feat: add PWA support with Android share intent

Make Favoritter installable as a Progressive Web App with offline
static asset caching and Web Share Target API for Android.

New files:
- internal/handler/pwa.go: handlers for manifest, service worker,
  and share target
- web/static/sw.js: service worker (cache-first static, network-first
  HTML) with {{BASE_PATH}} placeholder for subpath deployments
- web/static/icons/: placeholder PWA icons (192, 512, 512-maskable)

Key design decisions:
- Share target uses GET (not POST) to avoid CSRF token issues — Android
  apps cannot provide CSRF tokens
- Manifest is generated dynamically to inject BasePath into start_url,
  scope, icon paths, and share_target action
- Service worker served at /sw.js with Cache-Control: no-cache and
  BasePath injected via string replacement
- handleShare extracts URLs from Android's "text" field as fallback
  (many apps put the URL there instead of "url")
- handleFaveNew replaced with handleFaveNewPreFill that reads url,
  description, notes from query params (enables share + bookmarklets)
- SW registration in app.js reads base-path from <meta> tag (CSP-safe)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/handler/fave.go

@@ -48,19 +48,6 @@ func (h *Handler) handleFaveList(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
-// handleFaveNew shows the form for creating a new fave.
-func (h *Handler) handleFaveNew(w http.ResponseWriter, r *http.Request) {
-	user := middleware.UserFromContext(r.Context())
-
-	h.deps.Renderer.Page(w, r, "fave_form", render.PageData{
-		Title: "Ny favoritt",
-		Data: map[string]any{
-			"IsNew":          true,
-			"DefaultPrivacy": user.DefaultFavePrivacy,
-		},
-	})
-}
-
 // handleFaveCreate processes the form for creating a new fave.
 func (h *Handler) handleFaveCreate(w http.ResponseWriter, r *http.Request) {
 	user := middleware.UserFromContext(r.Context())

internal/handler/handler.go

@@ -74,6 +74,10 @@ func (h *Handler) Routes() *http.ServeMux {
 	// Health check.
 	mux.HandleFunc("GET /health", h.handleHealth)
 
+	// PWA: manifest and service worker (public, no auth).
+	mux.HandleFunc("GET /manifest.json", h.handleManifest)
+	mux.HandleFunc("GET /sw.js", h.handleServiceWorker)
+
 	// Auth routes (rate-limited).
 	mux.Handle("POST /login", h.rateLimiter.Limit(http.HandlerFunc(h.handleLoginPost)))
 	mux.Handle("POST /signup", h.rateLimiter.Limit(http.HandlerFunc(h.handleSignupPost)))
@@ -91,8 +95,9 @@ func (h *Handler) Routes() *http.ServeMux {
 
 	// Faves — authenticated routes use requireLogin wrapper.
 	requireLogin := middleware.RequireLogin(h.deps.Config.BasePath)
+	mux.Handle("GET /share", requireLogin(http.HandlerFunc(h.handleShare)))
 	mux.Handle("GET /faves", requireLogin(http.HandlerFunc(h.handleFaveList)))
-	mux.Handle("GET /faves/new", requireLogin(http.HandlerFunc(h.handleFaveNew)))
+	mux.Handle("GET /faves/new", requireLogin(http.HandlerFunc(h.handleFaveNewPreFill)))
 	mux.Handle("POST /faves", requireLogin(http.HandlerFunc(h.handleFaveCreate)))
 	mux.HandleFunc("GET /faves/{id}", h.handleFaveDetail)
 	mux.Handle("GET /faves/{id}/edit", requireLogin(http.HandlerFunc(h.handleFaveEdit)))

