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glib/glib/gbase64.c
Philip Withnall 8d3c502074 gbase64: Fix documentation for line wrapping lengths 
The implementation has always wrapped at 76 characters, rather than 72,
ever since it was introduced in commit 5cf8f1d4a8 in 2006. At this
stage, it’s probably best to fix the documentation rather than the
implementation.

The likely bug in the implementation is the comparison
```
(++already) >= 19
```

19 × 4 = 76, so it seems like an off-by-one error in the comparison.
What was actually wanted was 18 × 4 = 72.

Thanks to Simon McVittie for the investigation and diagnosis.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1997
2020-01-15 13:15:54 +00:00

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/* gbase64.c - Base64 encoding/decoding
*
* Copyright (C) 2006 Alexander Larsson <alexl@redhat.com>
* Copyright (C) 2000-2003 Ximian Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, see <http://www.gnu.org/licenses/>.
*
* This is based on code in camel, written by:
* Michael Zucchi <notzed@ximian.com>
* Jeffrey Stedfast <fejj@ximian.com>
*/
#include "config.h"
#include <string.h>
#include "gbase64.h"
#include "gtestutils.h"
#include "glibintl.h"
/**
* SECTION:base64
* @title: Base64 Encoding
* @short_description: encodes and decodes data in Base64 format
*
* Base64 is an encoding that allows a sequence of arbitrary bytes to be
* encoded as a sequence of printable ASCII characters. For the definition
* of Base64, see
* [RFC 1421](http://www.ietf.org/rfc/rfc1421.txt)
* or
* [RFC 2045](http://www.ietf.org/rfc/rfc2045.txt).
* Base64 is most commonly used as a MIME transfer encoding
* for email.
*
* GLib supports incremental encoding using g_base64_encode_step() and
* g_base64_encode_close(). Incremental decoding can be done with
* g_base64_decode_step(). To encode or decode data in one go, use
* g_base64_encode() or g_base64_decode(). To avoid memory allocation when
* decoding, you can use g_base64_decode_inplace().
*
* Support for Base64 encoding has been added in GLib 2.12.
*/
static const char base64_alphabet[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
/**
* g_base64_encode_step:
* @in: (array length=len) (element-type guint8): the binary data to encode
* @len: the length of @in
* @break_lines: whether to break long lines
* @out: (out) (array) (element-type guint8): pointer to destination buffer
* @state: (inout): Saved state between steps, initialize to 0
* @save: (inout): Saved state between steps, initialize to 0
*
* Incrementally encode a sequence of binary data into its Base-64 stringified
* representation. By calling this function multiple times you can convert
* data in chunks to avoid having to have the full encoded data in memory.
*
* When all of the data has been converted you must call
* g_base64_encode_close() to flush the saved state.
*
* The output buffer must be large enough to fit all the data that will
* be written to it. Due to the way base64 encodes you will need
* at least: (@len / 3 + 1) * 4 + 4 bytes (+ 4 may be needed in case of
* non-zero state). If you enable line-breaking you will need at least:
* ((@len / 3 + 1) * 4 + 4) / 76 + 1 bytes of extra space.
*
* @break_lines is typically used when putting base64-encoded data in emails.
* It breaks the lines at 76 columns instead of putting all of the text on
* the same line. This avoids problems with long lines in the email system.
* Note however that it breaks the lines with `LF` characters, not
* `CR LF` sequences, so the result cannot be passed directly to SMTP
* or certain other protocols.
*
* Returns: The number of bytes of output that was written
*
* Since: 2.12
*/
gsize
g_base64_encode_step (const guchar *in,
gsize len,
gboolean break_lines,
gchar *out,
gint *state,
gint *save)
{
char *outptr;
const guchar *inptr;
g_return_val_if_fail (in != NULL || len == 0, 0);
g_return_val_if_fail (out != NULL, 0);
g_return_val_if_fail (state != NULL, 0);
g_return_val_if_fail (save != NULL, 0);
if (len == 0)
return 0;
inptr = in;
outptr = out;
if (len + ((char *) save) [0] > 2)
{
const guchar *inend = in+len-2;
int c1, c2, c3;
int already;
already = *state;
switch (((char *) save) [0])
{
case 1:
c1 = ((unsigned char *) save) [1];
goto skip1;
case 2:
c1 = ((unsigned char *) save) [1];
c2 = ((unsigned char *) save) [2];
goto skip2;
}
/*
* yes, we jump into the loop, no i'm not going to change it,
* it's beautiful!
