Stats heatmap: empty hours same height; cname_chain only for long chains

The "Busiest times" grid's hours without data used the class "empty",
which picked up the padding of empty messages. One CNAME to another no
longer warns; three or more get an info note showing the chain.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -42,6 +42,11 @@ All notable changes to Jarl are documented here. The format follows
 
 ### Changed
 
+- `cname_chain` no longer warns about one CNAME pointing at another (a
+  service name at a host alias is common, and named answers the chain at
+  once). A chain of three or more CNAMEs gets an info note that shows
+  it.
+
 - A certificate's private key is only exported over HTTPS, the local
   socket, or to the server itself (plain HTTP from another host is
   refused with `https_required`).
@@ -70,6 +75,10 @@ All notable changes to Jarl are documented here. The format follows
 
 ### Fixed
 
+- The statistics' "Busiest times" grid drew hours without data taller
+  than the others (they picked up the page's padding for empty
+  messages).
+
 - A token for one view of a linked zone (such as an ACME token with
   `views=external`) couldn't add records: a new record is shared, and
   that reached the other view. A new name and type is now local to the

docs/validation.md

@@ -34,7 +34,7 @@ showing them.
 | `cname_multiple` | error | A name can have only one CNAME |
 | `cname_apex` | error | No CNAME at the zone apex (it needs SOA and NS) |
 | `cname_loop` | error | CNAMEs that point back to themselves |
-| `cname_chain` | warning | CNAME to a CNAME: works, but slows resolution |
+| `cname_chain` | info | a chain of three or more CNAMEs (one CNAME to another says nothing): works, but each is another lookup for some resolvers |
 | `cname_dangling` | warning | CNAME to a name that doesn't exist in the zone |
 | `dname_multiple`, `below_dname` | error | One DNAME per name, and nothing below a DNAME (RFC 6672) |
 | `apex_ns_missing` | error | A zone needs NS records at its apex |

internal/validate/records.go

@@ -385,8 +385,16 @@ func (c *checker) checkCNAMETarget(z *model.Zone, ix *zoneIndex, r *model.Record
 	if !ix.inZoneTarget(target) {
 		return
 	}
-	// Follow the chain inside the zone to detect loops.
+	// Follow the chain inside the zone to detect loops. One CNAME to
+	// another is common and costs nothing (named answers the chain in
+	// one response); a longer chain gets a note.
 	seen := map[string]bool{r.Name: true}
+	chain := []string{disp(r.Name), disp(target)}
+	note := func() {
+		if len(chain) > 3 {
+			c.recProblem(z, r, Info, "cname_chain", "%s reaches its address through %d CNAMEs (%s); fine, but each one is another lookup for resolvers that don't get the chain at once", disp(r.Name), len(chain)-1, strings.Join(chain, " → "))
+		}
+	}
 	cur := target
 	for hops := 0; hops < 20; hops++ {
 		if seen[cur] {
@@ -398,18 +406,18 @@ func (c *checker) checkCNAMETarget(z *model.Zone, ix *zoneIndex, r *model.Record
 		if len(next) == 0 {
 			break
 		}
-		if hops == 0 {
-			c.recProblem(z, r, Warning, "cname_chain", "%s is a CNAME to %s, which is itself a CNAME; chains slow down resolution", disp(r.Name), disp(target))
-		}
 		p := ix.parsed[next[0].ID]
 		if p == nil {
 			break
 		}
 		cur = p.RR.(*dns.CNAME).Target
+		chain = append(chain, disp(cur))
 		if !ix.inZoneTarget(cur) {
+			note()
 			return
 		}
 	}
+	note()
 	if len(ix.byName[target]) == 0 && !ix.hasAddress(target) && !hasDescendant(ix, target) {
 		c.recProblem(z, r, Warning, "cname_dangling", "%s is a CNAME to %s, which does not exist in the zone", disp(r.Name), disp(target))
 	}

