Distinguish failed avatar reads from committed empty blobs

tools/chatgui/db/db_manager.cpp

@@ -10,6 +10,7 @@
 #include <QJsonObject>
 #include <QCoreApplication>
 #include "chat/chat_poll.h"
+#include "chat/group_avatar.h"
 
 /* ── helpers ── */
 
@@ -119,14 +120,37 @@ QList<ChannelRow> DbManager::getChannels(ChannelSortMode sort) const {
     return list;
 }
 
-QByteArray DbManager::getChannelAvatar(const QString& channelId) const {
-    sqlite3_stmt* st = prepareOrNull("SELECT avatar_data FROM channels WHERE channel_id=?"); if (!st) return {};
-    const QByteArray id = channelId.toLatin1(); sqlite3_bind_text(st, 1, id.constData(), id.size(), SQLITE_TRANSIENT);
+QByteArray DbManager::getChannelAvatar(const QString& channelId, bool* ok) const {
+    if (ok) *ok = false;
+    if (!m_db) { GUI_WARN("group avatar: database unavailable channel=%s", qPrintable(channelId)); return {}; }
+    sqlite3_stmt* st = nullptr;
+    const char* stage = "prepare";
+    int rc = sqlite3_prepare_v2(m_db, "SELECT avatar_data FROM channels WHERE channel_id=?", -1, &st, nullptr);
+    const QByteArray id = channelId.toLatin1();
+    if (rc == SQLITE_OK) { stage = "bind"; rc = sqlite3_bind_text(st, 1, id.constData(), id.size(), SQLITE_TRANSIENT); }
+    if (rc == SQLITE_OK) { stage = "step"; rc = sqlite3_step(st); }
     QByteArray bytes;
-    int rc = sqlite3_step(st);
-    if (rc == SQLITE_ROW) bytes = colBlob(st, 0);
-    else if (rc != SQLITE_DONE) GUI_ERROR("group avatar: database read failed channel=%s rc=%d", qPrintable(channelId), rc);
-    sqlite3_finalize(st); return bytes;
+    int type = -1, length = 0;
+    if (rc == SQLITE_ROW) {
+        stage = "blob"; type = sqlite3_column_type(st, 0); length = sqlite3_column_bytes(st, 0);
+        if (type != SQLITE_BLOB) rc = SQLITE_CORRUPT;
+        else if (length > GROUP_AVATAR_MAX) rc = SQLITE_TOOBIG;
+        else {
+            const char* blob = static_cast<const char*>(sqlite3_column_blob(st, 0));
+            if (length && !blob) rc = SQLITE_NOMEM;
+            else bytes = QByteArray(blob, length);
+        }
+    }
+    const int final = sqlite3_finalize(st);
+    if ((rc != SQLITE_ROW && rc != SQLITE_DONE) || final != SQLITE_OK) {
+        GUI_ERROR("group avatar: read channel=%s stage=%s rc=%d finalize=%d type=%d bytes=%d: %s",
+                  qPrintable(channelId), stage, rc, final, type, length, sqlite3_errmsg(m_db)); return {};
+    }
+    if (rc == SQLITE_DONE) {
+        GUI_DEBUG("group avatar: channel disappeared during read channel=%s", qPrintable(channelId)); return {};
+    }
+    if (ok) *ok = true;
+    return bytes;
 }
 
 bool DbManager::isChannelMember(const QString& chId, quint64 nodeId) const {

tools/chatgui/db/db_manager.h

@@ -101,7 +101,10 @@ public:
 
     /* ── Каналы ── */
     QList<ChannelRow> getChannels(ChannelSortMode sort = ChannelSortMode::Alphabetical) const;
-    QByteArray getChannelAvatar(const QString& channelId) const;
+    /* Читает BLOB аватара канала <=16 KiB. Возвращает самостоятельные байты; при ошибке/нет строки — пустой массив.
+     * Необязательный ok отличает успешный пустой BLOB (удаление) от отказа; bind/step/finalize проверяются.
+     * Хеш/версию и формат JPEG проверяет GroupAvatarManager, запись не меняется. */
+    QByteArray getChannelAvatar(const QString& channelId, bool* ok = nullptr) const;
     QString getChannelLastMessage(const QString& channelId) const;
     int  getUnreadCount(const QString& channelId, qint64 lastReadMsgId) const;