copy.c

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/*-------------------------------------------------------------------------
 *
 * copy.c
 *      Implements the COPY utility command
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/copy.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <ctype.h>
#include <unistd.h>
#include <sys/stat.h>

#include "access/sysattr.h"
#include "access/table.h"
#include "access/xact.h"
#include "catalog/pg_authid.h"
#include "commands/copy.h"
#include "commands/defrem.h"
#include "executor/executor.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "optimizer/optimizer.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
#include "parser/parse_expr.h"
#include "parser/parse_relation.h"
#include "rewrite/rewriteHandler.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/rls.h"

/*
 *   DoCopy executes the SQL COPY statement
 *
 * Either unload or reload contents of table <relation>, depending on <from>.
 * (<from> = true means we are inserting into the table.)  In the "TO" case
 * we also support copying the output of an arbitrary SELECT, INSERT, UPDATE
 * or DELETE query.
 *
 * If <pipe> is false, transfer is between the table and the file named
 * <filename>.  Otherwise, transfer is between the table and our regular
 * input/output stream. The latter could be either stdin/stdout or a
 * socket, depending on whether we're running under Postmaster control.
 *
 * Do not allow a Postgres user without the 'pg_read_server_files' or
 * 'pg_write_server_files' role to read from or write to a file.
 *
 * Do not allow the copy if user doesn't have proper permission to access
 * the table or the specifically requested columns.
 */
void
DoCopy(ParseState *pstate, const CopyStmt *stmt,
       int stmt_location, int stmt_len,
       uint64 *processed)
{
    bool        is_from = stmt->is_from;
    bool        pipe = (stmt->filename == NULL);
    Relation    rel;
    Oid         relid;
    RawStmt    *query = NULL;
    Node       *whereClause = NULL;

    /*
     * Disallow COPY to/from file or program except to users with the
     * appropriate role.
     */
    if (!pipe)
    {
        if (stmt->is_program)
        {
            if (!is_member_of_role(GetUserId(), ROLE_PG_EXECUTE_SERVER_PROGRAM))
                ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("must be superuser or a member of the pg_execute_server_program role to COPY to or from an external program"),
                         errhint("Anyone can COPY to stdout or from stdin. "
                                 "psql's \\copy command also works for anyone.")));
        }
        else
        {
            if (is_from && !is_member_of_role(GetUserId(), ROLE_PG_READ_SERVER_FILES))
                ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("must be superuser or a member of the pg_read_server_files role to COPY from a file"),
                         errhint("Anyone can COPY to stdout or from stdin. "
                                 "psql's \\copy command also works for anyone.")));

            if (!is_from && !is_member_of_role(GetUserId(), ROLE_PG_WRITE_SERVER_FILES))
                ereport(ERROR,
                        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                         errmsg("must be superuser or a member of the pg_write_server_files role to COPY to a file"),
                         errhint("Anyone can COPY to stdout or from stdin. "
                                 "psql's \\copy command also works for anyone.")));
        }
    }

    if (stmt->relation)
    {
        LOCKMODE    lockmode = is_from ? RowExclusiveLock : AccessShareLock;
        ParseNamespaceItem *nsitem;
        RangeTblEntry *rte;
        TupleDesc   tupDesc;
        List       *attnums;
        ListCell   *cur;

        Assert(!stmt->query);

        /* Open and lock the relation, using the appropriate lock type. */
        rel = table_openrv(stmt->relation, lockmode);

        relid = RelationGetRelid(rel);

        nsitem = addRangeTableEntryForRelation(pstate, rel, lockmode,
                                               NULL, false, false);
        rte = nsitem->p_rte;
        rte->requiredPerms = (is_from ? ACL_INSERT : ACL_SELECT);

        if (stmt->whereClause)
        {
            /* add nsitem to query namespace */
            addNSItemToQuery(pstate, nsitem, false, true, true);

            /* Transform the raw expression tree */
            whereClause = transformExpr(pstate, stmt->whereClause, EXPR_KIND_COPY_WHERE);

            /* Make sure it yields a boolean result. */
            whereClause = coerce_to_boolean(pstate, whereClause, "WHERE");

            /* we have to fix its collations too */
            assign_expr_collations(pstate, whereClause);

            whereClause = eval_const_expressions(NULL, whereClause);

            whereClause = (Node *) canonicalize_qual((Expr *) whereClause, false);
            whereClause = (Node *) make_ands_implicit((Expr *) whereClause);
        }

        tupDesc = RelationGetDescr(rel);
        attnums = CopyGetAttnums(tupDesc, rel, stmt->attlist);
        foreach(cur, attnums)
        {
            int         attno = lfirst_int(cur) -
            FirstLowInvalidHeapAttributeNumber;

            if (is_from)
                rte->insertedCols = bms_add_member(rte->insertedCols, attno);
            else
                rte->selectedCols = bms_add_member(rte->selectedCols, attno);
        }
        ExecCheckRTPerms(pstate->p_rtable, true);

