Updated comments on template renderer

example-project/cmd/web-app/main.go

@@ -0,0 +1,419 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"expvar"
+	"fmt"
+	"log"
+	"net/http"
+	_ "net/http/pprof"
+	"net/url"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"syscall"
+	"time"
+	"html/template"
+
+	template_renderer "geeks-accelerator/oss/saas-starter-kit/example-project/internal/platform/web/template-renderer"
+	lru "github.com/hashicorp/golang-lru"
+	"geeks-accelerator/oss/saas-starter-kit/example-project/internal/platform/web"
+	"geeks-accelerator/oss/saas-starter-kit/example-project/cmd/web-app/handlers"
+	"geeks-accelerator/oss/saas-starter-kit/example-project/internal/platform/flag"
+	itrace "geeks-accelerator/oss/saas-starter-kit/example-project/internal/platform/trace"
+	"github.com/kelseyhightower/envconfig"
+	"go.opencensus.io/trace"
+)
+
+// build is the git version of this program. It is set using build flags in the makefile.
+var build = "develop"
+
+const LRU_CACHE_ITEMS = 128
+
+var (
+	localCache         *lru.Cache
+)
+
+func init() {
+	localCache, _ = lru.New(LRU_CACHE_ITEMS)
+}
+
+func main() {
+
+	// =========================================================================
+	// Logging
+
+	log := log.New(os.Stdout, "WEB_APP : ", log.LstdFlags|log.Lmicroseconds|log.Lshortfile)
+
+	// =========================================================================
+	// Configuration
+	var cfg struct {
+		Env            string        `default:"dev" envconfig:"ENV"`
+		HTTP struct {
+			Host            string        `default:"0.0.0.0:3000" envconfig:"HTTP_HOST"`
+			DebugHost       string        `default:"0.0.0.0:4000" envconfig:"DEBUG_HOST"`
+			ReadTimeout     time.Duration `default:"5s" envconfig:"READ_TIMEOUT"`
+			WriteTimeout    time.Duration `default:"5s" envconfig:"WRITE_TIMEOUT"`
+			ShutdownTimeout time.Duration `default:"5s" envconfig:"SHUTDOWN_TIMEOUT"`
+			TemplateDir       string        `default:"./templates" envconfig:"TEMPLATE_DIR"`
+			StaticDir       string        `default:"./static" envconfig:"STATIC_DIR"`
+		}
+		App struct {
+			Name             string       `default:"web-app" envconfig:"APP_NAME"`
+			StaticS3 struct {
+				S3Bucket       string        `envconfig:"APP_STATIC_S3_BUCKET"`
+				S3KeyPrefix       string        `envconfig:"APP_STATIC_S3_KEY_PREFIX"`
+				EnableCloudFront       bool        `envconfig:"APP_STATIC_S3_ENABLE_CLOUDFRONT"`
+			}
+		}
+		BuildInfo struct {
+			CiCommitRefName    string `envconfig:"CI_COMMIT_REF_NAME"`
+			CiCommitRefSlug    string `envconfig:"CI_COMMIT_REF_SLUG"`
+			CiCommitSha        string `envconfig:"CI_COMMIT_SHA"`
+			CiCommitTag        string `envconfig:"CI_COMMIT_TAG"`
+			CiCommitTitle      string `envconfig:"CI_COMMIT_TITLE"`
+			CiCommitDescription string `envconfig:"CI_COMMIT_DESCRIPTION"`
+			CiJobId            string `envconfig:"CI_COMMIT_JOB_ID"`
+			CiJobUrl           string `envconfig:"CI_COMMIT_JOB_URL"`
+			CiPipelineId       string `envconfig:"CI_COMMIT_PIPELINE_ID"`
+			CiPipelineUrl      string `envconfig:"CI_COMMIT_PIPELINE_URL"`
+		}
+		DB struct {
+			DialTimeout time.Duration `default:"5s" envconfig:"DIAL_TIMEOUT"`
+			Host        string        `default:"mongo:27017/gotraining" envconfig:"HOST"`
+		}
+		Trace struct {
+			Host         string        `default:"http://tracer:3002/v1/publish" envconfig:"HOST"`
+			BatchSize    int           `default:"1000" envconfig:"BATCH_SIZE"`
+			SendInterval time.Duration `default:"15s" envconfig:"SEND_INTERVAL"`
+			SendTimeout  time.Duration `default:"500ms" envconfig:"SEND_TIMEOUT"`
+		}
+		Auth struct {
+			KeyID          string `envconfig:"KEY_ID"`
+			PrivateKeyFile string `default:"/app/private.pem" envconfig:"PRIVATE_KEY_FILE"`
+			Algorithm      string `default:"RS256" envconfig:"ALGORITHM"`
+		}
+	}
+
+	if err := envconfig.Process("WEB_APP", &cfg); err != nil {
+		log.Fatalf("main : Parsing Config : %v", err)
+	}
+
+	if err := flag.Process(&cfg); err != nil {
+		if err != flag.ErrHelp {
+			log.Fatalf("main : Parsing Command Line : %v", err)
+		}
+		return // We displayed help.
