summaryrefslogtreecommitdiff
path: root/src/zipmap.c
blob: 22bfa1a4668eb2dab9501bd8a3d5111093b1b47d (plain)
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
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
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
/* String -> String Map data structure optimized for size.
 * This file implements a data structure mapping strings to other strings
 * implementing an O(n) lookup data structure designed to be very memory
 * efficient.
 *
 * The Redis Hash type uses this data structure for hashes composed of a small
 * number of elements, to switch to a hash table once a given number of
 * elements is reached.
 *
 * Given that many times Redis Hashes are used to represent objects composed
 * of few fields, this is a very big win in terms of used memory.
 *
 * --------------------------------------------------------------------------
 *
 * Copyright (c) 2009-2010, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/* Memory layout of a zipmap, for the map "foo" => "bar", "hello" => "world":
 *
 * <zmlen><len>"foo"<len><free>"bar"<len>"hello"<len><free>"world"
 *
 * <zmlen> is 1 byte length that holds the current size of the zipmap.
 * When the zipmap length is greater than or equal to 254, this value
 * is not used and the zipmap needs to be traversed to find out the length.
 *
 * <len> is the length of the following string (key or value).
 * <len> lengths are encoded in a single value or in a 5 bytes value.
 * If the first byte value (as an unsigned 8 bit value) is between 0 and
 * 253, it's a single-byte length. If it is 254 then a four bytes unsigned
 * integer follows (in the host byte ordering). A value of 255 is used to
 * signal the end of the hash.
 *
 * <free> is the number of free unused bytes after the string, resulting
 * from modification of values associated to a key. For instance if "foo"
 * is set to "bar", and later "foo" will be set to "hi", it will have a
 * free byte to use if the value will enlarge again later, or even in
 * order to add a key/value pair if it fits.
 *
 * <free> is always an unsigned 8 bit number, because if after an
 * update operation there are more than a few free bytes, the zipmap will be
 * reallocated to make sure it is as small as possible.
 *
 * The most compact representation of the above two elements hash is actually:
 *
 * "\x02\x03foo\x03\x00bar\x05hello\x05\x00world\xff"
 *
 * Note that because keys and values are prefixed length "objects",
 * the lookup will take O(N) where N is the number of elements
 * in the zipmap and *not* the number of bytes needed to represent the zipmap.
 * This lowers the constant times considerably.
 */

#include <stdio.h>
#include <string.h>
#include "zmalloc.h"
#include "endianconv.h"

#define ZIPMAP_BIGLEN 254
#define ZIPMAP_END 255

/* The following defines the max value for the <free> field described in the
 * comments above, that is, the max number of trailing bytes in a value. */
#define ZIPMAP_VALUE_MAX_FREE 4

/* The following macro returns the number of bytes needed to encode the length
 * for the integer value _l, that is, 1 byte for lengths < ZIPMAP_BIGLEN and
 * 5 bytes for all the other lengths. */
#define ZIPMAP_LEN_BYTES(_l) (((_l) < ZIPMAP_BIGLEN) ? 1 : sizeof(unsigned int)+1)

/* Create a new empty zipmap. */
unsigned char *zipmapNew(void) {
    unsigned char *zm = zmalloc(2);

    zm[0] = 0; /* Length */
    zm[1] = ZIPMAP_END;
    return zm;
}

/* Decode the encoded length pointed by 'p' */
static unsigned int zipmapDecodeLength(unsigned char *p) {
    unsigned int len = *p;

    if (len < ZIPMAP_BIGLEN) return len;
    memcpy(&len,p+1,sizeof(unsigned int));
    memrev32ifbe(&len);
    return len;
}

/* Encode the length 'l' writing it in 'p'. If p is NULL it just returns
 * the amount of bytes required to encode such a length. */
static unsigned int zipmapEncodeLength(unsigned char *p, unsigned int len) {
    if (p == NULL) {
        return ZIPMAP_LEN_BYTES(len);
    } else {
        if (len < ZIPMAP_BIGLEN) {
            p[0] = len;
            return 1;
        } else {
            p[0] = ZIPMAP_BIGLEN;
            memcpy(p+1,&len,sizeof(len));
            memrev32ifbe(p+1);
            return 1+sizeof(len);
        }
    }
}

