sh-interp-extract.go

package main

import (
	"fmt"
	"io"
	"log"
	"os"
	"strings"

	"mvdan.cc/sh/interp"
	"mvdan.cc/sh/syntax"
)

const src = `
name=firefox
version=52.4.0esr
release=1
source=(https://ftp.mozilla.org/pub/firefox/releases/$version/source/firefox-$version.source.tar.xz
	firefox-install-dir.patch firefox.desktop)
# uncomment lines below to see what is allowed
#ok_prog=$(echo foo | sed 's/o/a/g')
#ok_file=$(echo prog >/dev/null)
#hack=$(upload ~/.ssh)
`

func main() {
	strs, err := extract(src, "source")
	if err != nil {
		log.Fatal(err)
	}
	// use strings.Join to mimic "echo ..."
	fmt.Println(strs)
}

func extract(src, name string) ([]string, error) {
	p := syntax.NewParser()
	file, err := p.Parse(strings.NewReader(src), "")
	if err != nil {
		return nil, fmt.Errorf("could not parse: %v", err)
	}
	r := interp.Runner{}
	r.Exec = func(ctx interp.Ctxt, name string, args []string) error {
		switch name {
		case "sed", "grep":
		default:
			return fmt.Errorf("blacklisted: %s", name)
		}
		return interp.DefaultExec(ctx, name, args)
	}
	r.Open = func(ctx interp.Ctxt, path string, flags int, mode os.FileMode) (io.ReadWriteCloser, error) {
		// won't pass on windows, but ok for now
		if !strings.HasPrefix(path, "/dev/") {
			return nil, fmt.Errorf("non-dev: %s", path)
		}
		return interp.DefaultOpen(ctx, path, flags, mode)
	}
	r.Reset()
	if err := r.Run(file); err != nil {
		return nil, fmt.Errorf("could not run: %v", err)
	}
	// verbosity below is ${name[@]}
	fields := r.Fields([]*syntax.Word{
		{Parts: []syntax.WordPart{
			&syntax.ParamExp{
				Param: &syntax.Lit{Value: name},
				Index: &syntax.Word{Parts: []syntax.WordPart{&syntax.Lit{Value: "@"}}},
			},
		}},
	})
	return fields, nil
}