Initial commit

src/currencyservice/server.js

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+/*
+ * Copyright 2018 Google LLC.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const path = require('path');
+const grpc = require('grpc');
+const request = require('request');
+const xml2js = require('xml2js');
+
+const PROTO_PATH = path.join(__dirname, './proto/currency_service.proto');
+const PORT = 31337;
+const DATA_URL = 'http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml';
+const shopProto = grpc.load(PROTO_PATH).hipstershop;
+
+/**
+ * Helper function that gets currency data from an XML webpage
+ * Uses public data from European Central Bank
+ */
+function _getCurrencyData (callback) {
+  request(DATA_URL, (err, res) => {
+    if (err) {
+      throw new Error(`Error getting data: ${err}`);
+    }
+
+    const body = res.body.split('\n').slice(7, -2).join('\n');
+    xml2js.parseString(body, (err, resJs) => {
+      if (err) {
+        throw new Error(`Error parsing HTML: ${err}`);
+      }
+
+      const array = resJs['Cube']['Cube'].map(x => x['$']);
+      const results = array.reduce((acc, x) => {
+        acc[x['currency']] = x['rate'];
+        return acc;
+      }, { 'EUR': '1.0' });
+      callback(results);
+    });
+  });
+}
+
+/**
+ * Helper function that handles decimal/fractional carrying
+ */
+function _carry (amount) {
+  amount.fractional += (amount.decimal % 1) * 100;
+  amount.decimal = Math.floor(amount.decimal + amount.fractional / 100);
+  amount.fractional = amount.fractional % 100;
+  return amount;
+}
+
+/**
+ * Lists the supported currencies
+ */
+function getSupportedCurrencies (call, callback) {
+  _getCurrencyData((data) => {
+    callback(null, {currency_codes: data.keys()});
+  });
+}
+
+/**
+ * Converts between currencies
+ */
+function convert (call, callback) {
+  try {
+    _getCurrencyData((data) => {
+      const request = call.request;
+
+      // Convert: from_currency --> EUR
+      const from = request.from;
+      const euros = _carry({
+        decimal: from.amount.decimal / data[from.currency_code],
+        fractional: from.amount.fractional / data[from.currency_code]
+      });
+
+      // Convert: EUR --> to_currency
+      const target = _carry({
+        decimal: euros.decimal * data[request.to_code],
+        fractional: euros.fractional * data[request.to_code]
+      });
+      target.fractional = Math.round(target.fractional);
+
+      callback(null, {amount: target});
+    });
+  } catch (err) {
+    callback(err.message);
+  }
+}
+
+/**
+ * Starts an RPC server that receives requests for the
+ * CurrencyConverter service at the sample server port
+ */
+function main () {
+  var server = new grpc.Server();
+  server.addService(shopProto.CurrencyService.service, {getSupportedCurrencies, convert});
+  server.bind(`0.0.0.0:${PORT}`, grpc.ServerCredentials.createInsecure());
+  server.start();
+}
+
+main();