fix(runtime): don't error `child.output()` on consumed stream (#25657)

This fixes the fast path for `readableStreamCollectIntoUint8Array` to
only trigger if the readable stream has not yet been disturbed -
because otherwise we may not be able to close it if the
read errors.

2 files changed, 22 insertions, 1 deletions

diff --git a/ext/web/06_streams.js b/ext/web/06_streams.js
index 1dbf769b2..a4f2275c5 100644
--- a/ext/web/06_streams.js
+++ b/ext/web/06_streams.js
@@ -1054,7 +1054,7 @@ async function readableStreamCollectIntoUint8Array(stream) {
     getReadableStreamResourceBackingUnrefable(stream);
   const reader = acquireReadableStreamDefaultReader(stream);
 
-  if (resourceBacking) {
+  if (resourceBacking && !isReadableStreamDisturbed(stream)) {
     // fast path, read whole body in a single op call
     try {
       readableStreamDisturb(stream);
diff --git a/tests/unit/command_test.ts b/tests/unit/command_test.ts
index 523d20cf3..51bbdd860 100644
--- a/tests/unit/command_test.ts
+++ b/tests/unit/command_test.ts
@@ -1043,3 +1043,24 @@ Deno.test(
     }
   },
 );
+
+Deno.test(async function outputWhenManuallyConsumingStreams() {
+  const command = new Deno.Command(Deno.execPath(), {
+    args: ["eval", "console.log('hello world')"],
+    stdout: "piped",
+    stderr: "piped",
+  });
+  const child = command.spawn();
+  for await (const _ of child.stdout) {
+    // consume stdout
+  }
+  for await (const _ of child.stderr) {
+    // consume stderr
+  }
+  const status = await child.output();
+  assertEquals(status.success, true);
+  assertEquals(status.code, 0);
+  assertEquals(status.signal, null);
+  assertEquals(status.stdout, new Uint8Array());
+  assertEquals(status.stderr, new Uint8Array());
+});