From 0ea1c6f5b07e18dad60bca5f1c7631be5b5005b3 Mon Sep 17 00:00:00 2001
From: Casper Beyer <caspervonb@pm.me>
Date: Fri, 4 Dec 2020 02:57:35 +0800
Subject: feat(std/wasi): add return on exit option (#8605)

This adds an exitOnReturn option to context making it
possible to unwind the stack on the exit(2) syscall
instead of delegating to it directly.

Use case is being able to treat WASI execution contexts
as children that don't kill the parent on exit.
---
 std/wasi/snapshot_preview1.ts      | 21 ++++++++++++++++++++-
 std/wasi/snapshot_preview1_test.ts | 22 ++++++++++++++++++++--
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/std/wasi/snapshot_preview1.ts b/std/wasi/snapshot_preview1.ts
index 4c974fe1d..30756fe82 100644
--- a/std/wasi/snapshot_preview1.ts
+++ b/std/wasi/snapshot_preview1.ts
@@ -207,6 +207,10 @@ function syscall<T extends CallableFunction>(target: T) {
     try {
       return target(...args);
     } catch (err) {
+      if (err instanceof ExitStatus) {
+        throw err;
+      }
+
       switch (err.name) {
         case "NotFound":
           return ERRNO_NOENT;
@@ -266,15 +270,25 @@ interface FileDescriptor {
   entries?: Deno.DirEntry[];
 }
 
+export class ExitStatus {
+  code: number;
+
+  constructor(code: number) {
+    this.code = code;
+  }
+}
+
 export interface ContextOptions {
   args?: string[];
   env?: { [key: string]: string | undefined };
   preopens?: { [key: string]: string };
+  exitOnReturn?: boolean;
 }
 
 export default class Context {
   args: string[];
   env: { [key: string]: string | undefined };
+  exitOnReturn: boolean;
   memory: WebAssembly.Memory;
 
   fds: FileDescriptor[];
@@ -284,6 +298,7 @@ export default class Context {
   constructor(options: ContextOptions) {
     this.args = options.args ? options.args : [];
     this.env = options.env ? options.env : {};
+    this.exitOnReturn = options.exitOnReturn ?? true;
     this.memory = null!;
 
     this.fds = [
@@ -1497,7 +1512,11 @@ export default class Context {
       "proc_exit": syscall((
         rval: number,
       ): never => {
-        Deno.exit(rval);
+        if (this.exitOnReturn) {
+          Deno.exit(rval);
+        }
+
+        throw new ExitStatus(rval);
       }),
 
       "proc_raise": syscall((
diff --git a/std/wasi/snapshot_preview1_test.ts b/std/wasi/snapshot_preview1_test.ts
index d7e29e195..01b91bc3e 100644
--- a/std/wasi/snapshot_preview1_test.ts
+++ b/std/wasi/snapshot_preview1_test.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import Context from "./snapshot_preview1.ts";
-import { assertEquals, assertThrows } from "../testing/asserts.ts";
+import Context, { ExitStatus } from "./snapshot_preview1.ts";
+import { assert, assertEquals, assertThrows } from "../testing/asserts.ts";
 import { copy } from "../fs/mod.ts";
 import * as path from "../path/mod.ts";
 
@@ -179,6 +179,24 @@ Deno.test("context_start", function () {
     TypeError,
     "export _start must be a function",
   );
+
+  try {
+    const context = new Context({
+      exitOnReturn: false,
+    });
+    context.start({
+      exports: {
+        _start() {
+          const exit = context.exports["proc_exit"] as CallableFunction;
+          exit(0);
+        },
+        memory: new WebAssembly.Memory({ initial: 1 }),
+      },
+    });
+  } catch (err) {
+    assert(err instanceof ExitStatus);
+    assertEquals(err.code, 0);
+  }
 });
 
 Deno.test("context_initialize", function () {
-- 
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