Este/predictable size (#8)

* keep random string in a predictable lenght

* added some docs

* better docs

---------

Co-authored-by: Ronny Esterluss <[email protected]>

k6/src/k6/send-messages.test.ts

@@ -4,7 +4,6 @@ import { Counter, Trend } from "k6/metrics";
 import http, { RefinedParams, RefinedResponse, ResponseType } from "k6/http";
 import { check, fail } from "k6";
 import ws from "k6/ws";
-import crypto from 'k6/crypto';
 // 1. Begin Init section
 const nodes = __ENV.NODES || "many2many";
 
@@ -18,7 +17,9 @@ const amountOfReceivers = nodesData.nodes.filter(
     node.enabled && node.isReceiver != undefined && node.isReceiver,
 ).length;
 
-const MaxPayloadBytes = 325;
+const MaxPayloadBytes = 400;
+const Alphabet =
+  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 
 // Override API Token
 if (__ENV.HOPRD_API_TOKEN) {
@@ -247,15 +248,17 @@ export function multipleHopMessage(dataPool: {
   );
 }
 
+// use random ASCI chars to extend the payload
+// UTF-8 uses variying byte sizes - try to keep them in the single byte range
+// so we have a predicatble payload size
 function extendWrandomBytes(body: string): string {
   const count = MaxPayloadBytes - body.length - 1;
-  const bytes = crypto.randomBytes(count);
-  const uintArray = new Uint8Array(bytes);
-  const str = uintArray.reduce<string>((acc, v) => {
-    acc += String.fromCharCode(v);
-    return acc;
-  }, "");
-  return `${body} ${str}`;
+  let rndmContent = "";
+  for (let i = 0; i < count; i++) {
+    const idx = Math.floor(Math.random() * Alphabet.length);
+    rndmContent += Alphabet.charAt(idx);
+  }
+  return `${body} ${rndmContent}`;
 }
 
 export function teardown(dataPool: {