Mar/drandexample

.gitignore

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 *.out
 
 .idea/
+
+node_modules/

drandexample/README.md

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+# drandexample
+Example on how to use Drand as a client
+
+# What, Why, How?
+Created a small script to show & describe how to get random numbers from the drand network.
+
+Example: Imagine you are a full time L5 software engineer and have more important things to think about than what to get for lunch.
+    You decide to leave it up to randomness to choose your next meal. But you still have preferences.
+    You assign weights to your preferences such that items you would like to eat most often have heavier weights (chances of being chosen)
+    And things you don't want to eat as often, have smaller probability of being chosen.
+
+Things to note:
+    Drand mainnet releases a random number every 30 seconds. The problem that arises is if you want to test if the biased randomness works or not, it would take a really long time to test.
+    There is work to shorten this time frame to 3 seconds, which is better, but its not as convenient as instant access of psuedo-random numbers like math.random() or crypto.getRandomValues().
+
+This script shortens down a `randomness` value from the network and uses it as a probability for selecting an item.
+
+### Requirements 
+Node 12 and up
+
+# Run
+1. `npm install`
+
+2. `node bias.js`

drandexample/bias.js

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+import Client, { HTTP } from 'drand-client';
+import fetch from 'node-fetch';
+import AbortController from 'abort-controller';
+
+global.fetch = fetch;
+global.AbortController = AbortController;
+
+const chainHash = '8990e7a9aaed2ffed73dbd7092123d6f289930540d7651336225dc172e51b2ce'; // Mainnet chain hash (hex encoded)
+const urls = [
+  'https://api.drand.sh',
+  'https://drand.cloudflare.com'
+]; // various endpoint options to access Drand network. 
+
+const HEX = 16;
+const FoodOptions = { "pho": 0.3, "croquets": 0.29, "pizza": 0.28, "pasta": 0.07, "molé_verde": 0.03, "shrimp": .03 };
+
+// This function takes in a list of items and the probablilty of them being selected.
+//    returns the number that is randomly selected 
+async function weightedRandom(prob) {
+  if (validateWeights(prob) != 1) {
+    return "Weights not equal to 1"
+  }
+  const options = { chainHash };
+
+  const client = await Client.wrap(HTTP.forURLs(urls, chainHash), options);
+
+  // e.g. use the client to get the latest randomness round:
+  const res = await client.get();
+
+  // Get a number between 0 and 100 from Drand.
+  const rand = randomPercentFrom(res.randomness);
+
+  // This for loop selects which key:pair to return
+  let sum = 0, r = rand;
+  for (let [key, value] of Object.entries(prob)) {
+    sum += value * 100;
+    if (r <= sum) {
+      return key;
+    }
+  }
+}
+
+//runs code above
+weightedRandom(FoodOptions).then((lunch) => (console.log(lunch)))
+// Press Ctrl + C to stop example!
+
+// This function returns a number between 0 & 99.
+function randomPercentFrom(randomness) {
+  var i = 0;
+  var randomDecimal = -1;
+  var rand;
+
+  while (randomDecimal <= 0 || randomDecimal > 100) {
+    // Grab only 2 digits from randomness, in a "sliding window" fashion
+    rand = randomness.slice(0 + i, 2 + i);
+    // Convert hexadecimal randomness value to decimal (base16 -> base10)
+    randomDecimal = parseInt(rand, HEX);
+    i++;
+  }
+  return randomDecimal;
+}
+
+// This function checks the user input to make sure all probabilities add up to 1
+function validateWeights(probabilities) {
+  var sum = 0;
+  for (let [_, value] of Object.entries(probabilities)) {
+    sum += value;
+  }
+  return sum;
+}

drandexample/package.json

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+{
+    "name": "drandexample",
+    "version": "1.0.0",
+    "type": "module",
+    "description": "Example on how to use Drand",
+    "main": "bias.js",
+    "scripts": {
+      "test": "node bias.js"
+    },
+    "keywords": [
+      "drand",
+      "example"
+    ],
+    "author": "Marco Rodriguez-Salinas",
+    "license": "MIT",
+    "dependencies": {
+      "abort-controller": "^3.0.0",
+      "drand-client": "^0.2.0",
+      "node-fetch": "^3.2.10"
+    }
+  }