benchmark: add a large JSON body scenario

benchmark/scenarios/body-json-512kb.js

@@ -0,0 +1,28 @@
+'use strict';
+
+// The other body-parser scenario posts 57 bytes, which uWS hands over in a single
+// chunk, so it never exercises the accumulate path. This one is large enough to
+// arrive in several chunks and makes the cost of collecting a body visible.
+const PAD = 512 * 1024;
+
+module.exports = {
+    name: 'middlewares/body-json-512kb',
+    path: '/abc',
+    wrk: {
+        script: 'post-json-512kb.lua',
+        connections: 50
+    },
+    verify: {
+        method: 'POST',
+        headers: {
+            'Content-Type': 'application/json'
+        },
+        body: JSON.stringify({ n: 1, pad: 'x'.repeat(PAD) })
+    },
+    setup(app, express) {
+        app.use(express.json({ limit: '10mb' }));
+        app.post('/abc', (req, res) => {
+            res.send(`${req.body.pad.length}`);
+        });
+    }
+};

benchmark/wrk-scripts/post-json-512kb.lua

@@ -0,0 +1,7 @@
+wrk.method = "POST"
+wrk.path = "/abc"
+wrk.headers["Content-Type"] = "application/json"
+
+local kb = 1024
+local pad = string.rep("x", 512 * kb)
+wrk.body = '{"n":1,"pad":"' .. pad .. '"}'