/* Search for a matching key, returning a pointer to the entry inside the
 * zipmap. Returns NULL if the key is not found.
 *
 * If NULL is returned, and totlen is not NULL, it is set to the entire
 * size of the zimap, so that the calling function will be able to
 * reallocate the original zipmap to make room for more entries. */
static unsigned char *zipmapLookupRaw(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned int *totlen) {
    unsigned char *p = zm+1, *k = NULL;
    unsigned int l,llen;

    while(*p != ZIPMAP_END) {
        unsigned char free;

        /* Match or skip the key */
        l = zipmapDecodeLength(p);
        llen = zipmapEncodeLength(NULL,l);
        if (key != NULL && k == NULL && l == klen && !memcmp(p+llen,key,l)) {
            /* Only return when the user doesn't care
             * for the total length of the zipmap. */
            if (totlen != NULL) {
                k = p;
            } else {
                return p;
            }
        }
        p += llen+l;
        /* Skip the value as well */
        l = zipmapDecodeLength(p);
        p += zipmapEncodeLength(NULL,l);
        free = p[0];
        p += l+1+free; /* +1 to skip the free byte */
    }
    if (totlen != NULL) *totlen = (unsigned int)(p-zm)+1;
    return k;
}

static unsigned long zipmapRequiredLength(unsigned int klen, unsigned int vlen) {
    unsigned int l;

    l = klen+vlen+3;
    if (klen >= ZIPMAP_BIGLEN) l += 4;
    if (vlen >= ZIPMAP_BIGLEN) l += 4;
    return l;
}

/* Return the total amount used by a key (encoded length + payload) */
static unsigned int zipmapRawKeyLength(unsigned char *p) {
    unsigned int l = zipmapDecodeLength(p);
    return zipmapEncodeLength(NULL,l) + l;
}

/* Return the total amount used by a value
 * (encoded length + single byte free count + payload) */
static unsigned int zipmapRawValueLength(unsigned char *p) {
    unsigned int l = zipmapDecodeLength(p);
    unsigned int used;

    used = zipmapEncodeLength(NULL,l);
    used += p[used] + 1 + l;
    return used;
}

/* If 'p' points to a key, this function returns the total amount of
 * bytes used to store this entry (entry = key + associated value + trailing
 * free space if any). */
static unsigned int zipmapRawEntryLength(unsigned char *p) {
    unsigned int l = zipmapRawKeyLength(p);
    return l + zipmapRawValueLength(p+l);
}

static inline unsigned char *zipmapResize(unsigned char *zm, unsigned int len) {
    zm = zrealloc(zm, len);
    zm[len-1] = ZIPMAP_END;
    return zm;
}

/* Set key to value, creating the key if it does not already exist.
 * If 'update' is not NULL, *update is set to 1 if the key was
 * already preset, otherwise to 0. */
unsigned char *zipmapSet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char *val, unsigned int vlen, int *update) {
    unsigned int zmlen, offset;
    unsigned int freelen, reqlen = zipmapRequiredLength(klen,vlen);
    unsigned int empty, vempty;
    unsigned char *p;

    freelen = reqlen;
    if (update) *update = 0;
    p = zipmapLookupRaw(zm,key,klen,&zmlen);
    if (p == NULL) {
        /* Key not found: enlarge */
        zm = zipmapResize(zm, zmlen+reqlen);
        p = zm+zmlen-1;
        zmlen = zmlen+reqlen;

        /* Increase zipmap length (this is an insert) */
        if (zm[0] < ZIPMAP_BIGLEN) zm[0]++;
    } else {
        /* Key found. Is there enough space for the new value? */
        /* Compute the total length: */
        if (update) *update = 1;
        freelen = zipmapRawEntryLength(p);
        if (freelen < reqlen) {
            /* Store the offset of this key within the current zipmap, so
             * it can be resized. Then, move the tail backwards so this
             * pair fits at the current position. */
            offset = p-zm;
            zm = zipmapResize(zm, zmlen-freelen+reqlen);
            p = zm+offset;

            /* The +1 in the number of bytes to be moved is caused by the
             * end-of-zipmap byte. Note: the *original* zmlen is used. */
            memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
            zmlen = zmlen-freelen+reqlen;
            freelen = reqlen;
        }
    }

