Sensors: read-only tokens, live stream, Prometheus, status sensors, widgets, embeds

- sensors:read tokens open the sensor endpoints (here and on managed machines
  through the hub) and nothing else; full tokens are never accepted from a URL
- /api/sensors/stream: a shaped query that keeps answering, over SSE
- /metrics: Prometheus text format
- services, updates, ZFS and SMART as background status sensors
- widget library over the sensor API; custom widgets on the dashboard
- /embed/widget: one live widget in its own bundle, the only frameable path
- Dashboard tab is now Monitors

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/sensors/prom.go

@@ -0,0 +1,76 @@
+package sensors
+
+import (
+	"fmt"
+	"io"
+	"sort"
+	"strings"
+)
+
+// promFamily names the metric family for a sensor and scales its value to the base unit
+// Prometheus convention wants (seconds, not minutes).
+func promFamily(s Sensor) (name string, scale float64) {
+	scale = 1
+	unit := map[string]string{"%": "percent", "°C": "celsius", "rpm": "rpm", "B/s": "bytes_per_second", "B": "bytes",
+		"s": "seconds", "V": "volts", "W": "watts", "MHz": "megahertz"}[s.Unit]
+	if s.Unit == "min" {
+		unit, scale = "seconds", 60
+	}
+	if s.Kind == "count" { // hamlab_count{id=…} would say nothing; name it after the thing counted
+		return "hamlab_" + strings.ReplaceAll(Seg(strings.ReplaceAll(s.ID, ".", "_")), "-", "_"), 1
+	}
+	name = "hamlab_" + s.Kind
+	if unit != "" {
+		name += "_" + unit
+	}
+	return
+}
+
+var promEsc = strings.NewReplacer(`\`, `\\`, `"`, `\"`, "\n", `\n`)
+
+// WriteProm writes sensors in the Prometheus text exposition format: one family per kind
+// of measurement, the sensor's ID and its real-world labels as labels. Booleans are 0/1;
+// a text state is a 1 carrying the text as a label, the usual way to export an enum.
+func WriteProm(w io.Writer, all []Sensor) {
+	fams := map[string][]string{}
+	for _, s := range all {
+		name, scale := promFamily(s)
+		labels := []string{`id="` + promEsc.Replace(s.ID) + `"`}
+		keys := make([]string, 0, len(s.Labels))
+		for k := range s.Labels {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+		for _, k := range keys {
+			if s.Labels[k] != "" {
+				labels = append(labels, Seg(k)+`="`+promEsc.Replace(s.Labels[k])+`"`)
+			}
+		}
+		var v float64
+		switch x := s.Value.(type) {
+		case float64:
+			v = x * scale
+		case bool:
+			if x {
+				v = 1
+			}
+		case string:
+			v = 1
+			labels = append(labels, `value="`+promEsc.Replace(x)+`"`)
+		default:
+			continue
+		}
+		fams[name] = append(fams[name], fmt.Sprintf("%s{%s} %v", name, strings.Join(labels, ","), v))
+	}
+	names := make([]string, 0, len(fams))
+	for n := range fams {
+		names = append(names, n)
+	}
+	sort.Strings(names)
+	for _, n := range names {
+		fmt.Fprintf(w, "# TYPE %s gauge\n", n)
+		for _, line := range fams[n] {
+			fmt.Fprintln(w, line)
+		}
+	}
+}