/
format.go
246 lines (217 loc) · 5.83 KB
/
format.go
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// Copyright 2019 Google LLC
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
// Package format implements the age file format.
package internal
import (
"bufio"
"bytes"
"encoding/base64"
"errors"
"fmt"
"io"
"strings"
)
type Header struct {
Recipients []*Stanza
MAC []byte
}
// Stanza is assignable to age.Stanza, and if this package is made public,
// age.Stanza can be made a type alias of this type.
type Stanza struct {
Type string
Args []string
Body []byte
}
var b64 = base64.RawStdEncoding.Strict()
func DecodeString(s string) ([]byte, error) {
// CR and LF are ignored by DecodeString, but we don't want any malleability.
if strings.ContainsAny(s, "\n\r") {
return nil, errors.New(`unexpected newline character`)
}
return b64.DecodeString(s)
}
var EncodeToString = b64.EncodeToString
const ColumnsPerLine = 64
const BytesPerLine = ColumnsPerLine / 4 * 3
// NewlineWriter returns a Writer that writes to dst, inserting an LF character
// every ColumnsPerLine bytes. It does not insert a newline neither at the
// beginning nor at the end of the stream.
func NewlineWriter(dst io.Writer) io.Writer {
return &newlineWriter{dst: dst}
}
type newlineWriter struct {
dst io.Writer
written int
}
func (w *newlineWriter) Write(p []byte) (n int, err error) {
for len(p) > 0 {
remainingInLine := ColumnsPerLine - (w.written % ColumnsPerLine)
if remainingInLine == ColumnsPerLine && w.written != 0 {
if _, err := w.dst.Write([]byte("\n")); err != nil {
return n, err
}
}
toWrite := remainingInLine
if toWrite > len(p) {
toWrite = len(p)
}
nn, err := w.dst.Write(p[:toWrite])
n += nn
w.written += nn
p = p[nn:]
if err != nil {
return n, err
}
}
return n, nil
}
const intro = "age-encryption.org/v1\n"
var recipientPrefix = []byte("->")
var footerPrefix = []byte("---")
func (r *Stanza) Marshal(w io.Writer) error {
if _, err := w.Write(recipientPrefix); err != nil {
return err
}
for _, a := range append([]string{r.Type}, r.Args...) {
if _, err := io.WriteString(w, " "+a); err != nil {
return err
}
}
if _, err := io.WriteString(w, "\n"); err != nil {
return err
}
if len(r.Body) == 0 {
return nil
}
ww := base64.NewEncoder(b64, NewlineWriter(w))
if _, err := ww.Write(r.Body); err != nil {
return err
}
if err := ww.Close(); err != nil {
return err
}
_, err := io.WriteString(w, "\n")
return err
}
func (h *Header) MarshalWithoutMAC(w io.Writer) error {
if _, err := io.WriteString(w, intro); err != nil {
return err
}
for _, r := range h.Recipients {
if err := r.Marshal(w); err != nil {
return err
}
}
_, err := fmt.Fprintf(w, "%s", footerPrefix)
return err
}
func (h *Header) Marshal(w io.Writer) error {
if err := h.MarshalWithoutMAC(w); err != nil {
return err
}
mac := b64.EncodeToString(h.MAC)
_, err := fmt.Fprintf(w, " %s\n", mac)
return err
}
type ParseError string
func (e ParseError) Error() string {
return "parsing age header: " + string(e)
}
func errorf(format string, a ...interface{}) error {
return ParseError(fmt.Sprintf(format, a...))
}
// Parse returns the header and a Reader that begins at the start of the
// payload.
func Parse(input io.Reader) (*Header, io.Reader, error) {
h := &Header{}
rr := bufio.NewReader(input)
line, err := rr.ReadString('\n')
if err != nil {
return nil, nil, errorf("failed to read intro: %v", err)
}
if line != intro {
return nil, nil, errorf("unexpected intro: %q", line)
}
var r *Stanza
for {
line, err := rr.ReadBytes('\n')
if err != nil {
return nil, nil, errorf("failed to read header: %v", err)
}
if bytes.HasPrefix(line, footerPrefix) {
prefix, args := splitArgs(line)
if prefix != string(footerPrefix) || len(args) != 1 {
return nil, nil, errorf("malformed closing line: %q", line)
}
h.MAC, err = DecodeString(args[0])
if err != nil {
return nil, nil, errorf("malformed closing line %q: %v", line, err)
}
break
} else if bytes.HasPrefix(line, recipientPrefix) {
r = &Stanza{}
prefix, args := splitArgs(line)
if prefix != string(recipientPrefix) || len(args) < 1 {
return nil, nil, errorf("malformed recipient: %q", line)
}
for _, a := range args {
if !isValidString(a) {
return nil, nil, errorf("malformed recipient: %q", line)
}
}
r.Type = args[0]
r.Args = args[1:]
h.Recipients = append(h.Recipients, r)
} else if r != nil {
b, err := DecodeString(strings.TrimSuffix(string(line), "\n"))
if err != nil {
return nil, nil, errorf("malformed body line %q: %v", line, err)
}
if len(b) > BytesPerLine {
return nil, nil, errorf("malformed body line %q: too long", line)
}
if len(b) == 0 {
return nil, nil, errorf("malformed body line %q: line is empty", line)
}
r.Body = append(r.Body, b...)
if len(b) < BytesPerLine {
// Only the last line of a body can be short.
r = nil
}
} else {
return nil, nil, errorf("unexpected line: %q", line)
}
}
// If input is a bufio.Reader, rr might be equal to input because
// bufio.NewReader short-circuits. In this case we can just return it (and
// we would end up reading the buffer twice if we prepended the peek below).
if rr == input {
return h, rr, nil
}
// Otherwise, unwind the bufio overread and return the unbuffered input.
buf, err := rr.Peek(rr.Buffered())
if err != nil {
return nil, nil, errorf("internal error: %v", err)
}
payload := io.MultiReader(bytes.NewReader(buf), input)
return h, payload, nil
}
func splitArgs(line []byte) (string, []string) {
l := strings.TrimSuffix(string(line), "\n")
parts := strings.Split(l, " ")
return parts[0], parts[1:]
}
func isValidString(s string) bool {
if len(s) == 0 {
return false
}
for _, c := range s {
if c < 33 || c > 126 {
return false
}
}
return true
}