heapfuncs.c

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/*-------------------------------------------------------------------------
 *
 * heapfuncs.c
 *    Functions to investigate heap pages
 *
 * We check the input to these functions for corrupt pointers etc. that
 * might cause crashes, but at the same time we try to print out as much
 * information as possible, even if it's nonsense. That's because if a
 * page is corrupt, we don't know why and how exactly it is corrupt, so we
 * let the user judge it.
 *
 * These functions are restricted to superusers for the fear of introducing
 * security holes if the input checking isn't as water-tight as it should be.
 * You'd need to be superuser to obtain a raw page image anyway, so
 * there's hardly any use case for using these without superuser-rights
 * anyway.
 *
 * Copyright (c) 2007-2018, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    contrib/pageinspect/heapfuncs.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "pageinspect.h"

#include "access/htup_details.h"
#include "funcapi.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/rel.h"


/*
 * bits_to_text
 *
 * Converts a bits8-array of 'len' bits to a human-readable
 * c-string representation.
 */
static char *
bits_to_text(bits8 *bits, int len)
{
    int         i;
    char       *str;

    str = palloc(len + 1);

    for (i = 0; i < len; i++)
        str[i] = (bits[(i / 8)] & (1 << (i % 8))) ? '1' : '0';

    str[i] = '\0';

    return str;
}


/*
 * text_to_bits
 *
 * Converts a c-string representation of bits into a bits8-array. This is
 * the reverse operation of previous routine.
 */
static bits8 *
text_to_bits(char *str, int len)
{
    bits8      *bits;
    int         off = 0;
    char        byte = 0;

    bits = palloc(len + 1);

    while (off < len)
    {
        if (off % 8 == 0)
            byte = 0;

        if ((str[off] == '0') || (str[off] == '1'))
            byte = byte | ((str[off] - '0') << off % 8);
        else
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_CORRUPTED),
                     errmsg("illegal character '%c' in t_bits string", str[off])));

        if (off % 8 == 7)
            bits[off / 8] = byte;

        off++;
    }

    return bits;
}

/*
 * heap_page_items
 *
 * Allows inspection of line pointers and tuple headers of a heap page.
 */
PG_FUNCTION_INFO_V1(heap_page_items);

typedef struct heap_page_items_state
{
    TupleDesc   tupd;
    Page        page;
    uint16      offset;
} heap_page_items_state;

Datum
heap_page_items(PG_FUNCTION_ARGS)
{
    bytea      *raw_page = PG_GETARG_BYTEA_P(0);
    heap_page_items_state *inter_call_data = NULL;
    FuncCallContext *fctx;
    int         raw_page_size;

    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 (errmsg("must be superuser to use raw page functions"))));

    raw_page_size = VARSIZE(raw_page) - VARHDRSZ;

    if (SRF_IS_FIRSTCALL())
    {
        TupleDesc   tupdesc;
        MemoryContext mctx;

        if (raw_page_size < SizeOfPageHeaderData)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("input page too small (%d bytes)", raw_page_size)));

        fctx = SRF_FIRSTCALL_INIT();
        mctx = MemoryContextSwitchTo(fctx->multi_call_memory_ctx);

        inter_call_data = palloc(sizeof(heap_page_items_state));

        /* Build a tuple descriptor for our result type */
        if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
            elog(ERROR, "return type must be a row type");

        inter_call_data->tupd = tupdesc;

        inter_call_data->offset = FirstOffsetNumber;
        inter_call_data->page = VARDATA(raw_page);

        fctx->max_calls = PageGetMaxOffsetNumber(inter_call_data->page);
        fctx->user_fctx = inter_call_data;

        MemoryContextSwitchTo(mctx);
    }

    fctx = SRF_PERCALL_SETUP();
    inter_call_data = fctx->user_fctx;

    if (fctx->call_cntr < fctx->max_calls)
    {
        Page        page = inter_call_data->page;
        HeapTuple   resultTuple;
        Datum       result;
        ItemId      id;
        Datum       values[14];
        bool        nulls[14];
        uint16      lp_offset;
        uint16      lp_flags;
        uint16      lp_len;

        memset(nulls, 0, sizeof(nulls));

        /* Extract information from the line pointer */

        id = PageGetItemId(page, inter_call_data->offset);

        lp_offset = ItemIdGetOffset(id);
        lp_flags = ItemIdGetFlags(id);
        lp_len = ItemIdGetLength(id);

        values[0] = UInt16GetDatum(inter_call_data->offset);
        values[1] = UInt16GetDatum(lp_offset);
        values[2] = UInt16GetDatum(lp_flags);
        values[3] = UInt16GetDatum(lp_len);

        /*
         * We do just enough validity checking to make sure we don't reference
         * data outside the page passed to us. The page could be corrupt in
         * many other ways, but at least we won't crash.
         */
        if (ItemIdHasStorage(id) &&
            lp_len >= MinHeapTupleSize &&
            lp_offset == MAXALIGN(lp_offset) &&
            lp_offset + lp_len <= raw_page_size)
        {
            HeapTupleHeader tuphdr;
            bytea      *tuple_data_bytea;
            int         tuple_data_len;

