Project516 · Nov 4, 2026 · Nov 4, 2026 · Nov 4, 2026
diff --git a/src/natives/io.ts b/src/natives/io.ts
@@ -169,7 +169,9 @@ export function openFile(t: JThread, path: string, write: boolean, truncate: boo
   let data: Uint8Array;
   if (!st) {
     if (!write) notFound(path);
-    if (!fs.write(abs, new Uint8Array(0))) notFound(path, fs.writable(abs) ? "No such file or directory" : "Read-only file system");
+    if (!fs.write(abs, new Uint8Array(0))) {
+      notFound(path, ERRNO[fs.writeError(abs) ?? ""] ?? (fs.writable(abs) ? "No such file or directory" : "Read-only file system"));
+    }
     data = new Uint8Array(0);
   } else {
     if (write && !fs.writable(abs)) notFound(path, "Read-only file system");
@@ -224,7 +226,8 @@ export function flush(t: JThread, f: OpenFile): boolean {
 const ERRNO: Record<string, string> = {
   ENOSPC: "No space left on device", EFBIG: "File too large", EDQUOT: "Disk quota exceeded",
   EACCES: "Permission denied", EPERM: "Operation not permitted", EROFS: "Read-only file system",
-  ENOENT: "No such file or directory",
+  ENOENT: "No such file or directory", ENAMETOOLONG: "File name too long", ENOTDIR: "Not a directory",
+  EIO: "Input/output error", ELOOP: "Too many levels of symbolic links",
 };
 
 // Where Java learns of a write that failed: HotSpot reports it from write(),

diff --git a/src/natives/nio.ts b/src/natives/nio.ts
@@ -12,21 +12,23 @@ import type { Natives } from "./util.ts";
 
 export const EPERM = 1, ENOENT = 2, EINTR = 4, EIO = 5, EBADF = 9, ENOMEM = 12, EACCES = 13,
   EEXIST = 17, EXDEV = 18, ENOTDIR = 20, EISDIR = 21, EINVAL = 22, ENOSPC = 28, EROFS = 30,
-  ENOTEMPTY = 39, ENOSYS = 38, ELOOP = 40, ENOTSUP = 95, ESTALE = 116;
+  ENOTEMPTY = 39, ENOSYS = 38, ENAMETOOLONG = 36, ELOOP = 40, ENOTSUP = 95, ESTALE = 116, EDQUOT = 122;
 
 const MESSAGES: Record<number, string> = {
   [EPERM]: "Operation not permitted", [EINTR]: "Interrupted system call", [EIO]: "Input/output error",
   [ENOMEM]: "Cannot allocate memory", [ENOSPC]: "No space left on device",
   [ELOOP]: "Too many levels of symbolic links", [ENOTSUP]: "Operation not supported", [ESTALE]: "Stale file handle",
+  [ENAMETOOLONG]: "File name too long", [EDQUOT]: "Disk quota exceeded",
   [ENOENT]: "No such file or directory", [EBADF]: "Bad file descriptor", [EACCES]: "Permission denied",
   [EEXIST]: "File exists", [EXDEV]: "Invalid cross-device link", [ENOTDIR]: "Not a directory",
   [EISDIR]: "Is a directory", [EINVAL]: "Invalid argument", [EROFS]: "Read-only file system",
   [ENOTEMPTY]: "Directory not empty", [ENOSYS]: "Function not implemented",
 };
 
-const CHMOD_ERRNO: Record<string, number> = {
+// errno numbers of the host errors Node reports by name
+const HOST_ERRNO: Record<string, number> = {
   EPERM, ENOENT, EINTR, EIO, EBADF, ENOMEM, EACCES, ENOTDIR, EINVAL, ENOSPC, EROFS, ELOOP,
-  ENOTSUP, EOPNOTSUPP: ENOTSUP, ESTALE,
+  ENOTSUP, EOPNOTSUPP: ENOTSUP, ESTALE, ENAMETOOLONG, EDQUOT,
 };
 
