From 096218f68056a9bca5eec31e1f542a88ab0de66e Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sun, 20 Feb 2022 19:14:07 +0000
Subject: [PATCH 01/22] add some first working version

---
 README.md          |  12 ++++-
 certcal.go         |  60 ++++++++++++++++++++++++
 go.mod             |   8 ++++
 go.sum             |   7 +++
 handler/handler.go |  53 ++++++++++++++++++++++
 hosts/hosts.go     | 111 +++++++++++++++++++++++++++++++++++++++++++++
 ical/ical.go       |  79 ++++++++++++++++++++++++++++++++
 7 files changed, 329 insertions(+), 1 deletion(-)
 create mode 100644 certcal.go
 create mode 100644 go.mod
 create mode 100644 go.sum
 create mode 100644 handler/handler.go
 create mode 100644 hosts/hosts.go
 create mode 100644 ical/ical.go

diff --git a/README.md b/README.md
index 885c94d..3174661 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,12 @@
 # certcal
-provide an iCal web feed for certificate expiry
+
+Provide an iCal web feed for certificate expiry
+
+
+## Usage
+
+### Standalone
+
+
+### As part of an existing http mux
+
diff --git a/certcal.go b/certcal.go
new file mode 100644
index 0000000..e213c77
--- /dev/null
+++ b/certcal.go
@@ -0,0 +1,60 @@
+package main
+
+import (
+	"github.com/mrtazz/certcal/handler"
+	"github.com/mrtazz/certcal/hosts"
+	log "github.com/sirupsen/logrus"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+)
+
+func main() {
+
+	log.SetFormatter(&log.TextFormatter{
+		FullTimestamp: true,
+	})
+	logger := log.WithFields(log.Fields{
+		"package": "main",
+	})
+
+	checkHosts := os.Getenv("CERTCAL_HOSTS")
+	if checkHosts == "" {
+		logger.Error("missing env var CERTCAL_HOSTS")
+		os.Exit(1)
+	}
+
+	var duration time.Duration
+	durationString := os.Getenv("CERTCAL_INTERVAL")
+	switch durationString {
+	case "":
+		logger.Error("missing env var CERTCAL_INTERVAL, defaulting to 1 day")
+		duration = 24 * time.Hour
+	default:
+		var err error
+		duration, err = time.ParseDuration(durationString)
+		if err != nil {
+			logger.Error("unable to parse CERTCAL_INTERVAL, defaulting to 1 day")
+			duration = 24 * time.Hour
+		}
+	}
+
+	var port string
+	if port = os.Getenv("PORT"); port == "" {
+		port = "3000"
+	}
+
+	hosts.AddHosts(strings.Split(checkHosts, ","))
+	hosts.UpdateEvery(duration)
+
+	address := ":" + port
+
+	logger.WithFields(log.Fields{
+		"address": address,
+	}).Info("starting web server")
+	http.HandleFunc("/hosts", handler.Handler)
+	//http.HandleFunc("/metrics", headers)
+	http.ListenAndServe(address, nil)
+
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..c0a6fd3
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,8 @@
+module github.com/mrtazz/certcal
+
+go 1.17
+
+require (
+	github.com/sirupsen/logrus v1.8.1 // indirect
+	golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..58fa35a
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,7 @@
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.8.1 h1:dJKuHgqk1NNQlqoA6BTlM1Wf9DOH3NBjQyu0h9+AZZE=
+github.com/sirupsen/logrus v1.8.1/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 h1:YyJpGZS1sBuBCzLAR1VEpK193GlqGZbnPFnPV/5Rsb4=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
diff --git a/handler/handler.go b/handler/handler.go
new file mode 100644
index 0000000..a56b066
--- /dev/null
+++ b/handler/handler.go
@@ -0,0 +1,53 @@
+package handler
+
+import (
+	"fmt"
+	"github.com/mrtazz/certcal/hosts"
+	"github.com/mrtazz/certcal/ical"
+	log "github.com/sirupsen/logrus"
+	"net/http"
+	"time"
+)
+
+const (
+	contentType = "application/octet-stream"
+)
+
+var (
+	logger = log.WithFields(log.Fields{
+		"package": "handler",
+	})
+)
+
+// Handler implements the ical handler
+func Handler(w http.ResponseWriter, req *http.Request) {
+	checkedHosts := hosts.GetHosts()
+	cal := ical.Calendar{
+		Events: make([]ical.Event, 0, len(checkedHosts)),
+	}
+
+	for _, h := range checkedHosts {
+		if len(h.Certs) > 0 {
+			cal.Events = append(cal.Events,
+				ical.Event{
+					CreatedAt:    time.Now(),
+					LastModified: time.Now(),
+					DtStamp:      time.Now(),
+					Summary:      fmt.Sprintf("cert for %s expires", h.HostString),
+					Start:        h.Certs[0].NotAfter,
+					End:          h.Certs[0].NotAfter,
+					URL:          "",
+					Description:  fmt.Sprintf("cert for %s expires", h.HostString),
+				})
+		}
+	}
+
+	out, err := cal.Render()
+	if err != nil {
+		logger.Error(err)