            /* Extract information from the tuple header */

            tuphdr = (HeapTupleHeader) PageGetItem(page, id);

            values[4] = UInt32GetDatum(HeapTupleHeaderGetRawXmin(tuphdr));
            values[5] = UInt32GetDatum(HeapTupleHeaderGetRawXmax(tuphdr));
            /* shared with xvac */
            values[6] = UInt32GetDatum(HeapTupleHeaderGetRawCommandId(tuphdr));
            values[7] = PointerGetDatum(&tuphdr->t_ctid);
            values[8] = UInt32GetDatum(tuphdr->t_infomask2);
            values[9] = UInt32GetDatum(tuphdr->t_infomask);
            values[10] = UInt8GetDatum(tuphdr->t_hoff);

            /* Copy raw tuple data into bytea attribute */
            tuple_data_len = lp_len - tuphdr->t_hoff;
            tuple_data_bytea = (bytea *) palloc(tuple_data_len + VARHDRSZ);
            SET_VARSIZE(tuple_data_bytea, tuple_data_len + VARHDRSZ);
            memcpy(VARDATA(tuple_data_bytea), (char *) tuphdr + tuphdr->t_hoff,
                   tuple_data_len);
            values[13] = PointerGetDatum(tuple_data_bytea);

            /*
             * We already checked that the item is completely within the raw
             * page passed to us, with the length given in the line pointer.
             * Let's check that t_hoff doesn't point over lp_len, before using
             * it to access t_bits and oid.
             */
            if (tuphdr->t_hoff >= SizeofHeapTupleHeader &&
                tuphdr->t_hoff <= lp_len &&
                tuphdr->t_hoff == MAXALIGN(tuphdr->t_hoff))
            {
                if (tuphdr->t_infomask & HEAP_HASNULL)
                {
                    int         bits_len;

                    bits_len =
                        BITMAPLEN(HeapTupleHeaderGetNatts(tuphdr)) * BITS_PER_BYTE;
                    values[11] = CStringGetTextDatum(
                                                     bits_to_text(tuphdr->t_bits, bits_len));
                }
                else
                    nulls[11] = true;

                if (tuphdr->t_infomask & HEAP_HASOID)
                    values[12] = HeapTupleHeaderGetOid(tuphdr);
                else
                    nulls[12] = true;
            }
            else
            {
                nulls[11] = true;
                nulls[12] = true;
            }
        }
        else
        {
            /*
             * The line pointer is not used, or it's invalid. Set the rest of
             * the fields to NULL
             */
            int         i;

            for (i = 4; i <= 13; i++)
                nulls[i] = true;
        }

        /* Build and return the result tuple. */
        resultTuple = heap_form_tuple(inter_call_data->tupd, values, nulls);
        result = HeapTupleGetDatum(resultTuple);

        inter_call_data->offset++;

        SRF_RETURN_NEXT(fctx, result);
    }
    else
        SRF_RETURN_DONE(fctx);
}

/*
 * tuple_data_split_internal
 *
 * Split raw tuple data taken directly from a page into an array of bytea
 * elements. This routine does a lookup on NULL values and creates array
 * elements accordingly. This is a reimplementation of nocachegetattr()
 * in heaptuple.c simplified for educational purposes.
 */
static Datum
tuple_data_split_internal(Oid relid, char *tupdata,
                          uint16 tupdata_len, uint16 t_infomask,
                          uint16 t_infomask2, bits8 *t_bits,
                          bool do_detoast)
{
    ArrayBuildState *raw_attrs;
    int         nattrs;
    int         i;
    int         off = 0;
    Relation    rel;
    TupleDesc   tupdesc;

    /* Get tuple descriptor from relation OID */
    rel = relation_open(relid, NoLock);
    tupdesc = CreateTupleDescCopyConstr(rel->rd_att);
    relation_close(rel, NoLock);

    raw_attrs = initArrayResult(BYTEAOID, CurrentMemoryContext, false);
    nattrs = tupdesc->natts;

    if (nattrs < (t_infomask2 & HEAP_NATTS_MASK))
        ereport(ERROR,
                (errcode(ERRCODE_DATA_CORRUPTED),
                 errmsg("number of attributes in tuple header is greater than number of attributes in tuple descriptor")));

    for (i = 0; i < nattrs; i++)
    {
        Form_pg_attribute attr;
        bool        is_null;
        bytea      *attr_data = NULL;

        attr = TupleDescAttr(tupdesc, i);
        is_null = (t_infomask & HEAP_HASNULL) && att_isnull(i, t_bits);

