Refactor code structure for improved readability and maintainability

resolver/transport.go

@@ -0,0 +1,46 @@
+package resolver
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"strings"
+	"time"
+)
+
+// UDPQuery sends a raw DNS query to addr over UDP and returns the raw response bytes.
+//
+// addr may be "ip" or "ip:port" — ":53" is appended if no port is specified.
+// timeout sets the per-query deadline for the read/write operations.
+// ctx allows early cancellation; if the context already has a deadline that
+// is sooner than timeout, the context deadline takes precedence.
+func UDPQuery(ctx context.Context, addr string, query []byte, timeout time.Duration) ([]byte, error) {
+	if !strings.Contains(addr, ":") {
+		addr = addr + ":53"
+	}
+
+	dialer := net.Dialer{Timeout: timeout}
+	conn, err := dialer.DialContext(ctx, "udp", addr)
+	if err != nil {
+		return nil, fmt.Errorf("connecting to %s: %w", addr, err)
+	}
+	defer conn.Close()
+
+	// Determine the effective deadline: use ctx deadline if sooner than timeout.
+	deadline := time.Now().Add(timeout)
+	if ctxDeadline, ok := ctx.Deadline(); ok && ctxDeadline.Before(deadline) {
+		deadline = ctxDeadline
+	}
+	conn.SetDeadline(deadline) //nolint:errcheck
+
+	if _, err := conn.Write(query); err != nil {
+		return nil, fmt.Errorf("sending query to %s: %w", addr, err)
+	}
+
+	buf := make([]byte, udpBufSize)
+	n, err := conn.Read(buf)
+	if err != nil {
+		return nil, fmt.Errorf("reading response from %s: %w", addr, err)
+	}
+	return buf[:n], nil
+}