/src/glib/gio/strinfo.c

Source (jump to first uncovered line)
/*
 * Copyright © 2010 Codethink Limited
 *
 * 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/>.
 *
 * Author: Ryan Lortie <desrt@desrt.ca>
 */

#include <string.h>
#include <glib.h>

/*
 * The string info map is an efficient data structure designed to be
 * used with a small set of items.  It is used by GSettings schemas for
 * three purposes:
 *
 *  1) Implement <choices> with a list of valid strings
 *
 *  2) Implement <alias> by mapping one string to another
 *
 *  3) Implement enumerated types by mapping strings to integer values
 *     (and back).
 *
 * The map is made out of an array of uint32s.  Each entry in the array
 * is an integer value, followed by a specially formatted string value:
 *
 *   The string starts with the byte 0xff or 0xfe, followed by the
 *   content of the string, followed by a nul byte, followed by
 *   additional nul bytes for padding, followed by a 0xff byte.
 *
 *   Padding is added so that the entire formatted string takes up a
 *   multiple of 4 bytes, and not less than 8 bytes.  The requirement
 *   for a string to take up 8 bytes is so that the scanner doesn't lose
 *   synch and mistake a string for an integer value.
 *
 * The first byte of the formatted string depends on if the integer is
 * an enum value (0xff) or an alias (0xfe).  If it is an alias then the
 * number refers to the word offset within the info map at which the
 * integer corresponding to the "target" value is stored.
 *
 * For example, consider the case of the string info map representing an
 * enumerated type of 'foo' (value 1) and 'bar' (value 2) and 'baz'
 * (alias for 'bar').  Note that string info maps are always little
 * endian.
 *
 * x01 x00 x00 x00   xff 'f' 'o' 'o'   x00 x00 x00 xff   x02 x00 x00 x00
 * xff 'b' 'a' 'r'   x00 x00 x00 xff   x03 x00 x00 x00   xfe 'b' 'a' 'z'
 * x00 x00 x00 xff
 *
 *
 * The operations that someone may want to perform with the map:
 *
 *   - look up if a string is valid (and not an alias)
 *   - look up the integer value for a enum 'nick'
 *   - look up the integer value for the target of an alias
 *   - look up an alias and convert it to its target string
 *   - look up the enum nick for a given value
 *
 * In order to look up if a string is valid, it is padded on either side
 * (as described) and scanned for in the array.  For example, you might
 * look for "foo":
 *
 *                   xff 'f' 'o' 'o'   x00 x00 x00 xff
 *
 * In order to look up the integer value for a nick, the string is padded
 * on either side and scanned for in the array, as above.  Instead of
 * merely succeeding, we look at the integer value to the left of the
 * match.  This is the enum value.
 *
 * In order to look up an alias and convert it to its target enum value,
 * the string is padded on either side (as described, with 0xfe) and
 * scanned for.  For example, you might look for "baz":
 *
 *                   xfe 'b' 'a' 'z'  x00 x00 x00 xff
 *
 * The integer immediately preceding the match then contains the offset
 * of the integer value of the target.  In our example, that's '3'.
 * This index is dereferenced to find the enum value of '2'.
 *
 * To convert the alias to its target string, 5 bytes just need to be
 * added past the start of the integer value to find the start of the
 * string.
 *
 * To look up the enum nick for a given value, the value is searched for
 * in the array.  To ensure that the value isn't matching the inside of a
 * string, we must check that it is either the first item in the array or
 * immediately preceded by the byte 0xff.  It must also be immediately
 * followed by the byte 0xff.
 *
 * Because strings always take up a minimum of 2 words, because 0xff or
 * 0xfe never appear inside of a utf-8 string and because no two integer
 * values ever appear in sequence, the only way we can have the
 * sequence:
 *
 *     xff __ __ __ __ xff (or 0xfe)
 *
 * is in the event of an integer nested between two strings.
 *
 * For implementation simplicity/efficiency, strings may not be more
 * than 65 characters in length (ie: 17 32bit words after padding).
 *
 * In the event that we are doing <choices> (ie: not an enum type) then
 * the value of each choice is set to zero and ignored.
 */

