Useful Go Libraries

go-cmd/cmd - Makes it easy to run external commands concurrently and to pipe out to stdout.

go-cmd/cmd pitfalls
- setting cmd.Dir to a non-existent directory causes an error such as
```
fork/exec /bin/echo: no such file or directory
```
  - The error refers to the working directory though and not the binary being executed.
  - It is easy to get confused by this.
go-cmd/cmd race conditions with stopping and logs

see [racecondition/main.go]

Suppose you want to start an asynchronous long running process e.g. runServer() which uses cmd to asynchronously run the server. This presents the following challenges

We want to wait for the server to start before trying to send requests to the server
The server could fail immediately; e.g. an incorrect command line flag or fail half way through starting the server
When the client exits we want to terminate the server so that we don’t leave the process running.
So our code might look like this.


func runServer() *cmd.Cmd{
  c := cmd.NewCommandOptions(...)
  c.Start()
  return c
}
func main() {
  cmd := runServer()
  defer func() {
    if err := cmd.Stop(); err != nil {
            log.Error(err, "Error stopping weaviate")
        }
  }()

  sendRequest()
}

The above code has a race condition. runServer asynchronously starts the process. As a result, sendRequest might run before cmd.Start has a chance to actually send the request.

So we need to give the server time to start. There are different ways to do this

Add a Sleep in runServer; not great
If the server has a healthCheck we can keep polling until it passes or timeOut

Useful Go Libraries

go-cmd/cmd pitfalls

go-cmd/cmd race conditions with stopping and logs