[Server] Let users fetch their own private chat history

Players lose their private conversations on reconnect or on another
device. Servatrice can already log private messages, but only
moderators can read the logs.

Add Command_GetPrivateChatHistory / Response_PrivateChatHistory so a
registered user can page through their own logged conversation with one
other user. Operators opt in with logging/allow_user_chat_history
(default off, and log_user_msg_chat must be on). The caller is matched
by account id so reused guest or deleted-account names can't read older
messages; only time, sender name and text are returned. Pages hold
1..200 messages and never split a second, since log_time has 1-second
resolution.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

servatrice/servatrice.ini.example

@@ -534,6 +534,10 @@ log_user_msg_chat=false
 ; Log user messages coming from other servers in the network
 log_user_msg_isl=false
 
+; Allow registered users to read their retained private messages; requires log_user_msg_chat=true
+; Privacy: exposes previously logged conversations to their participants on any device
+allow_user_chat_history=false
+
 [audit]
 
 ; Servatrice can record certain actions being performed in the database for server operators to better understand

servatrice/src/servatrice_database_interface.cpp

@@ -2638,6 +2638,87 @@ int Servatrice_DatabaseInterface::clearBlacklistedBanners()
     return cleared;
 }
 
+bool Servatrice_DatabaseInterface::getPrivateChatHistory(int callerId,
+                                                         int peerId,
+                                                         quint64 before,
+                                                         int limit,
+                                                         QList<ServerInfo_PrivateChatMessage> &messages,
+                                                         bool &hasMore)
+{
+    messages.clear();
+    hasMore = false;
+    if (callerId < 1 || peerId < 1 || !checkSql()) {
+        return false;
+    }
+
+    // Both participants are matched by account id, never by name: names can be
+    // reused by guests or re-registered after deletion, and matching by name
+    // would merge conversations from different people.
+    const QString conversationFilter = " FROM {prefix}_log WHERE target_type = 'chat'"
+                                       " AND ((sender_id = :caller_sender_id AND target_id = :peer_target_id)"
+                                       " OR (target_id = :caller_target_id AND sender_id = :peer_sender_id))";
+    const QString selectMessages = "SELECT UNIX_TIMESTAMP(log_time), sender_name, log_message";
+    const auto bindParticipants = [&](QSqlQuery *query) {
+        query->bindValue(":caller_sender_id", callerId);
+        query->bindValue(":peer_target_id", peerId);
+        query->bindValue(":peer_sender_id", peerId);
+        query->bindValue(":caller_target_id", callerId);
+    };
+    const auto readMessages = [&](QSqlQuery *query) {
+        while (query->next()) {
+            ServerInfo_PrivateChatMessage message;
+            message.set_time(query->value(0).toULongLong());
+            message.set_sender_name(query->value(1).toString().toStdString());
+            message.set_message(query->value(2).toString().toStdString());
+            messages.append(message);
+        }
+    };
+
+    QString queryString = selectMessages + conversationFilter;
+    if (before) {
+        queryString.append(" AND log_time < FROM_UNIXTIME(:before)");
+    }
+    queryString.append(" ORDER BY log_time DESC LIMIT :limit_size");
+    QSqlQuery *query = prepareQuery(queryString);
+    bindParticipants(query);
+    if (before) {
+        query->bindValue(":before", before);
+    }
+    query->bindValue(":limit_size", limit + 1);
+    if (!execSqlQuery(query)) {
+        return false;
+    }
+    readMessages(query);
+
+    hasMore = messages.size() > limit;
+    if (hasMore) {
+        const quint64 boundary = messages.at(limit).time();
+        while (!messages.isEmpty() && messages.last().time() == boundary) {
+            messages.removeLast();
+        }
+        if (messages.isEmpty()) {
+            query = prepareQuery(selectMessages + conversationFilter + " AND log_time = FROM_UNIXTIME(:second)");
+            bindParticipants(query);
+            query->bindValue(":second", boundary);
+            if (!execSqlQuery(query)) {
+                return false;
+            }
+            readMessages(query);
+
+            query = prepareQuery("SELECT 1" + conversationFilter + " AND log_time < FROM_UNIXTIME(:before) LIMIT 1");
+            bindParticipants(query);
+            query->bindValue(":before", boundary);
+            if (!execSqlQuery(query)) {
+                return false;
+            }
+            hasMore = query->next();
+        }
+    }
+
+    std::reverse(messages.begin(), messages.end());
+    return true;
+}
+
 QList<ServerInfo_ChatMessage> Servatrice_DatabaseInterface::getMessageLogHistory(const QString &user,
                                                                                  const QString &ipaddress,
                                                                                  const QString &gamename,

servatrice/src/servatrice_database_interface.h

@@ -12,6 +12,7 @@
 #include <libcockatrice/protocol/pb/serverinfo_ban.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_chat_message.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_moderator_login.pb.h>
+#include <libcockatrice/protocol/pb/serverinfo_private_chat_message.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_user_alt.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_user_session.pb.h>
 #include <libcockatrice/protocol/pb/serverinfo_warning.pb.h>
@@ -224,6 +225,12 @@ public:
                                                        const QString &beforeTime = QString(),
                                                        bool *hasMore = nullptr);
     QList<ServerInfo_UserSession> getUserSessions(const QString &userName, int limit);
+    bool getPrivateChatHistory(int callerId,
+                               int peerId,
+                               quint64 before,
+                               int limit,
+                               QList<ServerInfo_PrivateChatMessage> &messages,
+                               bool &hasMore);
     QList<ServerInfo_UserAlt> getUserAlts(const QString &userName,
                                           int depth = 1,
                                           bool useEmail = true,

