[Client] adding nodejs cac and experimentation client wrapper

clients/nodejs/Readme.md

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+Set directory path that contains superposition object files in <span style="color: red" > SUPERPOSITION_LIB_PATH </span> env variable;
+
+## [<u> CAC Client </u>](./cac-client)
+
+1. This exports a class that exposes functions that internally call rust functions.
+2. For Different platform it read different superposition object files.
+    *  <span style="color: #808080" >For Mac </span> ->  libcac_client.dylib
+    *  <span style="color: #357EC7" >For Windows </span> ->  libcac_client.so
+    *  <span style="color: orange" >For Linux </span> ->  libcac_client.dll
+3. This run CAC CLient in two thread one is main thread another is worker thread.
+4. Worker thread is used to do polling updates ([ref](./cac-client/client.ts#L31)).
+
+
+## [<u> Experimentation Client </u>](./exp-client)
+
+1. This exports a class that exposes functions that internally call rust functions.
+2. For Different platform it read different superposition object files.
+    *  <span style="color: #808080" >For Mac </span> ->  libexperimentation_client.dylib
+    *  <span style="color: #357EC7" >For Windows </span> ->  libexperimentation_client.so
+    *  <span style="color: orange" >For Linux </span> ->  libexperimentation_client.dll
+3. This run Experimentation CLient in two thread one is main thread another is worker thread.
+4. Worker thread is used to do polling updates ([ref](./exp-client/client.ts#L31)).
+
+## [<u> Test </u>](./index.ts)
+
+1. To test this sample project follow below steps.
+    * Run superposition client.
+    * Run <u> **npm install** </u> (make sure your node version is <span style="color: red"> >18 </span>).
+    * Run <u> **npm run test** </u> this will start a server that runs on port 7000.
+2. By Default this sample code uses [dev](./index.ts#L11) tenant.
+3. By Default this sample code assumes superposition is running on [8080](./index.ts#L12) port.
+3. By Default this sample code polls superposition every [1 second](./index.ts#L13) port.
+4. This sample code creates both [CAC CLient](./index.ts#L15) and [Experimentation Client](./index.ts#L16) with above default values.

