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path: root/b64file/file.go
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// Package b64file implements signify file format
package b64file

import (
	"bufio"
	"encoding"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"strings"
)

const untrusted = "untrusted comment: "

// Original Error: "invalid comment in %s; must start with 'untrusted comment: '"
var (
	ErrUntrusted     = errors.New("comment must start with 'untrusted comment: '")
	ErrMissingHeader = errors.New("missing required header fields")
)

type Header struct {
	Comment string
	Bytes   []byte
}

type Reader struct {
	Header
	r io.Reader
}

type Writer struct {
	Header
	w           io.Writer
	wroteHeader bool
}

func NewReader(r io.Reader) (*Reader, error) {
	buf := bufio.NewReader(r)

	comment, err := buf.ReadString('\n')
	if err != nil {
		return nil, err
	}
	if !strings.HasPrefix(comment, untrusted) {
		return nil, ErrUntrusted
	}
	comment = strings.TrimSpace(comment[len(untrusted):])

	raw, err := buf.ReadString('\n')
	if err != nil {
		return nil, err
	}
	b, err := base64.StdEncoding.DecodeString(raw)
	if err != nil {
		return nil, err
	}

	return &Reader{
		Header: Header{
			Comment: comment,
			Bytes:   b,
		},
		r: buf,
	}, nil
}

func (r *Reader) Read(p []byte) (n int, err error) {
	return r.r.Read(p)
}

func (r *Reader) Close() error {
	return nil
}

func Decode(r io.Reader, u encoding.BinaryUnmarshaler) (string, []byte, error) {
	buf := bufio.NewReader(r)

	comment, err := buf.ReadString('\n')
	if err != nil {
		return "", nil, err
	}
	if !strings.HasPrefix(comment, untrusted) {
		return "", nil, ErrUntrusted
	}
	comment = strings.TrimSpace(comment[len(untrusted):])

	raw, err := buf.ReadString('\n')
	if err != nil {
		return "", nil, err
	}
	b, err := base64.StdEncoding.DecodeString(raw)
	if err != nil {
		return "", nil, err
	}
	if err := u.UnmarshalBinary(b); err != nil {
		return "", nil, err
	}

	message, err := ioutil.ReadAll(buf)
	if err != nil {
		return "", nil, err
	}

	return comment, message, nil
}

func NewWriter(w io.Writer) (*Writer, error) {
	return &Writer{w: w}, nil
}

func (w *Writer) writeHeader() error {
	if !w.wroteHeader {
		if w.Comment == "" || w.Bytes == nil {
			return ErrMissingHeader
		}
		fmt.Fprintf(w.w, "%s%s\n", untrusted, w.Comment)
		fmt.Fprintf(w.w, "%s\n", base64.StdEncoding.EncodeToString(w.Bytes))
		w.wroteHeader = true
	}
	return nil
}

func (w *Writer) Write(p []byte) (n int, err error) {
	if err := w.writeHeader(); err != nil {
		return 0, err
	}
	return w.w.Write(p)
}

func (w *Writer) Close() error {
	return w.writeHeader()
}

func Encode(w io.Writer, u encoding.BinaryMarshaler, comment string, msg []byte) error {
	raw, err := u.MarshalBinary()
	if err != nil {
		return err
	}
	fmt.Fprintf(w, "%s%s\n", untrusted, comment)
	fmt.Fprintf(w, "%s\n", base64.StdEncoding.EncodeToString(raw))
	w.Write(msg)
	return nil
}