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/*
* contrib/hstore/hstore_compat.c
*
* Notes on old/new hstore format disambiguation.
*
* There are three formats to consider:
* 1) old contrib/hstore (referred to as hstore-old)
* 2) prerelease pgfoundry hstore
* 3) new contrib/hstore
*
* (2) and (3) are identical except for the HS_FLAG_NEWVERSION
* bit, which is set in (3) but not (2).
*
* Values that are already in format (3), or which are
* unambiguously in format (2), are handled by the first
* "return immediately" test in hstoreUpgrade().
*
* To stress a point: we ONLY get here with possibly-ambiguous
* values if we're doing some sort of in-place migration from an
* old prerelease pgfoundry hstore-new; and we explicitly don't
* support that without fixing up any potentially padded values
* first. Most of the code here is serious overkill, but the
* performance penalty isn't serious (especially compared to the
* palloc() that we have to do anyway) and the belt-and-braces
* validity checks provide some reassurance. (If for some reason
* we get a value that would have worked on the old code, but
* which would be botched by the conversion code, the validity
* checks will fail it first so we get an error rather than bad
* data.)
*
* Note also that empty hstores are the same in (2) and (3), so
* there are some special-case paths for them.
*
* We tell the difference between formats (2) and (3) as follows (but
* note that there are some edge cases where we can't tell; see
* comments in hstoreUpgrade):
*
* First, since there must be at least one entry, we look at
* how the bits line up. The new format looks like:
*
* 10kkkkkkkkkkkkkkkkkkkkkkkkkkkkkk (k..k = keylen)
* 0nvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv (v..v = keylen+vallen)
*
* The old format looks like one of these, depending on endianness
* and bitfield layout: (k..k = keylen, v..v = vallen, p..p = pos,
* n = isnull)
*
* kkkkkkkkkkkkkkkkvvvvvvvvvvvvvvvv
* nppppppppppppppppppppppppppppppp
*
* kkkkkkkkkkkkkkkkvvvvvvvvvvvvvvvv
* pppppppppppppppppppppppppppppppn
*
* vvvvvvvvvvvvvvvvkkkkkkkkkkkkkkkk
* nppppppppppppppppppppppppppppppp
*
* vvvvvvvvvvvvvvvvkkkkkkkkkkkkkkkk
* pppppppppppppppppppppppppppppppn (usual i386 format)
*
* If the entry is in old format, for the first entry "pos" must be 0.
* We can obviously see that either keylen or vallen must be >32768
* for there to be any ambiguity (which is why lengths less than that
* are fasttracked in hstore.h) Since "pos"==0, the "v" field in the
* new-format interpretation can only be 0 or 1, which constrains all
* but three bits of the old-format's k and v fields. But in addition
* to all of this, the data length implied by the keylen and vallen
* must fit in the varlena size. So the only ambiguous edge case for
* hstores with only one entry occurs between a new-format entry with
* an excess (~32k) of padding, and an old-format entry. But we know
* which format to use in that case based on how we were compiled, so
* no actual data corruption can occur.
*
* If there is more than one entry, the requirement that keys do not
* decrease in length, and that positions increase contiguously, and
* that the end of the data not be beyond the end of the varlena
* itself, disambiguates in almost all other cases. There is a small
* set of ambiguous cases which could occur if the old-format value
* has a large excess of padding and just the right pattern of key
* sizes, but these are also handled based on how we were compiled.
*
* The otherwise undocumented function hstore_version_diag is provided
* for testing purposes.
*/
#include "postgres.h"
#include "hstore.h"
/*
* This is the structure used for entries in the old contrib/hstore
* implementation. Notice that this is the same size as the new entry
* (two 32-bit words per key/value pair) and that the header is the
* same, so the old and new versions of ARRPTR, STRPTR, CALCDATASIZE
* etc. are compatible.
