConnsPerHost:   10,
@@ -31,47 +16,10 @@ func newTransport(dialTimeout, tlsTimeout, headerTimeout time.Duration) *http.Tr
 		TLSHandshakeTimeout:   tlsTimeout,
 		ResponseHeaderTimeout: headerTimeout,
 		ExpectContinueTimeout: 1 * time.Second,
-		DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
+		DialContext:           dialer.DialContext,
-			host, port, err := net.SplitHostPort(addr)
-			if err != nil {
-				return nil, err
-			}
-
-			ips, ok := dnsCache.Load(host)
-			if !ok {
-				resolved, err := net.DefaultResolver.LookupIPAddr(ctx, host)
-				if err != nil {
-					return nil, fmt.Errorf("proxy dns lookup: %w", err)
-				}
-				dnsCache.Store(host, resolved)
-				ips = resolved
-			}
-
-			return dialIPs(ctx, network, host, port, ips.([]net.IPAddr), dialTimeout)
-		},
 	}
 }
 
-func dialIPs(ctx context.Context, network, host, port string, ips []net.IPAddr, timeout time.Duration) (net.Conn, error) {
-	var firstErr error
-	for _, ip := range ips {
-		select {
-		case <-ctx.Done():
-			return nil, ctx.Err()
-		default:
-		}
-		dialer := net.Dialer{Timeout: timeout}
-		conn, err := dialer.DialContext(ctx, network, net.JoinHostPort(ip.String(), port))
-		if err == nil {
-			return conn, nil
-		}
-		if firstErr == nil {
-			firstErr = err
-		}
-	}
-	return nil, fmt.Errorf("proxy dial %s: %w", host, firstErr)
-}
-
 func NewClient() *http.Client {
 	return &http.Client{
 		Transport: newTransport(10*time.Second, 10*time.Second, 30*time.Second),
@@ -82,5 +30,6 @@ func NewClient() *http.Client {
 func NewStreamingClient() *http.Client {
 	return &http.Client{
 		Transport: newTransport(10*time.Second, 10*time.Second, 15*time.Second),
+		// No client timeout: streaming responses may stay open indefinitely.
 	}
 }