modhex/cmd/modhex.go

// Command modhex is a simple modhex converstion command line tool.
package main

import (
	"encoding/hex"
	"flag"
	"fmt"
	"os"
	"strings"

	"git.trashheap.io/blinkthethings/modhex"
)

func main() {
	// configure command line flags
	var decode, hexdata bool
	flag.BoolVar(&decode, "d", false, "decode data (the default is to encode).")
	flag.BoolVar(&hexdata, "x", false, "Use hex encoding for non-modhex data.")
	flag.Usage = func() {
		fmt.Println("modhex - encode/decode data using modhex encoding.")
		fmt.Println()
		fmt.Println("Usage:\n\n  modex [-d] [-x] <data>")
		fmt.Println()
		fmt.Println("  Convert input DATA as specified and print output to STDOUT.")
		fmt.Println()
		fmt.Printf("Flags:\n\n")
		flag.PrintDefaults()
		fmt.Println()
	}
	flag.Parse()

	// display usage if no data is provided
	if flag.NArg() < 1 {
		flag.Usage()
		os.Exit(0)
	}

	if decode {
		// decode was selected

		// read the modhex string from the command line
		src := []byte(strings.Join(flag.Args(), " "))

		// create a buffer to hold the decoded data
		dst := make([]byte, modhex.DecodedLen(len(src)))

		// decode the input
		_, err := modhex.Decode(dst, src)
		if err != nil {
			// report the error to the user
			fmt.Fprintln(os.Stderr, err)
			os.Exit(-1)
		}

		// should the output be a hex string?
		if hexdata {
			// print out the decoded data as a hex string
			fmt.Println(hex.EncodeToString(src))
		} else {
			// print out the decoded bytes stdout
			os.Stdout.Write(dst)
		}
	} else {
		// encode was selected

		// read the input data
		var src []byte
		if hexdata {
			// read the input as a hex string
			var err error
			src, err = hex.DecodeString(flag.Arg(0))
			if err != nil {
				// report the hex decode error and exit
				fmt.Fprintf(os.Stderr, "modhex: %s\n", err)
				os.Exit(-1)
			}
		} else {
			// read the input as bytes
			src = []byte(strings.Join(flag.Args(), ""))
		}

		// encode the input
		s := modhex.EncodeToString(src)

		// print out the modhex encoded string
		fmt.Println(s)
	}
}