From 286997188e53e0fa0763724ca87e8040c1b1adcb Mon Sep 17 00:00:00 2001
From: Martin Michelsen <fuzziqersoftware+g@gmail.com>
Date: Sat, 30 Jul 2022 13:08:22 -0700
Subject: [PATCH] skip guild card file download if checksums match

---
 src/CommandFormats.hh  | 17 +++++++++++++++--
 src/Player.cc          |  5 +++++
 src/Player.hh          |  2 ++
 src/ReceiveCommands.cc | 13 +++++++------
 src/SendCommands.cc    |  3 +--
 5 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/src/CommandFormats.hh b/src/CommandFormats.hh
index dde7b3ea..fcb9448c 100644
--- a/src/CommandFormats.hh
+++ b/src/CommandFormats.hh
@@ -2284,9 +2284,13 @@ struct C_GuildCardChecksum_01E8 {
 };
 
 // 02E8 (S->C): Accept/decline guild card file checksum
+// If needs_update is nonzero, the client will request the guild card file by
+// sending an 03E8 command. If needs_update is zero, the client will skip
+// downloading the guild card file and send a 04EB command (requesting the
+// stream file) instead.
 
 struct S_GuildCardChecksumResponse_BB_02E8 {
-  le_uint32_t verify;
+  le_uint32_t needs_update;
   le_uint32_t unused;
 };
 
@@ -2436,7 +2440,7 @@ struct S_Unknown_GC_Ep3_EB {
   PlayerEntry players[12];
 };
 
-// EB (S->C): Send stream file index and chunks (BB)
+// 01EB (S->C): Send stream file index (BB)
 
 // Command is a list of these; header.flag is the entry count.
 struct S_StreamFileIndexEntry_BB_01EB {
@@ -2446,11 +2450,20 @@ struct S_StreamFileIndexEntry_BB_01EB {
   ptext<char, 0x40> filename;
 };
 
+// 02EB (S->C): Send stream file chunk (BB)
+
 struct S_StreamFileChunk_BB_02EB {
   le_uint32_t chunk_index;
   uint8_t data[0x6800];
 };
 
+// 03EB (C->S): Request a specific stream file chunk
+// header.flag is the chunk index. Server should respond with a 02EB command.
+
+// 04EB (C->S): Request stream file header
+// No arguments
+// Server should respond with a 01EB command.
+
 // EC: Create game (Episode 3)
 // Same format as C1; some fields are unused (e.g. episode, difficulty).
 
diff --git a/src/Player.cc b/src/Player.cc
index 5fcec9a4..774d2fdd 100644
--- a/src/Player.cc
+++ b/src/Player.cc
@@ -6,6 +6,7 @@
 
 #include <stdexcept>
 #include <phosg/Filesystem.hh>
+#include <phosg/Hash.hh>
 
 #include "FileContentsCache.hh"
 #include "Loggers.hh"
@@ -298,6 +299,10 @@ void GuildCardEntryBB::clear() {
   this->unknown_a1.clear();
 }
 
+uint32_t GuildCardFileBB::checksum() const {
+  return crc32(this, sizeof(*this));
+}
+
 
 
 void PlayerBank::load(const string& filename) {
diff --git a/src/Player.hh b/src/Player.hh
index 3fea0cf8..253ef20d 100644
--- a/src/Player.hh
+++ b/src/Player.hh
@@ -252,6 +252,8 @@ struct GuildCardFileBB {
   GuildCardBB blocked[0x1C];
   parray<uint8_t, 0x180> unknown_a2;
   GuildCardEntryBB entries[0x69];
+
+  uint32_t checksum() const;
 } __attribute__((packed));
 
 struct KeyAndTeamConfigBB {
diff --git a/src/ReceiveCommands.cc b/src/ReceiveCommands.cc
index 26e6fe76..f03c075c 100644
--- a/src/ReceiveCommands.cc
+++ b/src/ReceiveCommands.cc
@@ -1587,12 +1587,13 @@ void process_client_checksum_bb(shared_ptr<ServerState>, shared_ptr<Client> c,
   constexpr size_t max_blocked = sizeof(GuildCardFileBB::blocked) / sizeof(GuildCardBB);
   switch (command) {
     case 0x01E8: { // Check guild card file checksum
-      check_size_v(data.size(), sizeof(C_GuildCardChecksum_01E8));
-      // TODO: Presumably this response tells the client whether the file needs
-      // to be downloaded at all. In the future, we could actually use the
-      // checksum to skip downloading if the file isn't modified, to save time.
-      S_GuildCardChecksumResponse_BB_02E8 cmd = {1, 0};
-      send_command_t(c, 0x02E8, 0x00000000, cmd);
+      const auto& cmd = check_size_t<C_GuildCardChecksum_01E8>(data);
+      uint32_t checksum = c->game_data.account()->guild_cards.checksum();
+      c->log.info("(Guild card file) Server checksum = %08" PRIX32 ", client checksum = %08" PRIX32,
+          checksum, cmd.checksum.load());
+      S_GuildCardChecksumResponse_BB_02E8 response = {
+          (cmd.checksum != checksum), 0};
+      send_command_t(c, 0x02E8, 0x00000000, response);
       break;
     }
     case 0x03E8: // Download guild card file
diff --git a/src/SendCommands.cc b/src/SendCommands.cc
index bf6367da..84194693 100644
--- a/src/SendCommands.cc
+++ b/src/SendCommands.cc
@@ -322,8 +322,7 @@ void send_player_preview_bb(shared_ptr<Client> c, uint8_t player_index,
 }
 
 void send_guild_card_header_bb(shared_ptr<Client> c) {
-  uint32_t checksum = crc32(
-      &c->game_data.account()->guild_cards, sizeof(GuildCardFileBB));
+  uint32_t checksum = c->game_data.account()->guild_cards.checksum();
   S_GuildCardHeader_BB_01DC cmd = {1, sizeof(GuildCardFileBB), checksum};
   send_command_t(c, 0x01DC, 0x00000000, cmd);
 }