Better Auth V1.3.0 Memory Leak With CustomSession Plugin

Introduction

Hey guys! It looks like we've got a bit of a situation on our hands with Better Auth v1.3.0. A memory leak has been discovered when using the customSession plugin, and it's causing some serious memory growth. This article will dive into the details of the issue, how to reproduce it, and what might be the underlying cause. We'll also explore the system info and configurations involved, and hopefully, shed some light on a potential fix. So, let's get started and figure out how to tackle this memory leak!

The Problem: Memory Leak with customSession Plugin

In the realm of Better Auth, version 1.3.0 has brought with it an unexpected challenge – a memory leak specifically tied to the customSession plugin. This isn't just a minor hiccup; it's a persistent issue where memory usage continually increases, which, if left unchecked, can lead to application instability and performance degradation. Imagine your application slowly eating up more and more memory until it eventually crashes. Not a pretty picture, right? This memory leak means that resources aren't being released as they should be, leading to a steady accumulation of used memory over time. Understanding the specifics of this issue is crucial for developers relying on Better Auth, especially those utilizing the customSession plugin to tailor their session management.

Reproducing the Memory Leak

To get a handle on this memory leak, it’s essential to understand how to reproduce it. Luckily, a dedicated repository has been set up with all the steps and code necessary to replicate the issue. This is super helpful because it allows developers to see the problem in action and confirm that they're experiencing the same bug. The repository acts as a controlled environment where the memory leak can be consistently reproduced, making it easier to test potential solutions. If you're encountering unusual memory growth in your application, following the steps in the provided repository is a great way to verify if it's related to this specific Better Auth issue. By reproducing the leak, we can isolate the problem and focus our efforts on finding a fix. So, if you're seeing memory issues, definitely check out the repo – it's like a lab where we can study the bug in detail!

Current vs. Expected Behavior

The core issue here is a significant deviation from what we expect from a well-behaved application. The current behavior shows memory usage continuously growing without any signs of slowing down. This is a classic symptom of a memory leak, where memory allocated by the application isn't being released back to the system, leading to an ever-increasing memory footprint. On the other hand, the expected behavior is that memory usage should remain relatively stable, with temporary spikes during intensive operations, but returning to a baseline level after those operations are complete. Memory should be allocated and deallocated efficiently, ensuring the application doesn't hog unnecessary resources. This discrepancy between the current and expected behavior is what makes this memory leak such a critical issue. It's like a tap that keeps running, slowly but surely filling the sink until it overflows. We need to find that tap and turn it off to prevent the memory from overflowing and crashing our app!

System Information and Better Auth Version

To effectively troubleshoot this memory leak, we need to gather as much information as possible about the environment where it's occurring. In this case, the issue was reported on a macOS system running version 15.5, equipped with an Apple M1 Pro chip. The system has a hefty 32GB of memory, but even with that much RAM, the memory leak is still a problem. The shell being used is zsh, and the user has both Chrome (version 139.0.7258.68) and Safari (version 18.5) installed. As for Better Auth, the version in use is 1.3.6. This information helps us understand the context in which the memory leak is happening. It's like gathering clues in a detective case – the more details we have, the better chance we have of cracking the case. Knowing the OS, CPU, browser versions, and the specific version of Better Auth helps us narrow down potential causes and identify any environment-specific factors that might be contributing to the leak.

Affected Areas: Backend

When it comes to pinpointing the source of a memory leak, it's crucial to identify which parts of the application are affected. In this case, the issue seems to be primarily impacting the backend. This suggests that the memory leak is likely occurring within the server-side logic of Better Auth, particularly in how it handles sessions and user data. Backend memory leaks can be especially problematic because they can affect the overall stability and performance of the server, potentially impacting all users of the application. Think of it like a plumbing problem in a building – if the leak is in the main pipes, it can affect the water supply to every apartment. By focusing on the backend, we can narrow our investigation and concentrate on the code responsible for session management, data processing, and any other server-side operations performed by Better Auth. This targeted approach will help us efficiently identify the root cause of the memory leak and develop a solution.

Auth Configuration

Let's take a look at the auth configuration. This configuration snippet is super important because it shows how the customSession plugin is being used, which is the key area of concern in this memory leak. The code imports the necessary modules from Better Auth, including svelteKitHandler, betterAuth, and customSession. It also imports types for User and Session. The betterAuth function is then called with a configuration object that includes the plugins array. Inside this array, the customSession plugin is used. The plugin's function takes a user and session object and returns a modified session object. In this specific case, a new field called newField is added to the user object within the session. This is where things get interesting. The customSession plugin allows developers to extend the session object with custom data, but it seems like there might be an issue with how these extensions are being handled, potentially leading to the memory leak. By examining this configuration, we can see exactly how the customSession plugin is being used and identify any potential misconfigurations or patterns that might be contributing to the problem. It's like having a blueprint of the system – we can trace the flow of data and see where things might be going wrong.

import { svelteKitHandler } from 'better-auth/svelte-kit';
import { building } from '$app/environment';
import { betterAuth } from 'better-auth';
import { customSession } from 'better-auth/plugins';
import type { User, Session } from 'better-auth/types';

export const auth = betterAuth({
  plugins: [
    customSession(async ({ user, session }: { user: User; session: Session }) => {
      return {
        user: {
          ...user,
          newField: 'newField'
        },
        session
      };
    })
  ]
});

Additional Context and Potential Cause

Looking at the provided image and the memory dumps, there's a hint that this memory leak might be related to Zod. Zod is a popular library for data validation in TypeScript, and it's possible that it's being used internally by Better Auth or the customSession plugin. The fact that the retained items in memory dumps point towards Zod suggests that there might be an issue with how Zod schemas or instances are being managed. It's like finding a fingerprint at a crime scene – it doesn't tell us everything, but it gives us a direction to investigate. If Zod is indeed the culprit, the memory leak could be caused by circular references, improper schema caching, or other issues within the Zod library itself or its integration with Better Auth. While a deep dive is needed to confirm this, the Zod connection is a valuable clue that could help us track down the root cause of the memory leak. It highlights the importance of examining third-party libraries and their interactions within the application when troubleshooting memory issues.

Conclusion

Alright, guys, we've covered a lot of ground here! We've identified a memory leak in Better Auth v1.3.0 when using the customSession plugin. We've seen how to reproduce it, examined the affected areas, and even explored a potential connection to Zod. While we don't have a definitive solution just yet, we've gathered crucial information that will help in the debugging process. The next steps would involve a deeper investigation into the Zod integration, analyzing memory dumps in more detail, and potentially experimenting with different configurations or code changes to see if we can mitigate the leak. Memory leaks can be tricky to track down, but with a systematic approach and the information we've gathered, we're well on our way to squashing this bug and making Better Auth even better! Stay tuned for updates as we continue to investigate and work towards a fix.