fix: correctly wait for journalctl processes to not leave zombies when streaming machine logs (#325)

* fix: call cmd.Wait()

Even though the context is cancelled we still need to call cmd.Wait()
after a cmd.Start() to clean up the child (reap) process. Not doing so
results in a zombie journalctl.

I have manually tested this, as I'm still not sure how to e2e test for
this in a simple manner.

Before:

```
root@uncloud2:~# ps aux|grep jou
root         313  0.0  1.2  42272 23352 ?        S<s  Apr20   0:10 /usr/lib/systemd/systemd-journald
root       15751  0.0  0.0      0     0 pts/0    Z+   07:02   0:00 [journalctl] <defunct>
root       15754  0.0  0.0      0     0 pts/0    Z+   07:02   0:00 [journalctl] <defunct>
```

After:

```
root         313  0.0  1.2  42272 23592 ?        S<s  Apr20   0:10 /usr/lib/systemd/systemd-journald
```

* follow() doesnt need wait

We can keep the wait function more contraint, as follow does not need it

Signed-off-by: Miek Gieben <miek@miek.nl>

---------

Signed-off-by: Miek Gieben <miek@miek.nl>

internal/journal/journal.go

@@ -31,9 +31,9 @@ const journalctl = "journalctl"
 
 var commandContext = exec.CommandContext // allow override for test
 
-func logs(ctx context.Context, unit string, opts api.ServiceLogsOptions) (io.ReadCloser, error) {
+func logs(ctx context.Context, unit string, opts api.ServiceLogsOptions) (io.ReadCloser, func() error, error) {
 	if !ValidUnit(unit) {
-		return nil, fmt.Errorf("journal logs: invalid unit: %s", unit)
+		return nil, nil, fmt.Errorf("journal logs: invalid unit: %s", unit)
 	}
 	args := []string{"-u", unit, "--no-hostname"}
 	args = append(args, "-n")
@@ -61,14 +61,14 @@ func logs(ctx context.Context, unit string, opts api.ServiceLogsOptions) (io.Rea
 	cmd := commandContext(ctx, journalctl, args...)
 	p, err := cmd.StdoutPipe()
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	if err := cmd.Start(); err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
-	return p, nil
+	return p, cmd.Wait, nil
 }
 
 // follow synchronously follows the io.Reader, writing each new journal entry to channel.

internal/journal/logs.go

@@ -16,7 +16,7 @@ func Logs(ctx context.Context, unit string, opts api.ServiceLogsOptions) (<-chan
 		return nil, fmt.Errorf("journal logs: invalid unit: %s", unit)
 	}
 
-	reader, err := logs(ctx, unit, opts)
+	reader, wait, err := logs(ctx, unit, opts)
 	if err != nil {
 		return nil, err
 	}
@@ -26,6 +26,7 @@ func Logs(ctx context.Context, unit string, opts api.ServiceLogsOptions) (<-chan
 	go func() {
 		defer close(outCh)
 		follow(ctx, reader, outCh)
+		wait()
 	}()
 
 	return outCh, nil