    /* We now have a suitable block where the key/value entry can
     * be written. If there is too much free space, move the tail
     * of the zipmap a few bytes to the front and shrink the zipmap,
     * as we want zipmaps to be very space efficient. */
    empty = freelen-reqlen;
    if (empty >= ZIPMAP_VALUE_MAX_FREE) {
        /* First, move the tail <empty> bytes to the front, then resize
         * the zipmap to be <empty> bytes smaller. */
        offset = p-zm;
        memmove(p+reqlen, p+freelen, zmlen-(offset+freelen+1));
        zmlen -= empty;
        zm = zipmapResize(zm, zmlen);
        p = zm+offset;
        vempty = 0;
    } else {
        vempty = empty;
    }

    /* Just write the key + value and we are done. */
    /* Key: */
    p += zipmapEncodeLength(p,klen);
    memcpy(p,key,klen);
    p += klen;
    /* Value: */
    p += zipmapEncodeLength(p,vlen);
    *p++ = vempty;
    memcpy(p,val,vlen);
    return zm;
}

/* Remove the specified key. If 'deleted' is not NULL the pointed integer is
 * set to 0 if the key was not found, to 1 if it was found and deleted. */
unsigned char *zipmapDel(unsigned char *zm, unsigned char *key, unsigned int klen, int *deleted) {
    unsigned int zmlen, freelen;
    unsigned char *p = zipmapLookupRaw(zm,key,klen,&zmlen);
    if (p) {
        freelen = zipmapRawEntryLength(p);
        memmove(p, p+freelen, zmlen-((p-zm)+freelen+1));
        zm = zipmapResize(zm, zmlen-freelen);

        /* Decrease zipmap length */
        if (zm[0] < ZIPMAP_BIGLEN) zm[0]--;

        if (deleted) *deleted = 1;
    } else {
        if (deleted) *deleted = 0;
    }
    return zm;
}

/* Call before iterating through elements via zipmapNext() */
unsigned char *zipmapRewind(unsigned char *zm) {
    return zm+1;
}

/* This function is used to iterate through all the zipmap elements.
 * In the first call the first argument is the pointer to the zipmap + 1.
 * In the next calls what zipmapNext returns is used as first argument.
 * Example:
 *
 * unsigned char *i = zipmapRewind(my_zipmap);
 * while((i = zipmapNext(i,&key,&klen,&value,&vlen)) != NULL) {
 *     printf("%d bytes key at $p\n", klen, key);
 *     printf("%d bytes value at $p\n", vlen, value);
 * }
 */
unsigned char *zipmapNext(unsigned char *zm, unsigned char **key, unsigned int *klen, unsigned char **value, unsigned int *vlen) {
    if (zm[0] == ZIPMAP_END) return NULL;
    if (key) {
        *key = zm;
        *klen = zipmapDecodeLength(zm);
        *key += ZIPMAP_LEN_BYTES(*klen);
    }
    zm += zipmapRawKeyLength(zm);
    if (value) {
        *value = zm+1;
        *vlen = zipmapDecodeLength(zm);
        *value += ZIPMAP_LEN_BYTES(*vlen);
    }
    zm += zipmapRawValueLength(zm);
    return zm;
}

/* Search a key and retrieve the pointer and len of the associated value.
 * If the key is found the function returns 1, otherwise 0. */
int zipmapGet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char **value, unsigned int *vlen) {
    unsigned char *p;

    if ((p = zipmapLookupRaw(zm,key,klen,NULL)) == NULL) return 0;
    p += zipmapRawKeyLength(p);
    *vlen = zipmapDecodeLength(p);
    *value = p + ZIPMAP_LEN_BYTES(*vlen) + 1;
    return 1;
}

/* Return 1 if the key exists, otherwise 0 is returned. */
int zipmapExists(unsigned char *zm, unsigned char *key, unsigned int klen) {
    return zipmapLookupRaw(zm,key,klen,NULL) != NULL;
}

/* Return the number of entries inside a zipmap */
unsigned int zipmapLen(unsigned char *zm) {
    unsigned int len = 0;
    if (zm[0] < ZIPMAP_BIGLEN) {
        len = zm[0];
    } else {
        unsigned char *p = zipmapRewind(zm);
        while((p = zipmapNext(p,NULL,NULL,NULL,NULL)) != NULL) len++;