        /*
         * Tuple header can specify less attributes than tuple descriptor as
         * ALTER TABLE ADD COLUMN without DEFAULT keyword does not actually
         * change tuples in pages, so attributes with numbers greater than
         * (t_infomask2 & HEAP_NATTS_MASK) should be treated as NULL.
         */
        if (i >= (t_infomask2 & HEAP_NATTS_MASK))
            is_null = true;

        if (!is_null)
        {
            int         len;

            if (attr->attlen == -1)
            {
                off = att_align_pointer(off, attr->attalign, -1,
                                        tupdata + off);

                /*
                 * As VARSIZE_ANY throws an exception if it can't properly
                 * detect the type of external storage in macros VARTAG_SIZE,
                 * this check is repeated to have a nicer error handling.
                 */
                if (VARATT_IS_EXTERNAL(tupdata + off) &&
                    !VARATT_IS_EXTERNAL_ONDISK(tupdata + off) &&
                    !VARATT_IS_EXTERNAL_INDIRECT(tupdata + off))
                    ereport(ERROR,
                            (errcode(ERRCODE_DATA_CORRUPTED),
                             errmsg("first byte of varlena attribute is incorrect for attribute %d", i)));

                len = VARSIZE_ANY(tupdata + off);
            }
            else
            {
                off = att_align_nominal(off, attr->attalign);
                len = attr->attlen;
            }

            if (tupdata_len < off + len)
                ereport(ERROR,
                        (errcode(ERRCODE_DATA_CORRUPTED),
                         errmsg("unexpected end of tuple data")));

            if (attr->attlen == -1 && do_detoast)
                attr_data = DatumGetByteaPCopy(tupdata + off);
            else
            {
                attr_data = (bytea *) palloc(len + VARHDRSZ);
                SET_VARSIZE(attr_data, len + VARHDRSZ);
                memcpy(VARDATA(attr_data), tupdata + off, len);
            }

            off = att_addlength_pointer(off, attr->attlen,
                                        tupdata + off);
        }

        raw_attrs = accumArrayResult(raw_attrs, PointerGetDatum(attr_data),
                                     is_null, BYTEAOID, CurrentMemoryContext);
        if (attr_data)
            pfree(attr_data);
    }

    if (tupdata_len != off)
        ereport(ERROR,
                (errcode(ERRCODE_DATA_CORRUPTED),
                 errmsg("end of tuple reached without looking at all its data")));

    return makeArrayResult(raw_attrs, CurrentMemoryContext);
}

/*
 * tuple_data_split
 *
 * Split raw tuple data taken directly from page into distinct elements
 * taking into account null values.
 */
PG_FUNCTION_INFO_V1(tuple_data_split);

Datum
tuple_data_split(PG_FUNCTION_ARGS)
{
    Oid         relid;
    bytea      *raw_data;
    uint16      t_infomask;
    uint16      t_infomask2;
    char       *t_bits_str;
    bool        do_detoast = false;
    bits8      *t_bits = NULL;
    Datum       res;

    relid = PG_GETARG_OID(0);
    raw_data = PG_ARGISNULL(1) ? NULL : PG_GETARG_BYTEA_P(1);
    t_infomask = PG_GETARG_INT16(2);
    t_infomask2 = PG_GETARG_INT16(3);
    t_bits_str = PG_ARGISNULL(4) ? NULL :
        text_to_cstring(PG_GETARG_TEXT_PP(4));

    if (PG_NARGS() >= 6)
        do_detoast = PG_GETARG_BOOL(5);

    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("must be superuser to use raw page functions")));

    if (!raw_data)
        PG_RETURN_NULL();

    /*
     * Convert t_bits string back to the bits8 array as represented in the
     * tuple header.
     */
    if (t_infomask & HEAP_HASNULL)
    {
        int         bits_str_len;
        int         bits_len;

        bits_len = BITMAPLEN(t_infomask2 & HEAP_NATTS_MASK) * BITS_PER_BYTE;
        if (!t_bits_str)
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_CORRUPTED),
                     errmsg("argument of t_bits is null, but it is expected to be null and %d character long",
                            bits_len)));

        bits_str_len = strlen(t_bits_str);
        if (bits_len != bits_str_len)
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_CORRUPTED),
                     errmsg("unexpected length of t_bits %u, expected %d",
                            bits_str_len, bits_len)));

        /* do the conversion */
        t_bits = text_to_bits(t_bits_str, bits_str_len);
    }
    else
    {
        if (t_bits_str)
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_CORRUPTED),
                     errmsg("t_bits string is expected to be NULL, but instead it is %zu bytes length",
                            strlen(t_bits_str))));
    }

    /* Split tuple data */
    res = tuple_data_split_internal(relid, (char *) raw_data + VARHDRSZ,
                                    VARSIZE(raw_data) - VARHDRSZ,
                                    t_infomask, t_infomask2, t_bits,
                                    do_detoast);

    if (t_bits)
        pfree(t_bits);

    PG_RETURN_ARRAYTYPE_P(res);
}