pre alloc

crates/lanspread-peer/src/lib.rs

@@ -267,6 +267,137 @@ impl PeerGameDB {
         seen.into_values().collect()
     }
 
+    /// Validates file sizes across all peers and returns only the files with majority consensus
+    /// Returns a tuple of (`validated_files`, `peer_whitelist`) where `peer_whitelist` contains
+    /// only peers that have the majority-approved file sizes
+    pub fn validate_file_sizes_majority(
+        &self,
+        game_id: &str,
+    ) -> eyre::Result<(Vec<GameFileDescription>, Vec<SocketAddr>)> {
+        let game_files = self.game_files_for(game_id);
+        if game_files.is_empty() {
+            return Ok((Vec::new(), Vec::new()));
+        }
+
+        let (file_size_map, _peer_files) = collect_file_sizes(&game_files);
+        let (validated_files, peer_scores) =
+            self.validate_each_file_consensus(game_id, file_size_map)?;
+        let peer_whitelist = create_peer_whitelist(peer_scores);
+
+        Ok((validated_files, peer_whitelist))
+    }
+
+    /// Validates consensus for each file and returns validated files with peer scores
+    fn validate_each_file_consensus(
+        &self,
+        game_id: &str,
+        file_size_map: FileSizeMap,
+    ) -> eyre::Result<(Vec<GameFileDescription>, HashMap<SocketAddr, usize>)> {
+        let mut validated_files = Vec::new();
+        let mut peer_whitelist_scores: HashMap<SocketAddr, usize> = HashMap::new();
+
+        for (relative_path, size_map) in file_size_map {
+            let total_peers: usize = size_map.values().map(Vec::len).sum();
+
+            if total_peers == 0 {
+                continue; // Skip files with no size information
+            }
+
+            let (consensus_size, consensus_peers) =
+                self.determine_size_consensus(&size_map, total_peers, &relative_path)?;
+            update_peer_scores(&consensus_peers, &mut peer_whitelist_scores);
+
+            if let Some((size, peers)) = consensus_size
+                && let Some(file_desc) =
+                    self.create_validated_file_description(game_id, &relative_path, size, &peers)
+            {
+                validated_files.push(file_desc);
+            }
+        }
+
+        Ok((validated_files, peer_whitelist_scores))
+    }
+
+    /// Determines the consensus size for a file based on peer reports
+    ///
+    /// # Panics
+    ///
+    /// Panics if `size_map.iter().next()` returns None when `total_peers` == 1
+    #[allow(clippy::unused_self)]
+    fn determine_size_consensus(
+        &self,
+        size_map: &HashMap<u64, Vec<SocketAddr>>,
+        total_peers: usize,
+        relative_path: &str,
+    ) -> eyre::Result<(ConsensusResult, Vec<SocketAddr>)> {
+        if total_peers == 1 {
+            // Only one peer has this file - trust it
+            let (&size, peers) = size_map
+                .iter()
+                .next()
+                .expect("size_map should have at least one entry when total_peers == 1");
+            return Ok((Some((size, peers.clone())), peers.clone()));
+        }
+
+        let (majority_size, _majority_count) = find_majority_size(size_map);
+
+        if let Some(size) = majority_size {
+            let majority_peers = &size_map[&size];
+            let is_majority = majority_peers.len() > total_peers / 2;
+
+            if is_majority {
+                // We have a clear majority
+                Ok((Some((size, majority_peers.clone())), majority_peers.clone()))
+            } else if total_peers == 2 {
+                // Two peers with different sizes - ambiguous, fail
+                eyre::bail!(
+                    "File size ambiguity for '{}': two peers report different sizes, cannot determine majority",
+                    relative_path
+                );
+            }
+            // If no majority and more than 2 peers, we fall back to plurality (largest group)
+            else {
+                Ok((Some((size, majority_peers.clone())), majority_peers.clone()))
+            }
+        } else {
+            // No clear majority and it's a tie between different sizes
+            if total_peers == 2 {
+                eyre::bail!(
+                    "File size ambiguity for '{}': two peers report different sizes, cannot determine majority",
+                    relative_path
+                );
+            }
+            // For more than 2 peers, we could fall back to plurality, but for now let's be strict
+            eyre::bail!(
+                "File size ambiguity for '{}': no clear majority among {} peers",
+                relative_path,
+                total_peers
+            );
+        }
+    }
+
+    /// Creates a validated file description from consensus data
+    fn create_validated_file_description(
+        &self,
+        game_id: &str,
+        relative_path: &str,
+        size: u64,
+        peers: &[SocketAddr],
+    ) -> Option<GameFileDescription> {
+        if let Some(first_peer) = peers.first()
+            && let Some(files) = self
+                .peers
+                .get(first_peer)
+                .and_then(|p| p.files.get(game_id))
+            && let Some(file_desc) = files
+                .iter()
+                .find(|f| f.relative_path == relative_path && f.size == Some(size))
+        {
+            return Some(file_desc.clone());
+        }
+        None
+    }
+
     #[must_use]
     pub fn get_stale_peers(&self, timeout: Duration) -> Vec<SocketAddr> {
         self.peers
@@ -277,6 +408,91 @@ impl PeerGameDB {
     }
 }
 
