refactor(backend): turn index.html back into Go template

There are a few config keys that needs to be passed to ui code before react app starts, we'll render them in the index.html as template

assets.go

@@ -3,11 +3,14 @@ package main
 import (
 	"bytes"
 	"errors"
+	"html/template"
 	"net/http"
 	"strings"
 
-	assetfs "github.com/elazarl/go-bindata-assetfs"
 	"github.com/gin-gonic/gin"
+
+	assetfs "github.com/elazarl/go-bindata-assetfs"
+	log "github.com/sirupsen/logrus"
 )
 
 type binaryFileSystem struct {
@@ -43,6 +46,36 @@ func newBinaryFileSystem(root string) *binaryFileSystem {
 	return &binaryFileSystem{fs}
 }
 
+// load a template from binary asset resource
+func loadTemplate(t *template.Template, path string) *template.Template {
+	templateContent, err := Asset(path)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var tmpl *template.Template
+	if t == nil {
+		// if template wasn't yet initialized do it here
+		t = template.New(path)
+	}
+
+	if path == t.Name() {
+		tmpl = t
+	} else {
+		// if we already have an instance of template.Template then
+		// add a new file to it
+		tmpl = t.New(path)
+	}
+
+	_, err = tmpl.Parse(string(templateContent))
+	if err != nil {
+		log.Fatal(err)
+		return nil
+	}
+
+	return t
+}
+
 func responseFromStaticFile(c *gin.Context, filepath string, contentType string) {
 	if !staticFileSystem.Exists("/", filepath) {
 		c.String(404, "Not found")

main.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"html/template"
 	"net/http"
 	"path"
 	"strings"
@@ -172,6 +173,10 @@ func main() {
 
 	router := gin.New()
 
+	var t *template.Template
+	t = loadTemplate(t, "ui/build/index.html")
+	router.SetHTMLTemplate(t)
+
 	prom := ginprometheus.NewPrometheus("gin")
 	prom.MetricsPath = getViewURL("/metrics")
 	prom.Use(router)

views.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/base64"
 	"encoding/json"
 	"net/http"
 	"sort"
@@ -17,12 +18,6 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func index(c *gin.Context) {
-	// http.FileServer doesn't allow serving index.html, it will always redirect
-	// such request to ./ so we need to manually read that file and return it
-	responseFromStaticFile(c, "/index.html", "text/html")
-}
-
 func notFound(c *gin.Context) {
 	c.String(404, "404 page not found")
 }
@@ -31,6 +26,26 @@ func noCache(c *gin.Context) {
 	c.Header("Cache-Control", "no-cache, no-store, must-revalidate")
 }
 
+func index(c *gin.Context) {
+	start := time.Now()
+
+	noCache(c)
+
+	filtersJSON, err := json.Marshal(config.Config.Filters.Default)
+	if err != nil {
+		panic(err)
+	}
+	filtersB64 := base64.StdEncoding.EncodeToString(filtersJSON)
+
+	c.HTML(http.StatusOK, "ui/build/index.html", gin.H{
+		"Version":       version,
+		"SentryDSN":     config.Config.Sentry.Public,
+		"DefaultFilter": filtersB64,
+	})
+
+	log.Infof("[%s] %s %s took %s", c.ClientIP(), c.Request.Method, c.Request.RequestURI, time.Since(start))
+}
+
 func logAlertsView(c *gin.Context, cacheStatus string, duration time.Duration) {
 	log.Infof("[%s %s] <%d> %s %s took %s", c.ClientIP(), cacheStatus, http.StatusOK, c.Request.Method, c.Request.RequestURI, duration)
 }

views_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"html/template"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -39,6 +40,11 @@ func ginTestEngine() *gin.Engine {
 	gin.SetMode(gin.TestMode)
 	r := gin.New()
 	setupRouter(r)
+
+	var t *template.Template
+	t = loadTemplate(t, "ui/build/index.html")
+	r.SetHTMLTemplate(t)
+
 	return r
 }