On dedicated servers, save copy of last autosave on crash

This is to avoid all autosaves being overwritten when the server
is auto-restarted with a new map

src/crashlog.cpp

@@ -690,6 +690,32 @@ bool CrashLog::WriteScreenshot(char *filename, const char *filename_last, const
 	return res;
 }
 
+#ifdef DEDICATED
+static bool CopyAutosave(const std::string &old_name, const std::string &new_name)
+{
+	FILE *old_fh = FioFOpenFile(old_name, "rb", AUTOSAVE_DIR);
+	if (old_fh == nullptr) return false;
+	auto guard1 = scope_guard([=]() {
+		FioFCloseFile(old_fh);
+	});
+	FILE *new_fh = FioFOpenFile(new_name, "wb", AUTOSAVE_DIR);
+	if (new_fh == nullptr) return false;
+	auto guard2 = scope_guard([=]() {
+		FioFCloseFile(new_fh);
+	});
+
+	char buffer[4096 * 4];
+	size_t length;
+	do {
+		length = fread(buffer, 1, lengthof(buffer), old_fh);
+		if (fwrite(buffer, 1, length, new_fh) != length) {
+			return false;
+		}
+	} while (length == lengthof(buffer));
+	return true;
+}
+#endif
+
 /**
  * Makes the crash log, writes it to a file and then subsequently tries
  * to make a crash dump and crash savegame. It uses DEBUG to write
@@ -703,6 +729,27 @@ bool CrashLog::MakeCrashLog(char *buffer, const char *last)
 	if (crashlogged) return false;
 	crashlogged = true;
 
+	char *name_buffer_date = this->name_buffer + seprintf(this->name_buffer, lastof(this->name_buffer), "crash-");
+	time_t cur_time = time(nullptr);
+	strftime(name_buffer_date, lastof(this->name_buffer) - name_buffer_date, "%Y%m%dT%H%M%SZ", gmtime(&cur_time));
+
+#ifdef DEDICATED
+	if (!_settings_client.gui.keep_all_autosave) {
+		extern FiosNumberedSaveName &GetAutoSaveFiosNumberedSaveName();
+		FiosNumberedSaveName &autosave = GetAutoSaveFiosNumberedSaveName();
+		int num = autosave.GetLastNumber();
+		if (num >= 0) {
+			std::string old_file = autosave.FilenameUsingNumber(num, "");
+			char save_suffix[MAX_PATH];
+			seprintf(save_suffix, lastof(save_suffix), "-(%s)", this->name_buffer);
+			std::string new_file = autosave.FilenameUsingNumber(num, save_suffix);
+			if (CopyAutosave(old_file, new_file)) {
+				printf("Saving copy of last autosave: %s -> %s\n\n", old_file.c_str(), new_file.c_str());
+			}
+		}
+	}
+#endif
+
 	if (!VideoDriver::EmergencyAcquireGameLock(20, 2)) {
 		printf("Failed to acquire gamelock before filling crash log\n\n");
 	}
@@ -710,10 +757,6 @@ bool CrashLog::MakeCrashLog(char *buffer, const char *last)
 	char filename[MAX_PATH];
 	bool ret = true;
 
-	char *name_buffer_date = this->name_buffer + seprintf(this->name_buffer, lastof(this->name_buffer), "crash-");
-	time_t cur_time = time(nullptr);
-	strftime(name_buffer_date, lastof(this->name_buffer) - name_buffer_date, "%Y%m%dT%H%M%SZ", gmtime(&cur_time));
-
 	printf("Crash encountered, generating crash log...\n");
 	this->FillCrashLog(buffer, last);
 	printf("%s\n", buffer);

src/fios.cpp

@@ -791,7 +791,12 @@ FiosNumberedSaveName::FiosNumberedSaveName(const std::string &prefix) : prefix(p
 std::string FiosNumberedSaveName::Filename()
 {
 	if (++this->number >= _settings_client.gui.max_num_autosaves) this->number = 0;
-	return stdstr_fmt("%s%u.sav", this->prefix.c_str(), this->number);
+	return this->FilenameUsingNumber(this->number, "");
+}
+
+std::string FiosNumberedSaveName::FilenameUsingNumber(int num, const char *suffix) const
+{
+	return stdstr_fmt("%s%u%s.sav", this->prefix.c_str(), num, suffix);
 }
 
 /**

src/fios.h

@@ -136,7 +136,9 @@ FiosType FiosGetSavegameListCallback(SaveLoadOperation fop, const std::string &f
 struct FiosNumberedSaveName {
 	FiosNumberedSaveName(const std::string &prefix);
 	std::string Filename();
+	std::string FilenameUsingNumber(int num, const char *suffix) const;
 	std::string Extension();
+	int GetLastNumber() const { return this->number; }
 private:
 	std::string prefix;
 	int number;

src/openttd.cpp

@@ -1929,14 +1929,19 @@ void StateGameLoop()
 	assert(IsLocalCompany());
 }
 
+FiosNumberedSaveName &GetAutoSaveFiosNumberedSaveName()
+{
+	static FiosNumberedSaveName _autosave_ctr("autosave");
+	return _autosave_ctr;
+}
+
 /**
  * Create an autosave. The default name is "autosave#.sav". However with
  * the setting 'keep_all_autosave' the name defaults to company-name + date
  */
 static void DoAutosave()
 {
-	static FiosNumberedSaveName _autosave_ctr("autosave");
-	DoAutoOrNetsave(_autosave_ctr, true);
+	DoAutoOrNetsave(GetAutoSaveFiosNumberedSaveName(), true);
 }
 
 /**