feat: Remaining KV Functions, File-System KV Store, Cache API Stubs, Workers Sites Support (#57)

* feat(KVNamespace): bring kv implementation more in line with docs

This commit adds value types to get and put, the getWithMetadata and list functions, and returns null if a key could not be found. This brings the KV implementation more in line with the documentation here: https://developers.cloudflare.com/workers/runtime-apis/kv. The only things missing now are ReadableStream & FormData support, and potentially errors when data is too large.

* test(KVNamespace): add tests for new kv implementation

* fix(start): empty string kv namespace added to context

* feat(FileKVStore): add file system backed kv store

This commit adds an implementation of a KV store that uses the file system to store data. This is required for Workers Sites, but is also a simpler way (compared to Minio) of persisting local KV data between restarts.

* test(FileKVStore): add tests for file system backed kv store

* feat(caches): add caches api stubs to worker context

Workers Sites required the caches API to be in scope, but they don't actually need to cache any data to function. So this commit stubs out the API and puts it in the worker context.

* feat(Workers Sites): add Workers Sites support

If the passed wrangler.toml file has a [site] section with a bucket field, the __STATIC_CONTENT KV namespace and __STATIC_CONTENT_MANIFEST object will be injected into the worker context, allowing the Worker Site to be served.

* feat(FileKVStore): enable file system backed kv store by env

This allows the file system backed KV store to be used for all KV namespaces, not just for Workers Sites. Setting the "KV_FILE_ROOT" environment variable enables this. For namespace "NAMESPACE", files will be stored in "KV_FILE_ROOT/NAMESPACE". Values will be stored in files named the same as their key. Metadata and expiration information (if provided) is stored in a .meta.json file prefixed with the key.

* docs(README): add file system kv store and workers sites to README

* docs(README): add note add importing kv asset handler

Author: mrbbot

README.md

@@ -34,6 +34,7 @@ $ nodemon --watch /path/to/worker.js --signal SIGHUP --exec 'cloudflare-worker-l
 * Cloudflare key value store if you pass in the KV_NAMESPACE environment variable
 * Cloudflare [event.passThroughOnException()](https://workers.cloudflare.com/docs/reference/workers-concepts/fetch-event-lifecycle/#passthroughonexception) for runtime exception handling
 * Cloudflare Environment Variables and Secrets loaded from a wrangler.toml
+* Workers Sites
 * ... this list should probably have more things
 
 ## Contributors
@@ -42,6 +43,7 @@ $ nodemon --watch /path/to/worker.js --signal SIGHUP --exec 'cloudflare-worker-l
 * Jeremy Danyow (@jdanyow)
 * Rita Liu (@rita-liu)
 * Nolan Woods (@innovate-invent)
+* Brendan Coll (@mrbbot)
 
 ## Future enhancements
 
@@ -68,6 +70,11 @@ MINIO_PORT, MINIO_USE_SSL, MINIO_REGION, MINIO_TRANSPORT, MINIO_SESSIONTOKEN, an
 
 See [the Minio documentation](https://docs.min.io/docs/javascript-client-api-reference.html) for details on the various parameters.
 
+## CloudFlare KV Store emulation using the File System
+
+To use the File System as the KV store simply provide the KV_FILE_ROOT option as an environment
+variable. A directory will be created in here for each KV namespace.
+
 ## CloudFlare Environment Variables and Secrets
 
 Support for CloudFlare Environment Variables and Secrets is provided via a wrangler.toml file.
@@ -96,3 +103,11 @@ Two features are provided while loading the wrangler.toml:
 
 Additionally, any 'kv-namespaces' in the wrangler.toml will be appended to the list of namespaces
 provided by KV_NAMESPACES.
+
+## Workers Sites
+
+If a wrangler.toml file containing a `[site]` section with a `bucket` directory is loaded, the Workers Sites
+default KV namespace and manifest will be added to the worker's scope. Calls to `getAssetFromKV` will always
+return the latest version of an asset in the `bucket` directory. Note that you'll need to bundle your worker
+code (with Webpack for instance) before running it to use `@cloudflare/kv-asset-handler`, as `import`/
+`require` are not in workers' scopes.