feat: flagd in-process provider (#633)

Signed-off-by: Kavindu Dodanduwa <[email protected]>

Author: Kavindu-Dodan

.eslintrc.json

@@ -2,6 +2,10 @@
   "root": true,
   "ignorePatterns": ["**/*"],
   "plugins": ["@nx"],
+  "extends": [
+    "eslint:recommended",
+    "plugin:prettier/recommended"
+  ],
   "overrides": [
     {
       "files": ["*.ts", "*.tsx", "*.js", "*.jsx"],

libs/providers/flagd/README.md

@@ -6,56 +6,81 @@ This repository and package provides the client code for interacting with it via
 
 ## Installation
 
-```
-$ npm install @openfeature/flagd-provider
+### npm
+
+```sh
+npm install @openfeature/flagd-provider
 ```
 
-Required peer dependencies
+### yarn
 
+```sh
+yarn add @openfeature/server-sdk @grpc/grpc-js @openfeature/flagd-core
 ```
-$ npm install @openfeature/server-sdk
-```
 
-## Usage
+> [!NOTE]
+> yarn requires manual installation of peer dependencies
+
+## Configurations and Usage
+
+The `FlagdProvider` supports multiple configuration options and has the ability to resolve flags remotely over RPC or in-process.
+Options can be defined in the constructor or as environment variables. Constructor options having the highest precedence.
+
+### Available Configuration Options
+
+| Option name           | Environment variable name      | Type    | Default   | Supported values |
+|-----------------------|--------------------------------|---------|-----------|------------------|
+| host                  | FLAGD_HOST                     | string  | localhost |                  |
+| port                  | FLAGD_PORT                     | number  | 8013      |                  |
+| tls                   | FLAGD_TLS                      | boolean | false     |                  |
+| socketPath            | FLAGD_SOCKET_PATH              | string  | -         |                  |
+| resolverType          | FLAGD_SOURCE_RESOLVER          | string  | rpc       | rpc, in-process  |
+| selector              | FLAGD_SOURCE_SELECTOR          | string  | -         |                  |
+| cache                 | FLAGD_CACHE                    | string  | lru       | lru,disabled     |
+| maxCacheSize          | FLAGD_MAX_CACHE_SIZE           | int     | 1000      |                  |
+| maxEventStreamRetries | FLAGD_MAX_EVENT_STREAM_RETRIES | int     | 5         |                  |
 
-The `FlagdProvider` supports multiple configuration options that determine now the SDK communicates with flagd.
-Options can be defined in the constructor or as environment variables, with constructor options having the highest precedence.
+Below are examples of usage patterns.
 
-### Available Options
+### Remote flag resolving over RPC
 
-| Option name           | Environment variable name      | Type    | Default   | Values       |
-| --------------------- | ------------------------------ | ------- | --------- | ------------ |
-| host                  | FLAGD_HOST                     | string  | localhost |              |
-| port                  | FLAGD_PORT                     | number  | 8013      |              |
-| tls                   | FLAGD_TLS                      | boolean | false     |              |
-| socketPath            | FLAGD_SOCKET_PATH              | string  | -         |              |
-| cache                 | FLAGD_CACHE                    | string  | lru       | lru,disabled |
-| maxCacheSize          | FLAGD_MAX_CACHE_SIZE           | int     | 1000      |              |
-| maxEventStreamRetries | FLAGD_MAX_EVENT_STREAM_RETRIES | int     | 5         |              |
+This is the default mode of operation of the provider.
+In this mode, FlagdProvider communicates with flagd via the gRPC protocol.
+Flag evaluations take place remotely at the connected [flagd](https://flagd.dev/) instance.
 
-### Example Using TCP
+```ts
+  OpenFeature.setProvider(new FlagdProvider())
+```
+
+In the above example, the provider expects flagd to be available at `localhost:8013` (default host and port).
+
+Alternatively, you can use socket paths to connect to flagd.
 
 ```
   OpenFeature.setProvider(new FlagdProvider({
-      host: 'localhost',
-      port: 8013,
+      socketPath: "/tmp/flagd.socks",
   }))
 ```
 
-### Example Using a Unix Socket
+### In-process resolver
+
+This mode performs flag evaluations locally (in-process).
+Flag configurations for evaluation are obtained via gRPC protocol using [sync protobuf schema](https://buf.build/open-feature/flagd/file/main:sync/v1/sync_service.proto) service definition.
 
 ```
   OpenFeature.setProvider(new FlagdProvider({
-      socketPath: "/tmp/flagd.socks",
+      resolverType: 'in-process',
   }))
 ```
 
+In the above example, the provider expects a flag sync service implementation to be available at `localhost:8013` (default host and port).
+
 ### Supported Events
 
 The flagd provider emits `PROVIDER_READY`, `PROVIDER_ERROR` and `PROVIDER_CONFIGURATION_CHANGED` events.
 
 | SDK event                        | Originating action in flagd                                                     |
-| -------------------------------- | ------------------------------------------------------------------------------- |
+|----------------------------------|---------------------------------------------------------------------------------|
 | `PROVIDER_READY`                 | The streaming connection with flagd has been established.                       |
 | `PROVIDER_ERROR`                 | The streaming connection with flagd has been broken.                            |
 | `PROVIDER_CONFIGURATION_CHANGED` | A flag configuration (default value, targeting rule, etc) in flagd has changed. |
@@ -65,7 +90,7 @@ For general information on events, see the [official documentation](https://open
 ### Flag Metadata
 
 | Field   | Type   | Value                                             |
-| ------- | ------ | ------------------------------------------------- |
+|---------|--------|---------------------------------------------------|
 | `scope` | string | "selector" set for the associated source in flagd |
 
 ## Building