initial commit

.gitignore

@@ -0,0 +1,2 @@
+*.exe
+config.json

go.mod

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+module powerwatts
+
+go 1.22

main.go

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+package main
+
+import (
+	"embed"
+	"encoding/json"
+	"errors"
+	"html/template"
+	"log"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+)
+
+//go:embed static/*
+var indexHTML embed.FS
+
+type store struct {
+	mu    sync.RWMutex
+	value int
+}
+
+func (s *store) get() int {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	return s.value
+}
+
+func (s *store) set(v int) {
+	s.mu.Lock()
+	s.value = v
+	s.mu.Unlock()
+}
+
+func main() {
+	secret := os.Getenv("WRITE_SECRET")
+	addr := os.Getenv("ADDR")
+	if cfg, err := loadConfig("config.json"); err != nil {
+		if !errors.Is(err, os.ErrNotExist) {
+			log.Fatalf("load config: %v", err)
+		}
+	} else {
+		if secret == "" {
+			secret = cfg.WriteSecret
+		}
+		if addr == "" {
+			addr = cfg.Addr
+		}
+	}
+	if secret == "" {
+		log.Fatal("WRITE_SECRET is required")
+	}
+	if addr == "" {
+		addr = ":8080"
+	}
+
+	app := &server{
+		secret: secret,
+		store:  &store{},
+	}
+
+	log.Printf("listening on %s", addr)
+	log.Fatal(http.ListenAndServe(addr, app.routes()))
+}
+
+type server struct {
+	secret string
+	store  *store
+}
+
+type config struct {
+	WriteSecret string `json:"write_secret"`
+	Addr        string `json:"addr"`
+}
+
+func loadConfig(path string) (config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return config{}, err
+	}
+
+	var cfg config
+	if err := json.Unmarshal(data, &cfg); err != nil {
+		return config{}, err
+	}
+	return cfg, nil
+}
+
+func (s *server) routes() http.Handler {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/", s.handleIndex)
+	mux.HandleFunc("/favicon.svg", s.handleFavicon)
+	mux.HandleFunc("/write", s.handleWrite)
+	return mux
+}
+
+func (s *server) handleIndex(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path != "/" {
+		http.NotFound(w, r)
+		return
+	}
+
+	page, err := template.New("index.html").ParseFS(indexHTML, "static/index.html")
+	if err != nil {
+		http.Error(w, "template error", http.StatusInternalServerError)
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	if err := page.Execute(w, map[string]any{"Watts": s.store.get()}); err != nil {
+		http.Error(w, "render error", http.StatusInternalServerError)
+	}
+}
+
+const faviconSVG = `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Power meter">
+  <defs>
+    <linearGradient id="g" x1="16" y1="12" x2="48" y2="52" gradientUnits="userSpaceOnUse">
+      <stop offset="0" stop-color="#38bdf8"/>
+      <stop offset="1" stop-color="#22c55e"/>
+    </linearGradient>
+  </defs>
+  <rect x="10" y="14" width="44" height="36" rx="9" fill="#0f172a"/>
+  <rect x="14" y="18" width="36" height="28" rx="6" fill="none" stroke="url(#g)" stroke-width="3"/>
+  <path d="M32 22 L25 34 H31 L28 44 L39 30 H33 Z" fill="url(#g)"/>
+  <path d="M20 50h24" stroke="#334155" stroke-width="4" stroke-linecap="round"/>
+</svg>`
+
+func (s *server) handleFavicon(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path != "/favicon.svg" {
+		http.NotFound(w, r)
+		return
+	}
+
+	w.Header().Set("Content-Type", "image/svg+xml")
+	_, _ = w.Write([]byte(faviconSVG))
+}
+
+func (s *server) handleWrite(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	if got := r.Header.Get("X-Secret"); got == "" || got != s.secret {
+		http.Error(w, "unauthorized", http.StatusUnauthorized)
+		return
+	}
+
+	value, err := parseWatts(r)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	s.store.set(value)
+	w.Header().Set("Content-Type", "application/json")
+	_ = json.NewEncoder(w).Encode(map[string]any{"watts": value})
+}
+
+func parseWatts(r *http.Request) (int, error) {
+	contentType := r.Header.Get("Content-Type")
+	if strings.Contains(contentType, "application/json") {
+		var payload struct {
+			Watts *int `json:"watts"`
+		}
+		if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
+			return 0, errors.New("invalid json")
+		}
+		if payload.Watts == nil {
+			return 0, errors.New("missing watts")
+		}
+		return *payload.Watts, nil
+	}
+
+	if err := r.ParseForm(); err != nil {
+		return 0, errors.New("invalid form data")
+	}
+	if v := r.FormValue("watts"); v != "" {
+		return strconv.Atoi(v)
+	}
+	return 0, errors.New("missing watts")
+}