#define STRINFO_MAX_WORDS   17
G_GNUC_UNUSED static guint
strinfo_string_to_words (const gchar *string,
                         guint32     *words,
                         gboolean     alias)
{
  guint n_words;
  gsize size;

  size = strlen (string);

  n_words = MAX (2, (size + 6) >> 2);

  if (n_words > STRINFO_MAX_WORDS)
    return FALSE;

  words[0] = GUINT32_TO_LE (alias ? 0xfe : 0xff);
  words[n_words - 1] = GUINT32_TO_BE (0xff);
  memcpy (((gchar *) words) + 1, string, size + 1);

  return n_words;
}

G_GNUC_UNUSED static gint
strinfo_scan (const guint32 *strinfo,
              guint          length,
              const guint32 *words,
              guint          n_words)
{
  guint i = 0;

  if (length < n_words)
    return -1;

  while (i <= length - n_words)
    {
      guint j = 0;

      for (j = 0; j < n_words; j++)
        if (strinfo[i + j] != words[j])
          break;

      if (j == n_words)
        return i;   /* match */

      /* skip at least one word, continue */
      i += j ? j : 1;
    }

  return -1;
}

G_GNUC_UNUSED static gint
strinfo_find_string (const guint32 *strinfo,
                     guint          length,
                     const gchar   *string,
                     gboolean       alias)
{
  guint32 words[STRINFO_MAX_WORDS];
  guint n_words;

  if (length == 0)
    return -1;

  n_words = strinfo_string_to_words (string, words, alias);

  return strinfo_scan (strinfo + 1, length - 1, words, n_words);
}

G_GNUC_UNUSED static gint
strinfo_find_integer (const guint32 *strinfo,
                      guint          length,
                      guint32        value)
{
  guint i;

  for (i = 0; i < length; i++)
    if (strinfo[i] == GUINT32_TO_LE (value))
      {
        const guchar *charinfo = (const guchar *) &strinfo[i];

        /* make sure it has 0xff on either side */
        if ((i == 0 || charinfo[-1] == 0xff) && charinfo[4] == 0xff)
          return i;
      }

  return -1;
}

G_GNUC_UNUSED static gboolean
strinfo_is_string_valid (const guint32 *strinfo,
                         guint          length,
                         const gchar   *string)
{
  return strinfo_find_string (strinfo, length, string, FALSE) != -1;
}

G_GNUC_UNUSED static gboolean
strinfo_enum_from_string (const guint32 *strinfo,
                          guint          length,
                          const gchar   *string,
                          guint         *result)
{
  gint index;

  index = strinfo_find_string (strinfo, length, string, FALSE);

  if (index < 0)
    return FALSE;

  *result = GUINT32_FROM_LE (strinfo[index]);
  return TRUE;
}

G_GNUC_UNUSED static const gchar *
strinfo_string_from_enum (const guint32 *strinfo,
                          guint          length,
                          guint          value)
{
  gint index;

  index = strinfo_find_integer (strinfo, length, value);

  if (index < 0)
    return NULL;

  return 1 + (const gchar *) &strinfo[index + 1];
}

G_GNUC_UNUSED static const gchar *
strinfo_string_from_alias (const guint32 *strinfo,
                           guint          length,
                           const gchar   *alias)
{
  gint index;

  index = strinfo_find_string (strinfo, length, alias, TRUE);

  if (index < 0)
    return NULL;

  return 1 + (const gchar *) &strinfo[GUINT32_TO_LE (strinfo[index]) + 1];
}

G_GNUC_UNUSED static GVariant *
strinfo_enumerate (const guint32 *strinfo,
                   guint          length)
{
  GVariantBuilder builder;
  const gchar *ptr, *end;

  ptr = (gpointer) strinfo;
  end = ptr + 4 * length;

  ptr += 4;

  g_variant_builder_init (&builder, G_VARIANT_TYPE_STRING_ARRAY);

  while (ptr < end)
    {
      /* don't include aliases */
      if (*ptr == '\xff')
        g_variant_builder_add (&builder, "s", ptr + 1);

