net: change type of dnsConfig.timeout from int to time.Duration

Instead of keeping the desired number of seconds and converting to
time.Duration for every query, convert to time.Duration when
building the config.

Updates #15473

Change-Id: Ib24c050b593b3109011e359f4ed837a3fb45dc65
Reviewed-on: https://go-review.googlesource.com/22548Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/dnsclient_unix.go

@@ -180,8 +180,7 @@ func tryOneName(ctx context.Context, cfg *dnsConfig, name string, qtype uint16)
 		return "", nil, &DNSError{Err: "no DNS servers", Name: name}
 	}
 
-	timeout := time.Duration(cfg.timeout) * time.Second
-	deadline := time.Now().Add(timeout)
+	deadline := time.Now().Add(cfg.timeout)
 	if old, ok := ctx.Deadline(); !ok || deadline.Before(old) {
 		var cancel context.CancelFunc
 		ctx, cancel = context.WithDeadline(ctx, deadline)

src/net/dnsconfig_unix.go

@@ -22,7 +22,7 @@ type dnsConfig struct {
 	servers    []string      // servers to use
 	search     []string      // suffixes to append to local name
 	ndots      int           // number of dots in name to trigger absolute lookup
-	timeout    int       // seconds before giving up on packet
+	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
@@ -35,7 +35,7 @@ type dnsConfig struct {
 func dnsReadConfig(filename string) *dnsConfig {
 	conf := &dnsConfig{
 		ndots:    1,
-		timeout:  5,
+		timeout:  5 * time.Second,
 		attempts: 2,
 	}
 	file, err := open(filename)
@@ -101,7 +101,7 @@ func dnsReadConfig(filename string) *dnsConfig {
 					if n < 1 {
 						n = 1
 					}
-					conf.timeout = n
+					conf.timeout = time.Duration(n) * time.Second
 				case hasPrefix(s, "attempts:"):
 					n, _, _ := dtoi(s, 9)
 					if n < 1 {

src/net/dnsconfig_unix_test.go

@@ -24,7 +24,7 @@ var dnsReadConfigTests = []struct {
 			servers:    []string{"8.8.8.8", "2001:4860:4860::8888", "fe80::1%lo0"},
 			search:     []string{"localdomain"},
 			ndots:      5,
-			timeout:    10,
+			timeout:    10 * time.Second,
 			attempts:   3,
 			rotate:     true,
 			unknownOpt: true, // the "options attempts 3" line
@@ -36,7 +36,7 @@ var dnsReadConfigTests = []struct {
 			servers:  []string{"8.8.8.8"},
 			search:   []string{"localdomain"},
 			ndots:    1,
-			timeout:  5,
+			timeout:  5 * time.Second,
 			attempts: 2,
 		},
 	},
@@ -46,7 +46,7 @@ var dnsReadConfigTests = []struct {
 			servers:  []string{"8.8.8.8"},
 			search:   []string{"test", "invalid"},
 			ndots:    1,
-			timeout:  5,
+			timeout:  5 * time.Second,
 			attempts: 2,
 		},
 	},
@@ -55,7 +55,7 @@ var dnsReadConfigTests = []struct {
 		want: &dnsConfig{
 			servers:  defaultNS,
 			ndots:    1,
-			timeout:  5,
+			timeout:  5 * time.Second,
 			attempts: 2,
 			search:   []string{"domain.local"},
 		},
@@ -64,7 +64,7 @@ var dnsReadConfigTests = []struct {
 		name: "testdata/openbsd-resolv.conf",
 		want: &dnsConfig{
 			ndots:    1,
-			timeout:  5,
+			timeout:  5 * time.Second,
 			attempts: 2,
 			lookup:   []string{"file", "bind"},
 			servers:  []string{"169.254.169.254", "10.240.0.1"},
@@ -103,7 +103,7 @@ func TestDNSReadMissingFile(t *testing.T) {
 	want := &dnsConfig{
 		servers:  defaultNS,
 		ndots:    1,
-		timeout:  5,
+		timeout:  5 * time.Second,
 		attempts: 2,
 		search:   []string{"domain.local"},
 	}