feat: self-hosted favicon resolver via /favicon/<domain>

Adds a Kafka-hosted favicon proxy at /favicon/<domain>:
- Fetches favicon.ico from the target domain
- In-memory cache with 1-hour TTL and ETag support (304 Not Modified)
- Max 64KB per favicon to prevent memory abuse
- Privacy: user browser talks to Kafka, not Google/DuckDuckGo

New "Self (Kafka)" option in the favicon service selector.
Defaults to None. No third-party requests when self is chosen.

internal/httpapi/handlers.go

@@ -18,11 +18,17 @@ package httpapi
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
+	"io"
 	"net/http"
 	"strings"
+	"sync"
+	"time"
 
 	"github.com/metamorphosis-dev/samsa/internal/contracts"
+	"github.com/metamorphosis-dev/samsa/internal/httpclient"
 	"github.com/metamorphosis-dev/samsa/internal/search"
 	"github.com/metamorphosis-dev/samsa/internal/views"
 )
@@ -159,3 +165,114 @@ func (h *Handler) Preferences(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 	}
 }
+
+// faviconCacheEntry holds a cached favicon body and its ETag.
+type faviconCacheEntry struct {
+	body     []byte
+	etag     string
+	cachedAt time.Time
+}
+
+// faviconCache is a simple in-memory cache for fetched favicons.
+// Entries expire after 1 hour.
+var faviconCache = struct {
+	m map[string]faviconCacheEntry
+	sync.RWMutex
+}{m: make(map[string]faviconCacheEntry)}
+
+const faviconCacheTTL = 1 * time.Hour
+
+// Favicon serves a fetched favicon for the given domain, with ETag support
+// and a 1-hour in-memory cache. This lets Kafka act as a privacy-preserving
+// favicon proxy: the user's browser talks to Kafka, not Google or DuckDuckGo.
+func (h *Handler) Favicon(w http.ResponseWriter, r *http.Request) {
+	domain := strings.TrimPrefix(r.URL.Path, "/favicon/")
+	domain = strings.TrimSuffix(domain, "/")
+	domain = strings.TrimSpace(domain)
+
+	if domain == "" || strings.Contains(domain, "/") {
+		http.Error(w, "invalid domain", http.StatusBadRequest)
+		return
+	}
+
+	// Check cache.
+	faviconCache.RLock()
+	entry, ok := faviconCache.m[domain]
+	faviconCache.RUnlock()
+
+	now := time.Now()
+	if ok && now.Sub(entry.cachedAt) < faviconCacheTTL {
+		// ETag-based cache validation.
+		if etag := r.Header.Get("If-None-Match"); etag != "" && etag == entry.etag {
+			w.WriteHeader(http.StatusNotModified)
+			return
+		}
+		w.Header().Set("Content-Type", "image/x-icon")
+		w.Header().Set("ETag", entry.etag)
+		w.Header().Set("Cache-Control", "private, max-age=3600")
+		w.WriteHeader(http.StatusOK)
+		w.Write(entry.body)
+		return
+	}
+
+	// Fetch from the domain's favicon.ico.
+	fetchURL := "https://" + domain + "/favicon.ico"
+	req, err := http.NewRequestWithContext(r.Context(), http.MethodGet, fetchURL, nil)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	req.Header.Set("User-Agent", "Kafka/0.1 (+https://git.ashisgreat.xyz/penal-colony/samsa)")
+	req.Header.Set("Accept", "image/x-icon,image/png,image/webp,*/*")
+
+	client := httpclient.NewClient(5 * time.Second)
+	resp, err := client.Do(req)
+	if err != nil {
+		http.Error(w, "favicon fetch failed", http.StatusBadGateway)
+		return
+	}
+	defer resp.Body.Close()
+
+	// Upstream favicon server issues a redirect or error.
+	if resp.StatusCode != http.StatusOK {
+		http.Error(w, "favicon not found", http.StatusNotFound)
+		return
+	}
+
+	body, err := io.ReadAll(http.MaxBytesReader(w, resp.Body, 64*1024))
+	if err != nil {
+		http.Error(w, "favicon too large", http.StatusBadGateway)
+		return
+	}
+
+	etag := resp.Header.Get("ETag")
+	if etag == "" {
+		// Fallback ETag: hash of body.
+		h := sha256.Sum256(body)
+		etag = `"` + hex.EncodeToString(h[:8]) + `"`
+	}
+
+	// Store in cache.
+	faviconCache.Lock()
+	faviconCache.m[domain] = faviconCacheEntry{
+		body:     body,
+		etag:     etag,
+		cachedAt: now,
+	}
+	faviconCache.Unlock()
+
+	if etagMatch := r.Header.Get("If-None-Match"); etagMatch != "" && etagMatch == etag {
+		w.WriteHeader(http.StatusNotModified)
+		return
+	}
+
+	contentType := resp.Header.Get("Content-Type")
+	if contentType == "" {
+		contentType = "image/x-icon"
+	}
+	w.Header().Set("Content-Type", contentType)
+	w.Header().Set("ETag", etag)
+	w.Header().Set("Cache-Control", "private, max-age=3600")
+	w.WriteHeader(http.StatusOK)
+	w.Write(body)
+}

internal/views/static/js/settings.js

@@ -48,7 +48,8 @@ function applyTheme(theme) {
 function applyFavicon(service) {
   var faviconMap = {
     google: function(domain) { return 'https://www.google.com/s2/favicons?domain=' + encodeURIComponent(domain) + '&sz=32'; },
-    duckduckgo: function(domain) { return 'https://icons.duckduckgo.com/ip3/' + encodeURIComponent(domain) + '.ico'; }
+    duckduckgo: function(domain) { return 'https://icons.duckduckgo.com/ip3/' + encodeURIComponent(domain) + '.ico'; },
+    self: function(domain) { return '/favicon/' + encodeURIComponent(domain); }
   };
   var imgs = document.querySelectorAll('.result-favicon');
   imgs.forEach(function(img) {
@@ -56,7 +57,7 @@ function applyFavicon(service) {
     if (!domain) return;
     if (service === 'none') {
       img.style.display = 'none';
-    } else {
+    } else if (faviconMap[service]) {
       img.style.display = '';
       img.src = faviconMap[service](domain);
     }
@@ -125,8 +126,8 @@ function renderPanel(prefs) {
 
   
   var faviconOptions = '';
-  ['none', 'google', 'duckduckgo'].forEach(function(src) {
-    var labels = { none: 'None', google: 'Google', duckduckgo: 'DuckDuckGo' };
+  ['none', 'google', 'duckduckgo', 'self'].forEach(function(src) {
+    var labels = { none: 'None', google: 'Google', duckduckgo: 'DuckDuckGo', self: 'Self (Kafka)' };
     var selected = prefs.favicon === src ? ' selected' : '';
     faviconOptions += '<option value="' + src + '"' + selected + '>' + labels[src] + '</option>';
   });

internal/views/templates/preferences.html

@@ -78,6 +78,7 @@
           <option value="none" selected>None</option>
           <option value="google">Google</option>
           <option value="duckduckgo">DuckDuckGo</option>
+          <option value="self">Self (Kafka)</option>
         </select>
       </div>
     </section>