Add build version reporting to API and UI footer

Dockerfile

@@ -14,6 +14,13 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         libvips-dev pkg-config curl ca-certificates \
     && rm -rf /var/lib/apt/lists/*
 
+# VERSION is the release string shown in the UI footer (via /version). It is
+# passed in at build time because .git is dockerignored, so the build can't run
+# `git describe` itself — compute it on the host and forward it:
+#   docker build --build-arg VERSION="$(git describe --tags --always)" .
+# Falls back to "dev" when not supplied.
+ARG VERSION=dev
+
 WORKDIR /app
 COPY go.mod go.sum ./
 RUN go mod download
@@ -22,7 +29,10 @@ COPY . .
 COPY --from=frontend /app/frontend/dist ./frontend/dist
 # The `vips` tag compiles the govips/libvips integration (headers from
 # libvips-dev above). Local builds omit it so the toolchain works without libvips.
-RUN CGO_ENABLED=1 GOOS=linux go build -tags "vips" -o /app/image-optimizer .
+# -X main.version stamps the build version into the binary.
+RUN CGO_ENABLED=1 GOOS=linux go build -tags "vips" \
+        -ldflags "-X main.version=${VERSION}" \
+        -o /app/image-optimizer .
 
 # ---- Stage 3: minimal runtime ----
 FROM debian:bookworm-slim AS runtime

frontend/src/App.svelte

@@ -23,6 +23,25 @@
   // transform that would otherwise trap its position:fixed overlay.
   let cropping = $state(null);
 
+  // Build version shown in the footer. Fetched once from /version (injected at
+  // build time from the git tag); stays '' if the request fails so the footer
+  // simply omits it. 'dev' is the local-build fallback the server reports.
+  let appVersion = $state('');
+  $effect(() => {
+    let cancelled = false;
+    fetch('/version')
+      .then((r) => (r.ok ? r.json() : null))
+      .then((d) => {
+        if (cancelled || !d?.version) return;
+        // Show tags as "v0.3.1"; leave non-tag builds (e.g. "dev") as-is.
+        appVersion = /^\d/.test(d.version) ? `v${d.version}` : d.version;
+      })
+      .catch(() => {});
+    return () => {
+      cancelled = true;
+    };
+  });
+
   let status = $derived(progress.status);
   let canSubmit = $derived(
     status === 'idle' && files.length > 0 && selectedPresets.length > 0,
@@ -245,6 +264,9 @@
     <button type="button" class="hover:text-ctp-blue" onclick={() => (legalOpen = 'privacy')}>
       Privacy Policy
     </button>
+    {#if appVersion}
+      <span class="text-ctp-overlay0/70" title="Build version">{appVersion}</span>
+    {/if}
   </footer>
 </main>
 

handlers/routes.go

@@ -4,13 +4,15 @@ import "github.com/gofiber/fiber/v3"
 
 // RegisterRoutes wires every API route onto the app, sharing one in-memory job
 // store across upload, progress, and download. maxFileBytes is the per-file
-// upload cap. It returns the store so the caller can start its TTL reaper and
-// drain in-flight jobs on shutdown. Call this before the SPA catch-all so the
-// API paths are not swallowed by the wildcard route.
-func RegisterRoutes(app *fiber.App, maxFileBytes int64) *Store {
+// upload cap; version is the build version surfaced at /version (and in the UI
+// footer). It returns the store so the caller can start its TTL reaper and drain
+// in-flight jobs on shutdown. Call this before the SPA catch-all so the API paths
+// are not swallowed by the wildcard route.
+func RegisterRoutes(app *fiber.App, maxFileBytes int64, version string) *Store {
 	store := NewStore()
 
 	app.Get("/health", Health)
+	app.Get("/version", Version(version))
 	app.Post("/upload", Upload(store, maxFileBytes))
 	app.Get("/progress/:jobId", Progress(store))
 	app.Get("/download/:jobId", Download(store))

handlers/version.go

@@ -0,0 +1,12 @@
+package handlers
+
+import "github.com/gofiber/fiber/v3"
+
+// Version returns a handler that responds 200 with the build version as JSON, so
+// the frontend can show which release it is running. The value is injected at
+// build time (git tag via -ldflags); it falls back to "dev" for local builds.
+func Version(version string) fiber.Handler {
+	return func(c fiber.Ctx) error {
+		return c.JSON(fiber.Map{"version": version})
+	}
+}

handlers/version_test.go

@@ -0,0 +1,35 @@
+package handlers
+
+import (
+	"encoding/json"
+	"io"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gofiber/fiber/v3"
+)
+
+func TestVersionHandler(t *testing.T) {
+	app := fiber.New()
+	app.Get("/version", Version("v1.2.3"))
+
+	resp, err := app.Test(httptest.NewRequest("GET", "/version", nil))
+	if err != nil {
+		t.Fatalf("request: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != fiber.StatusOK {
+		t.Fatalf("status = %d, want 200", resp.StatusCode)
+	}
+
+	body, _ := io.ReadAll(resp.Body)
+	var got struct {
+		Version string `json:"version"`
+	}
+	if err := json.Unmarshal(body, &got); err != nil {
+		t.Fatalf("unmarshal %q: %v", body, err)
+	}
+	if got.Version != "v1.2.3" {
+		t.Errorf("version = %q, want %q", got.Version, "v1.2.3")
+	}
+}

main.go

@@ -33,6 +33,14 @@ var frontendDist embed.FS
 // open connections to close, and how long we wait for in-flight jobs to drain.
 const shutdownGrace = 30 * time.Second
 
+// version is the build version, surfaced at /version and in the UI footer. It is
+// injected at build time from the git tag via:
+//
+//	go build -ldflags "-X main.version=$(git describe --tags)"
+//
+// (the Dockerfile passes this through a build arg). Local builds keep "dev".
+var version = "dev"
+
 func main() {
 	// -healthcheck turns the binary into its own health probe (used by the
 	// Docker HEALTHCHECK so the minimal runtime image needs no curl/wget).
@@ -61,7 +69,7 @@ func main() {
 	// API routes (health, upload, progress SSE, download). Registered before the
 	// SPA catch-all so they are not swallowed by the wildcard route. The returned
 	// store owns job lifecycle; start its TTL reaper and drain it on shutdown.
-	store := handlers.RegisterRoutes(app, cfg.MaxFileBytes)
+	store := handlers.RegisterRoutes(app, cfg.MaxFileBytes, version)
 	store.StartReaper(ctx, cfg.JobTTL)
 
 	// Serve the embedded Svelte SPA at the root.