      /* find the end of this string */
      ptr = memchr (ptr, '\xff', end - ptr);
      g_assert (ptr != NULL);

      /* skip over the int to the next string */
      ptr += 5;
    }

  return g_variant_builder_end (&builder);
}

G_GNUC_UNUSED static void
strinfo_builder_append_item (GString     *builder,
                             const gchar *string,
                             guint        value)
{
  guint32 words[STRINFO_MAX_WORDS];
  guint n_words;

  value = GUINT32_TO_LE (value);

  n_words = strinfo_string_to_words (string, words, FALSE);
  g_string_append_len (builder, (void *) &value, sizeof value);
  g_string_append_len (builder, (void *) words, 4 * n_words);
}

G_GNUC_UNUSED static gboolean
strinfo_builder_append_alias (GString     *builder,
                              const gchar *alias,
                              const gchar *target)
{
  guint32 words[STRINFO_MAX_WORDS];
  guint n_words;
  guint value;
  gint index;

  index = strinfo_find_string ((const guint32 *) builder->str,
                               builder->len / 4, target, FALSE);

  if (index == -1)
    return FALSE;

  value = GUINT32_TO_LE (index);

  n_words = strinfo_string_to_words (alias, words, TRUE);
  g_string_append_len (builder, (void *) &value, sizeof value);
  g_string_append_len (builder, (void *) words, 4 * n_words);

  return TRUE;
}

G_GNUC_UNUSED static gboolean
strinfo_builder_contains (GString     *builder,
                          const gchar *string)
{
  return strinfo_find_string ((const guint32 *) builder->str,
                              builder->len / 4, string, FALSE) != -1 ||
         strinfo_find_string ((const guint32 *) builder->str,
                              builder->len / 4, string, TRUE) != -1;
}

G_GNUC_UNUSED static gboolean
strinfo_builder_contains_value (GString *builder,
                                guint    value)
{
  return strinfo_string_from_enum ((const guint32 *) builder->str,
                                   builder->len / 4, value) != NULL;
}

