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CLI that samples a running Go process's goroutines over time and flags stacks that never finish

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- - leak.go
- - parse.go
- - pprofclient.go
- - sampler.go
- main.go
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<h1 align="center">
🕵️ goleaked
</h1>

<p align="center">
Point it at a running Go process, catch the goroutines that never finish
</p>

![Go version](https://img.shields.io/badge/go-1.26-00ADD8.svg)
![Dependencies](https://img.shields.io/badge/dependencies-0-brightgreen)
![Status](https://img.shields.io/badge/status-early%20stage-orange)
![License](https://img.shields.io/badge/license-MIT-blue)

</p>

A dependency-free CLI that attaches to a running Go process over `net/http/pprof`, samples its
goroutines repeatedly on a timer, and flags the stack traces that keep recurring, sample after
sample, without ever finishing. That recurrence, not a single snapshot, is the actual signature
of a goroutine leak.

```
$ goleaked -url http://localhost:6060/debug/pprof/goroutine?debug=2 -duration 5m -interval 10s

goleaked: sampled 30 times over 5m0s (interval 10s)

found 1 possible leak(s):

[1] state: chan receive, 4 minutes
    main.handleUpload()
        /app/upload.go:42 +0x30
    created by main.main
        /app/main.go:88 +0x24
```

## What it is

A small, single-binary pipeline with four stages: **fetch** a goroutine dump over HTTP from a
target process's pprof endpoint, **parse** the raw text into structs, **sample** it repeatedly on
a timer, and **diff** the accumulated samples by hashing each goroutine's state + stack into a
signature and counting how many distinct samples each signature shows up in. A signature present
in a high enough fraction of samples (configurable, not hardcoded) gets flagged as a likely leak.
An allowlist filters out stacks you already know are supposed to run forever (an HTTP server's own
accept loop, for instance), so a legitimately permanent background goroutine doesn't get flagged
alongside an actual bug.

## What it solves

Go's built-in tools give you the pieces, but not this specific answer, without extra effort:

- **`go tool pprof` / a single `curl` of `/debug/pprof/goroutine`** gets you one snapshot. A
  snapshot alone can't tell you whether a stuck goroutine is a permanent, healthy part of the
  program or an actual leak that's about to take the process down: you'd have to pull several
  dumps by hand and diff them yourself to find out.
- **[`uber-go/goleak`](https://github.com/uber-go/goleak)**, the well-known library in this space,
  solves a different problem: it's a single before/after comparison run inside a *test*, asserting
  no unexpected goroutine survived past `t.Cleanup`. It doesn't watch a live, running process over
  time.
- **Continuous profiling platforms** (Grafana Pyroscope, Google Cloud Profiler, APM vendor
  add-ons) do sample a live process over time, but they're built for a human to browse a flame
  graph and *notice* something looks wrong, not to automatically hash-and-diff recurring stacks
  and hand back a yes/no list of suspects.

`goleaked` sits in the gap: point it at a suspicious process for a few minutes and get a short,
concrete list of candidates, without wiring up a test or standing up an observability platform.

## How it works

| stage | package | does |
|---|---|---|
| fetch | `internal/pprofclient` | HTTP GET the pprof goroutine dump (`?debug=2`) from a target URL |
| parse | `internal/parse` | turn the raw text dump into `[]Goroutine{ID, State, Stack}` structs |
| sample | `internal/sampler` | poll fetch+parse on a timer, accumulate timestamped samples behind a mutex |
| diff | `internal/leak` | hash each goroutine's state+stack into a signature, count which signatures recur across samples, filter via an allowlist, flag anything past a threshold |

Correctness has been verified against `testtarget/`, a small local server with two goroutines
deliberately stuck forever, confirming `goleaked` finds exactly those two and nothing else.

