Use statik to generate statusz template as code. (Stackdriver#206)

* Moving var statuszTmpl to func ServeHTTP

When trying to run $GOPATH/bin/stackdriver-prometheus-sidecar --help ,I get error panic: open statusz-tmpl.html: no such file or directory.
Moving the intialization of the statuszTmpl to func ServeHTTP which allows the use of --help

* Moving statusz-tmpl.html to a const in statusz.go and updating related files.

* Using statik as a code generator

* Updating statusz.go

* Updating statusz.go and main.go

* Updating statusz.go

* Adding dependcies from running go mod vendor

* Updating statik

Co-authored-by: Javier Kohen <jkohen@gmail.com>

Dockerfile

@@ -2,7 +2,6 @@ FROM  gcr.io/distroless/static:latest
 LABEL maintainer "Stackdriver Engineering <engineering@stackdriver.com>"
 
 COPY stackdriver-prometheus-sidecar         /bin/stackdriver-prometheus-sidecar
-COPY cmd/stackdriver-prometheus-sidecar/statusz-tmpl.html /statusz-tmpl.html
 
 EXPOSE     9091
 ENTRYPOINT [ "/bin/stackdriver-prometheus-sidecar" ]

cmd/stackdriver-prometheus-sidecar/statusz.go

@@ -11,23 +11,28 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
+//go:generate statik -f -src=./  -include=*.html
 package main
 
 import (
 	"html/template"
+	"io/ioutil"
 	"net/http"
 	"os"
 	"path/filepath"
 	"time"
 
+	_ "github.com/Stackdriver/stackdriver-prometheus-sidecar/cmd/stackdriver-prometheus-sidecar/statik"
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/prometheus/common/version"
+	"github.com/rakyll/statik/fs"
 )
 
 var (
 	serverStart = time.Now()
-	statuszTmpl = template.Must(template.ParseFiles("statusz-tmpl.html"))
+	statuszTmpl *template.Template
 )
 
 type statuszHandler struct {
@@ -36,6 +41,25 @@ type statuszHandler struct {
 	cfg       *mainConfig
 }
 
+func init() {
+	statikFS, err := fs.New()
+	if err != nil {
+		panic(err)
+	}
+	statuszFile, err := statikFS.Open("/statusz-tmpl.html")
+	if err != nil {
+		panic(err)
+	}
+	contents, err := ioutil.ReadAll(statuszFile)
+	if err != nil {
+		panic(err)
+	}
+	statuszTmpl, err = template.New("statusz-tmpl.html").Parse(string(contents))
+	if err != nil {
+		panic(err)
+	}
+}
+
 func (h *statuszHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	var data struct {
 		ServerName    string

go.mod

@@ -60,6 +60,7 @@ require (
 	github.com/prometheus/procfs v0.0.3 // indirect
 	github.com/prometheus/prometheus v0.0.0-20190710134608-e5b22494857d
 	github.com/prometheus/tsdb v0.10.0
+	github.com/rakyll/statik v0.1.6
 	github.com/rogpeppe/go-internal v1.5.0 // indirect
 	github.com/samuel/go-zookeeper v0.0.0-20190801204459-3c104360edc8 // indirect
 	github.com/shopspring/decimal v0.0.0-20191125035519-b054a8dfd10d // indirect

go.sum

@@ -474,6 +474,8 @@ github.com/prometheus/prometheus v0.0.0-20190710134608-e5b22494857d/go.mod h1:11
 github.com/prometheus/tsdb v0.9.1/go.mod h1:oi49uRhEe9dPUTlS3JRZOwJuVi6tmh10QSgwXEyGCt4=
 github.com/prometheus/tsdb v0.10.0 h1:If5rVCMTp6W2SiRAQFlbpJNgVlgMEd+U2GZckwK38ic=
 github.com/prometheus/tsdb v0.10.0/go.mod h1:oi49uRhEe9dPUTlS3JRZOwJuVi6tmh10QSgwXEyGCt4=
+github.com/rakyll/statik v0.1.6 h1:uICcfUXpgqtw2VopbIncslhAmE5hwc4g20TEyEENBNs=
+github.com/rakyll/statik v0.1.6/go.mod h1:OEi9wJV/fMUAGx1eNjq75DKDsJVuEv1U0oYdX6GX8Zs=
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/rlmcpherson/s3gof3r v0.5.0/go.mod h1:s7vv7SMDPInkitQMuZzH615G7yWHdrU2r/Go7Bo71Rs=
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=