Leaking goroutines

[george-angel]

As https://github.com/cesanta/docker_auth/issues/391 noticed - docker_auth is leaking memory by leaking goroutines.

Looking at the heap profile runtime.malg is using a lot of memory, this is because of a goroutine leak:

$ go tool pprof 2024-09-07T16:13:49+1000_goroutine.out
File: auth_server
Build ID: f0023e9b8e89438ff941b55f3266cd69dfff1f88
Type: goroutine
Time: Sep 7, 2024 at 4:13pm (AEST)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top5
Showing nodes accounting for 10539, 100% of 10542 total
Dropped 45 nodes (cum <= 52)
Showing top 5 nodes out of 9
      flat  flat%   sum%        cum   cum%
     10539   100%   100%      10539   100%  runtime.gopark
         0     0%   100%       4889 46.38%  github.com/schwarmco/go-cartesian-product.Iter.func1
         0     0%   100%       5638 53.48%  github.com/schwarmco/go-cartesian-product.iterate
         0     0%   100%       5638 53.48%  runtime.chansend
         0     0%   100%       5638 53.48%  runtime.chansend1
(pprof)

I also created an issue against https://github.com/schwarmco/go-cartesian-product/issues/6 with the potential solution, but posting it here for visibility as well:

diff --git a/auth_server/authz/acl.go b/auth_server/authz/acl.go
index 2f2e824..b0aa21c 100644
--- a/auth_server/authz/acl.go
+++ b/auth_server/authz/acl.go
@@ -1,6 +1,7 @@
 package authz

 import (
+   "context"
    "encoding/json"
    "fmt"
    "net"
@@ -11,7 +12,6 @@ import (
    "strings"

    "github.com/cesanta/glog"
-   "github.com/schwarmco/go-cartesian-product"

    "github.com/cesanta/docker_auth/auth_server/api"
 )
@@ -180,14 +180,17 @@ func matchStringWithLabelPermutations(pp *string, s string, vars []string, label
            }
        }
        if len(labelSets) > 0 {
-           for permuation := range cartesian.Iter(labelSets...) {
+           ctx, cancel := context.WithCancel(context.Background())
+           defer cancel()
+
+           for permuation := range IterWithContext(ctx, labelSets...) {
                var labelVars []string
                for _, val := range permuation {
                    labelVars = append(labelVars, val.([]string)...)
                }
                matched = matchString(pp, s, append(vars, labelVars...))
                if matched {
-                   break
+                   return matched
                }
            }
        }
@@ -195,6 +198,45 @@ func matchStringWithLabelPermutations(pp *string, s string, vars []string, label
    return matched
 }

+func IterWithContext(ctx context.Context, params ...[]interface{}) <-chan []interface{} {
+   c := make(chan []interface{})
+
+   if len(params) == 0 {
+       close(c)
+       return c
+   }
+
+   go func() {
+       defer close(c) // Ensure the channel is closed when the goroutine exits
+
+       iterate(ctx, c, params[0], []interface{}{}, params[1:]...)
+   }()
+
+   return c
+}
+
+func iterate(ctx context.Context, channel chan []interface{}, topLevel, result []interface{}, needUnpacking ...[]interface{}) {
+   if len(needUnpacking) == 0 {
+       for _, p := range topLevel {
+           select {
+           case <-ctx.Done():
+               return // Exit if the context is canceled
+           case channel <- append(append([]interface{}{}, result...), p):
+           }
+       }
+       return
+   }
+
+   for _, p := range topLevel {
+       select {
+       case <-ctx.Done():
+           return // Exit if the context is canceled
+       default:
+           iterate(ctx, channel, needUnpacking[0], append(result, p), needUnpacking[1:]...)
+       }
+   }
+}
+
 func matchIP(ipp *string, ip net.IP) bool {
    if ipp == nil {
        return true

I think the function is small and simple enough you can copy it into your code and not rely on a lib. Let me know if you want me to raise a PR with the above changes.

Thanks!