## Install

```bash
go install github.com/Aparajith24/goleaked@latest
```

Or build from source:

```bash
git clone https://github.com/Aparajith24/goleaked.git
cd goleaked
go build -o goleaked .
./goleaked -url http://localhost:6060/debug/pprof/goroutine?debug=2
```

Or run it directly without a separate build step:

```bash
go run . -url http://localhost:6060/debug/pprof/goroutine?debug=2
```

## Usage

```
goleaked [flags]

-url string
        pprof goroutine dump URL (default "http://localhost:6060/debug/pprof/goroutine?debug=2")
  -interval duration
        how often to sample (default 1s)
  -duration duration
        how long to sample for (default 5s)
  -threshold float
        fraction of samples a signature must appear in to be flagged, 0-1 (default 1)
  -ignore string
        comma-separated substrings of stacks to ignore (default "net/http.(*Server).Serve")
```

The target process just needs `_ "net/http/pprof"` blank-imported and an HTTP server running
somewhere reachable, nothing else to install on the target side.

## Who this is for

- You have (or suspect) a goroutine leak in a running Go service and want a quick, concrete list
  of candidate stacks, without writing a test or reaching for a full profiling platform.
- You're comfortable running a short-lived CLI against a process's pprof endpoint for a few
  minutes and reading a stack trace to figure out the fix yourself. `goleaked` finds candidates,
  it doesn't fix anything or explain *why* a stack is stuck.

## What this is not

- **Not a replacement for `uber-go/goleak` in tests.** If you want a CI-enforced "no leaked
  goroutines" assertion at the end of a test run, that's a different, already-solved problem:
  use `goleak`.
- **Not a production monitoring / always-on tool.** There's no persistence, no alerting, no
  dashboard, no long-term storage of samples across runs. It's a point-in-time diagnostic CLI you
  run when you already suspect a problem, not something you'd leave running against production
  indefinitely.
- **Not a fix, and not root-cause analysis.** It tells you *which* stack keeps recurring, not
  *why*; that part is still on you.
- **Not aware of process restarts.** Goroutine IDs and all in-memory sample state are scoped to
  one continuous `goleaked` run against one continuously-running target process. If the target
  restarts mid-run, samples from before and after the restart get compared as if they were the
  same process.

## Known limitations

- **The allowlist is a plain substring match** (`strings.Contains`) against the full signature
  text, not a structured pattern language. Effective for filtering out known infrastructure
  frames like an HTTP server's accept loop, but easy to over-match if a pattern happens to appear
  in an unrelated stack too.
- **A goroutine that's merely slow, not leaked, can still get flagged** if it happens to be
  running long enough to span every sample in a short observation window (e.g. `-duration 5s` with
  a task that legitimately takes 6s). Longer `-duration` values relative to your program's normal
  worst-case latency reduce this.
- **No goroutine count/growth tracking.** A signature that shows one stuck instance across every
  sample and a signature whose instance count is climbing every sample look the same to the
  current threshold logic: both just get counted as "present in this sample or not." Distinguishing
  a single permanently-stuck worker from an actively growing leak is a natural next step.

## Built to learn Go

`goleaked` was built as a hands-on way to actually learn Go: goroutines, channels,
`sync.Mutex`/`sync.WaitGroup`, the runtime scheduler, and `net/http/pprof`, not just to end up
with a working binary. Each piece was worked through by hand before moving to the next, most
notably the concurrency layer: deliberately reproducing a data race with `go run -race`, fixing it
with `sync.WaitGroup` and `sync.Mutex`, then carrying that same discipline into the sampling loop,
where a background goroutine polls on a timer while the main program reads accumulated results
safely through a mutex. Parsing the raw pprof dump was written by hand with `strings`/`bufio`
rather than reached for via a regex library, to actually understand what a parser does. The
signature-and-recurrence logic, threshold, and allowlist all came out of watching a real false
positive happen (an HTTP server's own accept loop getting flagged as a "leak") and fixing it, not
from designing it upfront.

## License

MIT, see [LICENSE](./LICENSE).

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