forked from OSchip/llvm-project
312 lines
6.9 KiB
Go
312 lines
6.9 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// Package ascii85 implements the ascii85 data encoding
|
|
// as used in the btoa tool and Adobe's PostScript and PDF document formats.
|
|
package ascii85
|
|
|
|
import (
|
|
"io"
|
|
"strconv"
|
|
)
|
|
|
|
/*
|
|
* Encoder
|
|
*/
|
|
|
|
// Encode encodes src into at most MaxEncodedLen(len(src))
|
|
// bytes of dst, returning the actual number of bytes written.
|
|
//
|
|
// The encoding handles 4-byte chunks, using a special encoding
|
|
// for the last fragment, so Encode is not appropriate for use on
|
|
// individual blocks of a large data stream. Use NewEncoder() instead.
|
|
//
|
|
// Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
|
|
// Encode does not add these.
|
|
func Encode(dst, src []byte) int {
|
|
if len(src) == 0 {
|
|
return 0
|
|
}
|
|
|
|
n := 0
|
|
for len(src) > 0 {
|
|
dst[0] = 0
|
|
dst[1] = 0
|
|
dst[2] = 0
|
|
dst[3] = 0
|
|
dst[4] = 0
|
|
|
|
// Unpack 4 bytes into uint32 to repack into base 85 5-byte.
|
|
var v uint32
|
|
switch len(src) {
|
|
default:
|
|
v |= uint32(src[3])
|
|
fallthrough
|
|
case 3:
|
|
v |= uint32(src[2]) << 8
|
|
fallthrough
|
|
case 2:
|
|
v |= uint32(src[1]) << 16
|
|
fallthrough
|
|
case 1:
|
|
v |= uint32(src[0]) << 24
|
|
}
|
|
|
|
// Special case: zero (!!!!!) shortens to z.
|
|
if v == 0 && len(src) >= 4 {
|
|
dst[0] = 'z'
|
|
dst = dst[1:]
|
|
src = src[4:]
|
|
n++
|
|
continue
|
|
}
|
|
|
|
// Otherwise, 5 base 85 digits starting at !.
|
|
for i := 4; i >= 0; i-- {
|
|
dst[i] = '!' + byte(v%85)
|
|
v /= 85
|
|
}
|
|
|
|
// If src was short, discard the low destination bytes.
|
|
m := 5
|
|
if len(src) < 4 {
|
|
m -= 4 - len(src)
|
|
src = nil
|
|
} else {
|
|
src = src[4:]
|
|
}
|
|
dst = dst[m:]
|
|
n += m
|
|
}
|
|
return n
|
|
}
|
|
|
|
// MaxEncodedLen returns the maximum length of an encoding of n source bytes.
|
|
func MaxEncodedLen(n int) int { return (n + 3) / 4 * 5 }
|
|
|
|
// NewEncoder returns a new ascii85 stream encoder. Data written to
|
|
// the returned writer will be encoded and then written to w.
|
|
// Ascii85 encodings operate in 32-bit blocks; when finished
|
|
// writing, the caller must Close the returned encoder to flush any
|
|
// trailing partial block.
|
|
func NewEncoder(w io.Writer) io.WriteCloser { return &encoder{w: w} }
|
|
|
|
type encoder struct {
|
|
err error
|
|
w io.Writer
|
|
buf [4]byte // buffered data waiting to be encoded
|
|
nbuf int // number of bytes in buf
|
|
out [1024]byte // output buffer
|
|
}
|
|
|
|
func (e *encoder) Write(p []byte) (n int, err error) {
|
|
if e.err != nil {
|
|
return 0, e.err
|
|
}
|
|
|
|
// Leading fringe.
|
|
if e.nbuf > 0 {
|
|
var i int
|
|
for i = 0; i < len(p) && e.nbuf < 4; i++ {
|
|
e.buf[e.nbuf] = p[i]
|
|
e.nbuf++
|
|
}
|
|
n += i
|
|
p = p[i:]
|
|
if e.nbuf < 4 {
|
|
return
|
|
}
|
|
nout := Encode(e.out[0:], e.buf[0:])
|
|
if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
|
|
return n, e.err
|
|
}
|
|
e.nbuf = 0
|
|
}
|
|
|
|
// Large interior chunks.
|
|
for len(p) >= 4 {
|
|
nn := len(e.out) / 5 * 4
|
|
if nn > len(p) {
|
|
nn = len(p)
|
|
}
|
|
nn -= nn % 4
|
|
if nn > 0 {
|
|
nout := Encode(e.out[0:], p[0:nn])
|
|
if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
|
|
return n, e.err
|
|
}
|
|
}
|
|
n += nn
|
|
p = p[nn:]
|
|
}
|
|
|
|
// Trailing fringe.
|
|
for i := 0; i < len(p); i++ {
|
|
e.buf[i] = p[i]
|
|
}
|
|
e.nbuf = len(p)
|
|
n += len(p)
|
|
return
|
|
}
|
|
|
|
// Close flushes any pending output from the encoder.
|
|
// It is an error to call Write after calling Close.