Coverage Report

Created: 2025-07-01 07:09

Line	Count	Source (jump to first uncovered line)
1		/*
2		* Copyright © 2010 Codethink Limited
3		*
4		* This library is free software; you can redistribute it and/or
5		* modify it under the terms of the GNU Lesser General Public
6		* License as published by the Free Software Foundation; either
7		* version 2.1 of the License, or (at your option) any later version.
8		*
9		* This library is distributed in the hope that it will be useful,
10		* but WITHOUT ANY WARRANTY; without even the implied warranty of
11		* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12		* Lesser General Public License for more details.
13		*
14		* You should have received a copy of the GNU Lesser General Public
15		* License along with this library; if not, see <http://www.gnu.org/licenses/>.
16		*
17		* Author: Ryan Lortie <desrt@desrt.ca>
18		*/
19
20		#include <string.h>
21		#include <glib.h>
22
23		/*
24		* The string info map is an efficient data structure designed to be
25		* used with a small set of items. It is used by GSettings schemas for
26		* three purposes:
27		*
28		* 1) Implement <choices> with a list of valid strings
29		*
30		* 2) Implement <alias> by mapping one string to another
31		*
32		* 3) Implement enumerated types by mapping strings to integer values
33		* (and back).
34		*
35		* The map is made out of an array of uint32s. Each entry in the array
36		* is an integer value, followed by a specially formatted string value:
37		*
38		* The string starts with the byte 0xff or 0xfe, followed by the
39		* content of the string, followed by a nul byte, followed by
40		* additional nul bytes for padding, followed by a 0xff byte.
41		*
42		* Padding is added so that the entire formatted string takes up a
43		* multiple of 4 bytes, and not less than 8 bytes. The requirement
44		* for a string to take up 8 bytes is so that the scanner doesn't lose
45		* synch and mistake a string for an integer value.
46		*
47		* The first byte of the formatted string depends on if the integer is
48		* an enum value (0xff) or an alias (0xfe). If it is an alias then the
49		* number refers to the word offset within the info map at which the
50		* integer corresponding to the "target" value is stored.
51		*
52		* For example, consider the case of the string info map representing an
53		* enumerated type of 'foo' (value 1) and 'bar' (value 2) and 'baz'
54		* (alias for 'bar'). Note that string info maps are always little
55		* endian.
56		*
57		* x01 x00 x00 x00 xff 'f' 'o' 'o' x00 x00 x00 xff x02 x00 x00 x00
58		* xff 'b' 'a' 'r' x00 x00 x00 xff x03 x00 x00 x00 xfe 'b' 'a' 'z'
59		* x00 x00 x00 xff
60		*
61		*
62		* The operations that someone may want to perform with the map:
63		*
64		* - look up if a string is valid (and not an alias)
65		* - look up the integer value for a enum 'nick'
66		* - look up the integer value for the target of an alias
67		* - look up an alias and convert it to its target string
68		* - look up the enum nick for a given value
69		*
70		* In order to look up if a string is valid, it is padded on either side
71		* (as described) and scanned for in the array. For example, you might
72		* look for "foo":
73		*
74		* xff 'f' 'o' 'o' x00 x00 x00 xff
75		*
76		* In order to look up the integer value for a nick, the string is padded
77		* on either side and scanned for in the array, as above. Instead of
78		* merely succeeding, we look at the integer value to the left of the
79		* match. This is the enum value.
80		*
81		* In order to look up an alias and convert it to its target enum value,
82		* the string is padded on either side (as described, with 0xfe) and
83		* scanned for. For example, you might look for "baz":
84		*
85		* xfe 'b' 'a' 'z' x00 x00 x00 xff
86		*
87		* The integer immediately preceding the match then contains the offset
88		* of the integer value of the target. In our example, that's '3'.
89		* This index is dereferenced to find the enum value of '2'.
90		*
91		* To convert the alias to its target string, 5 bytes just need to be
92		* added past the start of the integer value to find the start of the
93		* string.
94		*
95		* To look up the enum nick for a given value, the value is searched for
