switch DialContext to Dialer

client.go

@@ -2,15 +2,13 @@ package fastdns
 
 import (
 	"context"
-	"errors"
 	"net"
 	"time"
 )
 
-var (
-	// ErrMaxConns is returned when dns client reaches the max connections limitation.
-	ErrMaxConns = errors.New("dns client reaches the max connections limitation")
-)
+type Dialer interface {
+	DialContext(ctx context.Context, network, addr string) (net.Conn, error)
+}
 
 // Client is an UDP client that supports DNS protocol.
 type Client struct {
@@ -23,9 +21,9 @@ type Client struct {
 	// Timeout
 	Timeout time.Duration
 
-	// DialContext specifies the dial function for creating TCP/UDP connections.
+	// Dialer specifies the dialer for creating TCP/UDP connections.
 	// If it is set, Network, AddrPort and Timeout will be ignored.
-	DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
+	Dialer Dialer
 }
 
 // Exchange executes a single DNS transaction, returning
@@ -39,12 +37,12 @@ func (c *Client) Exchange(ctx context.Context, req, resp *Message) (err error) {
 }
 
 func (c *Client) exchange(ctx context.Context, req, resp *Message) error {
-	dial := c.DialContext
-	if dial == nil {
-		dial = defaultDialer.DialContext
+	dialer := c.Dialer
+	if dialer == nil {
+		dialer = &net.Dialer{Timeout: c.Timeout}
 	}
 
-	conn, err := dial(ctx, c.Network, c.Addr)
+	conn, err := dialer.DialContext(ctx, c.Network, c.Addr)
 	if err != nil {
 		return err
 	}

client_dailer.go

@@ -12,12 +12,6 @@ import (
 	"time"
 )
 
-var defaultDialer = &NetDialer{
-	Dialer: &net.Dialer{
-		Timeout: 5 * time.Second,
-	},
-}
-
 type NetDialer struct {
 	// MaxIdleConns int
 	// MaxConns     int

client_test.go

@@ -54,10 +54,10 @@ func TestLookupCNAME(t *testing.T) {
 		Network: "udp",
 		Addr:    "1.1.1.1:53",
 		Timeout: 1 * time.Second,
-		DialContext: (&HTTPDialer{
+		Dialer: &HTTPDialer{
 			Endpoint:  cloudflare,
 			UserAgent: "fastdns/0.9",
-		}).DialContext,
+		},
 	}
 
 	cname, err := client.LookupCNAME(context.Background(), host)
@@ -72,10 +72,10 @@ func TestLookupTXT(t *testing.T) {
 		Network: "udp",
 		Addr:    "1.1.1.1:53",
 		Timeout: 1 * time.Second,
-		DialContext: (&HTTPDialer{
+		Dialer: &HTTPDialer{
 			Endpoint:  cloudflare,
 			UserAgent: "fastdns/0.9",
-		}).DialContext,
+		},
 	}
 
 	txt, err := client.LookupTXT(context.Background(), host)
@@ -90,10 +90,10 @@ func TestLookupNetIP(t *testing.T) {
 		Network: "udp",
 		Addr:    "1.1.1.1:53",
 		Timeout: 1 * time.Second,
-		DialContext: (&HTTPDialer{
+		Dialer: &HTTPDialer{
 			Endpoint:  cloudflare,
 			UserAgent: "fastdns/0.9",
-		}).DialContext,
+		},
 	}
 
 	ips, err := client.LookupNetIP(context.Background(), "ip", host)

cmd/fastdig/fastdig.go

@@ -28,10 +28,10 @@ func main() {
 			fmt.Fprintf(os.Stderr, "client=%+v parse server(\"%s\") error: %+v\n", client, server, err)
 			os.Exit(1)
 		}
-		client.DialContext = (&fastdns.HTTPDialer{
+		client.Dialer = &fastdns.HTTPDialer{
 			Endpoint:  endpoint,
 			UserAgent: "fastdig/0.9",
-		}).DialContext
+		}
 	}
 
 	req, resp := fastdns.AcquireMessage(), fastdns.AcquireMessage()

message.go

@@ -96,6 +96,8 @@ var (
 	ErrInvalidQuestion = errors.New("dns message does not have the expected question size")
 	// ErrInvalidAnswer is returned when dns message does not have the expected answer size.
 	ErrInvalidAnswer = errors.New("dns message does not have the expected answer size")
+	// ErrMaxConns is returned when dns client reaches the max connections limitation.
+	ErrMaxConns = errors.New("dns client reaches the max connections limitation")
 )
 
 // ParseMessage parses dns request from payload into dst and returns the error.