internal/handler/pwa.go

@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+package handler
+
+import (
+	"encoding/json"
+	"io/fs"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"kode.naiv.no/olemd/favoritter/internal/middleware"
+	"kode.naiv.no/olemd/favoritter/internal/render"
+	"kode.naiv.no/olemd/favoritter/web"
+)
+
+// handleManifest serves the Web App Manifest with dynamic BasePath injection.
+func (h *Handler) handleManifest(w http.ResponseWriter, r *http.Request) {
+	bp := h.deps.Config.BasePath
+
+	manifest := map[string]any{
+		"name":             h.deps.Config.SiteName,
+		"short_name":       h.deps.Config.SiteName,
+		"description":      "Lagre og del dine favoritter",
+		"start_url":        bp + "/",
+		"scope":            bp + "/",
+		"display":          "standalone",
+		"background_color": "#ffffff",
+		"theme_color":      "#1095c1",
+		"icons": []map[string]any{
+			{"src": bp + "/static/icons/icon-192.png", "sizes": "192x192", "type": "image/png"},
+			{"src": bp + "/static/icons/icon-512.png", "sizes": "512x512", "type": "image/png"},
+			{"src": bp + "/static/icons/icon-512-maskable.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable"},
+		},
+		"share_target": map[string]any{
+			"action": bp + "/share",
+			"method": "GET",
+			"params": map[string]string{
+				"url":   "url",
+				"text":  "text",
+				"title": "title",
+			},
+		},
+	}
+
+	w.Header().Set("Content-Type", "application/manifest+json")
+	json.NewEncoder(w).Encode(manifest)
+}
+
+// handleServiceWorker serves the service worker JS from root scope.
+// BasePath is injected via placeholder replacement so the SW can
+// cache the correct static asset paths.
+func (h *Handler) handleServiceWorker(w http.ResponseWriter, r *http.Request) {
+	staticFS, err := fs.Sub(web.StaticFS, "static")
+	if err != nil {
+		http.Error(w, "Not found", http.StatusNotFound)
+		return
+	}
+
+	data, err := fs.ReadFile(staticFS, "sw.js")
+	if err != nil {
+		http.Error(w, "Not found", http.StatusNotFound)
+		return
+	}
+
+	content := strings.ReplaceAll(string(data), "{{BASE_PATH}}", h.deps.Config.BasePath)
+
+	w.Header().Set("Content-Type", "application/javascript")
+	w.Header().Set("Cache-Control", "no-cache")
+	w.Write([]byte(content))
+}
+
+// handleShare receives Android share intents via the Web Share Target API
+// and redirects to the new-fave form with pre-filled values.
+// Uses GET to avoid CSRF issues (Android cannot provide CSRF tokens).
+func (h *Handler) handleShare(w http.ResponseWriter, r *http.Request) {
+	user := middleware.UserFromContext(r.Context())
+	if user == nil {
+		http.Redirect(w, r, h.deps.Config.BasePath+"/login", http.StatusSeeOther)
+		return
+	}
+
+	sharedURL := r.URL.Query().Get("url")
+	sharedTitle := r.URL.Query().Get("title")
+	sharedText := r.URL.Query().Get("text")
+
+	// Many Android apps send the URL in the "text" field instead of "url".
+	if sharedURL == "" && sharedText != "" {
+		sharedURL = extractURL(sharedText)
+		if sharedURL != "" {
+			// Remove the URL from text so it's not duplicated.
+			sharedText = strings.TrimSpace(strings.Replace(sharedText, sharedURL, "", 1))
+		}
+	}
+
+	description := sharedTitle
+	if description == "" && sharedText != "" {
+		description = sharedText
+		sharedText = "" // Don't duplicate into notes.
+	}
+
+	target := h.deps.Config.BasePath + "/faves/new?"
+	params := url.Values{}
+	if sharedURL != "" {
+		params.Set("url", sharedURL)
+	}
+	if description != "" {
+		params.Set("description", description)
+	}
+	if sharedText != "" {
+		params.Set("notes", sharedText)
+	}
+
+	http.Redirect(w, r, target+params.Encode(), http.StatusSeeOther)
+}
+
+// handleFaveNewWithPreFill shows the new fave form, optionally pre-filled
+// from query parameters (used by share target and bookmarklets).
+func (h *Handler) handleFaveNewPreFill(w http.ResponseWriter, r *http.Request) {
+	user := middleware.UserFromContext(r.Context())
+
+	h.deps.Renderer.Page(w, r, "fave_form", render.PageData{
+		Title: "Ny favoritt",
+		Data: map[string]any{
+			"IsNew":          true,
+			"DefaultPrivacy": user.DefaultFavePrivacy,
+			"Description":    r.URL.Query().Get("description"),
+			"URL":            r.URL.Query().Get("url"),
+			"Notes":          r.URL.Query().Get("notes"),
+		},
+	})
+}
+
+// extractURL finds the first http:// or https:// URL in a string.
+func extractURL(s string) string {
+	for _, word := range strings.Fields(s) {
+		if strings.HasPrefix(word, "http://") || strings.HasPrefix(word, "https://") {
+			return word
+		}
+	}
+	return ""
+}

internal/handler/web_test.go

@@ -1133,6 +1133,155 @@ func TestDisplayNameFallbackToUsername(t *testing.T) {
 	}
 }
 