*
* If the above statement isn't true on some bizarre platform, we're
* a bit hosed (see StaticAssertStmt in hstoreValidOldFormat).
*/
typedef struct
{
uint16 keylen;
uint16 vallen;
uint32
valisnull:1,
pos:31;
} HOldEntry;
static int hstoreValidNewFormat(HStore *hs);
static int hstoreValidOldFormat(HStore *hs);
/*
* Validity test for a new-format hstore.
* 0 = not valid
* 1 = valid but with "slop" in the length
* 2 = exactly valid
*/
static int
hstoreValidNewFormat(HStore *hs)
{
int count = HS_COUNT(hs);
HEntry *entries = ARRPTR(hs);
int buflen = (count) ? HSE_ENDPOS(entries[2 * (count) - 1]) : 0;
int vsize = CALCDATASIZE(count, buflen);
int i;
if (hs->size_ & HS_FLAG_NEWVERSION)
return 2;
if (count == 0)
return 2;
if (!HSE_ISFIRST(entries[0]))
return 0;
if (vsize > VARSIZE(hs))
return 0;
/* entry position must be nondecreasing */
for (i = 1; i < 2 * count; ++i)
{
if (HSE_ISFIRST(entries[i])
|| (HSE_ENDPOS(entries[i]) < HSE_ENDPOS(entries[i - 1])))
return 0;
}
/* key length must be nondecreasing and keys must not be null */
for (i = 1; i < count; ++i)
{
if (HS_KEYLEN(entries, i) < HS_KEYLEN(entries, i - 1))
return 0;
if (HSE_ISNULL(entries[2 * i]))
return 0;
}
if (vsize != VARSIZE(hs))
return 1;
return 2;
}
/*
* Validity test for an old-format hstore.
* 0 = not valid
* 1 = valid but with "slop" in the length
* 2 = exactly valid
*/
static int
hstoreValidOldFormat(HStore *hs)
{
int count = hs->size_;
HOldEntry *entries = (HOldEntry *) ARRPTR(hs);
int vsize;
int lastpos = 0;
int i;
if (hs->size_ & HS_FLAG_NEWVERSION)
return 0;
/* New format uses an HEntry for key and another for value */
StaticAssertStmt(sizeof(HOldEntry) == 2 * sizeof(HEntry),
"old hstore format is not upward-compatible");
if (count == 0)
return 2;
if (count > 0xFFFFFFF)
return 0;
if (CALCDATASIZE(count, 0) > VARSIZE(hs))
return 0;
if (entries[0].pos != 0)
return 0;
/* key length must be nondecreasing */
for (i = 1; i < count; ++i)
{
if (entries[i].keylen < entries[i - 1].keylen)
return 0;
}
/*
* entry position must be strictly increasing, except for the first entry
* (which can be ""=>"" and thus zero-length); and all entries must be
* properly contiguous
*/
for (i = 0; i < count; ++i)
{
if (entries[i].pos != lastpos)
return 0;
lastpos += (entries[i].keylen
+ ((entries[i].valisnull) ? 0 : entries[i].vallen));
}
vsize = CALCDATASIZE(count, lastpos);
if (vsize > VARSIZE(hs))
return 0;
if (vsize != VARSIZE(hs))
return 1;
return 2;
}
/*
* hstoreUpgrade: PG_DETOAST_DATUM plus support for conversion of old hstores
*/
HStore *
hstoreUpgrade(Datum orig)
{
HStore *hs = (HStore *) PG_DETOAST_DATUM(orig);
int valid_new;
int valid_old;
bool writable;
/* Return immediately if no conversion needed */
if ((hs->size_ & HS_FLAG_NEWVERSION) ||
hs->size_ == 0 ||
(VARSIZE(hs) < 32768 && HSE_ISFIRST((ARRPTR(hs)[0]))))
return hs;
valid_new = hstoreValidNewFormat(hs);
valid_old = hstoreValidOldFormat(hs);
/* Do we have a writable copy? */
writable = ((void *) hs != (void *) DatumGetPointer(orig));
if (!valid_old || hs->size_ == 0)
{
if (valid_new)
{
/*
* force the "new version" flag and the correct varlena length,
* but only if we have a writable copy already (which we almost
