Known pubkey fallback, exclude on key collisions

php/utils/servers-rooms.php

@@ -218,6 +218,13 @@
 		 */
 		private array $room_hints = [];
 
+		/**
+		 * @var bool $merge_error
+		 * 
+		 * Flag specifying whether the server is invalidated as a result of merging.
+		 */
+		private bool $merge_error = false;
+
 		private function __construct() {}
 
 		/**
@@ -266,8 +273,10 @@
 		/**
 		 * Absorbs extra info from another instance of the same server.
 		 * @param CommunityServer $server
+		 *
+		 * @return True if successful, false in case of mistmatch.
 		 */
-		private function merge_from($server) {
+		private function merge_from($server): bool {
 			// Merge room hint information.
 			$this->room_hints = [
 				...$this->room_hints,
@@ -275,8 +284,24 @@
 			];
 
 			// Merge public key information.
-			if (!$this->has_pubkey() && $server->has_pubkey()) {
-				$this->pubkey = $server->pubkey;
+			// In case of error, set the `merge_error` flag.
+			if (!$this->set_pubkey($server->pubkey)) {
+				if ($this->merge_error) {
+					return false;
+				}
+				$base_url = $this->base_url;
+				$other_base_url = $server->base_url;
+				$pubkey_old = $this->pubkey;
+				$pubkey_new = $server->pubkey;
+				log_error(
+					"Key collision for $base_url:" .
+					"Have $pubkey_old, fetched $pubkey_new" .
+					"from server $other_base_url"
+				);
+
+				$this->merge_error = true;
+
+				return false;
 			}
 
 			// Prefer HTTPS URLs over HTTP.
@@ -288,14 +313,27 @@
 			if (filter_var($this->get_hostname(), FILTER_VALIDATE_IP)) {
 				$this->base_url = $this->get_scheme() . "://" . $server->get_hostname();
 			}
+
+			return true;
 		}
 
 		/**
-		 * Re-introduces the server to a consistent state after merging.
+		 * Re-introduces the servers to a consistent state after merging.
+		 * @param CommunityServer[] $servers
+		 * @return CommunityServer[]
 		 */
-		private function merge_consistency() {
+		private static function ensure_merge_consistency(array $servers) {
+			// Exclude servers with merge errors.
+			$servers = array_filter($servers, function(\CommunityServer $server) {
+				return !$server->merge_error;
+			});
+
 			// Remove duplicate room hints; does not require sorting.
-			$this->room_hints = array_unique($this->room_hints);
+			foreach ($servers as $server) {
+				$server->room_hints = array_unique($server->room_hints);
+			}
+
+			return $servers;
 		}
 
 		/**
@@ -336,7 +374,7 @@
 
 			CommunityServer::merge_by($servers, "get_hostname");
 
-			foreach ($servers as $server) $server->merge_consistency();
+			$servers = CommunityServer::ensure_merge_consistency($servers);
 
 			return $servers;
 		}
@@ -351,7 +389,7 @@
 
 			CommunityServer::merge_by($servers, "get_pubkey");
 
-			foreach ($servers as $server) $server->merge_consistency();
+			$servers = CommunityServer::ensure_merge_consistency($servers);
 
 			return $servers;
 		}
@@ -400,6 +438,7 @@
 			foreach ($join_urls as $join_url) {
 				$server = new CommunityServer();
 
+				// Call must succeed with no default public key.
 				$server->initialize_from_url($join_url);
 
 				$servers[] = $server;
@@ -465,8 +504,7 @@
 			// Synchronous for-loop for now.
 			foreach ($servers as $server) {
 				if (!($server->fetch_rooms())) continue;
-				// Accept failures to fetch pubkey if already known.
-				if (!$server->fetch_or_has_pubkey()) continue;
+				if (!($server->fetch_pubkey())) continue;
 				$reachable_servers[] = $server;
 			}
 
@@ -515,28 +553,44 @@
 			return $this->pubkey;
 		}
 
-		function set_pubkey($pubkey) {
+		/**
+		 * Attempts to set the server public key.
+		 * @param string $pubkey SOGS public key.
+		 * @return bool True if successful, false in case of mismatch.
+		 */
+		function set_pubkey(string $pubkey): bool {
 			if ($this->has_pubkey() && $this->pubkey != $pubkey) {
-				$base_url = $this->base_url;
-				throw new ValueError("Pubkey mismatch for $base_url");
+				return false;
 			}
 
