fix: address security and quality issues from code review

Security fixes:
- Fix XSS in Atom feed: escape user-supplied URLs in HTML content
- Wrap signup request approval in a transaction to prevent
  partial state on crash (user created but request still pending)
- Stop leaking internal error messages to admin UI
- Add request body size limit on API import endpoint
- Log SetMustResetPassword errors instead of silently discarding

Correctness fixes:
- Handle errors from API fave update/delete instead of returning
  success on failure
- Use actual data timestamp for feed <updated> instead of
  time.Now() (improves HTTP caching)
- Replace hardcoded 10000 export limit with named constant
  (maxExportFaves = 100000)

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

internal/handler/admin.go

@@ -101,8 +101,9 @@ func (h *Handler) handleAdminResetPassword(w http.ResponseWriter, r *http.Reques
 		return
 	}
 
-	// Force password reset on next login by setting the flag back.
-	h.deps.Users.SetMustResetPassword(id, true)
+	if err := h.deps.Users.SetMustResetPassword(id, true); err != nil {
+		slog.Error("set must-reset-password error", "error", err)
+	}
 
 	// Invalidate all sessions for this user.
 	if delErr := h.deps.Sessions.DeleteAllForUser(id); delErr != nil {
@@ -252,7 +253,7 @@ func (h *Handler) handleAdminSignupRequestAction(w http.ResponseWriter, r *http.
 	case "approve":
 		if err := h.deps.SignupRequests.Approve(id, admin.ID); err != nil {
 			slog.Error("approve signup request error", "error", err)
-			h.adminRequestsFlash(w, r, "Noe gikk galt: "+err.Error(), "error")
+			h.adminRequestsFlash(w, r, "Noe gikk galt ved godkjenning.", "error")
 			return
 		}
 		h.adminRequestsFlash(w, r, "Forespørsel godkjent. Brukeren må endre passord ved første innlogging.", "success")

internal/handler/api/api.go

@@ -6,6 +6,7 @@ package api
 import (
 	"encoding/json"
 	"errors"
+	"io"
 	"log/slog"
 	"net/http"
 	"strconv"
@@ -236,9 +237,15 @@ func (h *Handler) handleUpdateFave(w http.ResponseWriter, r *http.Request) {
 		req.Privacy = fave.Privacy
 	}
 
-	h.deps.Faves.Update(id, req.Description, req.URL, fave.ImagePath, req.Privacy)
+	if err := h.deps.Faves.Update(id, req.Description, req.URL, fave.ImagePath, req.Privacy); err != nil {
+		slog.Error("api: update fave error", "error", err)
+		jsonError(w, "Internal error", http.StatusInternalServerError)
+		return
+	}
 	if req.Tags != nil {
-		h.deps.Tags.SetFaveTags(id, req.Tags)
+		if err := h.deps.Tags.SetFaveTags(id, req.Tags); err != nil {
+			slog.Error("api: set tags error", "error", err)
+		}
 	}
 
 	updated, _ := h.deps.Faves.GetByID(id)
@@ -269,7 +276,11 @@ func (h *Handler) handleDeleteFave(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	h.deps.Faves.Delete(id)
+	if err := h.deps.Faves.Delete(id); err != nil {
+		slog.Error("api: delete fave error", "error", err)
+		jsonError(w, "Internal error", http.StatusInternalServerError)
+		return
+	}
 	w.WriteHeader(http.StatusNoContent)
 }
 
@@ -349,7 +360,7 @@ func (h *Handler) handleGetUserFaves(w http.ResponseWriter, r *http.Request) {
 
 func (h *Handler) handleExport(w http.ResponseWriter, r *http.Request) {
 	user := middleware.UserFromContext(r.Context())
-	faves, _, err := h.deps.Faves.ListByUser(user.ID, 10000, 0)
+	faves, _, err := h.deps.Faves.ListByUser(user.ID, 100000, 0)
 	if err != nil {
 		jsonError(w, "Internal error", http.StatusInternalServerError)
 		return
@@ -361,6 +372,9 @@ func (h *Handler) handleExport(w http.ResponseWriter, r *http.Request) {
 func (h *Handler) handleImport(w http.ResponseWriter, r *http.Request) {
 	user := middleware.UserFromContext(r.Context())
 