+	}
+
+	// =========================================================================
+	// App Starting
+
+	// Print the build version for our logs. Also expose it under /debug/vars.
+	expvar.NewString("build").Set(build)
+	log.Printf("main : Started : Application Initializing version %q", build)
+	defer log.Println("main : Completed")
+
+	cfgJSON, err := json.MarshalIndent(cfg, "", "    ")
+	if err != nil {
+		log.Fatalf("main : Marshalling Config to JSON : %v", err)
+	}
+
+	// TODO: Validate what is being written to the logs. We don't
+	// want to leak credentials or anything that can be a security risk.
+	log.Printf("main : Config : %v\n", string(cfgJSON))
+
+	// =========================================================================
+	// Template Renderer
+	// Implements interface web.Renderer to support alternative renderer
+
+	var (
+		staticS3BaseUrl string
+		staticS3CloudFrontOriginPrefix string
+	)
+	if cfg.App.StaticS3.S3Bucket != "" {
+		// TODO: lookup s3 url/cloud front distribution based on s3 bucket
+	}
+
+	// Append query string value to break browser cache used for services
+	// that render responses for a browser with the following:
+	// 	1. when env=dev, the current timestamp will be used to ensure every
+	// 		request will skip browser cache.
+	// 	2. all other envs, ie stage and prod. The commit hash will be used to
+	// 		ensure that all cache will be reset with each new deployment.
+	browserCacheBusterQueryString := func() string {
+		var v string
+		if cfg.Env == "dev" {
+			// On dev always break cache.
+			v = fmt.Sprintf("%d", time.Now().UTC().Unix())
+		} else {
+			// All other envs, use the current commit hash for the build
+			v = cfg.BuildInfo.CiCommitSha
+		}
+		return v
+	}
+
+	// Helper method for appending the browser cache buster as a query string to
+	// support breaking browser cache when necessary
+	browserCacheBusterFunc := browserCacheBuster(browserCacheBusterQueryString)
+
+	// Need defined functions below since they require config values, able to add additional functions
+	// here to extend functionality.
+	tmplFuncs := template.FuncMap{
+		"BuildInfo": func(k string) string {
+			r := reflect.ValueOf(cfg.BuildInfo)
+			f := reflect.Indirect(r).FieldByName(k)
+			return f.String()
+		},
+		"SiteBaseUrl": func(p string) string {
+			u, err := url.Parse(cfg.HTTP.Host)
+			if err != nil {
+				return "?"