96		* in the array. To ensure that the value isn't matching the inside of a
97		* string, we must check that it is either the first item in the array or
98		* immediately preceded by the byte 0xff. It must also be immediately
99		* followed by the byte 0xff.
100		*
101		* Because strings always take up a minimum of 2 words, because 0xff or
102		* 0xfe never appear inside of a utf-8 string and because no two integer
103		* values ever appear in sequence, the only way we can have the
104		* sequence:
105		*
106		* xff __ __ __ __ xff (or 0xfe)
107		*
108		* is in the event of an integer nested between two strings.
109		*
110		* For implementation simplicity/efficiency, strings may not be more
111		* than 65 characters in length (ie: 17 32bit words after padding).
112		*
113		* In the event that we are doing <choices> (ie: not an enum type) then
114		* the value of each choice is set to zero and ignored.
115		*/
116
117	0	#define STRINFO_MAX_WORDS 17
118		G_GNUC_UNUSED static guint
119		strinfo_string_to_words (const gchar *string,
120		guint32 *words,
121		gboolean alias)
122	0	{
123	0	guint n_words;
124	0	gsize size;
125
126	0	size = strlen (string);
127
128	0	n_words = MAX (2, (size + 6) >> 2);
129
130	0	if (n_words > STRINFO_MAX_WORDS)
131	0	return FALSE;
132
133	0	words[0] = GUINT32_TO_LE (alias ? 0xfe : 0xff);
134	0	words[n_words - 1] = GUINT32_TO_BE (0xff);
135	0	memcpy (((gchar *) words) + 1, string, size + 1);
136
137	0	return n_words;
138	0	} Unexecuted instantiation: gsettings.c:strinfo_string_to_words Unexecuted instantiation: gsettingsschema.c:strinfo_string_to_words
139
140		G_GNUC_UNUSED static gint
141		strinfo_scan (const guint32 *strinfo,
142		guint length,
143		const guint32 *words,
144		guint n_words)
145	0	{
146	0	guint i = 0;
147
148	0	if (length < n_words)
149	0	return -1;
150
151	0	while (i <= length - n_words)
152	0	{
153	0	guint j = 0;
154
155	0	for (j = 0; j < n_words; j++)
156	0	if (strinfo[i + j] != words[j])
157	0	break;
158
159	0	if (j == n_words)
160	0	return i; /* match */
161
162		/* skip at least one word, continue */
163	0	i += j ? j : 1;
164	0	}
165
166	0	return -1;
167	0	} Unexecuted instantiation: gsettings.c:strinfo_scan Unexecuted instantiation: gsettingsschema.c:strinfo_scan
168
169		G_GNUC_UNUSED static gint
170		strinfo_find_string (const guint32 *strinfo,
171		guint length,
172		const gchar *string,
173		gboolean alias)
174	0	{
175	0	guint32 words[STRINFO_MAX_WORDS];
176	0	guint n_words;
177
178	0	if (length == 0)
179	0	return -1;
180
181	0	n_words = strinfo_string_to_words (string, words, alias);
182
183	0	return strinfo_scan (strinfo + 1, length - 1, words, n_words);
184	0	} Unexecuted instantiation: gsettings.c:strinfo_find_string Unexecuted instantiation: gsettingsschema.c:strinfo_find_string
185
186		G_GNUC_UNUSED static gint
187		strinfo_find_integer (const guint32 *strinfo,
188		guint length,
189		guint32 value)
190	0	{
191	0	guint i;
192
193	0	for (i = 0; i < length; i++)
194	0	if (strinfo[i] == GUINT32_TO_LE (value))
195	0	{
196	0	const guchar charinfo = (const guchar ) &strinfo[i];
197
198		/* make sure it has 0xff on either side */
199	0	if ((i == 0 \|\| charinfo[-1] == 0xff) && charinfo[4] == 0xff)
200	0	return i;
201	0	}
202
203	0	return -1;
204	0	} Unexecuted instantiation: gsettings.c:strinfo_find_integer Unexecuted instantiation: gsettingsschema.c:strinfo_find_integer
205
206		G_GNUC_UNUSED static gboolean
207		strinfo_is_string_valid (const guint32 *strinfo,
208		guint length,
209		const gchar *string)
210	0	{
211	0	return strinfo_find_string (strinfo, length, string, FALSE) != -1;
212	0	} Unexecuted instantiation: gsettings.c:strinfo_is_string_valid Unexecuted instantiation: gsettingsschema.c:strinfo_is_string_valid
213
214		G_GNUC_UNUSED static gboolean
215		strinfo_enum_from_string (const guint32 *strinfo,
216		guint length,
217		const gchar *string,
218		guint *result)
219	0	{
220	0	gint index;
221
222	0	index = strinfo_find_string (strinfo, length, string, FALSE);
223
224	0	if (index < 0)
225	0	return FALSE;
226
227	0	*result = GUINT32_FROM_LE (strinfo[index]);
228	0	return TRUE;