clients/nodejs/cac-client/client.ts

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+import * as ffi from 'ffi-napi';
+import * as ref from 'ref-napi';
+import * as path from 'path';
+import os from 'os';
+import { Worker, isMainThread} from "node:worker_threads";
+import { parentPort } from 'worker_threads';
+
+let libPathEnc: string | undefined = process.env.SUPERPOSITION_LIB_PATH;
+
+if (libPathEnc == "" || libPathEnc == undefined) {
+    throw new Error("SUPERPOSITION_LIB_PATH not found in env");
+}
+
+let platform = os.platform();
+let fileName =
+        platform == "darwin" ?
+            'libcac_client.dylib' :
+            platform == "linux" ?
+                'libcac_client.dll' :
+                'libcac_client.so'
+
+const libPath = path.join(libPathEnc, fileName);
+
+const refType = ref.types;
+const int = refType.int;
+const string = refType.CString;
+const voidType = refType.void;
+
+// -------------------------------------
+// this code is running on Main Thread
+const worker = new Worker(__filename);
+// -------------------------------------
+
+
+// ----------------------------------------
+// this code runs on worker thread
+if (!isMainThread && parentPort) {
+    let cac_client: Map < String, CacClient > = new Map();
+    parentPort.on("message", (message) => {
+        try {
+            message = JSON.parse(message);
+            if (message.event === "startPollingUpdate") {
+                let {
+                    tenant,
+                    pollingFrequency,
+                    cacHostName,
+                } = message;
+                let tenantClient = cac_client.get(tenant);
+                if (tenantClient) {
+                    tenantClient.startPollingUpdate();
+                } else {
+                    tenantClient = new CacClient(tenant, pollingFrequency, cacHostName);
+                    cac_client.set(tenant, tenantClient);
+                    tenantClient.startPollingUpdate();
+                }
+            }
+        } catch (error) {
+            console.log("Error While starting polling Update for cac client ", error);
+        }
+    })
+}
+// -----------------------------------------
+
+export enum MergeStrategy {
+    MERGE = "MERGE",
+    REPLACE = "REPLACE"
+}
+
+export class CacClient {
+    tenant: string | null = null;
+    cacHostName: string | null = null;
+    pollingFrequency: number = 10;
+    delimeter: string = ",";
+
+    rustLib = ffi.Library(libPath, {
+        'cac_new_client': [int, [string, int, string]],
+        'cac_get_client': ["pointer", [string]],
+        'cac_start_polling_update': [voidType, [string]],
+        'cac_free_client': [voidType, ["pointer"]],
+        'cac_last_error_message': [string, []],
+        'cac_get_config': [string, ["pointer", "pointer", "pointer"]],
+        'cac_last_error_length': [int, [voidType]],
+        'cac_free_string': [voidType, ["pointer"]],
+        'cac_get_last_modified': [string, ["pointer"]],
+        'cac_get_resolved_config': [string, ["pointer", string, "pointer", string]],
+        'cac_get_default_config': [string, ["pointer", "pointer"]],
+
+    });
+
+    constructor(tenantName: string, pollingFrequency: number, cacHostName: string) {
+        if (!tenantName || tenantName == "") {
+            throw Error("tenantName cannot be null or empty")
+        }
+        if (!cacHostName || cacHostName == "") {
+            throw Error("cacHostName cannot be null or empty")
+        }
+        this.tenant = tenantName;
+        this.pollingFrequency = pollingFrequency;
+        this.cacHostName = cacHostName;
+        let resp = this.rustLib.cac_new_client(this.tenant, this.pollingFrequency, this.cacHostName);
+        if (resp == 1) {
+            let errorMessage = this.getLastErrorMessage();
+            throw Error("Some Error Occur while creating new client " + errorMessage);
+        }
+    }
+
+    public getLastErrorMessage(): string {
+        return this.rustLib.cac_last_error_message() || "";
+    }
+
+    public getLastErrorLength(): number {
+        return this.rustLib.cac_last_error_length()
+    }
+
+    public getClient(): ref.Pointer<unknown> {
+        return this.rustLib.cac_get_client(this.tenant);
+    }
+
+    public async startPollingUpdate() {
+        if (isMainThread && worker) {
+            worker.postMessage(
+                JSON.stringify({ tenant: this.tenant
+                    , event : "startPollingUpdate"
+                    , pollingFrequency: this.pollingFrequency
+                    , cacHostName: this.cacHostName
+                    })
+            );
+            return;
+        }
+        if (!isMainThread) {
+            this.rustLib.cac_start_polling_update(this.tenant)
+        }
+    }
+
+    public getConfig(filterQuery: Object | undefined, filterPrefix: string[] | undefined): string {
+        let strFilterQuery = filterQuery ? ref.allocCString(JSON.stringify(filterQuery)) : ref.NULL;
+        let strFilterPrefix = filterPrefix ? ref.allocCString(filterPrefix.join(this.delimeter)) : ref.NULL;
+        let clientPtr = this.getClient();
+        let resp = this.rustLib.cac_get_config(clientPtr, strFilterQuery, strFilterPrefix) || this.getLastErrorMessage();
+        return resp;
+    }
+
+    freeClient(clientPtr: ref.Pointer<unknown>) {
+        this.rustLib.cac_free_client(clientPtr);
+    }
+
+    freeString(str: ref.Pointer<unknown>) {
+        this.rustLib.cac_free_string(str);
+    }
+
+    public getLastModified(): string {
+        return this.rustLib.cac_get_last_modified(this.getClient()) || this.getLastErrorMessage();
+    }
+
+    public getResolvedConfig(query: Object, filterKeys: string[] | undefined, mergeStrategy: MergeStrategy): string {
+        let strQuery = JSON.stringify(query);
+        let strFilterKeys = filterKeys ? ref.allocCString (filterKeys.join("|")) : ref.NULL ;
+        let resp = this.rustLib.cac_get_resolved_config(
+            this.getClient(), strQuery, strFilterKeys, mergeStrategy
+        ) || this.getLastErrorMessage();
+        return resp;
+    }
+    public getDefaultConfig(filterKeys: string[] | undefined): string {
+        let strFilterKeys = filterKeys ? ref.allocCString(filterKeys.join("|")) : ref.NULL;
+        let resp = this.rustLib.cac_get_default_config(
+            this.getClient(), strFilterKeys
+        ) || this.getLastErrorMessage();
+        return resp;
+    }
+}

clients/nodejs/cac-client/package.json

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+{
+  "name": "nodejs_cac_client",
+  "version": "1.0.0",
+  "main": "dist/client.js",
+  "types": "dist/client.d.ts",
+  "files": [
+    "/dist"
+  ],
+  "devDependencies": {
+    "@types/express": "^4.17.21",
+    "@types/ffi-napi": "^4.0.10",
+    "@types/node": "^20.14.10",
+    "@types/ref-napi": "^3.0.12",
+    "@types/typescript": "^2.0.0",
+    "express": "^4.19.2",
+    "ffi-napi": "^4.0.3",
+    "ref-napi": "^3.0.3",
+    "ts-node": "^10.9.2",
+    "typescript": "^5.5.3"
+  },
+  "scripts": {
+    "postinstall" : "npx tsc"
+  }
+}

clients/nodejs/cac-client/tsconfig.json

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+{
+  "compilerOptions": {
+    "module": "CommonJS",
+    "target": "ES2015",
+    "outDir": "./dist",
+    "declaration": true,
+    "esModuleInterop": true
+  },
+  "exclude": ["node_modules"],
+  "include": ["./client.ts"]
+}