feat: Implement handling for gzip compressed responses. (#367)

This is working against the test harness and LD.

contract-tests/index.js

@@ -31,6 +31,7 @@ app.get('/', (req, res) => {
       'migrations',
       'event-sampling',
       'strongly-typed',
+      'polling-gzip'
     ],
   });
 });

packages/sdk/server-node/__tests__/platform/NodeRequests.test.ts

@@ -1,4 +1,5 @@
 import * as http from 'http';
+import * as zlib from 'zlib';
 
 import NodeRequests from '../../src/platform/NodeRequests';
 
@@ -57,6 +58,9 @@ describe('given a default instance of NodeRequests', () => {
           res.destroy();
           resetResolve();
         }, 0);
+      } else if ((req.url?.indexOf('gzip') || -1) >= 0) {
+        res.setHeader('Content-Encoding', 'gzip');
+        res.end(zlib.gzipSync(Buffer.from(JSON_RESPONSE, 'utf8')));
       } else {
         res.end(TEXT_RESPONSE);
       }
@@ -144,4 +148,21 @@ describe('given a default instance of NodeRequests', () => {
       await res.json();
     }).rejects.toThrow();
   });
+
+  it('includes accept-encoding header', async () => {
+    await requests.fetch(`http://localhost:${PORT}/gzip`, { method: 'GET' });
+    const serverResult = await promise;
+    expect(serverResult.method).toEqual('GET');
+    expect(serverResult.headers['accept-encoding']).toEqual('gzip');
+  });
+
+  it('can get compressed json from a response', async () => {
+    const res = await requests.fetch(`http://localhost:${PORT}/gzip`, { method: 'GET' });
+    expect(res.headers.get('content-type')).toEqual('text/plain');
+    const json = await res.json();
+    expect(json).toEqual({ text: 'value' });
+    const serverResult = await promise;
+    expect(serverResult.method).toEqual('GET');
+    expect(serverResult.body).toEqual('');
+  });
 });

packages/sdk/server-node/src/platform/NodeRequests.ts

@@ -110,12 +110,22 @@ export default class NodeRequests implements platform.Requests {
     const isSecure = url.startsWith('https://');
     const impl = isSecure ? https : http;
 
+    // For get requests we are going to automatically support compressed responses.
+    // Note this does not affect SSE as the event source is not using this fetch implementation.
+    const headers =
+      options.method?.toLowerCase() === 'get'
+        ? {
+            ...options.headers,
+            'accept-encoding': 'gzip',
+          }
+        : options.headers;
+
     return new Promise((resolve, reject) => {
       const req = impl.request(
         url,
         {
           timeout: options.timeout,
-          headers: options.headers,
+          headers,
           method: options.method,
           agent: this.agent,
         },

packages/sdk/server-node/src/platform/NodeResponse.ts

@@ -1,4 +1,6 @@
 import * as http from 'http';
+import { pipeline, Writable } from 'stream';
+import * as zlib from 'zlib';
 
 import { platform } from '@launchdarkly/js-server-sdk-common';
 
@@ -7,7 +9,15 @@ import HeaderWrapper from './HeaderWrapper';
 export default class NodeResponse implements platform.Response {
   incomingMessage: http.IncomingMessage;
 
-  body: any[] = [];
+  chunks: any[] = [];
+
+  memoryStream: Writable = new Writable({
+    decodeStrings: true,
+    write: (chunk, _enc, next) => {
+      this.chunks.push(chunk);
+      next();
+    },
+  });
 
   promise: Promise<string>;
 
@@ -26,20 +36,24 @@ export default class NodeResponse implements platform.Response {
     this.incomingMessage = res;
 
     this.promise = new Promise((resolve, reject) => {
-      res.on('data', (chunk) => {
-        this.body.push(chunk);
-      });
-
-      res.on('error', (err) => {
-        this.rejection = err;
-        if (this.listened) {
-          reject(err);
+      // Called on error or completion of the pipeline.
+      const pipelineCallback = (err: any) => {
+        if (err) {
+          this.rejection = err;
+          if (this.listened) {
+            reject(err);
+          }
         }
-      });
-
-      res.on('end', () => {
-        resolve(Buffer.concat(this.body).toString());
-      });
+        return resolve(Buffer.concat(this.chunks).toString());
+      };
+      switch (res.headers['content-encoding']) {
+        case 'gzip':
+          pipeline(res, zlib.createGunzip(), this.memoryStream, pipelineCallback);
+          break;
+        default:
+          pipeline(res, this.memoryStream, pipelineCallback);
+          break;
+      }
     });
   }