bugfix: ZENKO-2866 unit test showing the bug

Add a unit test counting the number of open sockets after an S3 client
closes the connection before the data backend has sent a GET request:
with the fix, there should be none remaining open.

Author: jonathan-gramain

tests/unit/s3routes/routesUtils/responseStreamData.js

@@ -0,0 +1,80 @@
+const assert = require('assert');
+const http = require('http');
+
+const werelogs = require('werelogs');
+const logger = new werelogs.Logger('test:routesUtils.responseStreamData');
+
+const { responseStreamData } = require('../../../../lib/s3routes/routesUtils.js');
+const AwsClient = require('../../../../lib/storage/data/external/AwsClient');
+const DummyObjectStream = require('../../storage/data/DummyObjectStream');
+
+werelogs.configure({
+    level: 'debug',
+    dump: 'error',
+});
+
+describe('routesUtils.responseStreamData', () => {
+    const awsAgent = new http.Agent({
+        keepAlive: true,
+    });
+    const awsConfig = {
+        s3Params: {
+            endpoint: 'http://localhost:8888',
+            maxRetries: 0,
+            s3ForcePathStyle: true,
+            accessKeyId: 'accessKey',
+            secretAccessKey: 'secretKey',
+            httpOptions: {
+                agent: awsAgent,
+            },
+        },
+        bucketName: 'awsTestBucketName',
+        dataStoreName: 'awsDataStore',
+        serverSideEncryption: false,
+        type: 'aws',
+    };
+    let httpServer;
+    let awsClient;
+
+    before(done => {
+        awsClient = new AwsClient(awsConfig);
+        httpServer = http.createServer((req, res) => {
+            const objStream = new DummyObjectStream(0, 10000000);
+            res.setHeader('content-length', 10000000);
+            objStream.pipe(res);
+        }).listen(8888);
+        httpServer.on('listening', done);
+        httpServer.on('error', err => assert.ifError(err));
+    });
+
+    after(() => {
+        httpServer.close();
+    });
+
+    it('should not leak socket if client closes the connection before ' +
+    'data backend starts streaming', done => {
+        responseStreamData(undefined, {}, {}, [{
+            key: 'foo',
+            size: 10000000,
+        }], {
+            client: awsClient,
+            implName: 'impl',
+            config: {},
+            locStorageCheckFn: () => {},
+        }, {
+            setHeader: () => {},
+            writeHead: () => {},
+            on: () => {},
+            once: () => {},
+            emit: () => {},
+            write: () => {},
+            end: () => setTimeout(() => {
+                const nOpenSockets = Object.keys(awsAgent.sockets).length;
+                assert.strictEqual(nOpenSockets, 0);
+                done();
+            }, 1000),
+            // fake a connection close from the S3 client by setting the "isclosed" flag
+            isclosed: true,
+        }, undefined, logger.newRequestLogger());
+    });
+});