+			}
+			u.Path = p
+			return u.String()
+		},
+		"AssetUrl": func(p string) string {
+			var u string
+			if staticS3BaseUrl != "" {
+				u = template_renderer.S3Url(staticS3BaseUrl, staticS3CloudFrontOriginPrefix, p)
+			} else {
+				if !strings.HasPrefix(p, "/") {
+					p = "/" + p
+				}
+				u = p
+			}
+
+			u = browserCacheBusterFunc( u)
+
+			return u
+		},
+		"SiteAssetUrl": func(p string) string {
+			var u string
+			if staticS3BaseUrl != "" {
+				u = template_renderer.S3Url(staticS3BaseUrl, staticS3CloudFrontOriginPrefix, filepath.Join(cfg.App.Name, p))
+			} else {
+				if !strings.HasPrefix(p, "/") {
+					p = "/" + p
+				}
+				u = p
+			}
+
+			u = browserCacheBusterFunc( u)
+
+			return u
+		},
+		"SiteS3Url": func(p string) string {
+			var u string
+			if staticS3BaseUrl != "" {
+				u = template_renderer.S3Url(staticS3BaseUrl, staticS3CloudFrontOriginPrefix, filepath.Join(cfg.App.Name, p))
+			} else {
+				u = p
+			}
+			return u
+		},
+		"S3Url": func(p string) string {
+			var u string
+			if staticS3BaseUrl != "" {
+				u = template_renderer.S3Url(staticS3BaseUrl, staticS3CloudFrontOriginPrefix, p)
+			} else {
+				u = p
+			}
+			return u
+		},
+	}
+
+	//
+	t := template_renderer.NewTemplate(tmplFuncs)
+
+	// global variables exposed for rendering of responses with templates
+	gvd := map[string]interface{}{
+		"_App": map[string]interface{}{
+			"ENV":            cfg.Env,
+			"BuildInfo":      cfg.BuildInfo,
+			"BuildVersion": build,
+		},
+	}
+
+	// Custom error handler to support rendering user friendly error page for improved web experience.
+	eh := func(ctx context.Context, w http.ResponseWriter, r *http.Request, renderer web.Renderer, statusCode int, er error) error {
+		data := map[string]interface{}{}
+
+		return renderer.Render(ctx, w, r,
+			"base.tmpl", // base layout file to be used for rendering of errors
+			"error.tmpl", // generic format for errors, could select based on status code
+								web.MIMETextHTMLCharsetUTF8,
+								http.StatusOK,
+								data,
+		)
+	}
+
+	// Enable template renderer to reload and parse template files when generating a response of dev
+	// for a more developer friendly process. Any changes to the template files will be included
+	// without requiring re-build/re-start of service.
+	// This only supports files that already exist, if a new template file is added, then the
+	// serivce needs to be restarted, but not rebuilt.
+	enableHotReload := cfg.Env == "dev"
+
+	// Template Renderer used to generate HTML response for web experience.
+	renderer, err := template_renderer.NewTemplateRenderer(cfg.HTTP.TemplateDir, enableHotReload, gvd, t, eh)
+	if err != nil {
+		log.Fatalf("main : Marshalling Config to JSON : %v", err)
+	}
+
+	// =========================================================================
+	// Start Tracing Support
+
+	logger := func(format string, v ...interface{}) {
+		log.Printf(format, v...)
+	}
+
+	log.Printf("main : Tracing Started : %s", cfg.Trace.Host)
+	exporter, err := itrace.NewExporter(logger, cfg.Trace.Host, cfg.Trace.BatchSize, cfg.Trace.SendInterval, cfg.Trace.SendTimeout)
+	if err != nil {
+		log.Fatalf("main : RegiTracingster : ERROR : %v", err)
+	}
+	defer func() {
+		log.Printf("main : Tracing Stopping : %s", cfg.Trace.Host)
+		batch, err := exporter.Close()
+		if err != nil {
+			log.Printf("main : Tracing Stopped : ERROR : Batch[%d] : %v", batch, err)
+		} else {
+			log.Printf("main : Tracing Stopped : Flushed Batch[%d]", batch)
+		}
+	}()
+
+	trace.RegisterExporter(exporter)
+	trace.ApplyConfig(trace.Config{DefaultSampler: trace.AlwaysSample()})
+
+	// =========================================================================
+	// Start Debug Service. Not concerned with shutting this down when the
+	// application is being shutdown.
+	//
+	// /debug/vars - Added to the default mux by the expvars package.
