--- a/src/date.cpp	Sat Jul 07 08:53:19 2007 +0000
+++ b/src/date.cpp	Sat Jul 07 10:06:10 2007 +0000
@@ -13,6 +13,9 @@
 #include "network/network_server.h"
 #include "functions.h"
 #include "currency.h"
+#ifdef DEBUG_DUMP_COMMANDS
+#include "saveload.h"
+#endif
 
 Year      _cur_year;
 Month     _cur_month;
@@ -259,6 +262,12 @@
 
 	/* yes, call various monthly loops */
 	if (_game_mode != GM_MENU) {
+#ifdef DEBUG_DUMP_COMMANDS
+		char name[MAX_PATH];
+		snprintf(name, lengthof(name), "dmp_cmds_%d.sav", _date);
+		SaveOrLoad(name, SL_SAVE, AUTOSAVE_DIR);
+		debug_dump_commands("ddc:save:%s\n", name);
+#endif /* DUMP_COMMANDS */
 		if (_opt.autosave != 0 && (_cur_month % _autosave_months[_opt.autosave]) == 0) {
 			_do_autosave = true;
 			RedrawAutosave();

--- a/src/network/network.cpp	Sat Jul 07 08:53:19 2007 +0000
+++ b/src/network/network.cpp	Sat Jul 07 10:06:10 2007 +0000
@@ -37,6 +37,7 @@
 #include "../console.h" /* IConsoleCmdExec */
 #include <stdarg.h> /* va_list */
 #include "../md5.h"
+#include "../fileio.h"
 
 /* Check whether NETWORK_NUM_LANDSCAPES is still in sync with NUM_LANDSCAPE */
 assert_compile((int)NETWORK_NUM_LANDSCAPES == (int)NUM_LANDSCAPE);
@@ -195,6 +196,9 @@
 			break;
 	}
 
+#ifdef DEBUG_DUMP_COMMANDS
+	debug_dump_commands("ddc:cmsg:%d;%d;%s\n", _date, _date_fract, message);
+#endif /* DUMP_COMMANDS */
 	IConsolePrintF(color, "%s", message);
 	AddTextMessage(color, duration, "%s", message);
 }
@@ -1235,6 +1239,9 @@
 			if (_sync_seed_1 != _random_seeds[0][0]) {
 #endif
 				NetworkError(STR_NETWORK_ERR_DESYNC);
+#ifdef DEBUG_DUMP_COMMANDS
+				debug_dump_commands("ddc:serr:%d;%d\n", _date, _date_fract);
+#endif /* DUMP_COMMANDS */
 				DEBUG(net, 0, "Sync error detected!");
 				NetworkClientError(NETWORK_RECV_STATUS_DESYNC, DEREF_CLIENT(0));
 				return false;
@@ -1280,6 +1287,37 @@
 	if (!NetworkReceive()) return;
 
 	if (_network_server) {
+#ifdef DEBUG_DUMP_COMMANDS
+		static FILE *f = FioFOpenFile("commands.log", "rb", SAVE_DIR);
+		static Date next_date = 0;
+		static uint32 next_date_fract;
+		static CommandPacket *cp = NULL;
+		if (f == NULL && next_date == 0) {
+			printf("Cannot open commands.log\n");
+			next_date = 1;
+		}
+
+		while (f != NULL && !feof(f)) {
+			if (cp != NULL && _date == next_date && _date_fract == next_date_fract) {
+				_current_player = cp->player;
+				_cmd_text = cp->text;
+				DoCommandP(cp->tile, cp->p1, cp->p2, NULL, cp->cmd);
+				free(cp);
+				cp = NULL;
+			}
+
+			if (cp != NULL) break;
+
+			char buff[4096];
+			if (fgets(buff, lengthof(buff), f) == NULL) break;
+			if (strncmp(buff, "ddc:cmd:", 8) != 0) continue;
+			cp = MallocT<CommandPacket>(1);
+			int player;
+			sscanf(&buff[8], "%d;%d;%d;%d;%d;%d;%d;%s", &next_date, &next_date_fract, &player, &cp->tile, &cp->p1, &cp->p2, &cp->cmd, cp->text);
+			cp->player = (Owner)player;
+		}
+#endif /* DUMP_COMMANDS */
+
 		bool send_frame = false;
 
 		// We first increase the _frame_counter
@@ -1436,4 +1474,18 @@
 			strncmp(_openttd_revision, other, NETWORK_REVISION_LENGTH - 1) == 0;
 }
 
+#ifdef DEBUG_DUMP_COMMANDS
+void CDECL debug_dump_commands(const char *s, ...)
+{
+	static FILE *f = FioFOpenFile("commands-out.log", "wb", SAVE_DIR);
+	if (f == NULL) return;
+
+	va_list va;
+	va_start(va, s);
+	vfprintf(f, s, va);
+	va_end(va);
+
+	fflush(f);
+}
+#endif /* DEBUG_DUMP_COMMANDS */
 #endif /* ENABLE_NETWORK */

--- a/src/network/network.h	Sat Jul 07 08:53:19 2007 +0000
+++ b/src/network/network.h	Sat Jul 07 10:06:10 2007 +0000
@@ -20,6 +20,17 @@
 //  nothing will happen.
 //#define ENABLE_NETWORK_SYNC_EVERY_FRAME
 
+/*
+ * Dumps all commands that are sent/received to stderr and saves every month.
+ * This log can become quite large over time; say in the order of two to three
+ * times the bandwidth used for network games.
+ */
+//#define DEBUG_DUMP_COMMANDS
+
+#ifdef DEBUG_DUMP_COMMANDS
+void CDECL debug_dump_commands(const char *s, ...);
+#endif /* DEBUG_DUMP_COMMANDS */
+
 // In theory sending 1 of the 2 seeds is enough to check for desyncs
 //   so in theory, this next define can be left off.
 //#define NETWORK_SEND_DOUBLE_SEED

--- a/src/network/network_data.cpp	Sat Jul 07 08:53:19 2007 +0000
+++ b/src/network/network_data.cpp	Sat Jul 07 10:06:10 2007 +0000
@@ -97,6 +97,11 @@
 		DEBUG(net, 0, "Received out-of-bounds callback (%d)", cp->callback);
 		cp->callback = 0;
 	}
+
+#ifdef DEBUG_DUMP_COMMANDS
+	debug_dump_commands("ddc:cmd:%d;%d;%d;%d;%d;%d;%d;%s\n", _date, _date_fract, (int)cp->player, cp->tile, cp->p1, cp->p2, cp->cmd, cp->text);
+#endif /* DUMP_COMMANDS */
+
 	DoCommandP(cp->tile, cp->p1, cp->p2, _callback_table[cp->callback], cp->cmd | CMD_NETWORK_COMMAND);
 }
 

--- a/src/saveload.cpp	Sat Jul 07 08:53:19 2007 +0000
+++ b/src/saveload.cpp	Sat Jul 07 10:06:10 2007 +0000
@@ -1677,6 +1677,9 @@
 		}
 	} else { /* LOAD game */
 		assert(mode == SL_LOAD);
+#ifdef DEBUG_DUMP_COMMANDS
+		debug_dump_commands("ddc:load:%s\n", filename);
+#endif /* DUMP_COMMANDS */
 
 		if (fread(hdr, sizeof(hdr), 1, _sl.fh) != 1) SlError(STR_GAME_SAVELOAD_ERROR_FILE_NOT_READABLE);