 			$this->pubkey = $pubkey;
+
+			return true;
 		}
 
-		function set_pubkey_from_url($join_url) {
-			$url_components = parse_url($join_url);
-			parse_str($url_components['query'], $query_components);
-			$this->pubkey = $query_components['public_key'];
+		/**
+		 * Attempts to read the server public key from a join URL.
+		 * @param string $join_url Join URL for any of the server's rooms.
+		 * @return bool True if successful, false in case of mismatch.
+		 */
+		function set_pubkey_from_url(string $join_url): bool {
+			return $this->set_pubkey(url_get_pubkey($join_url));
 		}
 
 		/**
-		 * Sets base url, pubkey, and room hint from join URL.
+		 * Learns server info from a room's join URL.
+		 * The base URL and public key are saved,
+		 * and the room token is added as a fallback for room polling.
+		 * @param string $join_url Room join URL to initialize with.
+		 * @return bool True if successful, false in case of public key mismatch.
 		 */
-		function initialize_from_url($join_url) {
+		function initialize_from_url($join_url): bool {
+			if (!$this->set_pubkey_from_url($join_url)) {
+				return false;
+			}
 			$this->base_url = url_get_base($join_url);
-			$this->set_pubkey_from_url($join_url);
 			$this->room_hints[] = url_get_token($join_url);
+			return true;
 		}
 
 		/**
@@ -641,21 +695,9 @@
 		}
 
 		/**
-		 * Fetch the server's SOGS public key if absent.
-		 * @return bool True if pubkey is present or has been fetched, false otherwise.
-		 */
-		function fetch_or_has_pubkey(): bool {
-			$base_url = $this->base_url;
-			// Do not use 'or' here; I learned the hard way.
-			$result = $this->fetch_pubkey() || $this->has_pubkey();
-			if (!$result) log_warning("Failed to fetch pubkey for $base_url.");
-			return $result;
-		}
-
-		/**
-		 * Attempt to fetch own public key by parsing SOGS HTML preview.
+		 * Attempt to fetch server public key by parsing SOGS HTML preview.
 		 *
-		 * @return bool True if successful, false otherwise.
+		 * @return bool True iff no key conflict has arised and we have a pubkey.
 		 */
 		function fetch_pubkey() {
 			if (empty($this->rooms)) {
@@ -672,17 +714,29 @@
 
 			if (!$room_view) {
 				log_debug("Failed to fetch room preview from $preview_url.");
-				return false;
+				return $has_pubkey;
 			}
 
 			$links = parse_join_links($room_view);
+			$link = $links[0];
 
-			if (!isset($links[0])) {
+			if (!isset($link)) {
 				log_debug("Could not locate join link in preview at $preview_url.");
-				return false;
+				return $has_pubkey;
 			}
 
-			$this->set_pubkey_from_url($links[0]);
+			if (!$this->set_pubkey_from_url($link)) {
+				// More information needs to be logged for errors
+				// in case of lack of context due to lower verbosity.
+				$base_url = $this->base_url;
+				$pubkey_old = $this->pubkey;
+				$pubkey_new = url_get_pubkey($link);
+				log_error(
+					"Key collision for $base_url:" .
+					"Have $pubkey_old, fetched $pubkey_new from $preview_url"
+				);
+				return false;
+			}
 
 			return true;
 		}

php/utils/utils.php

@@ -189,6 +189,16 @@
 		return str_replace("/", "", $token);
 	}
 
+	/**
+	 * Extracts the server public key from a join URL.
+	 * @param string $join_url Join URL for Session Community.
+	 * @return string SOGS public key
+	 */
+	function url_get_pubkey(string $join_url) {
+		$url_components = parse_url($join_url);
+		parse_str($url_components['query'], $query_components);
+		return $query_components['public_key'];
+	}
 
 	/**
 	 * Extracts join links that match $REGEX_JOIN_LINK.