+		w.WriteHeader(http.StatusInternalServerError)
+	}
+
+	w.Header().Set("Content-Type", contentType)
+	fmt.Fprintf(w, out)
+}
diff --git a/hosts/hosts.go b/hosts/hosts.go
new file mode 100644
index 0000000..f5f9ea1
--- /dev/null
+++ b/hosts/hosts.go
@@ -0,0 +1,111 @@
+package hosts
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	log "github.com/sirupsen/logrus"
+	"net"
+	"strings"
+	"sync"
+	"time"
+)
+
+var (
+	info   []*Info
+	lock   sync.Mutex
+	done   = make(chan bool)
+	logger = log.WithFields(log.Fields{
+		"package": "hosts",
+	})
+)
+
+// GetHosts returns all configured hosts
+func GetHosts() []*Info {
+	lock.Lock()
+	defer lock.Unlock()
+	return info
+}
+
+// UpdateEvery runs an update on all hosts every interval
+func UpdateEvery(interval time.Duration) {
+	ticker := time.NewTicker(interval)
+	go func() {
+		for {
+			select {
+			case <-done:
+				return
+			case <-ticker.C:
+				logger.Info("updating hosts")
+				updateAllHosts()
+			}
+		}
+	}()
+}
+
+func updateAllHosts() {
+	lock.Lock()
+	defer lock.Unlock()
+	for _, i := range info {
+		logger.WithFields(log.Fields{
+			"host": i.HostString,
+		}).Info("retrieving certs")
+		i.GetCerts(5 * time.Second)
+	}
+}
+
+// Info provides information for a host
+type Info struct {
+	HostString string
+	Certs      []*x509.Certificate
+}
+
+// AddHost adds a new host to watch
+func AddHost(hostString string) {
+	if !strings.Contains(hostString, ":") {
+		hostString = hostString + ":443"
+	}
+	info = append(info, &Info{
+		HostString: hostString,
+	})
+}
+
+// AddHosts adds a set of hosts to watch
+func AddHosts(hostStrings []string) {
+	for _, h := range hostStrings {
+		AddHost(h)
+	}
+}
+
+// GetCerts retrieves certs for the configure Host
+func (i *Info) GetCerts(timeout time.Duration) error {
+	dialer := &net.Dialer{Timeout: timeout}
+	conn, err := tls.DialWithDialer(dialer, "tcp", i.HostString,
+		&tls.Config{
+			InsecureSkipVerify: true,
+		})
+	if err != nil {
+		return err
+	}
+
+	defer conn.Close()
+
+	if err := conn.Handshake(); err != nil {
+		return err
+	}
+
+	peerCerts := conn.ConnectionState().PeerCertificates
+	i.Certs = make([]*x509.Certificate, 0, len(peerCerts))
+	logger.WithFields(log.Fields{
+		"num_certs": len(peerCerts),
+		"host":      i.HostString,
+	}).Info("found certs")
+
+	for _, cert := range peerCerts {
+		if cert.IsCA {
+			continue
+		}
+		i.Certs = append(i.Certs, cert)
+	}
+
+	return nil
+}
diff --git a/ical/ical.go b/ical/ical.go
new file mode 100644
index 0000000..3d86aee
--- /dev/null
+++ b/ical/ical.go
@@ -0,0 +1,79 @@
+package ical
+
+import (
+	"bytes"
+	"text/template"
+	"time"
+)
+
+// general calendar format
+//BEGIN:VCALENDAR
+//VERSION:2.0
+//METHOD:PUBLISH
+//PRODID:-//schulferien.org//iCal Generator//DE
+//BEGIN:VEVENT
+//CREATED:20220110T032314Z
+//LAST-MODIFIED:20220110T032314Z
+//DTSTAMP:20220110T032314Z
+//SUMMARY:Winterferien 2021 Berlin
+//DTSTART;VALUE=DATE:20210201
+//DTEND;VALUE=DATE:20210207
+//URL:http://www.schulferien.org
+//DESCRIPTION:Alle Termine auf www.schulferien.org
+//TRANSP:TRANSPARENT
+//UID:F_2021_termin61db9894553f9@schulferien.org
+//END:VEVENT
+//END:VCALENDAR
+
+const (
+	icalTemplate = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+PRODID:-//github.com/mrtazz/certcal//iCal cert feed//EN
+{{- range .Events }}
+BEGIN:VEVENT
+CREATED:{{ .CreatedAt.Format "20060102T150405Z"  }}
+LAST-MODIFIED:{{ .LastModified.Format "20060102T150405Z" }}
+DTSTAMP:{{ .DtStamp.Format "20060102T150405Z"}}
+SUMMARY:{{ .Summary }}
+DTSTART;VALUE=DATE:{{ .Start.Format "20060102"}}
+DTEND;VALUE=DATE:{{ .End.Format "20060102"}}
+URL:{{ .URL }}
+DESCRIPTION:{{ .Description }}
+TRANSP:TRANSPARENT
+UID: @certcal.mrtazz.github.com
+END:VEVENT
+{{- end }}
+END:VCALENDAR`
+)
+
+// Event represents a calendar
+type Event struct {
+	CreatedAt    time.Time
+	LastModified time.Time
+	DtStamp      time.Time
+	Summary      string
+	Start        time.Time
+	End          time.Time
+	URL          string
+	Description  string
+}
+
+// Calendar represents a calendar feed
+type Calendar struct {
+	Events []Event
+}
+
+// Render a calendar feed
+func (c *Calendar) Render() (string, error) {
+	tmpl, err := template.New("feed").Parse(icalTemplate)
+	if err != nil {
+		return "", err
+	}
+	var tpl bytes.Buffer
+	err = tmpl.Execute(&tpl, c)
+	if err != nil {
+		return "", err
+	}
+	return tpl.String(), nil
+}

