Release 2.3.3: Browsers now receive all cookies, not just the last one#60
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dcrockwell merged 2 commits intomainfrom Mar 7, 2026
Merged
Release 2.3.3: Browsers now receive all cookies, not just the last one#60dcrockwell merged 2 commits intomainfrom
dcrockwell merged 2 commits intomainfrom
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## Why This Change Was Made - The mist response converter used `http_response.set_header` for every header, which calls `list.key_set` and replaces any existing header with the same name - This is correct for most headers but violates RFC 6265 for `Set-Cookie` — each cookie MUST be sent as a separate `Set-Cookie` header - Browsers do not parse comma-separated `Set-Cookie` values, so when a Dream response had multiple cookies, only the last one survived the conversion to mist format - This meant authentication flows setting both a session cookie and a CSRF cookie (or any multi-cookie scenario) would silently lose all cookies except the last one ## What Was Changed - `src/dream/servers/mist/response.gleam`: `add_header` now uses `prepend_header` (which allows duplicates) for `set-cookie` headers, and `set_header` (which replaces) for everything else — matching the Gleam standard library's own `set_cookie` convention - `src/dream/http/response.gleam`: Updated `Response` type hexdoc to clarify each cookie becomes a separate `Set-Cookie` header - `test/dream/servers/mist/response_test.gleam`: Added 7 tests covering RFC 6265 multi-cookie compliance - `test/matchers/count_mist_headers.gleam`: New matcher for verifying header counts by name - `test/matchers/extract_all_mist_header_values.gleam`: New matcher for extracting all values of a header - `CHANGELOG.md`: Added 2.3.3 entry - `gleam.toml`: Bumped version to 2.3.3 - `releases/release-2.3.3.md`: New release notes ## Note to Future Engineer - The string match on `"set-cookie"` looks fragile but is safe: `convert_header_to_tuple` lowercases all header names, and `add_cookie_header` hardcodes lowercase `"set-cookie"` — plus `prepend_header` itself lowercases the key internally, so you'd have to try pretty hard to break this - If you're wondering why `Set-Cookie` is special: RFC 7230 §3.2.2 says you can comma-fold duplicate headers into one, EXCEPT for `Set-Cookie` which RFC 6265 says you absolutely cannot — because cookie values can contain commas (in Expires dates), so browsers gave up trying to parse them that way circa 2011 and never looked back - Yes, this means the entire fix is a three-line case expression. The other 250 lines are tests. You're welcome.
Browsers now receive all cookies, not just the last one
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Release 2.3.3
Summary
This release fixes a bug where multiple
Set-Cookieheaders were collapsed into a single header during mist response conversion, causing browsers to only receive the last cookie in multi-cookie responses.What's Included
Bug Fix — Multiple Set-Cookie headers (PR #59)
The mist response converter used
set_headerfor all headers, which replaces existing headers with the same name. This violates RFC 6265, which requires each cookie to be sent as its ownSet-Cookieheader. Browsers don't parse comma-separatedSet-Cookievalues — they only see the first (or last) cookie.The fix uses
prepend_header(which allows duplicates) forset-cookieheaders, andset_header(which replaces) for everything else. This matches the Gleam standard library's ownset_cookieconvention.Test Coverage
count_mist_headers,extract_all_mist_header_values)Documentation
convertandResponsetype to document per-cookie header behaviorUpgrade
Full Changelog