fix: Pipe process.stdout.write through Buffer to fix node incompatibility

[lindskogen]

What does this PR do?

Happened upon a bug in bun, where it currently ignores the encoding parameter of process.stdout.write. This PR makes it so it uses Buffer.from to encode the data.

How did you verify your code works?

• I used claude code to generate a few test cases and built bun locally to verify compatibility with node.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[coderabbitai]

Walkthrough

The changes add input normalization for string encoding handling in file stream write operations and introduce comprehensive regression tests for stdout write operations with various encodings.

Changes

Cohort / File(s)	Summary
File Stream Write Normalization src/js/internal/fs/streams.ts	Added buffer conversion step in three write paths (_write, underscoreWriteFast, writeFast) to normalize string data with non-UTF-8 encodings before passing to fileSink.write.
Process Stdout Write Tests test/js/node/process/process-stdio.test.ts	Added regression tests for process.stdout.write() validating encoding behavior with "binary", "latin1", "hex", and default UTF-8 encodings, ensuring correct byte sequences are emitted.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main fix: addressing a Node.js incompatibility in process.stdout.write by piping through Buffer to handle encoding parameters.
Description check	✅ Passed	The pull request description follows the required template with both sections completed. It clearly explains what the PR does and how it was verified.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@test/js/node/process/process-stdio.test.ts`:
- Around line 164-204: Each test that spawns a process (the three tests using
spawnSync with bunExe and bunEnv) lacks an assertion on the child process exit
code; update each test to capture the spawnSync result's exitCode (from the
object returned by spawnSync) and add an assertion after the existing stdout
Buffer checks to ensure exitCode is 0 (or the expected success code). Locate the
three tests named "process.stdout.write(string, '%s') writes raw bytes",
"process.stdout.write(string, 'hex') decodes hex", and
"process.stdout.write(string) defaults to UTF-8" and add the exitCode assertion
immediately after the Buffer.compare / stdout checks for each spawnSync call.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

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Run ID: 4401ef1f-f0f0-40a2-9359-e7472a07009e

📥 Commits

Reviewing files that changed from the base of the PR and between 7c75a87 and 0af9fb9.

📒 Files selected for processing (2)

• src/js/internal/fs/streams.ts
• test/js/node/process/process-stdio.test.ts

[coderabbitai]

⚠️ Potential issue | 🟠 Major

Add exit-code assertions to each new spawnSync regression test.

Each new test validates stdout bytes but never asserts process success. Please capture exitCode and assert it after stdout checks in all three tests.

Suggested patch

-    const { stdout } = spawnSync({
+    const { stdout, exitCode } = spawnSync({
       cmd: [
         bunExe(),
         "-e",
         `for (let i = 0; i <= 0xff; i++) process.stdout.write(String.fromCharCode(i), ${JSON.stringify(encoding)});`,
       ],
@@
     expect(stdout.length).toBe(256);
     const expected = Buffer.alloc(256);
     for (let i = 0; i < 256; i++) expected[i] = i;
     expect(Buffer.compare(stdout, expected)).toBe(0);
+    expect(exitCode).toBe(0);
   });

   test("process.stdout.write(string, 'hex') decodes hex", () => {
-    const { stdout } = spawnSync({
+    const { stdout, exitCode } = spawnSync({
       cmd: [bunExe(), "-e", `process.stdout.write("deadbeef", "hex");`],
       stdout: "pipe",
       stdin: null,
       stderr: "inherit",
       env: bunEnv,
     });
     expect(Buffer.compare(stdout, Buffer.from([0xde, 0xad, 0xbe, 0xef]))).toBe(0);
+    expect(exitCode).toBe(0);
   });

   test("process.stdout.write(string) defaults to UTF-8", () => {
-    const { stdout } = spawnSync({
+    const { stdout, exitCode } = spawnSync({
       cmd: [bunExe(), "-e", `process.stdout.write("héllo");`],
       stdout: "pipe",
       stdin: null,
       stderr: "inherit",
       env: bunEnv,
     });
     // é = U+00E9 = UTF-8 c3 a9
     expect(Buffer.compare(stdout, Buffer.from([0x68, 0xc3, 0xa9, 0x6c, 0x6c, 0x6f]))).toBe(0);
+    expect(exitCode).toBe(0);
   });

As per coding guidelines, “Always check exit codes and test error scenarios when spawning processes in tests” and “Expect stdout assertions before exit code assertions.”

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@test/js/node/process/process-stdio.test.ts` around lines 164 - 204, Each test
that spawns a process (the three tests using spawnSync with bunExe and bunEnv)
lacks an assertion on the child process exit code; update each test to capture
the spawnSync result's exitCode (from the object returned by spawnSync) and add
an assertion after the existing stdout Buffer checks to ensure exitCode is 0 (or
the expected success code). Locate the three tests named
"process.stdout.write(string, '%s') writes raw bytes",
"process.stdout.write(string, 'hex') decodes hex", and
"process.stdout.write(string) defaults to UTF-8" and add the exitCode assertion
immediately after the Buffer.compare / stdout checks for each spawnSync call.