From 5ed855a0ceab757facbacb132ca59f9af6673865 Mon Sep 17 00:00:00 2001
From: Jackie Tung <jackie.tung@nooks.in>
Date: Tue, 7 Apr 2026 14:51:43 -0700
Subject: [PATCH] Support configurable maxSockets for HTTP agents

The SDK creates HTTP agents with keepAlive: true but uses the Node.js
default maxSockets: Infinity. In high-throughput server environments,
concurrent track() calls can open an unbounded number of TCP connections
to Mixpanel's API, which can exhaust file descriptors or trigger rate
limits.

This adds support for a maxSockets init config option that gets passed
through to the underlying http.Agent / https.Agent. When not set,
behavior is unchanged (defaults to Infinity).

Usage:
  var mixpanel = Mixpanel.init('token', { maxSockets: 10 });

Confab-Link: https://confab.nooks.in/sessions/e7243277-5942-4965-8abe-99b18914a204
---
 lib/mixpanel-node.js |  5 +++--
 readme.md            |  5 +++++
 test/send_request.js | 23 +++++++++++++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/lib/mixpanel-node.js b/lib/mixpanel-node.js
index d7cdb85..c8d4abe 100644
--- a/lib/mixpanel-node.js
+++ b/lib/mixpanel-node.js
@@ -49,13 +49,14 @@ const create_client = function (token, config) {
     config: { ...DEFAULT_CONFIG },
   };
   const { keepAlive } = metrics.config;
+  const maxSockets = config && config.maxSockets;
 
   // mixpanel constants
   const MAX_BATCH_SIZE = 50;
   const REQUEST_LIBS = { http, https };
   const REQUEST_AGENTS = {
-    http: new http.Agent({ keepAlive }),
-    https: new https.Agent({ keepAlive }),
+    http: new http.Agent({ keepAlive, maxSockets }),
+    https: new https.Agent({ keepAlive, maxSockets }),
   };
   const proxyPath = process.env.HTTPS_PROXY || process.env.HTTP_PROXY;
   const proxyAgent = proxyPath
diff --git a/readme.md b/readme.md
index decd413..57e5ca8 100644
--- a/readme.md
+++ b/readme.md
@@ -28,6 +28,11 @@ var mixpanel = Mixpanel.init("<YOUR_TOKEN>", {
   keepAlive: false,
 });
 
+// limit the number of concurrent connections to Mixpanel
+var mixpanel = Mixpanel.init("<YOUR_TOKEN>", {
+  maxSockets: 10,
+});
+
 // pass the custom logger (default is console)
 var mixpanel = Mixpanel.init("<YOUR_TOKEN>", {
   debug: true,
diff --git a/test/send_request.js b/test/send_request.js
index 01be8dc..b77c6c3 100644
--- a/test/send_request.js
+++ b/test/send_request.js
@@ -182,6 +182,29 @@ describe("send_request", () => {
     expect(getConfig.agent).toBe(agent);
   });
 
+  it("uses custom maxSockets when configured", () => {
+    const agent = new https.Agent({ keepAlive: true });
+    const httpsStub = {
+      request: vi.fn().mockImplementation((_, cb) => {
+        cb(res);
+        return http_emitter;
+      }),
+      Agent: vi.fn().mockImplementation(function () {
+        return agent;
+      }),
+    };
+    delete process.env.HTTP_PROXY;
+    delete process.env.HTTPS_PROXY;
+    Mixpanel = proxyquire("../lib/mixpanel-node", {
+      https: httpsStub,
+    });
+    const proxyMixpanel = Mixpanel.init("token", { maxSockets: 10 });
+    proxyMixpanel.send_request({ endpoint: "", data: {} });
+
+    const agentOpts = httpsStub.Agent.mock.calls[0][0];
+    expect(agentOpts.maxSockets).toBe(10);
+  });
+
   it("uses correct hostname", () => {
     const host = "testhost.fakedomain";
     const customHostnameMixpanel = Mixpanel.init("token", { host: host });