2 files changed, 84 insertions, 3 deletions

diff --git a/std/wasi/snapshot_preview1.ts b/std/wasi/snapshot_preview1.ts
index bc63e82dd..b3d5274e6 100644
--- a/std/wasi/snapshot_preview1.ts
+++ b/std/wasi/snapshot_preview1.ts
@@ -306,6 +306,21 @@ export interface ContextOptions {
    * Determines if calls to exit from within the WebAssembly module will terminate the proess or return.
    */
   exitOnReturn?: boolean;
+
+  /**
+   * The resource descriptor used as standard input in the WebAssembly module.
+   */
+  stdin?: number;
+
+  /**
+   * The resource descriptor used as standard output in the WebAssembly module.
+   */
+  stdout?: number;
+
+  /**
+   * The resource descriptor used as standard error in the WebAssembly module.
+   */
+  stderr?: number;
 }
 
 /**
@@ -335,17 +350,17 @@ export default class Context {
 
     this.fds = [
       {
-        rid: Deno.stdin.rid,
+        rid: options.stdin ?? Deno.stdin.rid,
         type: FILETYPE_CHARACTER_DEVICE,
         flags: FDFLAGS_APPEND,
       },
       {
-        rid: Deno.stdout.rid,
+        rid: options.stdout ?? Deno.stdout.rid,
         type: FILETYPE_CHARACTER_DEVICE,
         flags: FDFLAGS_APPEND,
       },
       {
-        rid: Deno.stderr.rid,
+        rid: options.stderr ?? Deno.stderr.rid,
         type: FILETYPE_CHARACTER_DEVICE,
         flags: FDFLAGS_APPEND,
       },
diff --git a/std/wasi/snapshot_preview1_test.ts b/std/wasi/snapshot_preview1_test.ts
index 55982545f..1fe94a4cc 100644
--- a/std/wasi/snapshot_preview1_test.ts
+++ b/std/wasi/snapshot_preview1_test.ts
@@ -274,3 +274,69 @@ Deno.test("context_initialize", function () {
     "WebAssembly.Instance has already started",
   );
 });
+
+Deno.test("std_io_stdin.wasm with stdin as file", function () {
+  const stdinPath = Deno.makeTempFileSync();
+  Deno.writeTextFileSync(stdinPath, "Hello, stdin!");
+
+  const stdinFile = Deno.openSync(stdinPath);
+
+  const context = new Context({
+    exitOnReturn: false,
+    stdin: stdinFile.rid,
+  });
+
+  const binary = Deno.readFileSync(path.join(testdir, "std_io_stdin.wasm"));
+  const module = new WebAssembly.Module(binary);
+  const instance = new WebAssembly.Instance(module, {
+    wasi_snapshot_preview1: context.exports,
+  });
+
+  context.start(instance);
+
+  stdinFile.close();
+});
+
+Deno.test("std_io_stdout.wasm with stdout as file", function () {
+  const stdoutPath = Deno.makeTempFileSync();
+  const stdoutFile = Deno.openSync(stdoutPath, { create: true, write: true });
+
+  const context = new Context({
+    exitOnReturn: false,
+    stdout: stdoutFile.rid,
+  });
+
+  const binary = Deno.readFileSync(path.join(testdir, "std_io_stdout.wasm"));
+  const module = new WebAssembly.Module(binary);
+  const instance = new WebAssembly.Instance(module, {
+    wasi_snapshot_preview1: context.exports,
+  });
+
+  context.start(instance);
+
+  stdoutFile.close();
+
+  assertEquals(Deno.readTextFileSync(stdoutPath), "Hello, stdout!");
+});
+
+Deno.test("std_io_stderr.wasm with stderr as file", function () {
+  const stderrPath = Deno.makeTempFileSync();
+  const stderrFile = Deno.openSync(stderrPath, { create: true, write: true });
+
+  const context = new Context({
+    exitOnReturn: false,
+    stderr: stderrFile.rid,
+  });
+
+  const binary = Deno.readFileSync(path.join(testdir, "std_io_stderr.wasm"));
+  const module = new WebAssembly.Module(binary);
+  const instance = new WebAssembly.Instance(module, {
+    wasi_snapshot_preview1: context.exports,
+  });
+
+  context.start(instance);
+
+  stderrFile.close();
+
+  assertEquals(Deno.readTextFileSync(stderrPath), "Hello, stderr!");
+});