 // Linux open(2) flags
@@ -66,7 +68,7 @@ function chmod(t: JThread, p: string, mode: number) {
     if (!fs.stat(p)) unixError(ENOENT);
     unixError(EROFS);
   }
-  unixError(CHMOD_ERRNO[fs.chmodError(p) ?? "EIO"] ?? EIO);
+  unixError(HOST_ERRNO[fs.chmodError(p) ?? "EIO"] ?? EIO);
 }
 
 function fillAttrs(t: JThread, attrs: JObject, p: string): number {
@@ -148,7 +150,11 @@ export const natives: Natives = {
       fileOf(t, fd).ino = fileInode(t, abs);
       return fd;
     } catch (e) {
-      if (e instanceof PendingThrow) unixError(t.vm.fs.writable(abs) ? ENOENT : EROFS);
+      if (e instanceof PendingThrow) {
+        // a new file the host would not create: its reason
+        const host = st ? undefined : HOST_ERRNO[t.vm.fs.writeError(abs) ?? ""];
+        unixError(host ?? (t.vm.fs.writable(abs) ? ENOENT : EROFS));
+      }
       throw e;
     }
   },

diff --git a/src/node.ts b/src/node.ts
@@ -80,19 +80,20 @@ export class NodeBackend implements Backend {
     if (!this.writable) this.lists.set(p, names);
     return names;
   }
-  private writeErrors = new Map<string, string>();
+  // the host's reason for the last failed write, read right after it
+  private writeFailure: [string, string] | null = null;
   write(p: string, data: Uint8Array) {
     try {
       fs.writeFileSync(this.host(p), data);
-      this.writeErrors.delete(p);
+      this.writeFailure = null;
       return true;
     } catch (e) {
-      this.writeErrors.set(p, (e as NodeJS.ErrnoException).code ?? "EIO");
+      this.writeFailure = [p, (e as NodeJS.ErrnoException).code ?? "EIO"];
       return false;
     }
   }
   writeError(p: string) {
-    return this.writeErrors.get(p);
+    return this.writeFailure?.[0] === p ? this.writeFailure[1] : undefined;
   }
   denied(p: string) {
     const host = this.host(p);
@@ -103,19 +104,19 @@ export class NodeBackend implements Backend {
       return (e as NodeJS.ErrnoException).code === "EACCES" || (e as NodeJS.ErrnoException).code === "EPERM";
     }
   }
-  private chmodErrors = new Map<string, string>();
+  private chmodFailure: [string, string] | null = null;
   chmod(p: string, f: (mode: number) => number) {
     try {
       fs.chmodSync(this.host(p), f(fs.statSync(this.host(p)).mode & 0o7777));
-      this.chmodErrors.delete(p);
+      this.chmodFailure = null;
       return true;
     } catch (e) {
-      this.chmodErrors.set(p, (e as NodeJS.ErrnoException).code ?? "EIO");
+      this.chmodFailure = [p, (e as NodeJS.ErrnoException).code ?? "EIO"];
       return false;
     }
   }
   chmodError(p: string) {
-    return this.chmodErrors.get(p);
+    return this.chmodFailure?.[0] === p ? this.chmodFailure[1] : undefined;
   }
   access(p: string, mode: number) {
     try {

diff --git a/test/java/CreateRefused.java b/test/java/CreateRefused.java
@@ -0,0 +1,26 @@
+import java.io.*;
+import java.nio.file.*;
+
+// Creating a file the host refuses reports the host's reason, as HotSpot does.
+public class CreateRefused {
+  public static void main(String[] args) throws Exception {
+    String name = Path.of(System.getProperty("java.io.tmpdir"), "x".repeat(300)).toString();
+    try (var out = new FileOutputStream(name)) {
+      System.out.println("created");
+    } catch (IOException e) {
+      System.out.println(e.getClass().getName() + ": " + e.getMessage().replace(name, "<tmp>/<long>"));
+    }
+    try {
+      Files.createFile(Path.of(name));
+      System.out.println("created");
+    } catch (IOException e) {
+      System.out.println(e.getClass().getName() + ": " + e.getMessage().replace(name, "<tmp>/<long>"));
+    }
+    try {
+      Files.newOutputStream(Path.of(name)).close();
+      System.out.println("created");
+    } catch (IOException e) {
+      System.out.println(e.getClass().getName() + ": " + e.getMessage().replace(name, "<tmp>/<long>"));
+    }
+  }
+}