web + ui: Pass init cookie from server to client

pkg/server/web/app_json.go

@@ -0,0 +1,5 @@
+package web
+
+type jsonAppConfig struct {
+	MonitorVisible bool `json:"monitor-visible"`
+}

pkg/server/web/handlers.go

@@ -31,6 +31,16 @@ func (h Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	}
 }
 
+// cookieHandler injects an HTTP cookie into the response.
+func cookieHandler(cookie *http.Cookie, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		log.Debug().Str("module", "web").Str("remote", req.RemoteAddr).Str("proto", req.Proto).
+			Str("method", req.Method).Str("path", req.RequestURI).Msg("Injecting cookie")
+		http.SetCookie(w, cookie)
+		next.ServeHTTP(w, req)
+	})
+}
+
 // fileHandler creates a handler that sends the named file regardless of the requested URL.
 func fileHandler(name string) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {

pkg/server/web/server.go

@@ -3,10 +3,12 @@ package web
 
 import (
 	"context"
+	"encoding/json"
 	"expvar"
 	"net"
 	"net/http"
 	"net/http/pprof"
+	"net/url"
 	"path/filepath"
 	"time"
 
@@ -75,7 +77,8 @@ func Initialize(
 		fileHandler(filepath.Join(conf.Web.UIDir, "favicon.png")))
 
 	// SPA managed paths.
-	spaHandler := fileHandler(filepath.Join(conf.Web.UIDir, "index.html"))
+	spaHandler := cookieHandler(appConfigCookie(conf.Web),
+		fileHandler(filepath.Join(conf.Web.UIDir, "index.html")))
 	Router.Path("/").Handler(spaHandler)
 	Router.Path("/monitor").Handler(spaHandler)
 	Router.Path("/status").Handler(spaHandler)
@@ -126,6 +129,22 @@ func Start(ctx context.Context) {
 	}
 }
 
+func appConfigCookie(webConfig config.Web) *http.Cookie {
+	o := &jsonAppConfig{
+		MonitorVisible: webConfig.MonitorVisible,
+	}
+	b, err := json.Marshal(o)
+	if err != nil {
+		log.Error().Str("module", "web").Str("phase", "startup").Err(err).
+			Msg("Failed to convert app-config to JSON")
+	}
+	return &http.Cookie{
+		Name:  "app-config",
+		Value: url.PathEscape(string(b)),
+		Path:  "/",
+	}
+}
+
 // serve begins serving HTTP requests
 func serve(ctx context.Context) {
 	// server.Serve blocks until we close the listener

ui/src/Data/AppConfig.elm

@@ -0,0 +1,15 @@
+module Data.AppConfig exposing (AppConfig, decoder)
+
+import Json.Decode as D
+import Json.Decode.Pipeline as P
+
+
+type alias AppConfig =
+    { monitorVisible : Bool
+    }
+
+
+decoder : D.Decoder AppConfig
+decoder =
+    D.succeed AppConfig
+        |> P.required "monitor-visible" D.bool

ui/src/Data/Session.elm

@@ -4,11 +4,11 @@ module Data.Session exposing
     , Session
     , addRecent
     , clearFlash
-    , decodeValueWithDefault
     , decoder
     , disableRouting
     , enableRouting
     , init
+    , initError
     , showFlash
     )
 
@@ -54,6 +54,17 @@ init key location persistent =
     }
 
 
+initError : Nav.Key -> Url -> String -> Session
+initError key location error =
+    { key = key
+    , host = location.host
+    , flash = Just (Flash "Initialization failed" [ ( "Error", error ) ])
+    , routing = True
+    , zone = Time.utc
+    , persistent = Persistent []
+    }
+
+
 addRecent : String -> Session -> Session
 addRecent mailbox session =
     if List.head session.persistent.recentMailboxes == Just mailbox then
@@ -99,11 +110,6 @@ decoder =
         |> optional "recentMailboxes" (D.list D.string) []
 
 
-decodeValueWithDefault : D.Value -> Persistent
-decodeValueWithDefault =
-    D.decodeValue decoder >> Result.withDefault { recentMailboxes = [] }
-
-
 encode : Persistent -> E.Value
 encode persistent =
     E.object

ui/src/Main.elm

@@ -2,7 +2,8 @@ module Main exposing (main)
 
 import Browser exposing (Document, UrlRequest)
 import Browser.Navigation as Nav
-import Data.Session as Session exposing (Session, decoder)
+import Data.AppConfig as AppConfig exposing (AppConfig)
+import Data.Session as Session exposing (Session)
 import Html exposing (..)
 import Json.Decode as D exposing (Value)
 import Page.Home as Home
@@ -34,11 +35,27 @@ type alias Model =
     }
 
 
+type alias InitConfig =
+    { appConfig : AppConfig
+    , session : Session.Persistent
+    }
+
+
 init : Value -> Url -> Nav.Key -> ( Model, Cmd Msg )
-init sessionValue location key =
+init configValue location key =
     let
+        configDecoder =
+            D.map2 InitConfig
+                (D.field "app-config" AppConfig.decoder)
+                (D.field "session" Session.decoder)
+
         session =
-            Session.init key location (Session.decodeValueWithDefault sessionValue)
+            case D.decodeValue configDecoder configValue of
+                Ok config ->
+                    Session.init key location config.session
+
+                Err error ->
+                    Session.initError key location (D.errorToString error)
 
         ( subModel, _ ) =
             Home.init session

ui/src/index.js

@@ -4,10 +4,16 @@ import { Elm } from './Main.elm'
 import registerMonitorPorts from './registerMonitor'
 import './renderedHtml'
 
+// Initial configuration from Inbucket server to Elm App.
+var flags = {
+  "app-config": appConfig(),
+  "session": sessionObject(),
+}
+
 // App startup.
 var app = Elm.Main.init({
   node: document.getElementById('root'),
-  flags: sessionObject()
+  flags: flags,
 })
 
 // Message monitor.
@@ -24,9 +30,24 @@ window.addEventListener("storage", function (event) {
   }
 }, false)
 
+// Decode the JSON value of the app-config cookie, then delete it.
+function appConfig() {
+  var name = "app-config"
+  var c = getCookie(name)
+  if (c) {
+    deleteCookie(name)
+    return JSON.parse(decodeURIComponent(c))
+  }
+  console.warn("Inbucket " + name + " cookie not found, running with defaults.")
+  return {
+    "monitor-visible": true,
+  }
+}
+
+// Grab peristent session data out of local storage.
 function sessionObject() {
-  var s = localStorage.session
   try {
+    var s = localStorage.session
     if (s) {
       return JSON.parse(s)
     }
@@ -35,3 +56,20 @@ function sessionObject() {
   }
   return null
 }
+
+function getCookie(cookieName) {
+  var name = cookieName + "="
+  var cookies = decodeURIComponent(document.cookie).split(';')
+  for (var i=0; i<cookies.length; i++) {
+    var cookie = cookies[i].trim()
+    if (cookie.indexOf(name) == 0) {
+      return cookie.substring(name.length, cookie.length)
+    }
+  }
+  return null
+}
+
+function deleteCookie(cookieName) {
+  document.cookie = cookieName +
+    "=; expires=Thu, 01 Jan 1970 00:00:00 UTC; path=/;"
+}