servatrice/src/serversocketinterface.cpp

@@ -98,6 +98,7 @@
 #include <libcockatrice/protocol/pb/command_deck_share_list_mine.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_share_remove.pb.h>
 #include <libcockatrice/protocol/pb/command_deck_upload.pb.h>
+#include <libcockatrice/protocol/pb/command_get_private_chat_history.pb.h>
 #include <libcockatrice/protocol/pb/command_get_server_stats.pb.h>
 #include <libcockatrice/protocol/pb/command_replay_delete_match.pb.h>
 #include <libcockatrice/protocol/pb/command_replay_download.pb.h>
@@ -139,6 +140,7 @@
 #include <libcockatrice/protocol/pb/response_get_server_stats.pb.h>
 #include <libcockatrice/protocol/pb/response_moderator_last_logins.pb.h>
 #include <libcockatrice/protocol/pb/response_password_salt.pb.h>
+#include <libcockatrice/protocol/pb/response_private_chat_history.pb.h>
 #include <libcockatrice/protocol/pb/response_register.pb.h>
 #include <libcockatrice/protocol/pb/response_remove_user_avatar.pb.h>
 #include <libcockatrice/protocol/pb/response_remove_user_banner.pb.h>
@@ -414,6 +416,8 @@ Response::ResponseCode AbstractServerSocketInterface::processExtendedSessionComm
             return cmdDeckShareRemove(cmd.GetExtension(Command_DeckShareRemove::ext), rc);
         case SessionCommand::DECK_SHARE_DOWNLOAD:
             return cmdDeckShareDownload(cmd.GetExtension(Command_DeckShareDownload::ext), rc);
+        case SessionCommand::GET_PRIVATE_CHAT_HISTORY:
+            return cmdGetPrivateChatHistory(cmd.GetExtension(Command_GetPrivateChatHistory::ext), rc);
         case SessionCommand::ACCOUNT_PASSWORD:
             return cmdAccountPassword(cmd.GetExtension(Command_AccountPassword::ext), rc);
         case SessionCommand::REQUEST_PASSWORD_SALT:
@@ -1702,6 +1706,48 @@ Response::ResponseCode AbstractServerSocketInterface::cmdReplaySubmitCode(const
     return Response::RespOk;
 }
 
+Response::ResponseCode AbstractServerSocketInterface::cmdGetPrivateChatHistory(const Command_GetPrivateChatHistory &cmd,
+                                                                               ResponseContainer &rc)
+{
+    if (authState != PasswordRight) {
+        return Response::RespFunctionNotAllowed;
+    }
+    if (!userInfo || !(userInfo->user_level() & ServerInfo_User::IsRegistered)) {
+        return Response::RespFunctionNotAllowed;
+    }
+    if (!settingsCache->value("logging/log_user_msg_chat", false).toBool() ||
+        !settingsCache->value("logging/allow_user_chat_history", false).toBool()) {
+        return Response::RespFunctionNotAllowed;
+    }
+
+    const QString peer = nameFromStdString(cmd.user_name());
+    if (peer.isEmpty()) {
+        return Response::RespInvalidData;
+    }
+
+    // Resolve the peer to an account id. Matching by name alone would merge the
+    // conversations of everyone who has ever used that name.
+    const int peerId = sqlInterface->getUserIdInDB(peer);
+    if (peerId < 1) {
+        return Response::RespNameNotFound;
+    }
+
+    const int limit = qBound<quint32>(1, cmd.limit(), 200);
+    QList<ServerInfo_PrivateChatMessage> messages;
+    bool hasMore = false;
+    if (!sqlInterface->getPrivateChatHistory(userInfo->id(), peerId, cmd.before(), limit, messages, hasMore)) {
+        return Response::RespInternalError;
+    }
+
+    Response_PrivateChatHistory *re = new Response_PrivateChatHistory;
+    for (const auto &message : messages) {
+        re->add_messages()->CopyFrom(message);
+    }
+    re->set_has_more(hasMore);
+    rc.setResponseExtension(re);
+    return Response::RespOk;
+}
+
 // MODERATOR FUNCTIONS.
 // May be called by admins and moderators. Permission is checked by the calling function.
 Response::ResponseCode AbstractServerSocketInterface::cmdGetLogHistory(const Command_ViewLogHistory &cmd,

servatrice/src/serversocketinterface.h

@@ -81,6 +81,7 @@ class Command_ForgotPasswordReset;
 class Command_GetAdminNotes;
 class Command_GetBanHistory;
 class Command_GetModeratorLastLogins;
+class Command_GetPrivateChatHistory;
 class Command_GetServerStats;
 class Command_GetUserAlts;
 class Command_GetUserSessions;
@@ -142,6 +143,7 @@ private:
 
     Response::ResponseCode cmdAddToList(const Command_AddToList &cmd, ResponseContainer &rc);
     Response::ResponseCode cmdRemoveFromList(const Command_RemoveFromList &cmd, ResponseContainer &rc);
+    Response::ResponseCode cmdGetPrivateChatHistory(const Command_GetPrivateChatHistory &cmd, ResponseContainer &rc);
     int getDeckPathId(int basePathId, QStringList path);
     int getDeckPathId(const QString &path);
     bool deckListHelper(int folderId,