*/
while (inptr < inend)
{
c1 = *inptr++;
skip1:
c2 = *inptr++;
skip2:
c3 = *inptr++;
*outptr++ = base64_alphabet [ c1 >> 2 ];
*outptr++ = base64_alphabet [ c2 >> 4 |
((c1&0x3) << 4) ];
*outptr++ = base64_alphabet [ ((c2 &0x0f) << 2) |
(c3 >> 6) ];
*outptr++ = base64_alphabet [ c3 & 0x3f ];
/* this is a bit ugly ... */
if (break_lines && (++already) >= 19)
{
*outptr++ = '\n';
already = 0;
}
}
((char *)save)[0] = 0;
len = 2 - (inptr - inend);
*state = already;
}
g_assert (len == 0 || len == 1 || len == 2);
{
char *saveout;
/* points to the slot for the next char to save */
saveout = & (((char *)save)[1]) + ((char *)save)[0];
/* len can only be 0 1 or 2 */
switch(len)
{
case 2:
*saveout++ = *inptr++;
G_GNUC_FALLTHROUGH;
case 1:
*saveout++ = *inptr++;
}
((char *)save)[0] += len;
}
return outptr - out;
}
/**
* g_base64_encode_close:
* @break_lines: whether to break long lines
* @out: (out) (array) (element-type guint8): pointer to destination buffer
* @state: (inout): Saved state from g_base64_encode_step()
* @save: (inout): Saved state from g_base64_encode_step()
*
* Flush the status from a sequence of calls to g_base64_encode_step().
*
* The output buffer must be large enough to fit all the data that will
* be written to it. It will need up to 4 bytes, or up to 5 bytes if
* line-breaking is enabled.
*
* The @out array will not be automatically nul-terminated.
*
* Returns: The number of bytes of output that was written
*
* Since: 2.12
*/
gsize
g_base64_encode_close (gboolean break_lines,
gchar *out,
gint *state,
gint *save)
{
int c1, c2;
char *outptr = out;
g_return_val_if_fail (out != NULL, 0);
g_return_val_if_fail (state != NULL, 0);
g_return_val_if_fail (save != NULL, 0);
c1 = ((unsigned char *) save) [1];
c2 = ((unsigned char *) save) [2];
switch (((char *) save) [0])
{
case 2:
outptr [2] = base64_alphabet[ ( (c2 &0x0f) << 2 ) ];
g_assert (outptr [2] != 0);
goto skip;
case 1:
outptr[2] = '=';
c2 = 0; /* saved state here is not relevant */
skip:
outptr [0] = base64_alphabet [ c1 >> 2 ];
outptr [1] = base64_alphabet [ c2 >> 4 | ( (c1&0x3) << 4 )];
outptr [3] = '=';
outptr += 4;
break;
}
if (break_lines)
*outptr++ = '\n';
*save = 0;
*state = 0;
return outptr - out;
}
/**
* g_base64_encode:
* @data: (array length=len) (element-type guint8) (nullable): the binary data to encode
* @len: the length of @data
*
* Encode a sequence of binary data into its Base-64 stringified
* representation.
*
* Returns: (transfer full): a newly allocated, zero-terminated Base-64
* encoded string representing @data. The returned string must
* be freed with g_free().
*
* Since: 2.12
*/
gchar *
g_base64_encode (const guchar *data,
gsize len)
{
gchar *out;
gint state = 0, outlen;
gint save = 0;
g_return_val_if_fail (data != NULL || len == 0, NULL);
/* We can use a smaller limit here, since we know the saved state is 0,
+1 is needed for trailing \0, also check for unlikely integer overflow */
g_return_val_if_fail (len < ((G_MAXSIZE - 1) / 4 - 1) * 3, NULL);
out = g_malloc ((len / 3 + 1) * 4 + 1);
outlen = g_base64_encode_step (data, len, FALSE, out, &state, &save);
outlen += g_base64_encode_close (FALSE, out + outlen, &state, &save);
out[outlen] = '\0';
return (gchar *) out;
}
static const unsigned char mime_base64_rank[256] = {
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255, 62,255,255,255, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61,255,255,255, 0,255,255,
255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,255,255,255,255,255,
255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
};
/**
* g_base64_decode_step: (skip)
* @in: (array length=len) (element-type guint8): binary input data
* @len: max length of @in data to decode
* @out: (out caller-allocates) (array) (element-type guint8): output buffer
* @state: (inout): Saved state between steps, initialize to 0
* @save: (inout): Saved state between steps, initialize to 0
*
* Incrementally decode a sequence of binary data from its Base-64 stringified
* representation. By calling this function multiple times you can convert
* data in chunks to avoid having to have the full encoded data in memory.