|
|
func (e *encoder) Close() error {
|
|
// If there's anything left in the buffer, flush it out
|
|
if e.err == nil && e.nbuf > 0 {
|
|
nout := Encode(e.out[0:], e.buf[0:e.nbuf])
|
|
e.nbuf = 0
|
|
_, e.err = e.w.Write(e.out[0:nout])
|
|
}
|
|
return e.err
|
|
}
|
|
|
|
/*
|
|
* Decoder
|
|
*/
|
|
|
|
type CorruptInputError int64
|
|
|
|
func (e CorruptInputError) Error() string {
|
|
return "illegal ascii85 data at input byte " + strconv.FormatInt(int64(e), 10)
|
|
}
|
|
|
|
// Decode decodes src into dst, returning both the number
|
|
// of bytes written to dst and the number consumed from src.
|
|
// If src contains invalid ascii85 data, Decode will return the
|
|
// number of bytes successfully written and a CorruptInputError.
|
|
// Decode ignores space and control characters in src.
|
|
// Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
|
|
// Decode expects these to have been stripped by the caller.
|
|
//
|
|
// If flush is true, Decode assumes that src represents the
|
|
// end of the input stream and processes it completely rather
|
|
// than wait for the completion of another 32-bit block.
|
|
//
|
|
// NewDecoder wraps an io.Reader interface around Decode.
|
|
//
|
|
func Decode(dst, src []byte, flush bool) (ndst, nsrc int, err error) {
|
|
var v uint32
|
|
var nb int
|
|
for i, b := range src {
|
|
if len(dst)-ndst < 4 {
|
|
return
|
|
}
|
|
switch {
|
|
case b <= ' ':
|
|
continue
|
|
case b == 'z' && nb == 0:
|
|
nb = 5
|
|
v = 0
|
|
case '!' <= b && b <= 'u':
|
|
v = v*85 + uint32(b-'!')
|
|
nb++
|
|
default:
|
|
return 0, 0, CorruptInputError(i)
|
|
}
|
|
if nb == 5 {
|
|
nsrc = i + 1
|
|
dst[ndst] = byte(v >> 24)
|
|
dst[ndst+1] = byte(v >> 16)
|
|
dst[ndst+2] = byte(v >> 8)
|
|
dst[ndst+3] = byte(v)
|
|
ndst += 4
|
|
nb = 0
|
|
v = 0
|
|
}
|
|
}
|
|
if flush {
|
|
nsrc = len(src)
|
|
if nb > 0 {
|
|
// The number of output bytes in the last fragment
|
|
// is the number of leftover input bytes - 1:
|
|
// the extra byte provides enough bits to cover
|
|
// the inefficiency of the encoding for the block.
|
|
if nb == 1 {
|
|
return 0, 0, CorruptInputError(len(src))
|
|
}
|
|
for i := nb; i < 5; i++ {
|
|
// The short encoding truncated the output value.
|
|
// We have to assume the worst case values (digit 84)
|
|
// in order to ensure that the top bits are correct.
|
|
v = v*85 + 84
|
|
}
|
|
for i := 0; i < nb-1; i++ {
|
|
dst[ndst] = byte(v >> 24)
|
|
v <<= 8
|
|
ndst++
|
|
}
|
|
}
|
|
}
|
|
return
|
|
}
|
|
|
|
// NewDecoder constructs a new ascii85 stream decoder.
|
|
func NewDecoder(r io.Reader) io.Reader { return &decoder{r: r} }
|
|
|
|
type decoder struct {
|
|
err error
|
|
readErr error
|
|
r io.Reader
|
|
end bool // saw end of message
|
|
buf [1024]byte // leftover input
|
|
nbuf int
|
|
out []byte // leftover decoded output
|
|
outbuf [1024]byte
|
|
}
|
|
|
|
func (d *decoder) Read(p []byte) (n int, err error) {
|
|
if len(p) == 0 {
|
|
return 0, nil
|
|
}
|
|
if d.err != nil {
|
|
return 0, d.err
|
|
}
|
|
|
|
for {
|
|
// Copy leftover output from last decode.
|
|
if len(d.out) > 0 {
|
|
n = copy(p, d.out)
|
|
d.out = d.out[n:]
|
|
return
|
|
}
|
|
|
|
// Decode leftover input from last read.
|
|
var nn, nsrc, ndst int
|
|
if d.nbuf > 0 {
|
|
ndst, nsrc, d.err = Decode(d.outbuf[0:], d.buf[0:d.nbuf], d.readErr != nil)
|
|
if ndst > 0 {
|
|
d.out = d.outbuf[0:ndst]
|
|
d.nbuf = copy(d.buf[0:], d.buf[nsrc:d.nbuf])
|
|
continue // copy out and return
|
|
}
|
|
if ndst == 0 && d.err == nil {
|
|
// Special case: input buffer is mostly filled with non-data bytes.
|
|
// Filter out such bytes to make room for more input.
|
|
off := 0
|
|
for i := 0; i < d.nbuf; i++ {
|
|
if d.buf[i] > ' ' {
|
|
d.buf[off] = d.buf[i]
|
|
off++
|
|
}
|
|
}
|
|
d.nbuf = off
|
|
}
|
|
}
|
|
|
|
// Out of input, out of decoded output. Check errors.
|
|
if d.err != nil {
|
|
return 0, d.err
|
|
}
|
|
if d.readErr != nil {
|
|
d.err = d.readErr
|
|
return 0, d.err
|
|
}
|
|
|
|
// Read more data.
|
|
nn, d.readErr = d.r.Read(d.buf[d.nbuf:])
|
|
d.nbuf += nn
|
|
}
|
|
}
|