CLDSRV-894: fix turn-around time for 0-byte PutObject/UploadPart

The previous fix attached a `request.on('end', ...)` listener to set
startTurnAroundTime. For non-empty uploads the downstream API handler
consumes the body, which drives the stream to emit 'end'. For 0-byte
uploads nothing consumes the stream, so 'end' never fires and
startTurnAroundTime stays undefined, causing the access log to render
turn-around time as '-'.

Detect Content-Length: 0 and set startTurnAroundTime synchronously in
that case; keep the 'end' listener for the non-empty path.

Author: dvasilas

lib/api/api.js

@@ -263,11 +263,19 @@ const api = {
                     request.serverAccessLog.analyticsUserName    = authNames.userName;
                 }
                 if (apiMethod === 'objectPut' || apiMethod === 'objectPutPart') {
-                    request.on('end', () => {
+                    const setStartTurnAroundTime = () => {
                         if (request.serverAccessLog) {
                             request.serverAccessLog.startTurnAroundTime = process.hrtime.bigint();
                         }
-                    });
+                    };
+                    // For 0-byte uploads, downstream handlers do not consume
+                    // the request stream, so 'end' never fires. Set
+                    // startTurnAroundTime synchronously in that case.
+                    if (request.headers['content-length'] === '0') {
+                        setStartTurnAroundTime();
+                    } else {
+                        request.on('end', setStartTurnAroundTime);
+                    }
                     return next(null, userInfo, authorizationResults, streamingV4Params, infos);
                 }
                 // issue 100 Continue to the client

tests/unit/api/api.js

@@ -132,6 +132,21 @@ describe('api.callApiMethod', () => {
                 done();
             });
         });
+
+        it(`should set startTurnAroundTime synchronously for 0-byte ${method}`, done => {
+            sandbox.stub(api, method).callsFake(
+                (userInfo, _request, streamingV4Params, _log, cb) => {
+                    assert.strictEqual(typeof request.serverAccessLog.startTurnAroundTime, 'bigint');
+                    cb();
+                });
+            request.objectKey = 'testobject';
+            request.serverAccessLog = {};
+            request.headers = Object.assign({}, request.headers, { 'content-length': '0' });
+            api.callApiMethod(method, request, response, log, err => {
+                assert.ifError(err);
+                done();
+            });
+        });
     });
 
     describe('MD5 checksum validation', () => {