From 9e64e234c4f5c7e8ecdfe35d3771f8a82a1709a4 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sun, 20 Feb 2022 19:18:24 +0000
Subject: [PATCH 02/22] add first testing scaffold

---
 go.mod            |  9 ++++++++-
 go.sum            | 10 ++++++++++
 ical/ical_test.go | 11 +++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 ical/ical_test.go

diff --git a/go.mod b/go.mod
index c0a6fd3..2b3c2ba 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,13 @@ module github.com/mrtazz/certcal
 go 1.17
 
 require (
-	github.com/sirupsen/logrus v1.8.1 // indirect
+	github.com/sirupsen/logrus v1.8.1
+	github.com/stretchr/testify v1.7.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
 	golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c // indirect
 )
diff --git a/go.sum b/go.sum
index 58fa35a..d2ec8fa 100644
--- a/go.sum
+++ b/go.sum
@@ -1,7 +1,17 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sirupsen/logrus v1.8.1 h1:dJKuHgqk1NNQlqoA6BTlM1Wf9DOH3NBjQyu0h9+AZZE=
 github.com/sirupsen/logrus v1.8.1/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 h1:YyJpGZS1sBuBCzLAR1VEpK193GlqGZbnPFnPV/5Rsb4=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/ical/ical_test.go b/ical/ical_test.go
new file mode 100644
index 0000000..5d3a1be
--- /dev/null
+++ b/ical/ical_test.go
@@ -0,0 +1,11 @@
+package ical
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestRender(t *testing.T) {
+	assert := assert.New(t)
+
+}

From 4d9e1ddaa90bfac441f9c9d660beb0ef542a8691 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sun, 20 Feb 2022 19:20:08 +0000
Subject: [PATCH 03/22] add action for tests

---
 .github/workflows/tests.yml | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 .github/workflows/tests.yml

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..d893ff9
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,23 @@
+name: CI
+on: push
+jobs:
+
+  test:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: Set up Go 1.17
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.17
+      id: go
+
+    - name: Check out code
+      uses: actions/checkout@v2
+      with:
+        fetch-depth: 1
+
+    - name: Run tests
+      run: |
+        go test -v ./...

From 6988a323a3e84c64b963030e4191a5d7d24e9e25 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sun, 20 Feb 2022 19:20:44 +0000
Subject: [PATCH 04/22] tests are tests

---
 .github/workflows/tests.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index d893ff9..f6fd21e 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -3,7 +3,7 @@ on: push
 jobs:
 
   test:
-    name: Build
+    name: test
     runs-on: ubuntu-latest
     steps:
 

From ea58ed29736764aa29fdff2894725a76ccc18f1d Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 08:37:14 +0000
Subject: [PATCH 05/22] add basic ical rendering test

---
 ical/ical.go      | 19 ------------------
 ical/ical_test.go | 51 ++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/ical/ical.go b/ical/ical.go
index 3d86aee..1a8c2e7 100644
--- a/ical/ical.go
+++ b/ical/ical.go
@@ -6,25 +6,6 @@ import (
 	"time"
 )
 
-// general calendar format
-//BEGIN:VCALENDAR
-//VERSION:2.0
-//METHOD:PUBLISH
-//PRODID:-//schulferien.org//iCal Generator//DE
-//BEGIN:VEVENT
-//CREATED:20220110T032314Z
-//LAST-MODIFIED:20220110T032314Z
-//DTSTAMP:20220110T032314Z
-//SUMMARY:Winterferien 2021 Berlin
-//DTSTART;VALUE=DATE:20210201
-//DTEND;VALUE=DATE:20210207
-//URL:http://www.schulferien.org
-//DESCRIPTION:Alle Termine auf www.schulferien.org
-//TRANSP:TRANSPARENT
-//UID:F_2021_termin61db9894553f9@schulferien.org
-//END:VEVENT
-//END:VCALENDAR
-
 const (
 	icalTemplate = `BEGIN:VCALENDAR
 VERSION:2.0
diff --git a/ical/ical_test.go b/ical/ical_test.go
index 5d3a1be..78af527 100644
--- a/ical/ical_test.go
+++ b/ical/ical_test.go
@@ -3,9 +3,58 @@ package ical
 import (
 	"github.com/stretchr/testify/assert"
 	"testing"
+	"time"
 )
 
-func TestRender(t *testing.T) {
+func TestSomething(t *testing.T) {
+
+	testDate := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	assert := assert.New(t)
+	tests := map[string]struct {
+		input Calendar
+		want  string
+	}{
+		"simple": {
+			input: Calendar{
+				Events: []Event{
+					{
+						CreatedAt:    testDate,
+						LastModified: testDate,
+						DtStamp:      testDate,
+						Summary:      "test event",
+						Start:        testDate,
+						End:          testDate,
+						URL:          "",
+						Description:  "description of test event",
+					},
+				},
+			},
+			want: `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+PRODID:-//github.com/mrtazz/certcal//iCal cert feed//EN
+BEGIN:VEVENT
+CREATED:20091110T230000Z
+LAST-MODIFIED:20091110T230000Z
+DTSTAMP:20091110T230000Z
+SUMMARY:test event
+DTSTART;VALUE=DATE:20091110
+DTEND;VALUE=DATE:20091110
+URL:
+DESCRIPTION:description of test event
+TRANSP:TRANSPARENT
+UID: @certcal.mrtazz.github.com
+END:VEVENT
+END:VCALENDAR`,
+		},
+	}
+
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
 
