initial commit

main.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"crypto/tls"
+	"flag"
+	"fmt"
+	"net"
+	"os"
+	"time"
+)
+
+// main is the entry point for the program, handling SSL certificate validity checks for a specified host and port.
+func main() {
+	// Define command-line parameters
+	var (
+		host         string
+		port         int
+		warningDays  int
+		criticalDays int
+		timeout      int
+	)
+	flag.StringVar(&host, "H", "", "Hostname to check")
+	flag.IntVar(&port, "p", 443, "Port to connect to (default: 443)")
+	flag.IntVar(&warningDays, "w", 30, "Warning threshold in days (default: 30)")
+	flag.IntVar(&criticalDays, "c", 15, "Critical threshold in days (default: 15)")
+	flag.IntVar(&timeout, "t", 1000, "Connection timeout in milliseconds (default: 1000)")
+
+	flag.Parse()
+
+	if host == "" {
+		fmt.Fprintln(os.Stderr, "Usage: -H <hostname> [-p <port>] [-w <warning days>] [-c <critical days>] [-t <timeout>]")
+		os.Exit(1)
+	}
+
+	// Establish a connection with timeout
+	address := fmt.Sprintf("%s:%d", host, port)
+	dialer := &net.Dialer{Timeout: time.Duration(timeout) * time.Millisecond}
+
+	conn, err := tls.DialWithDialer(dialer, "tcp", address, &tls.Config{ServerName: host})
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "CRITICAL: Could not connect to %s (%v)\n", address, err)
+		os.Exit(2)
+	}
+	defer conn.Close()
+
+	// Fetch the certificate
+	cert := conn.ConnectionState().PeerCertificates[0]
+
+	// Validate hostname
+	err = cert.VerifyHostname(host)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "CRITICAL: Hostname verification failed for %s (%v)\n", host, err)
+		os.Exit(2)
+	}
+
+	// Check expiration
+	timeRemaining := cert.NotAfter.Sub(time.Now())
+	daysRemaining := int(timeRemaining.Hours() / 24)
+
+	if daysRemaining < 0 {
+		fmt.Fprintf(os.Stderr, "CRITICAL: Certificate for %s expired %d days ago.\n", host, -daysRemaining)
+		os.Exit(2)
+	} else if daysRemaining < criticalDays {
+		fmt.Printf("CRITICAL: Certificate for %s expires in %d days.\n", host, daysRemaining)
+		os.Exit(2)
+	} else if daysRemaining < warningDays {
+		fmt.Printf("WARNING: Certificate for %s expires in %d days.\n", host, daysRemaining)
+		os.Exit(1)
+	}
+
+	fmt.Printf("OK: Certificate for %s is valid, expires in %d days.\n", host, daysRemaining)
+	os.Exit(0)
+}