Buffer up res.body so we can send it off to the metrics server

Author: Dom Harrington

index.js

@@ -3,6 +3,30 @@ const config = require('config');
 
 const constructPayload = require('./lib/construct-payload');
 
+// We're doing this to buffer up the response body
+// so we can send it off to the metrics server
+// It's unfortunate that this isn't accessible
+// natively. This may take up lots of memory on
+// big responses, we can make it configurable in future
+function patchResponse(res) {
+  /* eslint-disable no-underscore-dangle */
+  const { write, end } = res;
+
+  res._body = '';
+
+  res.write = (chunk, encoding, cb) => {
+    res._body += chunk;
+    write.call(res, chunk, encoding, cb);
+  };
+
+  res.end = (chunk, encoding, cb) => {
+    // Chunk is optional in res.end
+    // http://nodejs.org/dist/latest/docs/api/http.html#http_response_end_data_encoding_callback
+    if (chunk) res._body += chunk;
+    end.call(res, chunk, encoding, cb);
+  };
+}
+
 module.exports = (apiKey, group, options) => {
   if (!apiKey) throw new Error('You must provide your ReadMe API key');
   if (!group) throw new Error('You must provide a grouping function');
@@ -11,6 +35,7 @@ module.exports = (apiKey, group, options) => {
 
   return (req, res, next) => {
     const startedDateTime = new Date();
+    patchResponse(res);
 
     function send() {
       request.post(`${config.host}/request`, {

lib/process-response.js

@@ -4,20 +4,31 @@ const removeOtherProperties = require('lodash.pick');
 const objectToArray = require('./object-to-array');
 
 module.exports = (res, options = {}) => {
-  if (options.blacklist) {
-    res.body = removeProperties(res.body, options.blacklist);
+  // Here we have to reconstruct the body
+  // from the string that we've buffered up
+  // We have to do this so we can strip out
+  // any whitelist/blacklist properties
+  let body;
+  try {
+    body = JSON.parse(res._body); // eslint-disable-line no-underscore-dangle
+  } catch (e) {
+    // Non JSON body, don't attempt to send it off
   }
 
-  if (options.whitelist) {
-    res.body = removeOtherProperties(res.body, options.whitelist);
+  if (options.blacklist && body) {
+    body = removeProperties(body, options.blacklist);
+  }
+
+  if (options.whitelist && body) {
+    body = removeOtherProperties(body, options.whitelist);
   }
 
   return {
     status: res.statusCode,
     statusText: res.statusMessage,
     headers: objectToArray(res.getHeaders()),
     content: {
-      text: JSON.stringify(res.body),
+      text: JSON.stringify(body),
       size: res.get('content-length'),
       mimeType: res.get('content-type'),
     },

test/index.test.js

@@ -43,11 +43,7 @@ describe('@readme/metrics', () => {
       .reply(200);
 
     const app = express();
-    app.use((req, res, next) => {
-      req.user = { group };
-      return next();
-    });
-    app.use(middleware(apiKey, req => req.user.group));
+    app.use(middleware(apiKey, () => group));
     app.get('/test', (req, res) => res.sendStatus(200));
 
     await request(app)
@@ -56,4 +52,70 @@ describe('@readme/metrics', () => {
 
     mock.done();
   });
+
+  describe('`res._body`', () => {
+    const responseBody = { a: 1, b: 2, c: 3 };
+    function createMock() {
+      return nock(config.host)
+        .post('/request', ([body]) => {
+          assert.equal(
+            body.request.log.entries[0].response.content.text,
+            JSON.stringify(responseBody),
+          );
+          return true;
+        })
+        .basicAuth({ user: apiKey })
+        .reply(200);
+    }
+
+    it('should buffer up res.write() calls', async function test() {
+      this.timeout(5000);
+
+      const mock = createMock();
+      const app = express();
+      app.use(middleware(apiKey, () => '123'));
+      app.get('/test', (req, res) => {
+        res.write('{"a":1,');
+        res.write('"b":2,');
+        res.write('"c":3}');
+        res.status(200).end();
+      });
+
+      await request(app)
+        .get('/test')
+        .expect(200);
+
+      mock.done();
+    });
+
+    it('should buffer up res.end() calls', async function test() {
+      this.timeout(5000);
+
+      const mock = createMock();
+      const app = express();
+      app.use(middleware(apiKey, () => '123'));
+      app.get('/test', (req, res) => res.end(JSON.stringify(responseBody)));
+
+      await request(app)
+        .get('/test')
+        .expect(200);
+
+      mock.done();
+    });
+
+    it('should work for res.send() calls', async function test() {
+      this.timeout(5000);
+
+      const mock = createMock();
+      const app = express();
+      app.use(middleware(apiKey, () => '123'));
+      app.get('/test', (req, res) => res.send(responseBody));
+
+      await request(app)
+        .get('/test')
+        .expect(200);
+
+      mock.done();
+    });
+  });
 });

test/process-response.test.js

@@ -12,6 +12,10 @@ function testResponse(assertion, response) {
   app.post('/*', (req, res) => {
     res.once('finish', assertion.bind(null, res));
 
+    // This is done in the main middleware by
+    // overwriting res.write/end
+    res._body = JSON.stringify(response); // eslint-disable-line no-underscore-dangle
+
     res.json(response);
   });
 
@@ -22,7 +26,7 @@ function testResponse(assertion, response) {
 }
 
 describe('processResponse()', () => {
-  describe.skip('options', () => {
+  describe('options', () => {
     it('should strip blacklisted properties', done => {
       testResponse(
         res => {
@@ -90,7 +94,7 @@ describe('processResponse()', () => {
         return done();
       }));
 
-    it.skip('#text', done => {
+    it('#text', done => {
       const body = { a: 1, b: 2, c: 3 };
       testResponse(res => {
         assert.deepEqual(processResponse(res).content.text, JSON.stringify(body));