fix(posix): ensure nonblocking file descriptor is nonblocking (#10080)

The FileReader is responsible for deciding what sort of file descriptor
has been passed to it. On MacOS, when stdin is provided to it the
FileReader assumes that it is nonblocking even if the descriptor is not,
this resulted in hangs as the socket would never raise the `EAGAIN`
error. There are a couple of ways to fix this but the one that seemed to
make the most sense was to set the fd to be nonblocking when the
FileReader deemed it so.

src/bun.js/webcore/streams.zig

@@ -3518,6 +3518,11 @@ pub const FileReader = struct {
                 if (this.nonblocking and this.file_type == .pipe) {
                     this.file_type = .nonblocking_pipe;
                 }
+
+                // ensure non blocking otherwise hangs will occur
+                if (this.nonblocking) {
+                    bun.ensureNonBlocking(fd.int());
+                }
             }
 
             this.fd = fd;

test/regression/issue/10080.test.ts

@@ -0,0 +1,29 @@
+import { test, expect } from "bun:test";
+import { bunEnv, bunExe, isPosix } from "harness";
+import { tmpdir } from "os";
+import { join } from "path";
+
+test.if(isPosix)("10080 - ensure nonblocking file descriptor is nonblocking in FileReader", async () => {
+  const expected = "foobar\n";
+  const filename = join(tmpdir(), "bun.test.stream." + Date.now() + ".js");
+  const contents = "for await (const line of console) {console.log(`foo${line}`)}"
+  await Bun.write(filename, contents);
+  const shellCommand = `exec &> >(${bunExe()} ${filename}); echo "bar"; while read -r line; do echo $line; done`;
+
+  const proc = Bun.spawn(["bash", "-c", shellCommand], {
+    stdin: "inherit",
+    stdout: "pipe",
+    stderr: "inherit",
+    env: bunEnv,
+  });
+  const { value }= await proc.stdout.getReader().read();
+  const output = new TextDecoder().decode(value);
+  if (output !== expected) {
+    expect(output).toEqual(expected);
+    throw new Error("Output didn't match!\n");
+  }
+
+  proc.kill(9);
+  await proc.exited;
+  expect(proc.killed).toBeTrue();
+}, 1000);