+	// Limit request body to prevent memory exhaustion.
+	r.Body = io.NopCloser(io.LimitReader(r.Body, h.deps.Config.MaxUploadSize))
+
 	var faves []struct {
 		Description string   `json:"description"`
 		URL         string   `json:"url"`

internal/handler/feed.go

@@ -4,6 +4,7 @@ package handler
 
 import (
 	"errors"
+	"html"
 	"log/slog"
 	"net/http"
 	"strconv"
@@ -42,7 +43,7 @@ func (h *Handler) handleFeedGlobal(w http.ResponseWriter, r *http.Request) {
 		Title:       siteName + " — Siste favoritter",
 		Link:        &feeds.Link{Href: baseURL},
 		Description: "Siste offentlige favoritter",
-		Updated:     time.Now(),
+		Updated:     feedUpdatedTime(faves),
 	}
 
 	feed.Items = favesToFeedItems(faves, baseURL)
@@ -84,7 +85,7 @@ func (h *Handler) handleFeedUser(w http.ResponseWriter, r *http.Request) {
 	feed := &feeds.Feed{
 		Title:   user.DisplayNameOrUsername() + " sine favoritter",
 		Link:    &feeds.Link{Href: baseURL + "/u/" + user.Username},
-		Updated: time.Now(),
+		Updated: feedUpdatedTime(faves),
 	}
 
 	feed.Items = favesToFeedItems(faves, baseURL)
@@ -110,7 +111,7 @@ func (h *Handler) handleFeedTag(w http.ResponseWriter, r *http.Request) {
 	feed := &feeds.Feed{
 		Title:   "Favoritter med merkelapp: " + tagName,
 		Link:    &feeds.Link{Href: baseURL + "/tags/" + tagName},
-		Updated: time.Now(),
+		Updated: feedUpdatedTime(faves),
 	}
 
 	feed.Items = favesToFeedItems(faves, baseURL)
@@ -129,7 +130,8 @@ func favesToFeedItems(faves []*model.Fave, baseURL string) []*feeds.Item {
 		}
 
 		if f.URL != "" {
-			item.Content = `<p><a href="` + f.URL + `">` + f.URL + `</a></p>`
+			escaped := html.EscapeString(f.URL)
+			item.Content = `<p><a href="` + escaped + `">` + escaped + `</a></p>`
 		}
 
 		if f.ImagePath != "" {
@@ -155,6 +157,15 @@ func (h *Handler) writeAtom(w http.ResponseWriter, feed *feeds.Feed) {
 	w.Write([]byte(atom))
 }
 
+// feedUpdatedTime returns the most recent UpdatedAt from the faves,
+// falling back to now if the list is empty.
+func feedUpdatedTime(faves []*model.Fave) time.Time {
+	if len(faves) > 0 {
+		return faves[0].UpdatedAt
+	}
+	return time.Now()
+}
+
 func itoa(n int64) string {
 	return strconv.FormatInt(n, 10)
 }

internal/handler/import_export.go

@@ -15,6 +15,8 @@ import (
 	"kode.naiv.no/olemd/favoritter/internal/render"
 )
 
+const maxExportFaves = 100000
+
 // ExportFave is the JSON representation for export/import.
 type ExportFave struct {
 	Description string   `json:"description"`
@@ -35,7 +37,7 @@ func (h *Handler) handleExportPage(w http.ResponseWriter, r *http.Request) {
 func (h *Handler) handleExportJSON(w http.ResponseWriter, r *http.Request) {
 	user := middleware.UserFromContext(r.Context())
 
-	faves, _, err := h.deps.Faves.ListByUser(user.ID, 10000, 0)
+	faves, _, err := h.deps.Faves.ListByUser(user.ID, maxExportFaves, 0)
 	if err != nil {
 		slog.Error("export: list faves error", "error", err)
 		http.Error(w, "Internal error", http.StatusInternalServerError)
@@ -72,7 +74,7 @@ func (h *Handler) handleExportJSON(w http.ResponseWriter, r *http.Request) {
 func (h *Handler) handleExportCSV(w http.ResponseWriter, r *http.Request) {
 	user := middleware.UserFromContext(r.Context())
 
-	faves, _, err := h.deps.Faves.ListByUser(user.ID, 10000, 0)
+	faves, _, err := h.deps.Faves.ListByUser(user.ID, maxExportFaves, 0)
 	if err != nil {
 		slog.Error("export: list faves error", "error", err)
 		http.Error(w, "Internal error", http.StatusInternalServerError)