Files
coder/coderd
Kyle Carberry cbe29e4e25 fix: encode non-ASCII filenames in chat file upload header (#23241)
## Problem

Uploading a file on the `/agents` chat page fails with:

```
Failed to execute 'setRequestHeader' on 'XMLHttpRequest': String contains non ISO-8859-1 code point.
```

This happens when the image filename contains non-ASCII characters (e.g.
CJK characters from macOS screenshots like `スクリーンショット.png`, accented
characters, emoji, etc.). HTTP headers only support ISO-8859-1 code
points, and the filename was being interpolated directly into the
`Content-Disposition` header.

## Fix

Use [RFC 5987](https://datatracker.ietf.org/doc/html/rfc5987)
`filename*=UTF-8''` encoding so the percent-encoded name is always valid
in the header. A static ASCII `filename="file"` fallback is included for
older clients.

The server already uses Go's `mime.ParseMediaType` which decodes
`filename*` automatically, so no backend changes are needed.

### Before
```ts
"Content-Disposition": `attachment; filename="${file.name}"`
```

### After
```ts
"Content-Disposition": `attachment; filename="file"; filename*=UTF-8''${encodeURIComponent(file.name)}`
```

## Testing

Added a server-side test (`TestGetChatFile/UnicodeFilename`) that
uploads with a Japanese filename and verifies it round-trips correctly
through the `Content-Disposition` header.
2026-03-18 14:11:30 -04:00
..