fix: conflicts

Signed-off-by: Luka Trovic <luka@nextcloud.com>

lib/Service/DocumentService.php

@@ -36,6 +36,7 @@
 use OCA\Text\Db\StepMapper;
 use OCA\Text\Exception\DocumentHasUnsavedChangesException;
 use OCA\Text\Exception\DocumentSaveConflictException;
+use OCA\Text\YjsMessage;
 use OCP\AppFramework\Db\DoesNotExistException;
 use OCP\Constants;
 use OCP\DB\Exception;
@@ -230,11 +231,16 @@ public function writeDocumentState(int $documentId, string $content): void {
 	public function addStep(Document $document, Session $session, $steps, $version, $shareToken): array {
 		$sessionId = $session->getId();
 		$documentId = $session->getDocumentId();
+		$readOnly = $this->isReadOnly($this->getFileForSession($session, $shareToken), $shareToken);
 		$stepsToInsert = [];
 		$querySteps = [];
 		$getStepsSinceVersion = null;
 		$newVersion = $version;
 		foreach ($steps as $step) {
+      $message = YjsMessage::fromBase64($step);
+			if ($readOnly && $message->isUpdate()) {
+				continue;
+			}
 			// Steps are base64 encoded messages of the yjs protocols
 			// https://github.com/yjs/y-protocols
 			// Base64 encoded values smaller than "AAE" belong to sync step 1 messages.
@@ -245,8 +251,8 @@ public function addStep(Document $document, Session $session, $steps, $version,
 				array_push($stepsToInsert, $step);
 			}
 		}
-		if (sizeof($stepsToInsert) > 0) {
-			if ($this->isReadOnly($this->getFileForSession($session, $shareToken), $shareToken)) {
+		if (count($stepsToInsert) > 0) {
+			if ($readOnly) {
 				throw new NotPermittedException('Read-only client tries to push steps with changes');
 			}
 			$newVersion = $this->insertSteps($document, $session, $stepsToInsert, $version);

lib/YjsMessage.php

@@ -0,0 +1,98 @@
+<?php
+
+namespace OCA\Text;
+
+use InvalidArgumentException;
+
+/**
+ * Steps are base64 encoded messages of the yjs protocols
+ * https://github.com/yjs/y-protocols
+ *
+ * This class is a simple representation of a message containing some methods
+ * to decode parts of it for what we need on the backend
+ *
+ * Relevant resources:
+ * https://github.com/yjs/y-protocols/blob/master/PROTOCOL.md
+ * https://github.com/yjs/y-websocket/blob/master/src/y-websocket.js#L19-L22
+ * https://github.com/yjs/y-protocols/blob/master/sync.js#L38-L40
+ * https://github.com/dmonad/lib0/blob/master/decoding.js
+ */
+class YjsMessage {
+
+	public const YJS_MESSAGE_SYNC = 0;
+	public const YJS_MESSAGE_AWARENESS = 1;
+	public const YJS_MESSAGE_AWARENESS_QUERY = 3;
+
+	public const YJS_MESSAGE_SYNC_STEP1 = 0;
+	public const YJS_MESSAGE_SYNC_STEP2 = 1;
+	public const YJS_MESSAGE_SYNC_UPDATE = 2;
+
+	private int $pos = 0;
+
+	public function __construct(
+		private string $data = ''
+	) {
+	}
+
+	public static function fromBase64(string $data = ''): self {
+		return new self(base64_decode($data));
+	}
+
+	/**
+	 * https://github.com/dmonad/lib0/blob/bd69ab4dc701d77e808f2bab08d96d63acd297da/decoding.js#L242
+	 */
+	public function readVarUint(): int {
+		$bytes = array_values(unpack('C*', $this->data));
+		$num = 0;
+		$mult = 1;
+		$len = count($bytes);
+		while ($this->pos < $len) {
+			$r = $bytes[$this->pos++];
+			// num = num | ((r & binary.BITS7) << len)
+			$num = $num + ($r & 0b1111111) * $mult;
+			$mult *= 128;
+			if ($r <= 0b1111111) {
+				return $num;
+			}
+			// Number.MAX_SAFE_INTEGER in JS
+			if ($num > 9007199254740990) {
+				throw new \OutOfBoundsException();
+			}
+		}
+		throw new InvalidArgumentException();
+	}
+
+	public function getYjsMessageType(): int {
+		$oldPos = $this->pos;
+		$this->pos = 0;
+		$messageType = $this->readVarUint();
+		$this->pos = $oldPos;
+		return $messageType;
+	}
+
+	public function getYjsSyncType(): int {
+		$oldPos = $this->pos;
+		$this->pos = 0;
+		$messageType = $this->readVarUint();
+		if ($messageType !== self::YJS_MESSAGE_SYNC) {
+			throw new \ValueError('Message is not a sync message');
+		}
+		$syncType = $this->readVarUint();
+		$this->pos = $oldPos;
+		return $syncType;
+	}
+
+	/**
+	 * Based on https://github.com/yjs/y-protocols/blob/master/PROTOCOL.md#handling-read-only-users
+	 */
+	public function isUpdate(): bool {
+		if ($this->getYjsMessageType() === self::YJS_MESSAGE_SYNC) {
+			if (in_array($this->getYjsSyncType(), [self::YJS_MESSAGE_SYNC_STEP2, self::YJS_MESSAGE_SYNC_UPDATE])) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+}