hstore_from_record(PG_FUNCTION_ARGS)
{
	HeapTupleHeader rec;
	int32		buflen;
	HStore	   *out;
	Pairs	   *pairs;
	Oid			tupType;
	int32		tupTypmod;
	TupleDesc	tupdesc;
	HeapTupleData tuple;
	RecordIOData *my_extra;
	int			ncolumns;
	int			i,
				j;
	Datum	   *values;
	bool	   *nulls;

	if (PG_ARGISNULL(0))
	{
		Oid			argtype = get_fn_expr_argtype(fcinfo->flinfo, 0);

		/*
		 * have no tuple to look at, so the only source of type info is the
		 * argtype. The lookup_rowtype_tupdesc call below will error out if we
		 * don't have a known composite type oid here.
		 */
		tupType = argtype;
		tupTypmod = -1;

		rec = NULL;
	}
	else
	{
		rec = PG_GETARG_HEAPTUPLEHEADER(0);

		/* Extract type info from the tuple itself */
		tupType = HeapTupleHeaderGetTypeId(rec);
		tupTypmod = HeapTupleHeaderGetTypMod(rec);
	}

	tupdesc = lookup_rowtype_tupdesc(tupType, tupTypmod);
	ncolumns = tupdesc->natts;

	/*
	 * We arrange to look up the needed I/O info just once per series of
	 * calls, assuming the record type doesn't change underneath us.
	 */
	my_extra = (RecordIOData *) fcinfo->flinfo->fn_extra;
	if (my_extra == NULL ||
		my_extra->ncolumns != ncolumns)
	{
		fcinfo->flinfo->fn_extra =
			MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
							   sizeof(RecordIOData) - sizeof(ColumnIOData)
							   + ncolumns * sizeof(ColumnIOData));
		my_extra = (RecordIOData *) fcinfo->flinfo->fn_extra;
		my_extra->record_type = InvalidOid;
		my_extra->record_typmod = 0;
	}

	if (my_extra->record_type != tupType ||
		my_extra->record_typmod != tupTypmod)
	{
		MemSet(my_extra, 0,
			   sizeof(RecordIOData) - sizeof(ColumnIOData)
			   + ncolumns * sizeof(ColumnIOData));
		my_extra->record_type = tupType;
		my_extra->record_typmod = tupTypmod;
		my_extra->ncolumns = ncolumns;
	}

	Assert(ncolumns <= MaxTupleAttributeNumber);		/* thus, no overflow */
	pairs = palloc(ncolumns * sizeof(Pairs));

	if (rec)
	{
		/* Build a temporary HeapTuple control structure */
		tuple.t_len = HeapTupleHeaderGetDatumLength(rec);
		ItemPointerSetInvalid(&(tuple.t_self));
		tuple.t_tableOid = InvalidOid;
		tuple.t_data = rec;

		values = (Datum *) palloc(ncolumns * sizeof(Datum));
		nulls = (bool *) palloc(ncolumns * sizeof(bool));

		/* Break down the tuple into fields */
		heap_deform_tuple(&tuple, tupdesc, values, nulls);
	}
	else
	{
		values = NULL;
		nulls = NULL;
	}

	for (i = 0, j = 0; i < ncolumns; ++i)
	{
		ColumnIOData *column_info = &my_extra->columns[i];
		Oid			column_type = tupdesc->attrs[i]->atttypid;
		char	   *value;

		/* Ignore dropped columns in datatype */
		if (tupdesc->attrs[i]->attisdropped)
			continue;

		pairs[j].key = NameStr(tupdesc->attrs[i]->attname);
		pairs[j].keylen = hstoreCheckKeyLen(strlen(NameStr(tupdesc->attrs[i]->attname)));

		if (!nulls || nulls[i])
		{
			pairs[j].val = NULL;
			pairs[j].vallen = 4;
			pairs[j].isnull = true;
			pairs[j].needfree = false;
			++j;
			continue;
		}

		/*
		 * Convert the column value to text
		 */
		if (column_info->column_type != column_type)
		{
			bool		typIsVarlena;

			getTypeOutputInfo(column_type,
							  &column_info->typiofunc,
							  &typIsVarlena);
			fmgr_info_cxt(column_info->typiofunc, &column_info->proc,
						  fcinfo->flinfo->fn_mcxt);
			column_info->column_type = column_type;
		}

		value = OutputFunctionCall(&column_info->proc, values[i]);

		pairs[j].val = value;
		pairs[j].vallen = hstoreCheckValLen(strlen(value));
		pairs[j].isnull = false;
		pairs[j].needfree = false;
		++j;
	}

	ncolumns = hstoreUniquePairs(pairs, j, &buflen);

	out = hstorePairs(pairs, ncolumns, buflen);

	ReleaseTupleDesc(tupdesc);

	PG_RETURN_POINTER(out);
}