on admin page, show warning when user hasn't enabled "check updates"

and send Accept-header when fetching changelog, so we can show an html version
instead of json when requested by regular browsers.

http/admin.go

@@ -1520,3 +1520,8 @@ func (Admin) LogLevelSet(ctx context.Context, pkg string, levelStr string) {
 func (Admin) LogLevelRemove(ctx context.Context, pkg string) {
 	mox.Conf.LogLevelRemove(pkg)
 }
+
+// CheckUpdatesEnabled returns whether checking for updates is enabled.
+func (Admin) CheckUpdatesEnabled(ctx context.Context) bool {
+	return mox.Conf.Static.CheckUpdates
+}

http/admin.html

@@ -190,9 +190,10 @@ const formatSize = n => {
 }
 
 const index = async () => {
-	const [domains, queueSize] = await Promise.all([
+	const [domains, queueSize, checkUpdatesEnabled] = await Promise.all([
 		await api.Domains(),
 		await api.QueueSize(),
+		await api.CheckUpdatesEnabled(),
 	])
 
 	let fieldset, domain, account, localpart
@@ -200,6 +201,7 @@ const index = async () => {
 	const page = document.getElementById('page')
 	dom._kids(page,
 		crumbs('Mox Admin'),
+		checkUpdatesEnabled ? [] : dom.p(box(yellow, 'Warning: Checking for updates has not been enabled in mox.conf (CheckUpdates: true).', dom.br(), 'Make sure you stay up to date through another mechanism!', dom.br(), 'You have a responsibility to keep the internet-connected software you run up to date and secure!', dom.br(), 'See ', link('https://updates.xmox.nl/changelog'))),
 		dom.p(
 			dom.a('Accounts', attr({href: '#accounts'})), dom.br(),
 			dom.a('Queue', attr({href: '#queue'})), ' ('+queueSize+')', dom.br(),

http/adminapi.json

@@ -636,6 +636,19 @@
 				}
 			],
 			"Returns": []
+		},
+		{
+			"Name": "CheckUpdatesEnabled",
+			"Docs": "CheckUpdatesEnabled returns whether checking for updates is enabled.",
+			"Params": [],
+			"Returns": [
+				{
+					"Name": "r0",
+					"Typewords": [
+						"bool"
+					]
+				}
+			]
 		}
 	],
 	"Sections": [],

updates/updates.go

@@ -151,6 +151,7 @@ func FetchChangelog(ctx context.Context, baseURL string, base Version, pubKey []
 	if err != nil {
 		return nil, fmt.Errorf("making request: %v", err)
 	}
+	req.Header.Add("Accept", "application/json")
 	resp, err := http.DefaultClient.Do(req)
 	if resp == nil {
 		resp = &http.Response{StatusCode: 0}