        /* Re-store length if small enough */
        if (len < ZIPMAP_BIGLEN) zm[0] = len;
    }
    return len;
}

/* Return the raw size in bytes of a zipmap, so that we can serialize
 * the zipmap on disk (or everywhere is needed) just writing the returned
 * amount of bytes of the C array starting at the zipmap pointer. */
size_t zipmapBlobLen(unsigned char *zm) {
    unsigned int totlen;
    zipmapLookupRaw(zm,NULL,0,&totlen);
    return totlen;
}

#ifdef REDIS_TEST
static void zipmapRepr(unsigned char *p) {
    unsigned int l;

    printf("{status %u}",*p++);
    while(1) {
        if (p[0] == ZIPMAP_END) {
            printf("{end}");
            break;
        } else {
            unsigned char e;

            l = zipmapDecodeLength(p);
            printf("{key %u}",l);
            p += zipmapEncodeLength(NULL,l);
            if (l != 0 && fwrite(p,l,1,stdout) == 0) perror("fwrite");
            p += l;

            l = zipmapDecodeLength(p);
            printf("{value %u}",l);
            p += zipmapEncodeLength(NULL,l);
            e = *p++;
            if (l != 0 && fwrite(p,l,1,stdout) == 0) perror("fwrite");
            p += l+e;
            if (e) {
                printf("[");
                while(e--) printf(".");
                printf("]");
            }
        }
    }
    printf("\n");
}

#define UNUSED(x) (void)(x)
int zipmapTest(int argc, char *argv[]) {
    unsigned char *zm;

    UNUSED(argc);
    UNUSED(argv);

    zm = zipmapNew();

    zm = zipmapSet(zm,(unsigned char*) "name",4, (unsigned char*) "foo",3,NULL);
    zm = zipmapSet(zm,(unsigned char*) "surname",7, (unsigned char*) "foo",3,NULL);
    zm = zipmapSet(zm,(unsigned char*) "age",3, (unsigned char*) "foo",3,NULL);
    zipmapRepr(zm);

    zm = zipmapSet(zm,(unsigned char*) "hello",5, (unsigned char*) "world!",6,NULL);
    zm = zipmapSet(zm,(unsigned char*) "foo",3, (unsigned char*) "bar",3,NULL);
    zm = zipmapSet(zm,(unsigned char*) "foo",3, (unsigned char*) "!",1,NULL);
    zipmapRepr(zm);
    zm = zipmapSet(zm,(unsigned char*) "foo",3, (unsigned char*) "12345",5,NULL);
    zipmapRepr(zm);
    zm = zipmapSet(zm,(unsigned char*) "new",3, (unsigned char*) "xx",2,NULL);
    zm = zipmapSet(zm,(unsigned char*) "noval",5, (unsigned char*) "",0,NULL);
    zipmapRepr(zm);
    zm = zipmapDel(zm,(unsigned char*) "new",3,NULL);
    zipmapRepr(zm);

    printf("\nLook up large key:\n");
    {
        unsigned char buf[512];
        unsigned char *value;
        unsigned int vlen, i;
        for (i = 0; i < 512; i++) buf[i] = 'a';

        zm = zipmapSet(zm,buf,512,(unsigned char*) "long",4,NULL);
        if (zipmapGet(zm,buf,512,&value,&vlen)) {
            printf("  <long key> is associated to the %d bytes value: %.*s\n",
                vlen, vlen, value);
        }
    }

    printf("\nPerform a direct lookup:\n");
    {
        unsigned char *value;
        unsigned int vlen;

        if (zipmapGet(zm,(unsigned char*) "foo",3,&value,&vlen)) {
            printf("  foo is associated to the %d bytes value: %.*s\n",
                vlen, vlen, value);
        }
    }
    printf("\nIterate through elements:\n");
    {
        unsigned char *i = zipmapRewind(zm);
        unsigned char *key, *value;
        unsigned int klen, vlen;

        while((i = zipmapNext(i,&key,&klen,&value,&vlen)) != NULL) {
            printf("  %d:%.*s => %d:%.*s\n", klen, klen, key, vlen, vlen, value);
        }
    }
    return 0;
}
#endif