SWW_APPS: an app's Core Rule Set fixes apply only to the hostnames that serve it (closes #220)

Each app's fixes are one .conf file and one entry in apps. They apply
only while Inspect has set the app's transaction variable, such as
tx.app_gitea. SWW_APPS names each hostname's apps. A hostname gets only
its apps' fixes; while SWW_APPS is unset, every hostname gets every
app's fixes.

A hostname in SWW_APPS that is not a DNS name, such as *.example.com,
stops the start. Unset, SWW_APPS is logged at start as null; set
empty, as "".

Model: opus-5-5

internal/coreruleset/nextcloud_test.go

@@ -50,7 +50,51 @@ const nextcloudOther = `{"other":"python3"}`
 func TestOrdinaryNextcloudRequestsPass(t *testing.T) {
 	t.Parallel()
 
-	wantRecordedRequestsPass(t, "nextcloud-requests.txt")
+	wantRecordedRequestsPass(t, "nextcloud-requests.txt", atDefaults(t), readingBodies(t))
+}
+
+// nextcloud is Nextcloud's name in SWW_APPS.
+const nextcloud = "nextcloud"
+
+func TestNextcloudFixesApplyOnlyToAHostnameThatServesNextcloud(t *testing.T) {
+	t.Parallel()
+
+	crs := servingApps(t, map[string][]string{
+		giteaHost: {gitea}, otherHost: {nextcloud},
+	})
+
+	// A search, which only Nextcloud's fixes let through.
+	search := get(nextcloudUsers + "?search=python3")
+
+	wantResult(t, crs, withHost(search, otherHost), coreruleset.Result{})
+	wantResult(t, crs, withHost(search, giteaHost), matched(932260))
+}
+
+func TestNextcloudWebDAVMethodsPassOnlyOnHostnamesThatServeNextcloud(t *testing.T) {
+	t.Parallel()
+
+	crs := servingApps(t, map[string][]string{
+		giteaHost: {gitea}, otherHost: {nextcloud},
+	})
+
+	// Listing a folder, as the sync client does.
+	list := request{nextcloudPropFind, nextcloudFiles, nil}
+
+	wantResult(t, crs, withHost(list, otherHost), coreruleset.Result{})
+	wantResult(t, crs, withHost(list, giteaHost), matched(911100))
+}
+
+func TestHostnameListingNextcloudLetsItsRecordedRequestsThrough(t *testing.T) {
+	t.Parallel()
+
+	apps := map[string][]string{recordedHost: {nextcloud}}
+
+	bodies := shared(t, coreruleset.Params{
+		ParanoiaLevel: 1, DisabledRules: defaultDisabledRules, BodyLimit: bodyLimit,
+		Apps: apps,
+	})
+
+	wantRecordedRequestsPass(t, "nextcloud-requests.txt", servingApps(t, apps), bodies)
 }
 
 // nextcloudQueryFields are the query fields that skip 930120, 932120, 932250