Part 3: A Copy per User

A Modal sandbox lasts as long as its command, so a user’s files can’t live in it. They live on the user’s volume, and every sandbox the user starts from Warm mounts it: the warm image, plus their own files on top.

Write a user’s files to their volume

src/Api.ts

        const match = /^\/users\/([a-z0-9-]+)\/files\/(.+)$/.exec(url.pathname);
        if (match !== null) {
          const home = yield* volumes.getOrCreate(`home-${match[1]}`);
          if (request.method === "PUT") yield* home.writeFile(`/${match[2]}`, yield* request.text);
          return yield* HttpServerResponse.json({ content: yield* home.readFileString(`/${match[2]}`) });
        }

The Worker writes the file straight to the volume. No sandbox runs.

Every sandbox they start sees them

The run function from Part 2 already mounts the user’s volume at /home/user, so their next command reads what they wrote:

pnpm

pnpm alchemy deploy
curl -X PUT "$URL/users/ada/files/notes.md" -d 'hello from ada'
curl -X POST "$URL/users/ada/run" -d 'ls && cat /home/user/notes.md'

bun

bun alchemy deploy
curl -X PUT "$URL/users/ada/files/notes.md" -d 'hello from ada'
curl -X POST "$URL/users/ada/run" -d 'ls && cat /home/user/notes.md'

npm

npx alchemy deploy
curl -X PUT "$URL/users/ada/files/notes.md" -d 'hello from ada'
curl -X POST "$URL/users/ada/run" -d 'ls && cat /home/user/notes.md'

yarn

yarn alchemy deploy
curl -X PUT "$URL/users/ada/files/notes.md" -d 'hello from ada'
curl -X POST "$URL/users/ada/run" -d 'ls && cat /home/user/notes.md'

The output lists the repository’s files from Warm, then hello from ada from Ada’s volume. Another user’s sandbox mounts their own volume and never sees hers.

Delete a user’s files

src/Api.ts

        const user = /^\/users\/([a-z0-9-]+)$/.exec(url.pathname)?.[1];
        if (request.method === "DELETE" && user !== undefined) {
          yield* volumes.delete(`home-${user}`);
          return HttpServerResponse.empty({ status: 204 });
        }

Volumes your Worker creates aren’t deleted with the Stack until its environment is, so delete them when their owner goes away.

Next

Part 4 changes the image.