add prepare chunks function

Author: carlosala

package.json

@@ -2,7 +2,7 @@
   "name": "@zondax/ledger-js",
   "author": "Zondax AG",
   "license": "Apache-2.0",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "description": "TS / Node API for apps running on Ledger Nano S/S+/X",
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",

src/GenericApp.ts

@@ -16,12 +16,14 @@ export default class GenericApp {
   readonly INS: INSGeneric;
   readonly P1_VALUES: P1_VALUESGeneric;
   readonly acceptedPathLengths?: number[];
+  readonly CHUNK_SIZE: number;
 
   constructor(transport: Transport, params: ConstructorParams) {
     this.transport = transport;
     this.CLA = params.cla;
     this.INS = params.ins;
     this.P1_VALUES = params.p1Values;
+    this.CHUNK_SIZE = params.chunkSize;
     this.acceptedPathLengths = params.acceptedPathLengths;
   }
 
@@ -56,6 +58,27 @@ export default class GenericApp {
     return buf;
   }
 
+  prepareChunks(path: string, message: Buffer): Buffer[] {
+    const chunks = [];
+    const serializedPathBuffer = this.serializePath(path);
+
+    // First chunk (only path)
+    chunks.push(serializedPathBuffer);
+
+    const messageBuffer = Buffer.from(message);
+
+    const buffer = Buffer.concat([messageBuffer]);
+    for (let i = 0; i < buffer.length; i += this.CHUNK_SIZE) {
+      let end = i + this.CHUNK_SIZE;
+      if (i > buffer.length) {
+        end = buffer.length;
+      }
+      chunks.push(buffer.subarray(i, end));
+    }
+
+    return chunks;
+  }
+
   async getVersion(): Promise<ResponseVersion> {
     const versionResponse: ResponseVersion = await this.transport
       .send(this.CLA, this.INS.GET_VERSION, 0, 0)

src/consts.ts

@@ -16,8 +16,6 @@
  *******************************************************************************
  */
 
-export const CHUNK_SIZE = 250;
-
 export const PAYLOAD_TYPE = {
   INIT: 0x00,
   ADD: 0x01,

src/types.ts

@@ -45,5 +45,6 @@ export interface ConstructorParams {
   cla: number;
   ins: INSGeneric;
   p1Values: P1_VALUESGeneric;
+  chunkSize: number;
   acceptedPathLengths?: number[];
 }