1 /*-------------------------------------------------------------------------
4 * POSTGRES Datum (abstract data type) manipulation routines.
6 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
11 * src/backend/utils/adt/datum.c
13 *-------------------------------------------------------------------------
17 * In the implementation of these routines we assume the following:
19 * A) if a type is "byVal" then all the information is stored in the
20 * Datum itself (i.e. no pointers involved!). In this case the
21 * length of the type is always greater than zero and not more than
24 * B) if a type is not "byVal" and it has a fixed length (typlen > 0),
25 * then the "Datum" always contains a pointer to a stream of bytes.
26 * The number of significant bytes are always equal to the typlen.
28 * C) if a type is not "byVal" and has typlen == -1,
29 * then the "Datum" always points to a "struct varlena".
30 * This varlena structure has information about the actual length of this
31 * particular instance of the type and about its value.
33 * D) if a type is not "byVal" and has typlen == -2,
34 * then the "Datum" always points to a null-terminated C string.
36 * Note that we do not treat "toasted" datums specially; therefore what
37 * will be copied or compared is the compressed data or toast reference.
38 * An exception is made for datumCopy() of an expanded object, however,
39 * because most callers expect to get a simple contiguous (and pfree'able)
40 * result from datumCopy(). See also datumTransfer().
45 #include "access/detoast.h"
47 #include "utils/datum.h"
48 #include "utils/expandeddatum.h"
51 /*-------------------------------------------------------------------------
54 * Find the "real" size of a datum, given the datum value,
55 * whether it is a "by value", and the declared type length.
56 * (For TOAST pointer datums, this is the size of the pointer datum.)
58 * This is essentially an out-of-line version of the att_addlength_datum()
59 * macro in access/tupmacs.h. We do a tad more error checking though.
60 *-------------------------------------------------------------------------
63 datumGetSize(Datum value, bool typByVal, int typLen)
69 /* Pass-by-value types are always fixed-length */
70 Assert(typLen > 0 && typLen <= sizeof(Datum));
77 /* Fixed-length pass-by-ref type */
80 else if (typLen == -1)
82 /* It is a varlena datatype */
83 struct varlena *s = (struct varlena *) DatumGetPointer(value);
85 if (!PointerIsValid(s))
87 (errcode(ERRCODE_DATA_EXCEPTION),
88 errmsg("invalid Datum pointer")));
90 size = (Size) VARSIZE_ANY(s);
92 else if (typLen == -2)
94 /* It is a cstring datatype */
95 char *s = (char *) DatumGetPointer(value);
97 if (!PointerIsValid(s))
99 (errcode(ERRCODE_DATA_EXCEPTION),
100 errmsg("invalid Datum pointer")));
102 size = (Size) (strlen(s) + 1);
106 elog(ERROR, "invalid typLen: %d", typLen);
107 size = 0; /* keep compiler quiet */
114 /*-------------------------------------------------------------------------
117 * Make a copy of a non-NULL datum.
119 * If the datatype is pass-by-reference, memory is obtained with palloc().
121 * If the value is a reference to an expanded object, we flatten into memory
122 * obtained with palloc(). We need to copy because one of the main uses of
123 * this function is to copy a datum out of a transient memory context that's
124 * about to be destroyed, and the expanded object is probably in a child
125 * context that will also go away. Moreover, many callers assume that the
126 * result is a single pfree-able chunk.
127 *-------------------------------------------------------------------------
130 datumCopy(Datum value, bool typByVal, int typLen)
136 else if (typLen == -1)
138 /* It is a varlena datatype */
139 struct varlena *vl = (struct varlena *) DatumGetPointer(value);
141 if (VARATT_IS_EXTERNAL_EXPANDED(vl))
143 /* Flatten into the caller's memory context */
144 ExpandedObjectHeader *eoh = DatumGetEOHP(value);
148 resultsize = EOH_get_flat_size(eoh);
149 resultptr = (char *) palloc(resultsize);
150 EOH_flatten_into(eoh, (void *) resultptr, resultsize);
151 res = PointerGetDatum(resultptr);
155 /* Otherwise, just copy the varlena datum verbatim */
159 realSize = (Size) VARSIZE_ANY(vl);
160 resultptr = (char *) palloc(realSize);
161 memcpy(resultptr, vl, realSize);
162 res = PointerGetDatum(resultptr);
167 /* Pass by reference, but not varlena, so not toasted */
171 realSize = datumGetSize(value, typByVal, typLen);
173 resultptr = (char *) palloc(realSize);
174 memcpy(resultptr, DatumGetPointer(value), realSize);
175 res = PointerGetDatum(resultptr);
180 /*-------------------------------------------------------------------------
183 * Transfer a non-NULL datum into the current memory context.
185 * This is equivalent to datumCopy() except when the datum is a read-write
186 * pointer to an expanded object. In that case we merely reparent the object
187 * into the current context, and return its standard R/W pointer (in case the
188 * given one is a transient pointer of shorter lifespan).
189 *-------------------------------------------------------------------------
192 datumTransfer(Datum value, bool typByVal, int typLen)
194 if (!typByVal && typLen == -1 &&
195 VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(value)))
196 value = TransferExpandedObject(value, CurrentMemoryContext);
198 value = datumCopy(value, typByVal, typLen);
202 /*-------------------------------------------------------------------------
205 * Return true if two datums are equal, false otherwise
208 * We just compare the bytes of the two values, one by one.
209 * This routine will return false if there are 2 different
210 * representations of the same value (something along the lines
211 * of say the representation of zero in one's complement arithmetic).
212 * Also, it will probably not give the answer you want if either
213 * datum has been "toasted".
