main.go

/*
Copyright 2025 Olivier Mengué

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/*
Command zipsum shows checksums of each file contained in a zip file.

## Install

	go install github.com/dolmen-go/zipsum@latest
*/
package main

import (
	"archive/zip"
	"fmt"
	"io"
	"log"
	"os"
	"path"
	"reflect"

	"crypto/md5"
)

func main() {
	log.SetFlags(0)
	if len(os.Args) != 2 {
		fmt.Printf("usage: %s <file.zip>\n", os.Args[0])
		os.Exit(2)
	}
	zr, err := zip.OpenReader(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}
	defer zr.Close()

	h := md5.New()
	checksum := h.Sum(nil) // Preallocate the output buffer for the checksum

	fmt.Printf("%*s file\n", -2*len(h.Sum(nil)), path.Base(reflect.TypeOf(h).Elem().PkgPath()))

	for _, f := range zr.File {
		if len(f.Name) == 0 || f.Name[len(f.Name)-1] == '/' {
			continue
		}

		rc, err := f.Open()
		if err != nil {
			log.Fatal(err)
		}

		h.Reset()
		if _, err := io.Copy(h, rc); err != nil {
			log.Fatal(err)
		}
		rc.Close()

		h.Sum(checksum[:0])
		fmt.Printf("%x %s\n", checksum, f.Name)
	}
}