+			out, err := tc.input.Render()
+			assert.Equal(nil, err)
+			assert.Equal(tc.want, out)
+		})
+	}
 }

From b39f320a13e9ccdbcfea94ff38111d2619f3a760 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 08:54:11 +0000
Subject: [PATCH 06/22] add unique IDs to calendar events

---
 handler/handler.go | 21 ++++++++++-----------
 ical/ical.go       | 11 ++++++++++-
 ical/ical_test.go  | 35 +++++++++++++++++++----------------
 3 files changed, 39 insertions(+), 28 deletions(-)

diff --git a/handler/handler.go b/handler/handler.go
index a56b066..abc3e02 100644
--- a/handler/handler.go
+++ b/handler/handler.go
@@ -28,17 +28,16 @@ func Handler(w http.ResponseWriter, req *http.Request) {
 
 	for _, h := range checkedHosts {
 		if len(h.Certs) > 0 {
-			cal.Events = append(cal.Events,
-				ical.Event{
-					CreatedAt:    time.Now(),
-					LastModified: time.Now(),
-					DtStamp:      time.Now(),
-					Summary:      fmt.Sprintf("cert for %s expires", h.HostString),
-					Start:        h.Certs[0].NotAfter,
-					End:          h.Certs[0].NotAfter,
-					URL:          "",
-					Description:  fmt.Sprintf("cert for %s expires", h.HostString),
-				})
+			cal.AddEvent(ical.Event{
+				CreatedAt:    time.Now(),
+				LastModified: time.Now(),
+				DtStamp:      time.Now(),
+				Summary:      fmt.Sprintf("cert for %s expires", h.HostString),
+				Start:        h.Certs[0].NotAfter,
+				End:          h.Certs[0].NotAfter,
+				URL:          "",
+				Description:  fmt.Sprintf("cert for %s expires", h.HostString),
+			})
 		}
 	}
 
diff --git a/ical/ical.go b/ical/ical.go
index 1a8c2e7..ddad60e 100644
--- a/ical/ical.go
+++ b/ical/ical.go
@@ -2,6 +2,8 @@ package ical
 
 import (
 	"bytes"
+	"crypto/sha256"
+	"fmt"
 	"text/template"
 	"time"
 )
@@ -22,7 +24,7 @@ DTEND;VALUE=DATE:{{ .End.Format "20060102"}}
 URL:{{ .URL }}
 DESCRIPTION:{{ .Description }}
 TRANSP:TRANSPARENT
-UID: @certcal.mrtazz.github.com
+UID:{{ .UID }}@certcal.mrtazz.github.com
 END:VEVENT
 {{- end }}
 END:VCALENDAR`
@@ -38,6 +40,7 @@ type Event struct {
 	End          time.Time
 	URL          string
 	Description  string
+	UID          string
 }
 
 // Calendar represents a calendar feed
@@ -45,6 +48,12 @@ type Calendar struct {
 	Events []Event
 }
 
+// AddEvent adds an event to the calendar
+func (c *Calendar) AddEvent(e Event) {
+	e.UID = fmt.Sprintf("%x", sha256.Sum256([]byte(e.Summary)))
+	c.Events = append(c.Events, e)
+}
+
 // Render a calendar feed
 func (c *Calendar) Render() (string, error) {
 	tmpl, err := template.New("feed").Parse(icalTemplate)
diff --git a/ical/ical_test.go b/ical/ical_test.go
index 78af527..d379eea 100644
--- a/ical/ical_test.go
+++ b/ical/ical_test.go
@@ -11,22 +11,20 @@ func TestSomething(t *testing.T) {
 	testDate := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	assert := assert.New(t)
 	tests := map[string]struct {
-		input Calendar
-		want  string
+		events []Event
+		want   string
 	}{
 		"simple": {
-			input: Calendar{
-				Events: []Event{
-					{
-						CreatedAt:    testDate,
-						LastModified: testDate,
-						DtStamp:      testDate,
-						Summary:      "test event",
-						Start:        testDate,
-						End:          testDate,
-						URL:          "",
-						Description:  "description of test event",
-					},
+			events: []Event{
+				{
+					CreatedAt:    testDate,
+					LastModified: testDate,
+					DtStamp:      testDate,
+					Summary:      "test event",
+					Start:        testDate,
+					End:          testDate,
+					URL:          "",
+					Description:  "description of test event",
 				},
 			},
 			want: `BEGIN:VCALENDAR
@@ -43,7 +41,7 @@ DTEND;VALUE=DATE:20091110
 URL:
 DESCRIPTION:description of test event
 TRANSP:TRANSPARENT
-UID: @certcal.mrtazz.github.com
+UID:3f81ea40a91ac4d91eda58327fcfae58bc6b6e8535a4531bb3f129e1abe7c0bc@certcal.mrtazz.github.com
 END:VEVENT
 END:VCALENDAR`,
 		},
@@ -52,7 +50,12 @@ END:VCALENDAR`,
 	for name, tc := range tests {
 		t.Run(name, func(t *testing.T) {
 
-			out, err := tc.input.Render()
+			c := Calendar{}
+			for _, e := range tc.events {
+				c.AddEvent(e)
+			}
+
+			out, err := c.Render()
 			assert.Equal(nil, err)
 			assert.Equal(tc.want, out)
 		})

From 1fcc3103336168d73663150fb005c9b6c01e336c Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 12:44:50 +0000
Subject: [PATCH 07/22] add Docker build