*
* The output buffer must be large enough to fit all the data that will
* be written to it. Since base64 encodes 3 bytes in 4 chars you need
* at least: (@len / 4) * 3 + 3 bytes (+ 3 may be needed in case of non-zero
* state).
*
* Returns: The number of bytes of output that was written
*
* Since: 2.12
**/
gsize
g_base64_decode_step (const gchar *in,
gsize len,
guchar *out,
gint *state,
guint *save)
{
const guchar *inptr;
guchar *outptr;
const guchar *inend;
guchar c, rank;
guchar last[2];
unsigned int v;
int i;
g_return_val_if_fail (in != NULL || len == 0, 0);
g_return_val_if_fail (out != NULL, 0);
g_return_val_if_fail (state != NULL, 0);
g_return_val_if_fail (save != NULL, 0);
if (len == 0)
return 0;
inend = (const guchar *)in+len;
outptr = out;
/* convert 4 base64 bytes to 3 normal bytes */
v=*save;
i=*state;
last[0] = last[1] = 0;
/* we use the sign in the state to determine if we got a padding character
in the previous sequence */
if (i < 0)
{
i = -i;
last[0] = '=';
}
inptr = (const guchar *)in;
while (inptr < inend)
{
c = *inptr++;
rank = mime_base64_rank [c];
if (rank != 0xff)
{
last[1] = last[0];
last[0] = c;
v = (v<<6) | rank;
i++;
if (i==4)
{
*outptr++ = v>>16;
if (last[1] != '=')
*outptr++ = v>>8;
if (last[0] != '=')
*outptr++ = v;
i=0;
}
}
}
*save = v;
*state = last[0] == '=' ? -i : i;
return outptr - out;
}
/**
* g_base64_decode:
* @text: (not nullable): zero-terminated string with base64 text to decode
* @out_len: (out): The length of the decoded data is written here
*
* Decode a sequence of Base-64 encoded text into binary data. Note
* that the returned binary data is not necessarily zero-terminated,
* so it should not be used as a character string.
*
* Returns: (transfer full) (array length=out_len) (element-type guint8):
* newly allocated buffer containing the binary data
* that @text represents. The returned buffer must
* be freed with g_free().
*
* Since: 2.12
*/
guchar *
g_base64_decode (const gchar *text,
gsize *out_len)
{
guchar *ret;
gsize input_length;
gint state = 0;
guint save = 0;
g_return_val_if_fail (text != NULL, NULL);
g_return_val_if_fail (out_len != NULL, NULL);
input_length = strlen (text);
/* We can use a smaller limit here, since we know the saved state is 0,
+1 used to avoid calling g_malloc0(0), and hence returning NULL */
ret = g_malloc0 ((input_length / 4) * 3 + 1);
*out_len = g_base64_decode_step (text, input_length, ret, &state, &save);
return ret;
}
/**
* g_base64_decode_inplace:
* @text: (inout) (array length=out_len) (element-type guint8): zero-terminated
* string with base64 text to decode
* @out_len: (inout): The length of the decoded data is written here
*
* Decode a sequence of Base-64 encoded text into binary data
* by overwriting the input data.
*
* Returns: (transfer none): The binary data that @text responds. This pointer
* is the same as the input @text.
*
* Since: 2.20
*/
guchar *
g_base64_decode_inplace (gchar *text,
gsize *out_len)
{
gint input_length, state = 0;
guint save = 0;
g_return_val_if_fail (text != NULL, NULL);
g_return_val_if_fail (out_len != NULL, NULL);
input_length = strlen (text);
g_return_val_if_fail (input_length > 1, NULL);
*out_len = g_base64_decode_step (text, input_length, (guchar *) text, &state, &save);
return (guchar *) text;
}
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