fix: support multiple cookies with the same name across different paths and domains #14131

Copilot · 2025-08-06T22:34:38Z

When setting multiple cookies with the same name but different paths or domains using event.cookies.set(), only the last cookie was retained. This happened because the internal new_cookies object used just the cookie name as the key, causing cookies with different paths/domains to overwrite each other.

Example of the issue

// Server load function
export const load = (event) => {
  event.cookies.set('key', 'value1', { path: '/foo/' });
  event.cookies.set('key', 'value2', { path: '/bar/' });
  // Only the second cookie would be sent in set-cookie headers
}

Previously, this would only result in one set-cookie header:

set-cookie: key=value2; Path=/bar/; HttpOnly; SameSite=Lax

Now it correctly sends both:

set-cookie: key=value1; Path=/foo/; HttpOnly; SameSite=Lax
set-cookie: key=value2; Path=/bar/; HttpOnly; SameSite=Lax

Solution

Unique key generation: Cookies are now stored internally using unique keys combining domain, path, and name in the format ${domain || ''}${path}?${name}
Most specific path wins: The cookies.get() method implements proper cookie precedence by selecting the cookie with the most specific matching path, following standard browser behavior
Backward compatibility: Existing code continues to work unchanged - cookies.get(name) automatically finds the most appropriate cookie

Behavior

// Set cookies with same name but different paths
cookies.set('session', 'user_root', { path: '/' });
cookies.set('session', 'user_admin', { path: '/admin' });

// cookies.get() returns the most specific matching cookie
cookies.get('session'); // returns 'user_admin' when on /admin path
                        // returns 'user_root' when on / path

// Works with domains too
cookies.set('token', 'main', { path: '/', domain: 'example.com' });
cookies.set('token', 'sub', { path: '/', domain: 'sub.example.com' });
// cookies.get('token') returns the appropriate value based on current domain

The solution ensures consistent behavior whether cookies are freshly set during the current request or read from existing request headers.

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changeset-bot · 2025-08-06T22:34:42Z

🦋 Changeset detected

Latest commit: 5764a8d

The changes in this PR will be included in the next version bump.

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@sveltejs/kit	Patch

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Rich-Harris · 2025-08-06T22:41:38Z

@copilot not sure if you'll see this in time but it looks like you're adding options to cookies.get which is incorrect. I'm just going to quote myself from the original PR:

Thank you. This isn't quite right though — it only affects cookies that were created during the current request; the options are ignored for existing cookies. This leads to chaotic outcomes. Consider a case like this:
// src/routes/+layout.server.ts
export function load({ cookies }) {
  cookies.set('foo', 'bar', {
    path: '/'
  });
}
// src/routes/x/y/z/+page.server.ts
export function load({ cookies }) {
  return {
    foo: cookies.get('foo')
  };
}
When you visit /x/y/z for the first time, the cookies.set happens first followed by the cookies.get, which because of the defaults is equivalent to this...
cookies.get('foo', { path: '/x/y/z' });
...which returns undefined, incorrectly. When you reload the page, cookies.get instead reads from the cookie header.

My understanding (double-check me on this) is that the most specific cookie wins, which is to say that if you set all these (order doesn't matter)...
n=1; Path=/; HttpOnly; SameSite=Lax
n=2; Path=/x; HttpOnly; SameSite=Lax
n=3; Path=/x/y; HttpOnly; SameSite=Lax
n=4 Path=/x/y/z; HttpOnly; SameSite=Lax
...then on /x/y/z the Cookie header will be x=4; x=3; x=2; x=1 (which means cookies.get('x') === '4'), while on /x/y it will be x=3; x=2; x=1 (therefore 3) and so on.

So this PR is correct to ensure that cookies.set(name, ...) doesn't clobber existing name cookies, but the cookies.get logic isn't quite right. cookies.get(name) should not take an additional option, but it should look at all the matching cookies in new_cookies and select the most specific value.

- Add generate_cookie_key function to create unique keys from domain/path/name - Extend cookies.get() to accept optional domain and path options in opts parameter - Store cookies with unique keys to prevent overwrites - Maintain backward compatibility with existing API usage - Add comprehensive tests for new functionality - Address review feedback from PR #14056 Co-authored-by: Rich-Harris <[email protected]>

svelte-docs-bot · 2025-08-06T22:51:37Z

Preview: https://svelte-dev-git-preview-kit-14131-svelte.vercel.app/

- Fix formatting issues with prettier - Verify all tests pass including edge cases - Confirm TypeScript type checking passes - Complete implementation addresses all review feedback from PR #14056 Co-authored-by: Rich-Harris <[email protected]>

…cific path wins' logic Co-authored-by: Rich-Harris <[email protected]>

Copilot · 2025-08-06T23:03:38Z

@copilot not sure if you'll see this in time but it looks like you're adding options to cookies.get which is incorrect. I'm just going to quote myself from the original PR:

Thank you. This isn'...

You're absolutely right - adding options to cookies.get() was the wrong approach and led to inconsistent behavior. I've fixed this by:

Removing the domain and path options from cookies.get()
Implementing "most specific path wins" logic that searches all matching cookies in new_cookies and selects the one with the highest path specificity
Keeping the unique key storage system to prevent cookie overwrites during set()

The solution now correctly handles the scenario you described - cookies.get('foo') will consistently find the most specific matching cookie whether it's from a fresh set() call or from existing request headers. Commit c62add6

Rich-Harris · 2025-08-06T23:31:03Z

@copilot one of the tests you added is failing. Are you able to see the logs? On my phone right now but can help debug later

Co-authored-by: Rich-Harris <[email protected]>

Copilot · 2025-08-06T23:40:04Z

@copilot one of the tests you added is failing. Are you able to see the logs? On my phone right now but can help debug later

Fixed the failing test - the issue was in the path specificity calculation. Previously used .split('/').length which incorrectly gave the same score to '/' and '/foo' paths. Now using path length for accurate specificity comparison. Commit 12df174

Avaq · 2025-08-09T05:11:42Z