---
 .github/workflows/docker-build.yml | 15 +++++++++++++++
 Dockerfile                         | 21 +++++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 .github/workflows/docker-build.yml
 create mode 100644 Dockerfile

diff --git a/.github/workflows/docker-build.yml b/.github/workflows/docker-build.yml
new file mode 100644
index 0000000..f530211
--- /dev/null
+++ b/.github/workflows/docker-build.yml
@@ -0,0 +1,15 @@
+name: docker
+
+on:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    name: build
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Build image
+        run: docker build . --file Dockerfile --tag github.com/mrtazz/certcal
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..f66f02a
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,21 @@
+FROM golang:1.17-alpine3.15 AS builder
+
+RUN mkdir /app
+
+WORKDIR /app
+
+ADD . /app/
+
+RUN go build certcal.go - certcal
+
+FROM alpine:3.15
+RUN apk --no-cache add ca-certificates
+
+WORKDIR /app
+COPY --from=builder /app/certcal /app/certcal
+RUN chown -R nobody /app && chmod +x /app/certcal
+
+USER nobody
+ENV PORT=3000
+ENV CERTCAL_HOSTS="unwiredcouch.com,github.com"
+ENTRYPOINT ["/app/certcal"]

From 276679778557269007048758c317f5e93b91dc36 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 12:49:41 +0000
Subject: [PATCH 08/22] forgot -o

---
 Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Dockerfile b/Dockerfile
index f66f02a..dcd41ba 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,7 +6,7 @@ WORKDIR /app
 
 ADD . /app/
 
-RUN go build certcal.go - certcal
+RUN go build certcal.go -o certcal
 
 FROM alpine:3.15
 RUN apk --no-cache add ca-certificates

From 9654a2b3ad9fcb0d361c5871efbeabbb7dfed07c Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 14:40:31 +0000
Subject: [PATCH 09/22] fix go build argument order

---
 Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Dockerfile b/Dockerfile
index dcd41ba..a2a8fc5 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,7 +6,7 @@ WORKDIR /app
 
 ADD . /app/
 
-RUN go build certcal.go -o certcal
+RUN go build -o certcal certcal.go
 
 FROM alpine:3.15
 RUN apk --no-cache add ca-certificates

From f8cda4677dd6cce07662144d5bb0b83926f7956d Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 14:54:08 +0000
Subject: [PATCH 10/22] update the README some more

---
 README.md | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 3174661..6d1d5d9 100644
--- a/README.md
+++ b/README.md
@@ -1,12 +1,64 @@
 # certcal
 
-Provide an iCal web feed for certificate expiry
+Provide an iCal web feed for certificate expiry.
 
 
 ## Usage
 
+There are a couple of ways to run this
+
 ### Standalone
+You can download one of the binaries and run it as a standalone:
+
+```shell
+% PORT=3000 CERTCAL_INTERVAL=5h CERTCAL_HOSTS="unwiredcouch.com" ./certcal
+```
 
 
 ### As part of an existing http mux
 
+You can include the handler in your existing mux, something along the lines
+of:
+
+```go
+import (
+	"github.com/mrtazz/certcal/handler"
+	"github.com/mrtazz/certcal/hosts"
+	"net/http"
+  "time"
+)
+
+func Run() {
+
+  ...
+
+	hosts.AddHosts([]string{"unwiredcouch.com"})
+	hosts.UpdateEvery(5 * time.Hour)
+
+	http.HandleFunc("/hosts", handler.Handler)
+	http.ListenAndServe(":3000", nil)
+
+}
+```
+
+
+### Via Docker
+There is a docker image as well that you can use
+
+
+## FAQ
+
+### Shouldn't certs renew automatically?
+Probably. But sometimes they aren't.
+
+### Shouldn't this be an alert somewhere?
+Maybe, up to you.
+
+### Old expiry events are disappearing!
+That is by design. The UID of the `VEVENT` is the `sha256sum` of the summary
+of the event. Because generally if the cert got renewed the old event is just
+cruft.
+
+
+## Inspiration
+[genuinetools/certok](https://github.com/genuinetools/certok) inspired this

From 4de9dfd903efcfdfbc2eeedf4743d14c9997763a Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 14:54:30 +0000
Subject: [PATCH 11/22] add LICENSE

---
 LICENSE | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 LICENSE

diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..3860573
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,19 @@
+Copyright (C) 2022 Daniel Schauenberg
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

From d3a25448f43d6b87c4cb4f648ebdf23a1de8cb92 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Mon, 21 Feb 2022 14:55:20 +0000
Subject: [PATCH 12/22] retab README

---
 README.md | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index 6d1d5d9..6febe8a 100644
--- a/README.md
+++ b/README.md
@@ -22,9 +22,9 @@ of:
 
 ```go
 import (
-	"github.com/mrtazz/certcal/handler"
-	"github.com/mrtazz/certcal/hosts"
-	"net/http"
+  "github.com/mrtazz/certcal/handler"
+  "github.com/mrtazz/certcal/hosts"
+  "net/http"
   "time"
 )
 
@@ -32,11 +32,11 @@ func Run() {
 
   ...
 
-	hosts.AddHosts([]string{"unwiredcouch.com"})
-	hosts.UpdateEvery(5 * time.Hour)
+  hosts.AddHosts([]string{"unwiredcouch.com"})
+  hosts.UpdateEvery(5 * time.Hour)
 
-	http.HandleFunc("/hosts", handler.Handler)
-	http.ListenAndServe(":3000", nil)
+  http.HandleFunc("/hosts", handler.Handler)
+  http.ListenAndServe(":3000", nil)
 
 }
 ```