+	// /debug/pprof - Added to the default mux by the net/http/pprof package.
+	if cfg.HTTP.DebugHost != "" {
+		go func() {
+			log.Printf("main : Debug Listening %s", cfg.HTTP.DebugHost)
+			log.Printf("main : Debug Listener closed : %v", http.ListenAndServe(cfg.HTTP.DebugHost, http.DefaultServeMux))
+		}()
+	}
+
+	// =========================================================================
+	// Start APP Service
+
+	// Make a channel to listen for an interrupt or terminate signal from the OS.
+	// Use a buffered channel because the signal package requires it.
+	shutdown := make(chan os.Signal, 1)
+	signal.Notify(shutdown, os.Interrupt, syscall.SIGTERM)
+
+	api := http.Server{
+		Addr:           cfg.HTTP.Host,
+		Handler:        handlers.APP(shutdown, log, cfg.HTTP.StaticDir, cfg.HTTP.TemplateDir, nil, nil, renderer),
+		ReadTimeout:    cfg.HTTP.ReadTimeout,
+		WriteTimeout:   cfg.HTTP.WriteTimeout,
+		MaxHeaderBytes: 1 << 20,
+	}
+
+	// Make a channel to listen for errors coming from the listener. Use a
+	// buffered channel so the goroutine can exit if we don't collect this error.
+	serverErrors := make(chan error, 1)
+
+	// Start the service listening for requests.
+	go func() {
+		log.Printf("main : APP Listening %s", cfg.HTTP.Host)
+		serverErrors <- api.ListenAndServe()
+	}()
+
+	// =========================================================================
+	// Shutdown
+
+	// Blocking main and waiting for shutdown.
+	select {
+	case err := <-serverErrors:
+		log.Fatalf("main : Error starting server: %v", err)
+
+	case sig := <-shutdown:
+		log.Printf("main : %v : Start shutdown..", sig)
+
+		// Create context for Shutdown call.
+		ctx, cancel := context.WithTimeout(context.Background(), cfg.HTTP.ShutdownTimeout)
+		defer cancel()
+
+		// Asking listener to shutdown and load shed.
+		err := api.Shutdown(ctx)
+		if err != nil {
+			log.Printf("main : Graceful shutdown did not complete in %v : %v", cfg.HTTP.ShutdownTimeout, err)
+			err = api.Close()
+		}
+
+		// Log the status of this shutdown.
+		switch {
+		case sig == syscall.SIGSTOP:
+			log.Fatal("main : Integrity issue caused shutdown")
+		case err != nil:
+			log.Fatalf("main : Could not stop server gracefully : %v", err)
+		}
+	}
+}
+
+// browserCacheBuster appends a the query string param v to a given url with
+// a value based on the value returned from cacheBusterValueFunc
+func browserCacheBuster(cacheBusterValueFunc func() string) func(uri string) string {
+	f := func(uri string) string {
+		v := cacheBusterValueFunc()
+		if v == "" {
+			return uri
+		}
+
+		u, err := url.Parse(uri)
+		if err != nil {
+			return ""
+		}
+		q := u.Query()
+		q.Set("v", v)
+		u.RawQuery = q.Encode()
+
+		return u.String()
+	}
+
+	return f
+}
+
+/*
+	"S3ImgSrcLarge": func(p string) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, []int{320, 480, 800}, true)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgThumbSrcLarge": func(p string) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, []int{320, 480, 800}, false)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgSrcMedium": func(p string) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, []int{320, 640}, true)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgThumbSrcMedium": func(p string) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, []int{320, 640}, false)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgSrcSmall": func(p string) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, []int{320}, true)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgThumbSrcSmall": func(p string) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, []int{320}, false)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgSrc": func(p string, sizes []int) template.HTMLAttr {
+			res, _ := blower_display.S3ImgSrc(cfg, site, p, sizes, true)
+			return template.HTMLAttr(res)
+		},
+		"S3ImgUrl": func(p string, size int) string {
+			res, _ := blower_display.S3ImgUrl(cfg, site, p, size)
+			return res
+		},
+ */