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path: root/zhead/header.go
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package zhead

import (
	"bufio"
	"bytes"
	"encoding/hex"
	"errors"
	"io"
	"strconv"
	"strings"
	"text/template"
	"time"
)

const header = `{{define "header" -}}
date={{.Date.Format "2006-01-02T15:04:05Z07:00"}}
key={{.KeyFile}}
algorithm={{.Alg}}
bocksize={{.BlockSize}}

{{range .Sums}}{{printf "%x" .}}
{{end}}{{end}}`

type Header struct {
	Date      time.Time
	KeyFile   string
	Alg       string
	BlockSize int
	Sums      [][]byte
}

const (
	DefaultAlg       = "SHA512/256"
	DefaultBlockSize = 65535
)

func (h Header) Print() ([]byte, error) {
	t, err := template.New("header").Parse(header)
	if err != nil {
		return nil, err
	}
	buf := new(bytes.Buffer)
	err = t.ExecuteTemplate(buf, "header", h)
	return buf.Bytes(), err
}

func Parse(r io.Reader) (Header, error) {
	var inSum bool
	var h Header
	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		line := scanner.Text()
		switch {
		case strings.HasPrefix(line, "date="):
			t, err := time.Parse(time.RFC3339, line[5:])
			if err != nil {
				return Header{}, err
			}
			h.Date = t
		case strings.HasPrefix(line, "key="):
			h.KeyFile = line[4:]
		case strings.HasPrefix(line, "algorithm="):
			h.Alg = line[10:]
		case strings.HasPrefix(line, "blocksize="):
			i, err := strconv.Atoi(line[9:])
			if err != nil {
				return Header{}, err
			}
			h.BlockSize = i
		case line == "":
			if inSum {
				return Header{}, errors.New("already in sum part")
			}
			inSum = true
		}
		if inSum {
			sum, err := hex.DecodeString(line)
			if err != nil {
				return Header{}, err
			}
			h.Sums = append(h.Sums, sum)
		}
	}
	return h, scanner.Err()
}