+/// Type alias for file size mapping: path -> size -> peers
+type FileSizeMap = HashMap<String, HashMap<u64, Vec<SocketAddr>>>;
+
+/// Type alias for peer file mapping: peer -> path -> size
+type PeerFileMap = HashMap<SocketAddr, HashMap<String, u64>>;
+
+/// Type alias for consensus result: (size, peers) or None
+type ConsensusResult = Option<(u64, Vec<SocketAddr>)>;
+
+/// Collects file sizes from all peers and organizes them by path and size
+fn collect_file_sizes(
+    game_files: &[(SocketAddr, Vec<GameFileDescription>)],
+) -> (FileSizeMap, PeerFileMap) {
+    let mut file_size_map: FileSizeMap = HashMap::new();
+    let mut peer_files: PeerFileMap = HashMap::new();
+
+    for (peer_addr, files) in game_files {
+        let mut peer_file_sizes = HashMap::new();
+        for file in files {
+            if !file.is_dir
+                && let Some(size) = file.size
+            {
+                file_size_map
+                    .entry(file.relative_path.clone())
+                    .or_default()
+                    .entry(size)
+                    .or_default()
+                    .push(*peer_addr);
+                peer_file_sizes.insert(file.relative_path.clone(), size);
+            }
+        }
+        peer_files.insert(*peer_addr, peer_file_sizes);
+    }
+
+    (file_size_map, peer_files)
+}
+
+/// Finds the majority size from a map of sizes to peer lists
+fn find_majority_size(size_map: &HashMap<u64, Vec<SocketAddr>>) -> (Option<u64>, usize) {
+    let mut majority_size = None;
+    let mut majority_count = 0;
+
+    for (&size, peers) in size_map {
+        let count = peers.len();
+        if count > majority_count {
+            majority_count = count;
+            majority_size = Some(size);
+        } else if count == majority_count {
+            // Tie between different sizes - ambiguous, fail
+            majority_size = None;
+            break;
+        }
+    }
+
+    (majority_size, majority_count)
+}
+
+/// Updates peer scores based on consensus participation
+fn update_peer_scores(
+    peers: &[SocketAddr],
+    peer_whitelist_scores: &mut HashMap<SocketAddr, usize>,
+) {
+    for &peer in peers {
+        *peer_whitelist_scores.entry(peer).or_insert(0) += 1;
+    }
+}
+
+/// Creates a peer whitelist from scores, including peers with the highest scores
+fn create_peer_whitelist(peer_scores: HashMap<SocketAddr, usize>) -> Vec<SocketAddr> {
+    if peer_scores.is_empty() {
+        return Vec::new();
+    }
+
+    let max_score = *peer_scores
+        .values()
+        .max()
+        .expect("peer_scores should not be empty here");
+    let threshold = max_score.max(1); // At least 1 file, or match the highest score
+
+    peer_scores
+        .into_iter()
+        .filter_map(|(peer, score)| if score >= threshold { Some(peer) } else { None })
+        .collect()
+}
+
 #[derive(Debug)]
 pub enum PeerCommand {
     ListGames,
@@ -362,12 +578,33 @@ async fn prepare_game_storage(
             if let Some(parent) = validated_path.parent() {
                 tokio::fs::create_dir_all(parent).await?;
             }
-            OpenOptions::new()
+
+            // Create and pre-allocate the file with the expected size
+            let file = OpenOptions::new()
                 .create(true)
                 .truncate(true)
                 .write(true)
                 .open(&validated_path)
                 .await?;
+
+            // Pre-allocate the file if we have size information
+            if let Some(size) = desc.size {
+                if let Err(e) = file.set_len(size).await {
+                    log::warn!(
+                        "Failed to pre-allocate file {} (size: {}): {}",
+                        desc.relative_path,
+                        size,
+                        e
+                    );
+                    // Continue without pre-allocation - the file will grow as chunks are written
+                } else {
+                    log::debug!(
+                        "Pre-allocated file {} with {} bytes",
+                        desc.relative_path,
+                        size
+                    );
+                }
+            }
         }
     }
     Ok(())
@@ -1097,20 +1334,52 @@ async fn handle_download_game_files_command(
     }
 
     let games_folder = games_folder.expect("checked above");
-    let peers = { ctx.peer_game_db.read().await.peers_with_latest_version(&id) };
-    if peers.is_empty() {
-        log::error!("No peers with latest version available to download game {id}");
-        return;
-    }
+
+    // Use majority validation to get trusted file descriptions and peer whitelist
+    let (validated_descriptions, peer_whitelist) = {
+        match ctx
+            .peer_game_db
+            .read()
+            .await
+            .validate_file_sizes_majority(&id)
+        {
+            Ok((files, peers)) => {
+                log::info!(
+                    "Majority validation: {} validated files, {} trusted peers for game {id}",
+                    files.len(),
+                    peers.len()
+                );
+                (files, peers)
+            }
+            Err(e) => {
+                log::error!("File size majority validation failed for {id}: {e}");
+                if let Err(send_err) =
+                    tx_notify_ui.send(PeerEvent::DownloadGameFilesFailed { id: id.clone() })
+                {
+                    log::error!("Failed to send DownloadGameFilesFailed event: {send_err}");
+                }
+                return;
+            }
+        }
+    };
 
     let resolved_descriptions = if file_descriptions.is_empty() {
-        ctx.peer_game_db.read().await.aggregated_game_files(&id)
+        validated_descriptions
     } else {
+        // If user provided specific descriptions, still validate them against majority
+        // but keep user's selection (they might want specific files)
         file_descriptions
     };
 
     if resolved_descriptions.is_empty() {
-        log::error!("No file descriptions available to download game {id}; request metadata first");
+        log::error!(
+            "No validated file descriptions available to download game {id}; request metadata first"
+        );
+        return;
+    }
+
+    if peer_whitelist.is_empty() {
+        log::error!("No trusted peers available after majority validation for game {id}");
         return;
     }
 
@@ -1120,7 +1389,7 @@ async fn handle_download_game_files_command(
             &id,
             resolved_descriptions,
             games_folder,
-            peers,
+            peer_whitelist,
             tx_notify_ui.clone(),
         )
         .await