* always will, since short new-format values won't come through
* here)
*/
if (writable)
{
HS_SETCOUNT(hs, HS_COUNT(hs));
HS_FIXSIZE(hs, HS_COUNT(hs));
}
return hs;
}
else
{
elog(ERROR, "invalid hstore value found");
}
}
/*
* this is the tricky edge case. It is only possible in some quite extreme
* cases (the hstore must have had a lot of wasted padding space at the
* end). But the only way a "new" hstore value could get here is if we're
* upgrading in place from a pre-release version of hstore-new (NOT
* contrib/hstore), so we work off the following assumptions: 1. If you're
* moving from old contrib/hstore to hstore-new, you're required to fix up
* any potential conflicts first, e.g. by running ALTER TABLE ... USING
* col::text::hstore; on all hstore columns before upgrading. 2. If you're
* moving from old contrib/hstore to new contrib/hstore, then "new" values
* are impossible here 3. If you're moving from pre-release hstore-new to
* hstore-new, then "old" values are impossible here 4. If you're moving
* from pre-release hstore-new to new contrib/hstore, you're not doing so
* as an in-place upgrade, so there is no issue So the upshot of all this
* is that we can treat all the edge cases as "new" if we're being built
* as hstore-new, and "old" if we're being built as contrib/hstore.
*
* XXX the WARNING can probably be downgraded to DEBUG1 once this has been
* beta-tested. But for now, it would be very useful to know if anyone can
* actually reach this case in a non-contrived setting.
*/
if (valid_new)
{
#if HSTORE_IS_HSTORE_NEW
elog(WARNING, "ambiguous hstore value resolved as hstore-new");
/*
* force the "new version" flag and the correct varlena length, but
* only if we have a writable copy already (which we almost always
* will, since short new-format values won't come through here)
*/
if (writable)
{
HS_SETCOUNT(hs, HS_COUNT(hs));
HS_FIXSIZE(hs, HS_COUNT(hs));
}
return hs;
#else
elog(WARNING, "ambiguous hstore value resolved as hstore-old");
#endif
}
/*
* must have an old-style value. Overwrite it in place as a new-style one,
* making sure we have a writable copy first.
*/
if (!writable)
hs = (HStore *) PG_DETOAST_DATUM_COPY(orig);
{
int count = hs->size_;
HEntry *new_entries = ARRPTR(hs);
HOldEntry *old_entries = (HOldEntry *) ARRPTR(hs);
int i;
for (i = 0; i < count; ++i)
{
uint32 pos = old_entries[i].pos;
uint32 keylen = old_entries[i].keylen;
uint32 vallen = old_entries[i].vallen;
bool isnull = old_entries[i].valisnull;
if (isnull)
vallen = 0;
new_entries[2 * i].entry = (pos + keylen) & HENTRY_POSMASK;
new_entries[2 * i + 1].entry = (((pos + keylen + vallen) & HENTRY_POSMASK)
| ((isnull) ? HENTRY_ISNULL : 0));
}
if (count)
new_entries[0].entry |= HENTRY_ISFIRST;
HS_SETCOUNT(hs, count);
HS_FIXSIZE(hs, count);
}
return hs;
}
PG_FUNCTION_INFO_V1(hstore_version_diag);
Datum
hstore_version_diag(PG_FUNCTION_ARGS)
{
HStore *hs = (HStore *) PG_DETOAST_DATUM(PG_GETARG_DATUM(0));
int valid_new = hstoreValidNewFormat(hs);
int valid_old = hstoreValidOldFormat(hs);
PG_RETURN_INT32(valid_old * 10 + valid_new);
}
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