Make rawQuery timeout handling more thread-safe

Previous an `elapsed` duration was saved on the `Client` object and was updated multiple times on each call to `rawQuery`. This could lead to a race condition when calling `whois.Whois(...)` in parallel, where one thread halfway through the function has a non-zero elapsed duration and another thread entering the function sets it to 0. This removes the `elapsed` field on the `Client` object and uses a local variable instead, which avoids the aforementioned issue.

whois.go

@@ -48,7 +48,6 @@ var DefaultClient = NewClient()
 type Client struct {
 	dialer          proxy.Dialer
 	timeout         time.Duration
-	elapsed         time.Duration
 	disableStats    bool
 	disableReferral bool
 }
@@ -175,7 +174,6 @@ func (c *Client) Whois(domain string, servers ...string) (result string, err err
 
 // rawQuery do raw query to the server
 func (c *Client) rawQuery(domain, server, port string) (string, error) {
-	c.elapsed = 0
 	start := time.Now()
 
 	if server == "whois.arin.net" {
@@ -202,24 +200,22 @@ func (c *Client) rawQuery(domain, server, port string) (string, error) {
 	}
 
 	defer conn.Close()
-	c.elapsed = time.Since(start)
+	elapsed := time.Since(start)
 
-	_ = conn.SetWriteDeadline(time.Now().Add(c.timeout - c.elapsed))
+	_ = conn.SetWriteDeadline(time.Now().Add(c.timeout - elapsed))
 	_, err = conn.Write([]byte(domain + "\r\n"))
 	if err != nil {
 		return "", fmt.Errorf("whois: send to whois server failed: %w", err)
 	}
 
-	c.elapsed = time.Since(start)
+	elapsed = time.Since(start)
 
-	_ = conn.SetReadDeadline(time.Now().Add(c.timeout - c.elapsed))
+	_ = conn.SetReadDeadline(time.Now().Add(c.timeout - elapsed))
 	buffer, err := io.ReadAll(conn)
 	if err != nil {
 		return "", fmt.Errorf("whois: read from whois server failed: %w", err)
 	}
 
-	c.elapsed = time.Since(start)
-
 	return string(buffer), nil
 }