From 81869ac6c56172d5cb9cc346719eb65420c9d93a Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Thu, 24 Feb 2022 20:28:59 +0000
Subject: [PATCH 13/22] add initial definition for a release workflow

---
 .github/workflows/release.yml | 64 +++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 .github/workflows/release.yml

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
new file mode 100644
index 0000000..7df5e13
--- /dev/null
+++ b/.github/workflows/release.yml
@@ -0,0 +1,64 @@
+name: release
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  release:
+    name: github
+    runs-on: ubuntu-latest
+    env:
+      BUILDER_NAME: "GitHub Actions"
+      BUILDER_EMAIL: noreply@actions.github.com
+
+    steps:
+
+    - name: Set up Go 1.17
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.17
+      id: go
+
+    - name: Check out code
+      uses: actions/checkout@v2
+      with:
+        fetch-depth: 1
+
+    - name: build for platforms
+      run: |
+        BUILD_GOARCH=amd64 BUILD_GOOS=freebsd make build-standalone
+        BUILD_GOARCH=amd64 BUILD_GOOS=linux   make build-standalone
+        BUILD_GOARCH=amd64 BUILD_GOOS=darwin  make build-standalone
+
+    - name: create release
+      run: make github-release
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  docker:
+    name: docker
+    env:
+      BUILDER_NAME: "GitHub Actions"
+      BUILDER_EMAIL: noreply@actions.github.com
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Build the Docker image
+      run: docker build . --file Dockerfile --tag mrtazz/certcal:${GITHUB_SHA} --tag mrtazz/certcal:latest
+
+    - name: push to docker hub
+      run: |
+        echo ${{ secrets.DOCKER_HUB_TOKEN }} | docker login -u mrtazz --password-stdin
+        docker push mrtazz/certcal:${GITHUB_SHA}
+        docker push mrtazz/certcal:latest
+        docker logout hub.docker.com
+
+    - name: push to ghcr
+      run: |
+        echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin
+        docker push mrtazz/certcal:${GITHUB_SHA}
+        docker push mrtazz/certcal:latest
+        docker logout ghcr.io

From 7abe8b0a367d53eb7926353ac8455d252b3ed735 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 12:50:15 +0000
Subject: [PATCH 14/22] add Makefile and .gitignore

---
 .gitignore |  2 ++
 Makefile   | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6fd55ee
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+certcal
+.release_artifacts
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4f266a2
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,77 @@
+#
+# some housekeeping tasks
+#
+
+# variable definitions
+NAME := certcal
+DESC := provide an iCal web feed for certificate expiration
+PREFIX ?= usr/local
+VERSION := $(shell git describe --tags --always --dirty)
+GOVERSION := $(shell go version)
+
+BUILD_GOOS ?= $(shell go env GOOS)
+BUILD_GOARCH ?= $(shell go env GOARCH)
+
+RELEASE_ARTIFACTS_DIR := .release_artifacts
+CHECKSUM_FILE := checksums.txt
+
+$(RELEASE_ARTIFACTS_DIR):
+	install -d $@
+
+BUILDER := $(shell echo "${BUILDER_NAME} <${EMAIL}>")
+
+PKG_RELEASE ?= 1
+PROJECT_URL := "https://github.com/mrtazz/$(NAME)"
+LDFLAGS := -X 'main.version=$(VERSION)' \
+           -X 'main.goversion=$(GOVERSION)'
+
+TARGETS := certcal
+INSTALLED_TARGETS = $(addprefix $(PREFIX)/bin/, $(TARGETS))
+
+certcal: certcal.go
+	GOOS=$(BUILD_GOOS) GOARCH=$(BUILD_GOARCH) go build -ldflags "$(LDFLAGS)" -o $@ $<
+
+.PHONY: all
+all: $(TARGETS) $(MAN_TARGETS)
+.DEFAULT_GOAL:=all
+
+# development tasks
+.PHONY: test
+test:
+	go test -v ./...
+
+.PHONY: coverage
+coverage:
+	go test -v -race -coverprofile=cover.out ./...
+	@-go tool cover -html=cover.out -o cover.html
+
+.PHONY: benchmark
+benchmark:
+	@echo "Running tests..."
+	@go test -bench=. ${NAME}
+
+# install tasks
+$(PREFIX)/bin/%: %
+	install -d $$(dirname $@)
+	install -m 755 $< $@
+
+.PHONY: install
+install: $(INSTALLED_TARGETS) $(INSTALLED_MAN_TARGETS)
+
+.PHONY: local-install
+local-install:
+	$(MAKE) install PREFIX=usr/local
+
+.PHONY: build-artifact
+build-artifact: certcal $(RELEASE_ARTIFACTS_DIR)
+	mv certcal $(RELEASE_ARTIFACTS_DIR)/certcal-$(VERSION).$(BUILD_GOOS).$(BUILD_GOARCH)
+	cd $(RELEASE_ARTIFACTS_DIR) && shasum -a 256 certcal-$(VERSION).$(BUILD_GOOS).$(BUILD_GOARCH) >> $(CHECKSUM_FILE)
+
+.PHONY: github-release
+github-release:
+	gh release create $(VERSION) --title 'Release $(VERSION)' --notes-file docs/releases/$(VERSION).md $(RELEASE_ARTIFACTS_DIR)/*
+
+# clean up tasks
+.PHONY: clean
+clean:
+	git clean -fdx

