Start child processes under Node

README.md

@@ -45,7 +45,8 @@ See [docs/node.md](docs/node.md).
   `BufferedImage`, with HotSpot's pixels except for text.
 - Sockets: real ones under Node; in the browser, loopback inside the VM and
   `http:`/`https:` through `fetch`.
-- Not yet: AWT and Swing windows, child processes, IPv6.
+- Child processes under Node, through the host's own programs.
+- Not yet: AWT and Swing windows, child processes in the browser, IPv6.
 
 Details: [docs/support.md](docs/support.md).
 

docs/support.md

@@ -12,8 +12,13 @@ java-web targets headless Java: console apps, libraries and javac.
 - `Deflater` writes valid DEFLATE streams using stored blocks. Compression
   levels and strategies currently do not reduce output size; compressed bytes
   and compression ratios differ from HotSpot's zlib output.
+- Child processes (`ProcessBuilder`, `Runtime.exec`, `ProcessHandle`) work
+  under Node and run the host's programs. Starting `java` starts another
+  java-web VM on the same image. A child cannot use a directory that exists only
+  in the VM, such as `/jdk`, as its working directory. `ProcessHandle` reads
+  other processes from Linux's `/proc`; elsewhere it sees only its own children.
 - Not supported: GUI apps (AWT and Swing windows), `ConvolveOp`, child
-  processes, and native libraries other than JS natives.
+  processes in the browser, and native libraries other than JS natives.
 
 ## Locales
 

src/natives/io.ts

@@ -9,6 +9,29 @@ import { closeSockFd } from "../sockets.ts";
 import { nonNull, u8 } from "./util.ts";
 import type { Natives } from "./util.ts";
 
+export interface ProcessPipe {
+  read(dst: Uint8Array, off: number, len: number): Promise<number>;
+  write(bytes: Uint8Array): Promise<string | null>;
+  available(): number;
+  close(): void;
+}
+
+function pipes(t: JThread): Map<number, ProcessPipe> {
+  let map = t.vm.state.get("processPipes") as Map<number, ProcessPipe> | undefined;
+  if (!map) t.vm.state.set("processPipes", (map = new Map()));
+  return map;
+}
+
+export function addProcessPipe(t: JThread, pipe: ProcessPipe): number {
+  const fd = newFd(t);
+  pipes(t).set(fd, pipe);
+  return fd;
+}
+
+export function processPipe(t: JThread, fd: number): ProcessPipe | undefined {
+  return (t.vm.state.get("processPipes") as Map<number, ProcessPipe> | undefined)?.get(fd);
+}
+
 // A file's bytes, shared by every descriptor open on it, as an inode is.
 interface Contents {
   data: Uint8Array;
@@ -20,6 +43,7 @@ export class OpenFile {
   // "" once the file is unlinked: it lives until closed, but no path reaches it
   path: string;
   pos = 0;
+  append = false;
   writable: boolean;
   contents: Contents;
   ino?: number;
@@ -181,7 +205,7 @@ export function openFile(t: JThread, path: string, write: boolean, truncate: boo
   }
   const f = new OpenFile(abs, data, write, shared);
   if (truncate && st) f.setLength(0);
-  if (append) f.pos = f.size;
+  if (append) { f.pos = f.size; f.append = true; }
   const tab = table(t);
   const fd = tab.next++;
   tab.files.set(fd, f);
@@ -246,6 +270,12 @@ export function newFd(t: JThread): number {
 
 export function closeFd(t: JThread, fd: number) {
   if (closeSockFd(t.vm.state, t.vm.net, fd)) return;
+  const pipe = processPipe(t, fd);
+  if (pipe) {
+    pipes(t).delete(fd);
+    pipe.close();
+    return;
+  }
   const tab = table(t);
   const f = tab.files.get(fd);
   if (f) {
@@ -310,9 +340,19 @@ function setFd(t: JThread, stream: JObject, owner: string, fd: number) {
   t.vm.setField(fdObj, "java/io/FileDescriptor", "fd", fd);
 }
 
+function* readProcessPipe(t: JThread, pipe: ProcessPipe, dst: Uint8Array, off: number, len: number): NativeGen {
+  return yield t.block(pipe.read(dst, off, len));
+}
+
+function* writeProcessPipe(t: JThread, pipe: ProcessPipe, bytes: Uint8Array): NativeGen {
+  const error: string | null = yield t.block(pipe.write(bytes));
+  if (error) throw new PendingThrow("java/io/IOException", error);
+}
+
 function writeOut(t: JThread, fd: number, bytes: Uint8Array) {
   if (fd === 1) t.vm.opts.stdout(bytes.slice());
   else if (fd === 2) t.vm.opts.stderr(bytes.slice());
+  else if (processPipe(t, fd)) return writeProcessPipe(t, processPipe(t, fd)!, bytes);
   else {
     const f = fileOf(t, fd);
     if (!f.writable) throw new PendingThrow("java/io/IOException", "Bad file descriptor");
@@ -448,7 +488,7 @@ export const natives: Natives = {
   [`${FOS}.writeBytes([BIIZ)V`]: (t, [self, b, off, len]) => {
     const a = nonNull<JArray>(b);
     if (off < 0 || len < 0 || off + len > a.a.length) throw new PendingThrow("java/lang/IndexOutOfBoundsException");
-    writeOut(t, fdOf(t, self, FOS), u8(a, off, len));
+    return writeOut(t, fdOf(t, self, FOS), u8(a, off, len));
   },
   [`${FOS}.write(IZ)V`]: (t, [self, b]) => writeOut(t, fdOf(t, self, FOS), Uint8Array.of(b & 0xff)),
 
