simplified code across the app and consolidated duplicated helpers

lib/widget/user_avatar.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
+import 'dart:math';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
@@ -76,13 +77,16 @@ final Map<String, Future<AvatarPayload?>> _pendingAvatars = {};
 final ValueNotifier<int> _avatarCacheGeneration = ValueNotifier<int>(0);
 
 String avatarUrl({required String id, required bool isGroup, int size = 512}) {
-  final host = EndpointData().nextcloud().full();
   if (isGroup) {
+    final host = EndpointData().nextcloud().full();
     return 'https://$host/ocs/v2.php/apps/spreed/api/v1/room/$id/avatar';
   }
-  return 'https://$host/avatar/$id/$size';
+  return '${_userAvatarUrlPrefix(id)}$size';
 }
 
+String _userAvatarUrlPrefix(String id) =>
+    'https://${EndpointData().nextcloud().full()}/avatar/$id/';
+
 /// Resolves an avatar through the shared caches: in-memory first, then disk,
 /// then the network — the fetch being deduped across every concurrent caller
 /// and written back to both caches.
@@ -109,26 +113,32 @@ Future<AvatarPayload?> loadAvatarPayload({
     return payload;
   }
 
-  final payload = await _fetchDeduped(url);
-  _commitAvatar(url, id: id, isGroup: isGroup, size: size, payload: payload);
-  return payload;
+  return _fetchDeduped(url, id: id, isGroup: isGroup, size: size);
 }
 
-/// Shares one in-flight request per URL across all callers.
-Future<AvatarPayload?> _fetchDeduped(String url) =>
-    _pendingAvatars.putIfAbsent(url, () {
-      final future = _fetchAvatarPayload(url);
-      // Cleanup hangs off an error-neutralised copy: whenComplete on `future`
-      // itself returns a second future that forwards the error unawaited.
-      unawaited(
-        future.then<void>((_) {}, onError: (_) {}).whenComplete(() {
-          if (identical(_pendingAvatars[url], future)) {
-            _pendingAvatars.remove(url);
-          }
-        }),
-      );
-      return future;
-    });
+/// Shares one in-flight request per URL across all callers; the result is
+/// committed to the caches once, not once per waiting caller.
+Future<AvatarPayload?> _fetchDeduped(
+  String url, {
+  required String id,
+  required bool isGroup,
+  required int size,
+}) => _pendingAvatars.putIfAbsent(url, () {
+  final future = _fetchAvatarPayload(url).then((payload) {
+    _commitAvatar(url, id: id, isGroup: isGroup, size: size, payload: payload);
+    return payload;
+  });
+  // Cleanup hangs off an error-neutralised copy: whenComplete on `future`
+  // itself returns a second future that forwards the error unawaited.
+  unawaited(
+    future.then<void>((_) {}, onError: (_) {}).whenComplete(() {
+      if (identical(_pendingAvatars[url], future)) {
+        _pendingAvatars.remove(url);
+      }
+    }),
+  );
+  return future;
+});
 
 /// Persists a resolved result to the in-memory and disk caches.
 void _commitAvatar(
@@ -189,10 +199,7 @@ AvatarPayload _payloadFromBytes(Uint8List bytes) =>
 
 bool _looksLikeSvg(Uint8List bytes) {
   final head = utf8
-      .decode(
-        bytes.sublist(0, bytes.length < 256 ? bytes.length : 256),
-        allowMalformed: true,
-      )
+      .decode(bytes.sublist(0, min(bytes.length, 256)), allowMalformed: true)
       .trimLeft();
   return head.startsWith('<?xml') || head.startsWith('<svg');
 }
@@ -220,8 +227,7 @@ void invalidateAvatarCache({String? id, bool? isGroup}) {
     unawaited(PushAvatarStore.evict(id));
   } else {
     // User avatars include the rendered size in the URL — drop every variant.
-    final host = EndpointData().nextcloud().full();
-    final prefix = 'https://$host/avatar/$id/';
+    final prefix = _userAvatarUrlPrefix(id);
     _resolvedAvatars.removeWhere((url, _) => url.startsWith(prefix));
     _pendingAvatars.removeWhere((url, _) => url.startsWith(prefix));
     unawaited(AvatarDiskCache.instance.evict(id: id, isGroup: false));
@@ -285,14 +291,15 @@ class _UserAvatarState extends State<UserAvatar> {
   int _resolvedRequestSize() =>
       widget.requestSize ?? (widget.size * 4).clamp(64, 1024);
 
-  String _url() => avatarUrl(
+  String _url([int? size]) => avatarUrl(
     id: widget.id,
     isGroup: widget.isGroup,
-    size: _resolvedRequestSize(),
+    size: size ?? _resolvedRequestSize(),
   );
 
   void _attach() {
-    final url = _url();
+    final size = _resolvedRequestSize();
+    final url = _url(size);
     final cached = _readAvatarCache(url);
     if (cached != null) {
       _payload = cached.payload;
@@ -302,7 +309,6 @@ class _UserAvatarState extends State<UserAvatar> {
     // the widget may have been recycled onto a different id by then.
     final id = widget.id;
     final isGroup = widget.isGroup;
-    final size = _resolvedRequestSize();
 
     // Persistent disk cache: on a warm session (cache directory already known)
     // this hits synchronously, so a cold app start paints the last-known
@@ -348,14 +354,13 @@ class _UserAvatarState extends State<UserAvatar> {
 
     AvatarPayload? fresh;
     try {
-      fresh = await _fetchDeduped(url);
+      fresh = await _fetchDeduped(url, id: id, isGroup: isGroup, size: size);
     } on Object {
       // Transient failure (offline, 5xx). Keep showing the cached picture; the
       // next mount retries. Deliberately no null-cache so we don't mask it.
       return;
     }
 
-    _commitAvatar(url, id: id, isGroup: isGroup, size: size, payload: fresh);
     if (!mounted || _url() != url) return;
     if (fresh == null) {
       // HTTP 404 — the avatar was removed server-side. Fall back to the icon.