215 * Do not try to make this any smarter than it currently is with respect
216 * to "toasted" datums, because some of the callers could be working in the
217 * context of an aborted transaction.
218 *-------------------------------------------------------------------------
221 datumIsEqual(Datum value1, Datum value2, bool typByVal, int typLen)
228 * just compare the two datums. NOTE: just comparing "len" bytes will
229 * not do the work, because we do not know how these bytes are aligned
230 * inside the "Datum". We assume instead that any given datatype is
231 * consistent about how it fills extraneous bits in the Datum.
233 res = (value1 == value2);
243 * Compare the bytes pointed by the pointers stored in the datums.
245 size1 = datumGetSize(value1, typByVal, typLen);
246 size2 = datumGetSize(value2, typByVal, typLen);
249 s1 = (char *) DatumGetPointer(value1);
250 s2 = (char *) DatumGetPointer(value2);
251 res = (memcmp(s1, s2, size1) == 0);
256 /*-------------------------------------------------------------------------
259 * Compares two datums for identical contents, based on byte images. Return
260 * true if the two datums are equal, false otherwise.
261 *-------------------------------------------------------------------------
264 datum_image_eq(Datum value1, Datum value2, bool typByVal, int typLen)
273 len1 = toast_raw_datum_size(value1);
274 len2 = toast_raw_datum_size(value2);
275 /* No need to de-toast if lengths don't match. */
280 struct varlena *arg1val;
281 struct varlena *arg2val;
283 arg1val = PG_DETOAST_DATUM_PACKED(value1);
284 arg2val = PG_DETOAST_DATUM_PACKED(value2);
286 result = (memcmp(VARDATA_ANY(arg1val),
287 VARDATA_ANY(arg2val),
288 len1 - VARHDRSZ) == 0);
290 /* Only free memory if it's a copy made here. */
291 if ((Pointer) arg1val != (Pointer) value1)
293 if ((Pointer) arg2val != (Pointer) value2)
299 result = (value1 == value2);
303 result = (memcmp(DatumGetPointer(value1),
304 DatumGetPointer(value2),
311 /*-------------------------------------------------------------------------
314 * Compute the amount of space that datumSerialize will require for a
316 *-------------------------------------------------------------------------
319 datumEstimateSpace(Datum value, bool isnull, bool typByVal, int typLen)
321 Size sz = sizeof(int);
325 /* no need to use add_size, can't overflow */
328 else if (typLen == -1 &&
329 VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(value)))
331 /* Expanded objects need to be flattened, see comment below */
332 sz += EOH_get_flat_size(DatumGetEOHP(value));
335 sz += datumGetSize(value, typByVal, typLen);
341 /*-------------------------------------------------------------------------
344 * Serialize a possibly-NULL datum into caller-provided storage.
346 * Note: "expanded" objects are flattened so as to produce a self-contained
347 * representation, but other sorts of toast pointers are transferred as-is.
348 * This is because the intended use of this function is to pass the value
349 * to another process within the same database server. The other process
350 * could not access an "expanded" object within this process's memory, but
351 * we assume it can dereference the same TOAST pointers this one can.
353 * The format is as follows: first, we write a 4-byte header word, which
354 * is either the length of a pass-by-reference datum, -1 for a
355 * pass-by-value datum, or -2 for a NULL. If the value is NULL, nothing
356 * further is written. If it is pass-by-value, sizeof(Datum) bytes
357 * follow. Otherwise, the number of bytes indicated by the header word
358 * follow. The caller is responsible for ensuring that there is enough
359 * storage to store the number of bytes that will be written; use
360 * datumEstimateSpace() to find out how many will be needed.
361 * *start_address is updated to point to the byte immediately following
363 *-------------------------------------------------------------------------
366 datumSerialize(Datum value, bool isnull, bool typByVal, int typLen,
367 char **start_address)
369 ExpandedObjectHeader *eoh = NULL;
372 /* Write header word. */
377 else if (typLen == -1 &&
378 VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(value)))
380 eoh = DatumGetEOHP(value);
381 header = EOH_get_flat_size(eoh);
384 header = datumGetSize(value, typByVal, typLen);
385 memcpy(*start_address, &header, sizeof(int));
386 *start_address += sizeof(int);
388 /* If not null, write payload bytes. */
393 memcpy(*start_address, &value, sizeof(Datum));
394 *start_address += sizeof(Datum);
401 * EOH_flatten_into expects the target address to be maxaligned,
402 * so we can't store directly to *start_address.
404 tmp = (char *) palloc(header);
405 EOH_flatten_into(eoh, (void *) tmp, header);
406 memcpy(*start_address, tmp, header);
407 *start_address += header;
414 memcpy(*start_address, DatumGetPointer(value), header);
415 *start_address += header;
420 /*-------------------------------------------------------------------------
423 * Restore a possibly-NULL datum previously serialized by datumSerialize.
424 * *start_address is updated according to the number of bytes consumed.
425 *-------------------------------------------------------------------------
428 datumRestore(char **start_address, bool *isnull)
433 /* Read header word. */
434 memcpy(&header, *start_address, sizeof(int));
435 *start_address += sizeof(int);
437 /* If this datum is NULL, we can stop here. */
444 /* OK, datum is not null. */
447 /* If this datum is pass-by-value, sizeof(Datum) bytes follow. */
452 memcpy(&val, *start_address, sizeof(Datum));
453 *start_address += sizeof(Datum);
457 /* Pass-by-reference case; copy indicated number of bytes. */
460 memcpy(d, *start_address, header);
461 *start_address += header;
462 return PointerGetDatum(d);