feat: Add [DOMAIN_EXPIRATION] placeholder for monitoring domain expiration using WHOIS (#325)

* feat: Add [DOMAIN_EXPIRATION] placeholder for monitoring domain expiration using WHOIS

* test: Fix issue caused by possibility of millisecond elapsed during previous tests

* test: Fix test with different behavior based on architecture

* docs: Revert accidental change to starttls example

* docs: Fix mistake in comment for Condition.hasIPPlaceholder()

vendor/github.com/TwiN/whois/whois.go

@@ -0,0 +1,94 @@
+package whois
+
+import (
+	"io"
+	"net"
+	"strings"
+	"time"
+)
+
+const (
+	ianaWHOISServerAddress = "whois.iana.org:43"
+)
+
+type Client struct {
+	whoisServerAddress string
+}
+
+func NewClient() *Client {
+	return &Client{
+		whoisServerAddress: ianaWHOISServerAddress,
+	}
+}
+
+func (c Client) Query(domain string) (string, error) {
+	parts := strings.Split(domain, ".")
+	output, err := c.query(c.whoisServerAddress, parts[len(parts)-1])
+	if err != nil {
+		return "", err
+	}
+	if strings.Contains(output, "whois:") {
+		startIndex := strings.Index(output, "whois:") + 6
+		endIndex := strings.Index(output[startIndex:], "\n") + startIndex
+		whois := strings.TrimSpace(output[startIndex:endIndex])
+		if referOutput, err := c.query(whois+":43", domain); err == nil {
+			return referOutput, nil
+		}
+		return "", err
+	}
+	return output, nil
+}
+
+func (c Client) query(whoisServerAddress, domain string) (string, error) {
+	connection, err := net.DialTimeout("tcp", whoisServerAddress, 10*time.Second)
+	if err != nil {
+		return "", err
+	}
+	defer connection.Close()
+	connection.SetDeadline(time.Now().Add(5 * time.Second))
+	_, err = connection.Write([]byte(domain + "\r\n"))
+	if err != nil {
+		return "", err
+	}
+	output, err := io.ReadAll(connection)
+	if err != nil {
+		return "", err
+	}
+	return string(output), nil
+}
+
+type Response struct {
+	ExpirationDate time.Time
+	DomainStatuses []string
+	NameServers    []string
+}
+
+// QueryAndParse tries to parse the response from the WHOIS server
+// There is no standardized format for WHOIS responses, so this is an attempt at best.
+//
+// Being the selfish person that I am, I also only parse the fields that I need.
+// If you need more fields, please open an issue or pull request.
+func (c Client) QueryAndParse(domain string) (*Response, error) {
+	text, err := c.Query(domain)
+	if err != nil {
+		return nil, err
+	}
+	response := Response{}
+	for _, line := range strings.Split(text, "\n") {
+		line = strings.TrimSpace(line)
+		valueStartIndex := strings.Index(line, ":")
+		if valueStartIndex == -1 {
+			continue
+		}
+		key := strings.ToLower(strings.TrimSpace(line[:valueStartIndex]))
+		value := strings.TrimSpace(line[valueStartIndex+1:])
+		if response.ExpirationDate.Unix() != 0 && strings.Contains(key, "expir") && strings.Contains(key, "date") {
+			response.ExpirationDate, _ = time.Parse(time.RFC3339, strings.ToUpper(value))
+		} else if strings.Contains(key, "domain status") {
+			response.DomainStatuses = append(response.DomainStatuses, value)
+		} else if strings.Contains(key, "name server") {
+			response.NameServers = append(response.NameServers, value)
+		}
+	}
+	return &response, nil
+}