+// --- PWA ---
+
+func TestManifestJSON(t *testing.T) {
+	_, mux := testServer(t)
+
+	req := httptest.NewRequest("GET", "/manifest.json", nil)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("manifest: got %d, want 200", rr.Code)
+	}
+
+	ct := rr.Header().Get("Content-Type")
+	if !strings.Contains(ct, "manifest+json") {
+		t.Errorf("content-type = %q, want manifest+json", ct)
+	}
+
+	var manifest map[string]any
+	if err := json.Unmarshal(rr.Body.Bytes(), &manifest); err != nil {
+		t.Fatalf("parse manifest: %v", err)
+	}
+
+	if manifest["name"] != "Test" {
+		t.Errorf("name = %v, want Test", manifest["name"])
+	}
+
+	// share_target should exist with GET method.
+	st, ok := manifest["share_target"].(map[string]any)
+	if !ok {
+		t.Fatal("manifest missing share_target")
+	}
+	if st["method"] != "GET" {
+		t.Errorf("share_target method = %v, want GET", st["method"])
+	}
+}
+
+func TestServiceWorkerContent(t *testing.T) {
+	_, mux := testServer(t)
+
+	req := httptest.NewRequest("GET", "/sw.js", nil)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("sw.js: got %d, want 200", rr.Code)
+	}
+
+	ct := rr.Header().Get("Content-Type")
+	if !strings.Contains(ct, "javascript") {
+		t.Errorf("content-type = %q, want javascript", ct)
+	}
+
+	cc := rr.Header().Get("Cache-Control")
+	if cc != "no-cache" {
+		t.Errorf("Cache-Control = %q, want no-cache", cc)
+	}
+
+	body := rr.Body.String()
+	if strings.Contains(body, "{{BASE_PATH}}") {
+		t.Error("sw.js should have BASE_PATH placeholder replaced")
+	}
+	if !strings.Contains(body, "CACHE_NAME") {
+		t.Error("sw.js should contain service worker code")
+	}
+}
+
+func TestShareRedirectsToFaveNew(t *testing.T) {
+	h, mux := testServer(t)
+	cookie := loginUser(t, h, "testuser", "pass123", "user")
+
+	req := httptest.NewRequest("GET", "/share?url=https://example.com&title=Test+Page", nil)
+	req.AddCookie(cookie)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusSeeOther {
+		t.Fatalf("share: got %d, want 303", rr.Code)
+	}
+
+	loc := rr.Header().Get("Location")
+	if !strings.Contains(loc, "/faves/new") {
+		t.Errorf("redirect = %q, should point to /faves/new", loc)
+	}
+	if !strings.Contains(loc, "url=https") {
+		t.Errorf("redirect = %q, should contain url param", loc)
+	}
+	if !strings.Contains(loc, "description=Test") {
+		t.Errorf("redirect = %q, should contain description from title", loc)
+	}
+}
+
+func TestShareTextFieldFallback(t *testing.T) {
+	h, mux := testServer(t)
+	cookie := loginUser(t, h, "testuser", "pass123", "user")
+
+	// Some Android apps put the URL in "text" instead of "url".
+	req := httptest.NewRequest("GET", "/share?text=Check+this+out+https://example.com/article", nil)
+	req.AddCookie(cookie)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	loc := rr.Header().Get("Location")
+	if !strings.Contains(loc, "url=https") {
+		t.Errorf("should extract URL from text field: %q", loc)
+	}
+}
+
+func TestShareRequiresLogin(t *testing.T) {
+	_, mux := testServer(t)
+
+	req := httptest.NewRequest("GET", "/share?url=https://example.com", nil)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusSeeOther {
+		t.Errorf("unauthenticated share: got %d, want 303", rr.Code)
+	}
+	loc := rr.Header().Get("Location")
+	if !strings.Contains(loc, "/login") {
+		t.Errorf("should redirect to login: %q", loc)
+	}
+}
+
+func TestFaveNewPreFill(t *testing.T) {
+	h, mux := testServer(t)
+	cookie := loginUser(t, h, "testuser", "pass123", "user")
+
+	req := httptest.NewRequest("GET", "/faves/new?url=https://example.com&description=Shared+Page&notes=Great+article", nil)
+	req.AddCookie(cookie)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("fave new pre-fill: got %d, want 200", rr.Code)
+	}
+
+	body := rr.Body.String()
+	if !strings.Contains(body, "https://example.com") {
+		t.Error("URL should be pre-filled")
+	}
+	if !strings.Contains(body, "Shared Page") {
+		t.Error("description should be pre-filled")
+	}
+	if !strings.Contains(body, "Great article") {
+		t.Error("notes should be pre-filled")
+	}
+}
+
 // --- Export page ---
 
