fix(studio-server): a history lock that cannot be read fails the open instead of spinning

Author: miguel-heygen

packages/studio-server/src/history/ownerLock.ts

@@ -24,8 +24,9 @@ function ownerOf(file: string): number | null {
   try {
     const text = readFileSync(file, "utf-8");
     return /^\d+$/.test(text) ? Number(text) : Number.NaN;
-  } catch {
-    return null;
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === "ENOENT") return null;
+    throw error;
   }
 }
 
@@ -50,9 +51,8 @@ function releaseOwn(file: string): void {
 }
 
 /**
- * Removes a dead owner's lock. One evictor at a time, re-reading the owner under its own lock, so a lock a live
- * process took after the caller's check survives. False when another evictor is at it. ponytail: an evictor that
- * dies mid-eviction leaves its lock to the next one that finds it dead, unguarded.
+ * Removes a dead owner's lock under an evict lock, re-reading the owner, so a live owner's lock survives. False when
+ * another evictor holds it. ponytail: a crashed evictor's lock is cleared unguarded; racing that can give two owners.
  */
 function evictDeadOwner(file: string): boolean {
   const evictor = `${file}.evict`;

packages/studio-server/src/history/projectHistory.test.ts

@@ -235,6 +235,15 @@ describe("openProjectHistory", () => {
     );
   });
 
+  it("fails an open whose lock cannot be read, instead of retrying it forever", async () => {
+    const { history, projectDir, historyRoot } = await project({ "index.html": "v1" });
+    await history.close();
+    mkdirSync(join(historyRoot, history.projectId, "owner.pid"));
+    await expect(openProjectHistory({ projectDir, historyRoot, ownerWaitMs: 0 })).rejects.toThrow(
+      /EISDIR/,
+    );
+  });
+
   it("takes over a lock file that holds no pid", async () => {
     const { history, projectDir, historyRoot } = await project({ "index.html": "v1" });
     await history.close();