fix(teeny-request): set Content-Length for buffered request bodies in Bun (#9748)

## Description

Sets `Content-Length` for `string`, `Buffer`, and `Uint8Array` bodies in
`bunFetch`.

## Impact

Prevents unexpected chunked transfer encoding on buffered requests under
Bun.

## Changes

- **Stack Overview** (for `b/578555176`, replacing #9741):
1. **#9748 (this PR — kept as small as possible)**:
`fix/teeny-request-bun-part-1` $\to$ `main` — Set `Content-Length` for
buffered request bodies (`string`, `Buffer`, `Uint8Array`) in
`bunFetch`.
2. #9749: `fix/teeny-request-bun-part-2` $\to$
`fix/teeny-request-bun-part-1` — Default `Content-Length: '0'` for
bodyless `POST` and `PUT` requests in `bunFetch`.
3. #9750: `fix/teeny-request-bun-part-3` $\to$
`fix/teeny-request-bun-part-2` — Lazily initialize `zlib` decompressor
in `bunFetch` so `0`-byte compressed responses do not throw
`Z_BUF_ERROR`.
4. #9751: `fix/teeny-request-bun-part-4` $\to$
`fix/teeny-request-bun-part-3` — Auto-detect RFC 1950 vs. raw RFC 1951
`deflate` streams in `bunFetch`.
5. #9752: `fix/teeny-request-bun-style-maintenance` $\to$
`fix/teeny-request-bun-part-4` — `[Style Maintenance]` JSDoc
documentation and `CONTRIBUTING.md` / `gts` alignment.
- Compute `headers['Content-Length'] =
String(Buffer.byteLength(init.body))` in `bunFetch`
(`core/packages/teeny-request/src/index.ts`) for `string`, `Buffer`, and
`Uint8Array` request bodies when neither `Content-Length` nor
`Transfer-Encoding` is already set.

## Testing

- Added unit test in `core/packages/teeny-request/test/index.ts`
verifying `Content-Length: 5` on `POST` requests with a string body
under `bunFetch`.
- **Steps to Reproduce (in terminal)**:
- Direct terminal command: Run `pnpm --dir core/packages/teeny-request
run compile && node bin/run-test.cjs --no-c8
core/packages/teeny-request/build/test/index.js` against `main` (fails
`matchHeader('content-length', '5')`), then re-run on
`fix/teeny-request-bun-part-1` to confirm it passes.
- Or via shortened reproduction Gist
([repro.mjs](https://gist.github.com/danieljbruce/990f5fdb7806eb3454cccea3c1ceb3bd)):
`gh gist view
https://gist.github.com/danieljbruce/990f5fdb7806eb3454cccea3c1ceb3bd
--raw | node --input-type=module -`

## Alternatives

- Relying on Node's `http.request` default chunked encoding for buffered
bodies was considered and rejected because `node-fetch` sets
`Content-Length` on in-memory request payloads and downstream Google
Cloud endpoints expect `Content-Length`.
- Not merging this PR was considered, but doing so leaves `bunFetch`
omitting `Content-Length` on buffered request bodies under Bun.

Author: danieljbruce

core/packages/teeny-request/src/index.ts

@@ -83,6 +83,21 @@ function bunFetch(
     }
   }
 
+  const hasContentLength = Object.keys(headers).some(
+    k =>
+      k.toLowerCase() === 'content-length' ||
+      k.toLowerCase() === 'transfer-encoding',
+  );
+  if (!hasContentLength) {
+    if (
+      typeof init.body === 'string' ||
+      Buffer.isBuffer(init.body) ||
+      init.body instanceof Uint8Array
+    ) {
+      headers['Content-Length'] = String(Buffer.byteLength(init.body));
+    }
+  }
+
   const reqOptions: https.RequestOptions & {proto?: string} = {
     protocol: parsedUrl.protocol,
     proto: isHttps ? 'https' : 'http',

core/packages/teeny-request/test/index.ts

@@ -706,6 +706,27 @@ describe('teeny', () => {
         await new Promise<void>(resolve => server.close(() => resolve()));
         nock.disableNetConnect();
       }
+
+      const contentLengthScope = nock(uri)
+        .post('/content-length', 'hello')
+        .matchHeader('content-length', '5')
+        .reply(200, 'ok');
+      await new Promise<void>((resolve, reject) => {
+        teenyRequest(
+          {uri: `${uri}/content-length`, method: 'POST', body: 'hello'},
+          (err, res, body) => {
+            if (err) return reject(err);
+            try {
+              assert.strictEqual(res.statusCode, 200);
+              assert.strictEqual(body, 'ok');
+              contentLengthScope.done();
+              resolve();
+            } catch (e) {
+              reject(e);
+            }
+          },
+        );
+      });
     } finally {
       if (!hadBun) {
         delete globalRecord.Bun;