From 8c18cf4245263a25bd53ac54183ad2a6d4485014 Mon Sep 17 00:00:00 2001
From: Yat Ho <lagoho7@gmail.com>
Date: Wed, 5 Mar 2025 08:42:26 +0800
Subject: [PATCH] fix: use message id to check for pex and metadata xfer
 support (#7177)

* refactor: use metadata id to check for ut metadata support

* refactor: use pex id to check for ut pex support

* refactor: start pex timer after ltep handshake

* refactor: harden metadata xfer sanity checks

* code review: constexpr

* code review: don't save peer ut_pex_id and ut_metadata_id if on private torrent
---
 libtransmission/peer-msgs.cc | 49 ++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 24 deletions(-)

diff --git a/libtransmission/peer-msgs.cc b/libtransmission/peer-msgs.cc
index be6f5fbc4..58ebbc5ea 100644
--- a/libtransmission/peer-msgs.cc
+++ b/libtransmission/peer-msgs.cc
@@ -308,12 +308,6 @@ public:
         , callback_{ callback }
         , callback_data_{ callback_data }
     {
-        if (tor_.allows_pex())
-        {
-            pex_timer_ = session->timerMaker().create([this]() { send_ut_pex(); });
-            pex_timer_->start_repeating(SendPexInterval);
-        }
-
         if (io_->supports_ltep())
         {
             send_ltep_handshake();
@@ -591,6 +585,11 @@ private:
 
     // ---
 
+    [[nodiscard]] constexpr bool can_xfer_metadata() const noexcept
+    {
+        return tor_.is_public() && ut_metadata_id_ != 0U;
+    }
+
     [[nodiscard]] std::optional<int64_t> pop_next_metadata_request()
     {
         auto& reqs = peer_requested_metadata_pieces_;
@@ -618,6 +617,12 @@ private:
     void parse_ut_pex(MessageReader& payload);
     void parse_ltep(MessageReader& payload);
 
+    [[nodiscard]] constexpr bool can_send_ut_pex() const noexcept
+    {
+        // only send pex if both the torrent and peer support it
+        return tor_.allows_pex() && ut_pex_id_ != 0U;
+    }
+
     void send_ut_pex();
 
     int client_got_block(std::unique_ptr<Cache::BlockData> block_data, tr_block_index_t block);
@@ -689,8 +694,6 @@ private:
 
     // ---
 
-    bool peer_supports_pex_ = false;
-    bool peer_supports_metadata_xfer_ = false;
     bool client_sent_ltep_handshake_ = false;
 
     size_t desired_request_count_ = 0;
@@ -933,19 +936,19 @@ void tr_peerMsgsImpl::parse_ltep(MessageReader& payload)
         // in the reserved bytes of the BT handshake.
         send_ltep_handshake();
 
-        if (io_->supports_ltep())
+        if (can_send_ut_pex())
         {
+            pex_timer_ = session->timerMaker().create([this]() { send_ut_pex(); });
+            pex_timer_->start_repeating(SendPexInterval);
             send_ut_pex();
         }
     }
     else if (ltep_msgid == UT_PEX_ID)
     {
-        peer_supports_pex_ = true;
         parse_ut_pex(payload);
     }
     else if (ltep_msgid == UT_METADATA_ID)
     {
-        peer_supports_metadata_xfer_ = true;
         parse_ut_metadata(payload);
     }
     else
@@ -1005,8 +1008,7 @@ void tr_peerMsgsImpl::parse_ut_pex(MessageReader& payload)
 
 void tr_peerMsgsImpl::send_ut_pex()
 {
-    // only send pex if both the torrent and peer support it
-    if (!peer_supports_pex_ || !tor_.allows_pex())
+    if (!can_send_ut_pex())
     {
         return;
     }
@@ -1232,22 +1234,20 @@ void tr_peerMsgsImpl::parse_ltep_handshake(MessageReader& payload)
     }
 
     // check supported messages for utorrent pex
-    peer_supports_pex_ = false;
-    peer_supports_metadata_xfer_ = false;
     auto holepunch_supported = false;
 
     if (tr_variant* sub = nullptr; tr_variantDictFindDict(&*var, TR_KEY_m, &sub))
     {
-        if (auto ut_pex = int64_t{}; tr_variantDictFindInt(sub, TR_KEY_ut_pex, &ut_pex))
+        auto const tor_is_public = tor_.is_public();
+
+        if (auto ut_pex = int64_t{}; tor_is_public && tr_variantDictFindInt(sub, TR_KEY_ut_pex, &ut_pex))
         {
-            peer_supports_pex_ = ut_pex != 0;
             ut_pex_id_ = static_cast<uint8_t>(ut_pex);
             logtrace(this, fmt::format("msgs->ut_pex is {:d}", ut_pex_id_));
         }
 
-        if (auto ut_metadata = int64_t{}; tr_variantDictFindInt(sub, TR_KEY_ut_metadata, &ut_metadata))
+        if (auto ut_metadata = int64_t{}; tor_is_public && tr_variantDictFindInt(sub, TR_KEY_ut_metadata, &ut_metadata))
         {
-            peer_supports_metadata_xfer_ = ut_metadata != 0;
             ut_metadata_id_ = static_cast<uint8_t>(ut_metadata);
             logtrace(this, fmt::format("msgs->ut_metadata_id_ is {:d}", ut_metadata_id_));
         }
@@ -1271,11 +1271,11 @@ void tr_peerMsgsImpl::parse_ltep_handshake(MessageReader& payload)
 
     // look for metainfo size (BEP 9)
     if (auto metadata_size = int64_t{};
-        peer_supports_metadata_xfer_ && tr_variantDictFindInt(&*var, TR_KEY_metadata_size, &metadata_size))
+        can_xfer_metadata() && tr_variantDictFindInt(&*var, TR_KEY_metadata_size, &metadata_size))
     {
         if (!tr_metadata_download::is_valid_metadata_size(metadata_size))
         {
-            peer_supports_metadata_xfer_ = false;
+            ut_metadata_id_ = 0U;
         }
         else
         {
@@ -1366,9 +1366,10 @@ void tr_peerMsgsImpl::parse_ut_metadata(MessageReader& payload_in)
 
     if (msg_type == MetadataMsgType::Request)
     {
-        if (piece >= 0 && tor_.has_metainfo() && tor_.is_public() && std::size(peer_requested_metadata_pieces_) < MetadataReqQ)
+        auto& reqs = peer_requested_metadata_pieces_;
+        if (piece >= 0 && tor_.has_metainfo() && can_xfer_metadata() && std::size(reqs) < MetadataReqQ)
         {
-            peer_requested_metadata_pieces_.push(piece);
+            reqs.push(piece);
         }
         else
         {
@@ -1845,7 +1846,7 @@ void tr_peerMsgsImpl::pulse()
 
 void tr_peerMsgsImpl::maybe_send_metadata_requests(time_t now) const
 {
-    if (!peer_supports_metadata_xfer_)
+    if (!can_xfer_metadata())
     {
         return;
     }