229	0	} Unexecuted instantiation: gsettings.c:strinfo_enum_from_string Unexecuted instantiation: gsettingsschema.c:strinfo_enum_from_string
230
231		G_GNUC_UNUSED static const gchar *
232		strinfo_string_from_enum (const guint32 *strinfo,
233		guint length,
234		guint value)
235	0	{
236	0	gint index;
237
238	0	index = strinfo_find_integer (strinfo, length, value);
239
240	0	if (index < 0)
241	0	return NULL;
242
243	0	return 1 + (const gchar *) &strinfo[index + 1];
244	0	} Unexecuted instantiation: gsettings.c:strinfo_string_from_enum Unexecuted instantiation: gsettingsschema.c:strinfo_string_from_enum
245
246		G_GNUC_UNUSED static const gchar *
247		strinfo_string_from_alias (const guint32 *strinfo,
248		guint length,
249		const gchar *alias)
250	0	{
251	0	gint index;
252
253	0	index = strinfo_find_string (strinfo, length, alias, TRUE);
254
255	0	if (index < 0)
256	0	return NULL;
257
258	0	return 1 + (const gchar *) &strinfo[GUINT32_TO_LE (strinfo[index]) + 1];
259	0	} Unexecuted instantiation: gsettings.c:strinfo_string_from_alias Unexecuted instantiation: gsettingsschema.c:strinfo_string_from_alias
260
261		G_GNUC_UNUSED static GVariant *
262		strinfo_enumerate (const guint32 *strinfo,
263		guint length)
264	0	{
265	0	GVariantBuilder builder;
266	0	const gchar ptr, end;
267
268	0	ptr = (gpointer) strinfo;
269	0	end = ptr + 4 * length;
270
271	0	ptr += 4;
272
273	0	g_variant_builder_init (&builder, G_VARIANT_TYPE_STRING_ARRAY);
274
275	0	while (ptr < end)
276	0	{
277		/* don't include aliases */
278	0	if (*ptr == '\xff')
279	0	g_variant_builder_add (&builder, "s", ptr + 1);
280
281		/* find the end of this string */
282	0	ptr = memchr (ptr, '\xff', end - ptr);
283	0	g_assert (ptr != NULL);
284
285		/* skip over the int to the next string */
286	0	ptr += 5;
287	0	}
288
289	0	return g_variant_builder_end (&builder);
290	0	} Unexecuted instantiation: gsettings.c:strinfo_enumerate Unexecuted instantiation: gsettingsschema.c:strinfo_enumerate
291
292		G_GNUC_UNUSED static void
293		strinfo_builder_append_item (GString *builder,
294		const gchar *string,
295		guint value)
296	0	{
297	0	guint32 words[STRINFO_MAX_WORDS];
298	0	guint n_words;
299	0
300	0	value = GUINT32_TO_LE (value);
301	0
302	0	n_words = strinfo_string_to_words (string, words, FALSE);
303	0	g_string_append_len (builder, (void *) &value, sizeof value);
304	0	g_string_append_len (builder, (void ) words, 4 n_words);
305	0	} Unexecuted instantiation: gsettings.c:strinfo_builder_append_item Unexecuted instantiation: gsettingsschema.c:strinfo_builder_append_item
306
307		G_GNUC_UNUSED static gboolean
308		strinfo_builder_append_alias (GString *builder,
309		const gchar *alias,
310		const gchar *target)
311	0	{
312	0	guint32 words[STRINFO_MAX_WORDS];
313	0	guint n_words;
314	0	guint value;
315	0	gint index;
316	0
317	0	index = strinfo_find_string ((const guint32 *) builder->str,
318	0	builder->len / 4, target, FALSE);
319	0
320	0	if (index == -1)
321	0	return FALSE;
322	0
323	0	value = GUINT32_TO_LE (index);
324	0
325	0	n_words = strinfo_string_to_words (alias, words, TRUE);
326	0	g_string_append_len (builder, (void *) &value, sizeof value);
327	0	g_string_append_len (builder, (void ) words, 4 n_words);
328	0
329	0	return TRUE;
330	0	} Unexecuted instantiation: gsettings.c:strinfo_builder_append_alias Unexecuted instantiation: gsettingsschema.c:strinfo_builder_append_alias
331
332		G_GNUC_UNUSED static gboolean
333		strinfo_builder_contains (GString *builder,
334		const gchar *string)
335	0	{
336	0	return strinfo_find_string ((const guint32 *) builder->str,
337	0	builder->len / 4, string, FALSE) != -1 \|\|
338	0	strinfo_find_string ((const guint32 *) builder->str,
339	0	builder->len / 4, string, TRUE) != -1;
340	0	} Unexecuted instantiation: gsettings.c:strinfo_builder_contains Unexecuted instantiation: gsettingsschema.c:strinfo_builder_contains
341
342		G_GNUC_UNUSED static gboolean
343		strinfo_builder_contains_value (GString *builder,
344		guint value)
345	0	{
346	0	return strinfo_string_from_enum ((const guint32 *) builder->str,
347	0	builder->len / 4, value) != NULL;
348	0	} Unexecuted instantiation: gsettings.c:strinfo_builder_contains_value Unexecuted instantiation: gsettingsschema.c:strinfo_builder_contains_value