bloblang: hostname() errors without Benthos

[billgraziano]

I'm looking at using bloblang in another app. The only issue I've found so far is that hostname doesn't seem to work.

package main

import (
	"encoding/json"
	"fmt"
	"log"

	"github.com/benthosdev/benthos/v4/public/bloblang"
)

func main() {
	mapping := `
		root.host = hostname()
		root.ksuid = ksuid()
	`
	exe, err := bloblang.Parse(mapping)
	if err != nil {
		log.Fatal(err)
	}
	src := "{}"
	var object interface{}
	err = json.Unmarshal([]byte(src), &object)
	if err != nil {
		log.Fatal(err)
	}
	res, err := exe.Query(object)
	if err != nil {
		log.Fatal(err)
	}
	jsonBytes, err := json.MarshalIndent(res, "", "  ")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(string(jsonBytes))
}

The output is below. If you comment out hostname, then ksuid works just fine.

2022/06/14 08:56:46 unrecognised function 'hostname': hostn
exit status 1

Bloblang is fantastic! This is a great little scripting tool and works really well for what you're doing -- and hopefully what I'm doing. My only other concern is that it pulls A LOT of dependencies into my application when I include it.

[mihaitodor]

For the env() function, can you try importing https://pkg.go.dev/github.com/benthosdev/benthos/v4@v4.2.0/public/components/io? For the dependencies, I'll let Ash chime in.

[billgraziano]

Changing my imports as shown below worked. I'd still classify this as a bug -- assuming you want anyone to use BlobLang outside Benthos. At the very least it would be nice to fix the examples in the documentation.

import (
	"encoding/json"
	"fmt"
	"log"

	"github.com/benthosdev/benthos/v4/public/bloblang"
	_ "github.com/benthosdev/benthos/v4/public/components/io"
)

[Jeffail]

Hey @billgraziano, yeah at the very least we need to document this better and improve some of the ergonomics. I'll mark this issue as a documentation enhancement.

The rationality with the optional imports is that functions that interact with the outter machine are potentially harmful in cases where bloblang is embedded in third party applications. I'm definitely open to eventually breaking bloblang out into a separate package but we'd need to consider how exactly to present these optional functions.

There's also some thought needed as to how exactly we separate benthos-owned methods and functions versus bloblang standard ones, as breaking it out into its own repo would mean a hard separation of them.

[billgraziano]

I don't envy you those tasks. :-) But I think BlobLang is a very good thing you have made.