From 9b231df8caaba14100815237bd30c3807b277e68 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 12:51:11 +0000
Subject: [PATCH 15/22] rename TestSomething to TestRender

---
 ical/ical_test.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ical/ical_test.go b/ical/ical_test.go
index d379eea..9122fef 100644
--- a/ical/ical_test.go
+++ b/ical/ical_test.go
@@ -6,7 +6,7 @@ import (
 	"time"
 )
 
-func TestSomething(t *testing.T) {
+func TestRender(t *testing.T) {
 
 	testDate := time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC)
 	assert := assert.New(t)

From 052da7309850bb027322acb3c1a09af80f1e092a Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 12:51:50 +0000
Subject: [PATCH 16/22] use makefile in test

---
 .github/workflows/tests.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index f6fd21e..59555bb 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -20,4 +20,4 @@ jobs:
 
     - name: Run tests
       run: |
-        go test -v ./...
+        make test

From 47861e951a64b0acba94d77a6aa303fddba39d11 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 12:58:53 +0000
Subject: [PATCH 17/22] remove docker hub push

the free account only allows for a single access token and I don't want
to share that one between open source projects
---
 .github/workflows/release.yml | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 7df5e13..8c1cdd3 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -27,9 +27,9 @@ jobs:
 
     - name: build for platforms
       run: |
-        BUILD_GOARCH=amd64 BUILD_GOOS=freebsd make build-standalone
-        BUILD_GOARCH=amd64 BUILD_GOOS=linux   make build-standalone
-        BUILD_GOARCH=amd64 BUILD_GOOS=darwin  make build-standalone
+        BUILD_GOARCH=amd64 BUILD_GOOS=freebsd make build-artifact
+        BUILD_GOARCH=amd64 BUILD_GOOS=linux   make build-artifact
+        BUILD_GOARCH=amd64 BUILD_GOOS=darwin  make build-artifact
 
     - name: create release
       run: make github-release
@@ -40,7 +40,7 @@ jobs:
     name: docker
     env:
       BUILDER_NAME: "GitHub Actions"
-      BUILDER_EMAIL: noreply@actions.github.com
+      BUILDER_EMAIL: actions@noreply.github.com
 
     runs-on: ubuntu-latest
 
@@ -49,13 +49,6 @@ jobs:
     - name: Build the Docker image
       run: docker build . --file Dockerfile --tag mrtazz/certcal:${GITHUB_SHA} --tag mrtazz/certcal:latest
 
-    - name: push to docker hub
-      run: |
-        echo ${{ secrets.DOCKER_HUB_TOKEN }} | docker login -u mrtazz --password-stdin
-        docker push mrtazz/certcal:${GITHUB_SHA}
-        docker push mrtazz/certcal:latest
-        docker logout hub.docker.com
-
     - name: push to ghcr
       run: |
         echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin

From 52003bc0e15a75967bb363e40075def64eafb695 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 13:14:21 +0000
Subject: [PATCH 18/22] remove all target

---
 Makefile | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 4f266a2..8820a35 100644
--- a/Makefile
+++ b/Makefile
@@ -28,12 +28,10 @@ LDFLAGS := -X 'main.version=$(VERSION)' \
 TARGETS := certcal
 INSTALLED_TARGETS = $(addprefix $(PREFIX)/bin/, $(TARGETS))
 
+.PHONY: certcal
 certcal: certcal.go
 	GOOS=$(BUILD_GOOS) GOARCH=$(BUILD_GOARCH) go build -ldflags "$(LDFLAGS)" -o $@ $<
-
-.PHONY: all
-all: $(TARGETS) $(MAN_TARGETS)
-.DEFAULT_GOAL:=all
+.DEFAULT_GOAL:=certcal
 
 # development tasks
 .PHONY: test

From 137b4eb06f46cac6487f057509df028dcca8edff Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 13:15:13 +0000
Subject: [PATCH 19/22] use kong for cli flags

---
 certcal.go | 64 +++++++++++++++++++++++++++---------------------------
 go.mod     |  4 +++-
 go.sum     |  7 ++++++
 3 files changed, 42 insertions(+), 33 deletions(-)

diff --git a/certcal.go b/certcal.go
index e213c77..37f07a2 100644
--- a/certcal.go
+++ b/certcal.go
@@ -1,15 +1,29 @@
 package main
 
 import (
+	"fmt"
+	"github.com/alecthomas/kong"
 	"github.com/mrtazz/certcal/handler"
 	"github.com/mrtazz/certcal/hosts"
 	log "github.com/sirupsen/logrus"
 	"net/http"
-	"os"
-	"strings"
 	"time"
 )
 
+var (
+	version   = ""
+	goversion = ""
+)
+
+// CLI defines the command line arguments
+var CLI struct {
+	Serve struct {
+		Hosts    []string `required:"" help:"hosts to check certs for." env:"CERTCAL_HOSTS"`
+		Interval string   `required:"" help:"interval in which to check certs" env:"CERTCAL_INTERVAL" default:"24h"`
+		Port     int      `help:"port for the server to listen on" env:"PORT" default:"3000"`
+	} `cmd:"" help:"run the server."`
+}
+
 func main() {
 
 	log.SetFormatter(&log.TextFormatter{
@@ -19,42 +33,28 @@ func main() {
 		"package": "main",
 	})
 