 func TestExportPageRendering(t *testing.T) {

web/static/js/app.js

@@ -188,4 +188,11 @@
         var match = document.cookie.match(new RegExp("(^| )" + name + "=([^;]+)"));
         return match ? match[2] : null;
     }
+
+    // Register service worker for PWA support.
+    if ("serviceWorker" in navigator) {
+        var baseMeta = document.querySelector('meta[name="base-path"]');
+        var base = baseMeta ? baseMeta.getAttribute("content") : "";
+        navigator.serviceWorker.register(base + "/sw.js", { scope: base + "/" });
+    }
 })();

web/static/sw.js

@@ -0,0 +1,66 @@
+// Favoritter — Service Worker for PWA offline support.
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+var BASE = "{{BASE_PATH}}";
+var CACHE_NAME = "favoritter-v1";
+var STATIC_URLS = [
+    BASE + "/static/vendor/pico.min.css",
+    BASE + "/static/vendor/htmx.min.js",
+    BASE + "/static/css/style.css",
+    BASE + "/static/js/app.js",
+    BASE + "/static/icons/icon-192.png"
+];
+
+self.addEventListener("install", function (event) {
+    event.waitUntil(
+        caches.open(CACHE_NAME).then(function (cache) {
+            return cache.addAll(STATIC_URLS);
+        })
+    );
+    self.skipWaiting();
+});
+
+self.addEventListener("activate", function (event) {
+    event.waitUntil(
+        caches.keys().then(function (names) {
+            return Promise.all(
+                names.filter(function (n) { return n !== CACHE_NAME; })
+                    .map(function (n) { return caches.delete(n); })
+            );
+        })
+    );
+    self.clients.claim();
+});
+
+self.addEventListener("fetch", function (event) {
+    var url = new URL(event.request.url);
+
+    // Cache-first for static assets.
+    if (url.pathname.startsWith(BASE + "/static/")) {
+        event.respondWith(
+            caches.match(event.request).then(function (cached) {
+                return cached || fetch(event.request).then(function (response) {
+                    var clone = response.clone();
+                    caches.open(CACHE_NAME).then(function (cache) {
+                        cache.put(event.request, clone);
+                    });
+                    return response;
+                });
+            })
+        );
+        return;
+    }
+
+    // Network-first for navigation (HTML pages).
+    if (event.request.mode === "navigate") {
+        event.respondWith(
+            fetch(event.request).catch(function () {
+                return caches.match(event.request);
+            })
+        );
+        return;
+    }
+
+    // Default: network only.
+    event.respondWith(fetch(event.request));
+});

web/templates/layouts/base.html

@@ -6,6 +6,11 @@
     <title>{{if .Title}}{{.Title}} — {{end}}{{.SiteName}}</title>
     <link rel="stylesheet" href="{{basePath}}/static/vendor/pico.min.css">
     <link rel="stylesheet" href="{{basePath}}/static/css/style.css">
+    <meta name="theme-color" content="#1095c1">
+    <link rel="manifest" href="{{basePath}}/manifest.json">
+    <link rel="icon" type="image/png" sizes="192x192" href="{{basePath}}/static/icons/icon-192.png">
+    <link rel="apple-touch-icon" href="{{basePath}}/static/icons/icon-192.png">
+    <meta name="base-path" content="{{basePath}}">
     {{block "head" .}}{{end}}
 </head>
 <body>