main_test.go

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+package main
+
+import (
+	"bytes"
+	"os"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestHandleIndexRendersWatts(t *testing.T) {
+	srv := &server{secret: "secret", store: &store{value: 123}}
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	rec := httptest.NewRecorder()
+
+	srv.handleIndex(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+	if !strings.Contains(rec.Body.String(), "123") {
+		t.Fatalf("response did not contain watt value: %s", rec.Body.String())
+	}
+}
+
+func TestHandleWriteRequiresSecret(t *testing.T) {
+	srv := &server{secret: "secret", store: &store{}}
+	req := httptest.NewRequest(http.MethodPost, "/write", bytes.NewBufferString(`{"watts":456}`))
+	req.Header.Set("Content-Type", "application/json")
+	rec := httptest.NewRecorder()
+
+	srv.handleWrite(rec, req)
+
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusUnauthorized)
+	}
+}
+
+func TestHandleWriteStoresValue(t *testing.T) {
+	srv := &server{secret: "secret", store: &store{}}
+	req := httptest.NewRequest(http.MethodPost, "/write", bytes.NewBufferString(`{"watts":456}`))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("X-Secret", "secret")
+	rec := httptest.NewRecorder()
+
+	srv.handleWrite(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+	if got := srv.store.get(); got != 456 {
+		t.Fatalf("stored watts = %d, want %d", got, 456)
+	}
+}
+
+func TestLoadConfig(t *testing.T) {
+	path := t.TempDir() + "/config.json"
+	if err := os.WriteFile(path, []byte(`{"write_secret":"secret","addr":":9090"}`), 0o600); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
+
+	cfg, err := loadConfig(path)
+	if err != nil {
+		t.Fatalf("loadConfig returned error: %v", err)
+	}
+	if cfg.WriteSecret != "secret" {
+		t.Fatalf("write_secret = %q, want %q", cfg.WriteSecret, "secret")
+	}
+	if cfg.Addr != ":9090" {
+		t.Fatalf("addr = %q, want %q", cfg.Addr, ":9090")
+	}
+}

static/favicon.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Power meter">
+  <defs>
+    <linearGradient id="g" x1="16" y1="12" x2="48" y2="52" gradientUnits="userSpaceOnUse">
+      <stop offset="0" stop-color="#38bdf8"/>
+      <stop offset="1" stop-color="#22c55e"/>
+    </linearGradient>
+  </defs>
+  <rect x="10" y="14" width="44" height="36" rx="9" fill="#0f172a"/>
+  <rect x="14" y="18" width="36" height="28" rx="6" fill="none" stroke="url(#g)" stroke-width="3"/>
+  <path d="M32 22 L25 34 H31 L28 44 L39 30 H33 Z" fill="url(#g)"/>
+  <path d="M20 50h24" stroke="#334155" stroke-width="4" stroke-linecap="round"/>
+</svg>

static/index.html

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+<!doctype html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Power Display</title>
+  <link rel="icon" href="/favicon.svg" type="image/svg+xml">
+  <style>
+    :root { color-scheme: light dark; }
+    body { font-family: system-ui, sans-serif; margin: 0; min-height: 100vh; display: grid; place-items: center; background: #0f172a; color: #e2e8f0; }
+    main { text-align: center; padding: 2rem; }
+    .value { font-size: clamp(3rem, 12vw, 8rem); font-weight: 800; line-height: 1; }
+    .unit { margin-top: 0.75rem; font-size: 1.25rem; color: #94a3b8; }
+  </style>
+</head>
+<body>
+  <main>
+    <div class="value">{{.Watts}}</div>
+    <div class="unit">watts</div>
+  </main>
+</body>
+</html>