*: basics of a DNS cert expiration alart

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

go.mod

@@ -0,0 +1,8 @@
+module git.batts.cloud/vbatts/too-soon
+
+go 1.22.5
+
+require (
+	github.com/sirupsen/logrus v1.9.3 // indirect
+	golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 // indirect
+)

main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"crypto/x509"
+	"encoding/pem"
+	"flag"
+	"os"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func main() {
+	fDays := flag.Int("d", 20, "number of days to alert on")
+	fDebug := flag.Bool("D", false, "debug mode")
+
+	flag.Parse()
+
+	if *fDebug {
+		log.SetLevel(log.DebugLevel)
+	}
+
+	for _, file := range flag.Args() {
+		var certs []*x509.Certificate
+
+		buf, err := os.ReadFile(file)
+		if err != nil {
+			log.Errorf("%q could not be read: %s", file, err)
+			continue
+		}
+
+		more := true
+		for more {
+			block, rest := pem.Decode(buf)
+			log.Debugf("%q : %s", file, block.Type)
+
+			cert, err := x509.ParseCertificate(block.Bytes)
+			if err != nil {
+				log.Errorf("%q cert could not be parsed: %s", file, err)
+				continue
+			}
+			certs = append(certs, cert)
+
+			if len(rest) == 0 {
+				more = false
+			}
+			// reset the buffer if there is more
+			buf = rest
+		}
+
+		for _, cert := range certs {
+			if len(cert.DNSNames) == 0 {
+				continue
+			}
+
+			hours := time.Duration(*fDays * -24)
+			alertTime := cert.NotAfter.Add(hours * time.Hour)
+			today := time.Now()
+			if today.After(alertTime) {
+				log.Warnf("%q : TIME TO RENEW CERTIFICATE (expires in less than %d days)", file, *fDays)
+				log.Infof("%q : %v", file, cert.NotAfter)
+				log.Infof("%q : %v", file, cert.DNSNames)
+			} else {
+				log.Debugf("%q : %v", file, cert.NotAfter)
+				log.Debugf("%q : %v", file, cert.DNSNames)
+			}
+		}
+	}
+
+}