Fixing quadratic runtime when setting a maxContentLength (#3738)

Previously checking whether a response has exceeded `maxContentLength` was
quadratic with respect to the number of chunks in the response stream and
also caused unnecessary additional memory usage.
Co-authored-by: NJay <jasonsaayman@gmail.com>

lib/adapters/http.js

@@ -238,11 +238,13 @@ module.exports = function httpAdapter(config) {
         settle(resolve, reject, response);
       } else {
         var responseBuffer = [];
+        var totalResponseBytes = 0;
         stream.on('data', function handleStreamData(chunk) {
           responseBuffer.push(chunk);
+          totalResponseBytes += chunk.length;
 
           // make sure the content length is not over the maxContentLength if specified
-          if (config.maxContentLength > -1 && Buffer.concat(responseBuffer).length > config.maxContentLength) {
+          if (config.maxContentLength > -1 && totalResponseBytes > config.maxContentLength) {
             stream.destroy();
             reject(createError('maxContentLength size of ' + config.maxContentLength + ' exceeded',
               config, null, lastRequest));