-	checkHosts := os.Getenv("CERTCAL_HOSTS")
-	if checkHosts == "" {
-		logger.Error("missing env var CERTCAL_HOSTS")
-		os.Exit(1)
-	}
-
-	var duration time.Duration
-	durationString := os.Getenv("CERTCAL_INTERVAL")
-	switch durationString {
-	case "":
-		logger.Error("missing env var CERTCAL_INTERVAL, defaulting to 1 day")
-		duration = 24 * time.Hour
-	default:
-		var err error
-		duration, err = time.ParseDuration(durationString)
+	ctx := kong.Parse(&CLI)
+	switch ctx.Command() {
+	case "serve":
+		duration, err := time.ParseDuration(CLI.Serve.Interval)
 		if err != nil {
 			logger.Error("unable to parse CERTCAL_INTERVAL, defaulting to 1 day")
 			duration = 24 * time.Hour
 		}
-	}
-
-	var port string
-	if port = os.Getenv("PORT"); port == "" {
-		port = "3000"
-	}
+		hosts.AddHosts(CLI.Serve.Hosts)
+		hosts.UpdateEvery(duration)
 
-	hosts.AddHosts(strings.Split(checkHosts, ","))
-	hosts.UpdateEvery(duration)
+		address := fmt.Sprintf(":%d", CLI.Serve.Port)
 
-	address := ":" + port
+		logger.WithFields(log.Fields{
+			"address": address,
+		}).Info("starting web server")
+		http.HandleFunc("/hosts", handler.Handler)
+		//http.HandleFunc("/metrics", headers)
+		http.ListenAndServe(address, nil)
 
-	logger.WithFields(log.Fields{
-		"address": address,
-	}).Info("starting web server")
-	http.HandleFunc("/hosts", handler.Handler)
-	//http.HandleFunc("/metrics", headers)
-	http.ListenAndServe(address, nil)
+	default:
+		logger.Error("Unknown command: " + ctx.Command())
+	}
 
 }
diff --git a/go.mod b/go.mod
index 2b3c2ba..a75cbe1 100644
--- a/go.mod
+++ b/go.mod
@@ -8,8 +8,10 @@ require (
 )
 
 require (
+	github.com/alecthomas/kong v0.4.1 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 // indirect
-	gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )
diff --git a/go.sum b/go.sum
index d2ec8fa..d619aaf 100644
--- a/go.sum
+++ b/go.sum
@@ -1,6 +1,11 @@
+github.com/alecthomas/kong v0.4.1 h1:0sFnMts+ijOiFuSHsMB9MlDi3NGINBkx9KIw1/gcuDw=
+github.com/alecthomas/kong v0.4.1/go.mod h1:uzxf/HUh0tj43x1AyJROl3JT7SgsZ5m+icOv1csRhc0=
+github.com/alecthomas/repr v0.0.0-20210801044451-80ca428c5142/go.mod h1:2kn6fqh/zIyPLmm3ugklbEi5hg5wS435eygvNfaDQL8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sirupsen/logrus v1.8.1 h1:dJKuHgqk1NNQlqoA6BTlM1Wf9DOH3NBjQyu0h9+AZZE=
@@ -15,3 +20,5 @@ gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

From dfab25be2390042747f86fc647577fc6630e8b9d Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 13:18:29 +0000
Subject: [PATCH 20/22] remove metrics handler for now

---
 certcal.go | 1 -
 1 file changed, 1 deletion(-)

diff --git a/certcal.go b/certcal.go
index 37f07a2..292119d 100644
--- a/certcal.go
+++ b/certcal.go
@@ -50,7 +50,6 @@ func main() {
 			"address": address,
 		}).Info("starting web server")
 		http.HandleFunc("/hosts", handler.Handler)
-		//http.HandleFunc("/metrics", headers)
 		http.ListenAndServe(address, nil)
 
 	default:

From df0f872ea9454b2d7c3a223681da2cf248ebea3b Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 13:18:53 +0000
Subject: [PATCH 21/22] update README

---
 README.md | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 6febe8a..51ee4d6 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,18 @@ There are a couple of ways to run this
 You can download one of the binaries and run it as a standalone:
 
 ```shell
+% ./certcal serve --help
+Usage: certcal serve --hosts=HOSTS,... --interval="24h"
+
+run the server.
+
+Flags:
+  -h, --help               Show context-sensitive help.
+
+      --hosts=HOSTS,...    hosts to check certs for ($CERTCAL_HOSTS).
+      --interval="24h"     interval in which to check certs ($CERTCAL_INTERVAL)
+      --port=3000          port for the server to listen on ($PORT)
+
 % PORT=3000 CERTCAL_INTERVAL=5h CERTCAL_HOSTS="unwiredcouch.com" ./certcal
 ```
 
@@ -43,7 +55,11 @@ func Run() {
 
 
 ### Via Docker
-There is a docker image as well that you can use
+There is a docker image as well that you can use:
+
+```sh
+docker pull ghcr.io/mrtazz/certcal
+```
 
 
 ## FAQ

From de01a2c0fab298b3de3d270cc2f9a0a4db20a380 Mon Sep 17 00:00:00 2001
From: Daniel Schauenberg <d@unwiredcouch.com>
Date: Sat, 26 Feb 2022 13:20:26 +0000
Subject: [PATCH 22/22] add docs with initial releases changelog

---
 docs/releases/0.1.0.md | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 docs/releases/0.1.0.md

diff --git a/docs/releases/0.1.0.md b/docs/releases/0.1.0.md
new file mode 100644
index 0000000..9bbcd0c
--- /dev/null
+++ b/docs/releases/0.1.0.md
@@ -0,0 +1,3 @@
+## v0.1.0 (2022-??-??)
+- initial version
+