@@ -459,12 +499,15 @@ export const natives: Natives = {
     if (len === 0) return 0;
     const fd = fdOf(t, self, FIS);
     if (fd === 0) return readStdin(t, u8(a), off, len);
+    const pipe = processPipe(t, fd);
+    if (pipe) return readProcessPipe(t, pipe, u8(a), off, len);
     return fileOf(t, fd).read(u8(a), off, len);
   },
   [`${FIS}.read0()I`]: function* (t, [self]): NativeGen {
     const fd = fdOf(t, self, FIS);
     const one = new Uint8Array(1);
-    const n = fd === 0 ? yield* readStdin(t, one, 0, 1) : fileOf(t, fd).read(one, 0, 1);
+    const pipe = processPipe(t, fd);
+    const n = fd === 0 ? yield* readStdin(t, one, 0, 1) : pipe ? yield t.block(pipe.read(one, 0, 1)) : fileOf(t, fd).read(one, 0, 1);
     return n <= 0 ? -1 : one[0];
   },
   [`${FIS}.length0()J`]: (t, [self]) => BigInt(fileOf(t, fdOf(t, self, FIS)).size),
@@ -479,10 +522,12 @@ export const natives: Natives = {
   [`${FIS}.available0()I`]: (t, [self]) => {
     const fd = fdOf(t, self, FIS);
     if (fd === 0) return (t.vm.state.get("stdin") as Stdin | undefined)?.buf.length ?? 0;
+    const pipe = processPipe(t, fd);
+    if (pipe) return pipe.available();
     const f = fileOf(t, fd);
     return Math.min(Math.max(0, f.size - f.pos), 0x7fffffff);
   },
-  [`${FIS}.isRegularFile0(Ljava/io/FileDescriptor;)Z`]: (t, [, fdObj]) => t.vm.getField(fdObj, "java/io/FileDescriptor", "fd") > 2,
+  [`${FIS}.isRegularFile0(Ljava/io/FileDescriptor;)Z`]: (t, [, fdObj]) => t.vm.getField(fdObj, "java/io/FileDescriptor", "fd") > 2 && !processPipe(t, t.vm.getField(fdObj, "java/io/FileDescriptor", "fd")),
 
   [`${RAF}.open0(Ljava/lang/String;I)V`]: (t, [self, path, mode]) =>
     setFd(t, self, RAF, openFile(t, t.vm.jsString(path), (mode & 2) !== 0, false, false)),

src/node.ts

@@ -16,6 +16,7 @@ import type { SnapshotImage } from "./snapshot.ts";
 import { hostNatives } from "./hostnatives.ts";
 import { ImageBackend, imageFd } from "./image.ts";
 import { NodeNet } from "./net-node.ts";
+import { processNatives } from "./process-node.ts";
 import { PendingThrow } from "./thread.ts";
 import { setMaxHeap } from "./runtime.ts";
 import type { NetBackend } from "./sockets.ts";
@@ -351,7 +352,7 @@ function nodeVm(o: NodeRunOptions): JVM {
   vfs.mount("/", new NodeBackend("/", true));
   // built as dist/node.js, it reads the packaged image next to it
   const packaged = !o.jdk && fs.existsSync(path.join(here, "boot.pack"));
-  const jdk = o.jdk ?? defaultJdk;
+  const jdk = path.resolve(o.jdk ?? defaultJdk);
   if (!packaged && !fs.existsSync(path.join(jdk, "lib", "packages.txt"))) {
     throw new Error(`no JDK image at ${jdk}: run \`pnpm jdk\` in a checkout, or keep dist/node.js next to boot.pack and jdk/`);
   }
@@ -397,6 +398,7 @@ function nodeVm(o: NodeRunOptions): JVM {
       process.stdin.resume();
     }),
   });
+  vm.registerNatives(processNatives(fileURLToPath(import.meta.url), jdk, packaged, o.input === undefined));
   bridges.set(vm, bridge);
   // A runaway must not take the machine down; per-site caps catch most.
   const maxRss = (o.maxRssMb ?? 2048) * 2 ** 20;
@@ -476,6 +478,8 @@ function heapSize(s: string): number {
 export function main(argv: string[]) {
   const o: NodeRunOptions = { classpath: ["."], props: {} };
   let i = 0;
+  const javaChild = argv[0] === "--java-child";
+  if (javaChild) i++;
   for (; i < argv.length; i++) {
     const a = argv[i];
     if (a === "-cp" || a === "-classpath" || a === "--class-path") o.classpath = argv[++i].split(":");
@@ -498,10 +502,14 @@ export function main(argv: string[]) {
       }
       setMaxHeap(Math.ceil(n / 2 ** 21) * 2 ** 21);
     }
-    else if (/^(-X|--add-|-verbose|-server|-client)/.test(a)) continue;
     else if (a === "--jdk") o.jdk = argv[++i];
-    else if (a === "--max-rss") o.maxRssMb = Number(argv[++i]);
     else if (a === "-jar") { o.jar = argv[++i]; i++; break; }
+    else if (/^(-X|--add-|-verbose|-server|-client)/.test(a)) continue;
+    else if (javaChild && a.startsWith("-")) {
+      console.error(`Unrecognized option: ${a}\nError: Could not create the Java Virtual Machine.\nError: A fatal exception has occurred. Program will exit.`);
+      process.exit(1);
+    }
+    else if (a === "--max-rss") o.maxRssMb = Number(argv[++i]);
     else { o.mainClass = a; i++; break; }
   }
   o.args = argv.slice(i);