internal/validate/validate_test.go

@@ -161,8 +161,9 @@ func TestRecordConflicts(t *testing.T) {
 		}, "cname_loop", Error},
 		{"cname chain", func(b *builder, z *model.Zone) {
 			b.rec(z, "a", "CNAME", "b")
-			b.rec(z, "b", "CNAME", "ns1")
+			b.rec(z, "b", "CNAME", "c")
-		}, "cname_chain", Warning},
+			b.rec(z, "c", "CNAME", "ns1")
+		}, "cname_chain", Info},
 		{"dangling cname", func(b *builder, z *model.Zone) { b.rec(z, "a", "CNAME", "nothing") }, "cname_dangling", Warning},
 		{"null mx not alone", func(b *builder, z *model.Zone) {
 			b.rec(z, "@", "MX", "0 .")
@@ -380,3 +381,16 @@ func TestProblemStringDisplaysZone(t *testing.T) {
 		t.Errorf("String() = %q, want %q", got, want)
 	}
 }
+
+// One CNAME to another is common and says nothing.
+func TestShortCNAMEChain(t *testing.T) {
+	b := newBuilder()
+	z := b.primary("example.com", nil)
+	b.rec(z, "songshare", "CNAME", "navidrome")
+	b.rec(z, "navidrome", "CNAME", "ns1")
+	for _, p := range State(b.s, Options{}) {
+		if p.Code == "cname_chain" {
+			t.Errorf("one extra CNAME: %s %s", p.Severity, p.Message)
+		}
+	}
+}

internal/web/static/assets/charts.js

@@ -283,7 +283,7 @@ export function heatmap(hm, unit) {
       const n = hm.samples[d][hr];
       const text = v < 0 ? day + " " + pad(hr) + ":00 – no data" :
         day + " " + pad(hr) + ":00 – " + Math.round(v).toLocaleString() + " " + unit + " per hour (average of " + n + (n === 1 ? " hour)" : " hours)");
-      const cell = h("div", { class: "hm-cell " + (v < 0 ? "empty" : "heat-" + level(v)), tabindex: "-1", "aria-label": text });
+      const cell = h("div", { class: "hm-cell " + (v < 0 ? "hm-empty" : "heat-" + level(v)), tabindex: "-1", "aria-label": text });
       const showTip = () => {
         tip.textContent = text;
         tip.hidden = false;
@@ -313,7 +313,7 @@ export function heatmap(hm, unit) {
     h("span", { class: "muted small" }, "0"),
     Array.from({ length: steps }, (_, i) => h("span", { class: "hm-swatch heat-" + i })),
     h("span", { class: "muted small" }, compact(peak) + " " + unit + "/hour"),
-    h("span", { class: "hm-swatch empty" }), h("span", { class: "muted small" }, "no data"));
+    h("span", { class: "hm-swatch hm-empty" }), h("span", { class: "muted small" }, "no data"));
   return h("div", { class: "heatmap-wrap" }, grid, tip, scale);
 }
 

internal/web/static/assets/style.css

@@ -398,7 +398,7 @@ td.num, th.num { text-align: right; font-variant-numeric: tabular-nums; }
 .hm-row { display: flex; align-items: center; }
 .hm-cell { height: 22px; border-radius: 3px; }
 .hm-cell:hover, .hm-cell:focus { outline: 2px solid var(--text); outline-offset: -1px; }
-.hm-cell.empty, .hm-swatch.empty { background: transparent; box-shadow: inset 0 0 0 1px var(--chart-grid); }
+.hm-empty { background: transparent; box-shadow: inset 0 0 0 1px var(--chart-grid); }
 .heat-0 { background: var(--heat-0); } .heat-1 { background: var(--heat-1); } .heat-2 { background: var(--heat-2); }
 .heat-3 { background: var(--heat-3); } .heat-4 { background: var(--heat-4); } .heat-5 { background: var(--heat-5); }
 .heat-6 { background: var(--heat-6); }