Integrity checking & lock files

Introduction

Let's say your module depends on remote module https://some.url/a.ts. When you compile your module for the first time a.ts is retrieved, compiled and cached. It will remain this way until you run your module on a new machine (say in production) or reload the cache (through deno cache --reload for example). But what happens if the content in the remote url https://some.url/a.ts is changed? This could lead to your production module running with different dependency code than your local module. Deno's solution to avoid this is to use integrity checking and lock files.

Caching and lock files

Deno can store and check subresource integrity for modules using a small JSON file. Use the --lock=lock.json to enable and specify lock file checking. To update or create a lock use --lock=lock.json --lock-write. The --lock=lock.json tells Deno what the lock file to use is, while the --lock-write is used to output dependency hashes to the lock file (--lock-write must be used in conjunction with --lock).

A lock.json might look like this, storing a hash of the file against the dependency:

{
  "https://deno.land/std@0.138.0/textproto/mod.ts": "3118d7a42c03c242c5a49c2ad91c8396110e14acca1324e7aaefd31a999b71a4",
  "https://deno.land/std@0.138.0/io/util.ts": "ae133d310a0fdcf298cea7bc09a599c49acb616d34e148e263bcb02976f80dee",
  "https://deno.land/std@0.138.0/async/delay.ts": "35957d585a6e3dd87706858fb1d6b551cb278271b03f52c5a2cb70e65e00c26a",
   ...
}

A typical workflow will look like this:

src/deps.ts

// Add a new dependency to "src/deps.ts", used somewhere else.
export { xyz } from "https://unpkg.com/xyz-lib@v0.9.0/lib.ts";

Then:

# Create/update the lock file "lock.json".
deno cache --lock=lock.json --lock-write src/deps.ts

# Include it when committing to source control.
git add -u lock.json
git commit -m "feat: Add support for xyz using xyz-lib"
git push

Collaborator on another machine -- in a freshly cloned project tree:

# Download the project's dependencies into the machine's cache, integrity
# checking each resource.
deno cache --reload --lock=lock.json src/deps.ts

# Done! You can proceed safely.
deno test --allow-read src

Runtime verification

Like caching above, you can also use the --lock=lock.json option during use of the deno run sub command, validating the integrity of any locked modules during the run. Remember that this only validates against dependencies previously added to the lock.json file. New dependencies will be cached but not validated.

You can take this a step further as well by using the --cached-only flag to require that remote dependencies are already cached.

deno run --lock=lock.json --cached-only mod.ts

This will fail if there are any dependencies in the dependency tree for mod.ts which are not yet cached.