webapi: Abort requests if web cache not ready.

A new middleware aborts any requests which require the data cache if the
cache is not yet initialized. An explicit error is returned so the admin
will be immediately aware what has gone wrong.

Previously, webpages were rendered and JSON responses were sent with
zero values, and with no indication of anything being wrong. This was
sometimes difficult to notice, and even when noticed the cause was not
immediately apparent.

internal/webapi/admin.go

@@ -144,8 +144,10 @@ func (w *WebAPI) statusJSON(c *gin.Context) {
 
 // adminPage is the handler for "GET /admin".
 func (w *WebAPI) adminPage(c *gin.Context) {
+	cacheData := c.MustGet(cacheKey).(cacheData)
+
 	c.HTML(http.StatusOK, "admin.html", gin.H{
-		"WebApiCache":  w.cache.getData(),
+		"WebApiCache":  cacheData,
 		"WebApiCfg":    w.cfg,
 		"WalletStatus": w.walletStatus(c),
 		"DcrdStatus":   w.dcrdStatus(c),
@@ -155,6 +157,8 @@ func (w *WebAPI) adminPage(c *gin.Context) {
 // ticketSearch is the handler for "POST /admin/ticket". The hash param will be
 // used to retrieve a ticket from the database.
 func (w *WebAPI) ticketSearch(c *gin.Context) {
+	cacheData := c.MustGet(cacheKey).(cacheData)
+
 	hash := c.PostForm("hash")
 
 	ticket, found, err := w.db.GetTicketByHash(hash)
@@ -218,7 +222,7 @@ func (w *WebAPI) ticketSearch(c *gin.Context) {
 			VoteChanges:     voteChanges,
 			MaxVoteChanges:  w.cfg.MaxVoteChangeRecords,
 		},
-		"WebApiCache":  w.cache.getData(),
+		"WebApiCache":  cacheData,
 		"WebApiCfg":    w.cfg,
 		"WalletStatus": w.walletStatus(c),
 		"DcrdStatus":   w.dcrdStatus(c),
@@ -228,12 +232,14 @@ func (w *WebAPI) ticketSearch(c *gin.Context) {
 // adminLogin is the handler for "POST /admin". If a valid password is provided,
 // the current session will be authenticated as an admin.
 func (w *WebAPI) adminLogin(c *gin.Context) {
+	cacheData := c.MustGet(cacheKey).(cacheData)
+
 	password := c.PostForm("password")
 
 	if password != w.cfg.AdminPass {
 		w.log.Warnf("Failed login attempt from %s", c.ClientIP())
 		c.HTML(http.StatusUnauthorized, "login.html", gin.H{
-			"WebApiCache":    w.cache.getData(),
+			"WebApiCache":    cacheData,
 			"WebApiCfg":      w.cfg,
 			"FailedLoginMsg": "Incorrect password",
 		})

internal/webapi/cache.go

@@ -30,6 +30,10 @@ type cache struct {
 }
 
 type cacheData struct {
+	// Initialized is set true after all of the below values have been set for
+	// the first time.
+	Initialized bool
+
 	UpdateTime          string
 	PubKey              string
 	DatabaseSize        string
@@ -45,6 +49,13 @@ type cacheData struct {
 	MissedProportion    float32
 }
 
+func (c *cache) initialized() bool {
+	c.mtx.RLock()
+	defer c.mtx.RUnlock()
+
+	return c.data.Initialized
+}
+
 func (c *cache) getData() cacheData {
 	c.mtx.RLock()
 	defer c.mtx.RUnlock()
@@ -106,6 +117,7 @@ func (c *cache) update() error {
 	c.mtx.Lock()
 	defer c.mtx.Unlock()
 
+	c.data.Initialized = true
 	c.data.UpdateTime = dateTime(time.Now().Unix())
 	c.data.DatabaseSize = humanize.Bytes(dbSize)
 	c.data.Voting = voting

internal/webapi/homepage.go

@@ -11,8 +11,10 @@ import (
 )
 
 func (w *WebAPI) homepage(c *gin.Context) {
+	cacheData := c.MustGet(cacheKey).(cacheData)
+
 	c.HTML(http.StatusOK, "homepage.html", gin.H{
-		"WebApiCache": w.cache.getData(),
+		"WebApiCache": cacheData,
 		"WebApiCfg":   w.cfg,
 	})
 }

internal/webapi/middleware.go

@@ -93,15 +93,31 @@ func (w *WebAPI) withSession(store *sessions.CookieStore) gin.HandlerFunc {
 	}
 }
 
