Ping With Proxy

Understanding Unloaded vs. Loaded Latency

Traditional latency tests often measure a single round-trip time (e.g. via a simple HTTP HEAD request). However, real-world performance can differ when the network is under load. Unloaded latency refers to round-trip time with no other traffic, while loaded latency measures round-trip time under heavy network usage. The difference (sometimes called bufferbloat) reflects how much extra delay is introduced by network congestion. In the context of HTTP proxies, measuring both gives insight into how a proxy performs under normal conditions versus saturated conditions.

Why basic HEAD timing is insufficient: A single request might not represent typical client behavior. It may include one-time setup costs (DNS lookup, TCP and TLS handshakes) and doesn't show how the proxy handles concurrent traffic. To mimic real-world client traffic, we need to gather multiple samples and introduce parallelism to simulate load.

Multi-Stream Latency Measurements

Rather than relying on one request, send multiple small HTTP requests through the proxy and collect their response times. For example, services like Cloudflare's and Netflix's speed tests send many small GET requests (with minimal payload) to measure latency more reliably. Fast.com's client issues a batch of latency requests and computes a median latency as the result. Using the median (50th percentile) helps filter out outliers caused by jitter.

Simulating Loaded Latency Under Traffic

To measure loaded latency (latency under stress), generate traffic in parallel with the latency probes. Netflix's Fast.com and Cloudflare's speed test both perform latency checks while the connection is busy to see how congestion affects responsiveness. Essentially, you saturate the proxy connection with data and simultaneously measure latency.

Measuring TCP-Level Handshake Time

To delve deeper, you can measure TCP-level responsiveness through the proxy. This involves timing the connection setup phases (TCP and TLS handshakes) which contribute to latency but are usually hidden in a single HTTP request measurement.

Node.js Tools and Libraries for Implementation

Implementing these strategies in Node.js is facilitated by a few libraries and patterns such as HTTP(S) Proxy Agents like https-proxy-agent or http-proxy-agent. These agents plug into Node's request options and handle the CONNECT tunneling for HTTPS.

Summary

By combining multiple sample measurements, parallel traffic simulation, and low-level timing, you can closely mimic how a real client experiences latency through an HTTP(S) proxy. Instead of a simplistic single ping, this approach measures both unloaded latency and loaded latency (bufferbloat), much like fast.com and other modern speed tests. It uses multi-stream concurrency to create realistic load, as Netflix's fast.com does to saturate links for testing.

How httping Achieves Low HTTP Ping Latency

The open-source httping tool (written in Go) is designed to measure HTTP(S) round-trip times (RTT) with minimal overhead. It employs several techniques to ensure latency measurements are as low and precise as possible:

• High-Precision Timing: httping uses Go's high-resolution monotonic clock to measure RTT with sub-millisecond precision. By capturing the timestamp immediately before sending the request and immediately after the response is received, it obtains an accurate measurement of the request's round-trip time.
• Minimal HTTP Request Overhead: The tool restricts HTTP methods to GET or HEAD only, favoring HEAD when possible to avoid downloading a response body. This means each "ping" carries minimal payload and the server's response is small (often just headers), reducing transfer time.
• Direct Socket/Transport Control: Instead of using a high-level abstraction that might add overhead, httping configures a custom HTTP transport for each request. For example, it explicitly enables HTTP/2 usage and adjusts TLS settings for speed.
• Proxy Handling: For measuring through proxies, httping integrates proxy support at the transport level. It looks up the system proxy settings and, if a proxy is configured, attaches it to the HTTP transport before the request.

Enhancements for a Node.js HTTP Proxy Latency Tester

To bring similar "absolute lowest, most precise" latency measurements to a Node.js-based HTTP proxy latency tester, consider the following enhancements:

• Use High-Resolution Timing APIs: Replace any usage of Date.now() with Node's high-precision timers such as process.hrtime.bigint() and performance.now() for sub-millisecond timing precision.
• Disable Nagle's Algorithm: Ensure that the TCP sockets used by your HTTP requests are not buffering small packets by using request.setNoDelay(true) on the client request to force the network stack to send out HTTP requests immediately.
• Reuse Connections with Keep-Alive: If measuring minimal latency for repeated requests through the same proxy, leverage HTTP keep-alive using an http.Agent with keepAlive: true to avoid TCP/TLS handshake overhead on subsequent requests.
• Streamline the HTTP Request: Use the simplest possible request that yields a response, such as HEAD or a lightweight GET to a known small resource through the proxy with minimal headers.