+// requireWebCache will only allow the request to proceed if the web API cache
+// has been initialized with data, otherwise it will return a 500 Internal
+// Server Error.
+func (w *WebAPI) requireWebCache(c *gin.Context) {
+	if !w.cache.initialized() {
+		const str = "Cache is not yet initialized"
+		w.log.Errorf(str)
+		c.String(http.StatusInternalServerError, str)
+		c.Abort()
+		return
+	}
+
+	c.Set(cacheKey, w.cache.getData())
+}
+
 // requireAdmin will only allow the request to proceed if the current session is
 // authenticated as an admin, otherwise it will render the login template.
 func (w *WebAPI) requireAdmin(c *gin.Context) {
+	cacheData := c.MustGet(cacheKey).(cacheData)
 	session := c.MustGet(sessionKey).(*sessions.Session)
 	admin := session.Values["admin"]
 
 	if admin == nil {
 		c.HTML(http.StatusUnauthorized, "login.html", gin.H{
-			"WebApiCache": w.cache.getData(),
+			"WebApiCache": cacheData,
 			"WebApiCfg":   w.cfg,
 		})
 		c.Abort()

internal/webapi/vspinfo.go

@@ -14,7 +14,8 @@ import (
 
 // vspInfo is the handler for "GET /api/v3/vspinfo".
 func (w *WebAPI) vspInfo(c *gin.Context) {
-	cachedStats := w.cache.getData()
+	cachedStats := c.MustGet(cacheKey).(cacheData)
+
 	w.sendJSONResponse(types.VspInfoResponse{
 		APIVersions:         []int64{3},
 		Timestamp:           time.Now().Unix(),

internal/webapi/webapi.go

@@ -57,6 +57,7 @@ const (
 	dcrdKey              = "DcrdClient"
 	dcrdHostKey          = "DcrdHostname"
 	dcrdErrorKey         = "DcrdClientErr"
+	cacheKey             = "Cache"
 	walletsKey           = "WalletClients"
 	failedWalletsKey     = "FailedWalletClients"
 	requestBytesKey      = "RequestBytes"
@@ -240,7 +241,7 @@ func (w *WebAPI) router(cookieSecret []byte, dcrd rpc.DcrdConnect, wallets rpc.W
 	// API routes.
 
 	api := router.Group("/api/v3")
-	api.GET("/vspinfo", w.vspInfo)
+	api.GET("/vspinfo", w.requireWebCache, w.vspInfo)
 	api.POST("/setaltsignaddr", w.vspMustBeOpen, w.withDcrdClient(dcrd), w.broadcastTicket, w.vspAuth, w.setAltSignAddr)
 	api.POST("/feeaddress", w.vspMustBeOpen, w.withDcrdClient(dcrd), w.broadcastTicket, w.vspAuth, w.feeAddress)
 	api.POST("/ticketstatus", w.withDcrdClient(dcrd), w.vspAuth, w.ticketStatus)
@@ -249,26 +250,31 @@ func (w *WebAPI) router(cookieSecret []byte, dcrd rpc.DcrdConnect, wallets rpc.W
 
 	// Website routes.
 
-	router.GET("", w.homepage)
+	router.GET("", w.requireWebCache, w.homepage)
 
 	login := router.Group("/admin").Use(
 		w.withSession(cookieStore),
 	)
 
 	// Limit login attempts to 3 per second.
 	loginRateLmiter := rateLimit(3, func(c *gin.Context) {
+		cacheData := c.MustGet(cacheKey).(cacheData)
+
 		w.log.Warnf("Login rate limit exceeded by %s", c.ClientIP())
 		c.HTML(http.StatusTooManyRequests, "login.html", gin.H{
-			"WebApiCache":    w.cache.getData(),
+			"WebApiCache":    cacheData,
 			"WebApiCfg":      w.cfg,
 			"FailedLoginMsg": "Rate limit exceeded",
 		})
 	})
-	login.POST("", loginRateLmiter, w.adminLogin)
+	login.POST("", w.requireWebCache, loginRateLmiter, w.adminLogin)
 
 	admin := router.Group("/admin").Use(
-		w.withWalletClients(wallets), w.withSession(cookieStore), w.requireAdmin,
-	)
+		w.requireWebCache,
+		w.withWalletClients(wallets),
+		w.withSession(cookieStore),
+		w.requireAdmin)
+
 	admin.GET("", w.withDcrdClient(dcrd), w.adminPage)
 	admin.POST("/ticket", w.withDcrdClient(dcrd), w.ticketSearch)
 	admin.GET("/backup", w.downloadDatabaseBackup)