        /*
         * Permission check for row security policies.
         *
         * check_enable_rls will ereport(ERROR) if the user has requested
         * something invalid and will otherwise indicate if we should enable
         * RLS (returns RLS_ENABLED) or not for this COPY statement.
         *
         * If the relation has a row security policy and we are to apply it
         * then perform a "query" copy and allow the normal query processing
         * to handle the policies.
         *
         * If RLS is not enabled for this, then just fall through to the
         * normal non-filtering relation handling.
         */
        if (check_enable_rls(rte->relid, InvalidOid, false) == RLS_ENABLED)
        {
            SelectStmt *select;
            ColumnRef  *cr;
            ResTarget  *target;
            RangeVar   *from;
            List       *targetList = NIL;

            if (is_from)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("COPY FROM not supported with row-level security"),
                         errhint("Use INSERT statements instead.")));

            /*
             * Build target list
             *
             * If no columns are specified in the attribute list of the COPY
             * command, then the target list is 'all' columns. Therefore, '*'
             * should be used as the target list for the resulting SELECT
             * statement.
             *
             * In the case that columns are specified in the attribute list,
             * create a ColumnRef and ResTarget for each column and add them
             * to the target list for the resulting SELECT statement.
             */
            if (!stmt->attlist)
            {
                cr = makeNode(ColumnRef);
                cr->fields = list_make1(makeNode(A_Star));
                cr->location = -1;

                target = makeNode(ResTarget);
                target->name = NULL;
                target->indirection = NIL;
                target->val = (Node *) cr;
                target->location = -1;

                targetList = list_make1(target);
            }
            else
            {
                ListCell   *lc;

                foreach(lc, stmt->attlist)
                {
                    /*
                     * Build the ColumnRef for each column.  The ColumnRef
                     * 'fields' property is a String 'Value' node (see
                     * nodes/value.h) that corresponds to the column name
                     * respectively.
                     */
                    cr = makeNode(ColumnRef);
                    cr->fields = list_make1(lfirst(lc));
                    cr->location = -1;

                    /* Build the ResTarget and add the ColumnRef to it. */
                    target = makeNode(ResTarget);
                    target->name = NULL;
                    target->indirection = NIL;
                    target->val = (Node *) cr;
                    target->location = -1;

                    /* Add each column to the SELECT statement's target list */
                    targetList = lappend(targetList, target);
                }
            }

            /*
             * Build RangeVar for from clause, fully qualified based on the
             * relation which we have opened and locked.
             */
            from = makeRangeVar(get_namespace_name(RelationGetNamespace(rel)),
                                pstrdup(RelationGetRelationName(rel)),
                                -1);

            /* Build query */
            select = makeNode(SelectStmt);
            select->targetList = targetList;
            select->fromClause = list_make1(from);

            query = makeNode(RawStmt);
            query->stmt = (Node *) select;
            query->stmt_location = stmt_location;
            query->stmt_len = stmt_len;

            /*
             * Close the relation for now, but keep the lock on it to prevent
             * changes between now and when we start the query-based COPY.
             *
             * We'll reopen it later as part of the query-based COPY.
             */
            table_close(rel, NoLock);
            rel = NULL;
        }
    }
    else
    {
        Assert(stmt->query);

        query = makeNode(RawStmt);
        query->stmt = stmt->query;
        query->stmt_location = stmt_location;
        query->stmt_len = stmt_len;

        relid = InvalidOid;
        rel = NULL;
    }

    if (is_from)
    {
        CopyFromState cstate;

        Assert(rel);

        /* check read-only transaction and parallel mode */
        if (XactReadOnly && !rel->rd_islocaltemp)
            PreventCommandIfReadOnly("COPY FROM");

        cstate = BeginCopyFrom(pstate, rel, whereClause,
                               stmt->filename, stmt->is_program,
                               NULL, stmt->attlist, stmt->options);
        *processed = CopyFrom(cstate);  /* copy from file to database */
        EndCopyFrom(cstate);
    }
    else
    {
        CopyToState cstate;

        cstate = BeginCopyTo(pstate, rel, query, relid,
                             stmt->filename, stmt->is_program,
                             stmt->attlist, stmt->options);
        *processed = DoCopyTo(cstate);  /* copy from database to file */
        EndCopyTo(cstate);
    }

    if (rel != NULL)
        table_close(rel, NoLock);
}

/*
 * Process the statement option list for COPY.
 *
 * Scan the options list (a list of DefElem) and transpose the information
 * into *opts_out, applying appropriate error checking.
 *
 * If 'opts_out' is not NULL, it is assumed to be filled with zeroes initially.
 *
 * This is exported so that external users of the COPY API can sanity-check
 * a list of options.  In that usage, 'opts_out' can be passed as NULL and
 * the collected data is just leaked until CurrentMemoryContext is reset.
 *
 * Note that additional checking, such as whether column names listed in FORCE
 * QUOTE actually exist, has to be applied later.  This just checks for
 * self-consistency of the options list.
 */
void
ProcessCopyOptions(ParseState *pstate,
                   CopyFormatOptions *opts_out,
                   bool is_from,
                   List *options)
{
    bool        format_specified = false;
    bool        freeze_specified = false;
    bool        header_specified = false;
    ListCell   *option;

    /* Support external use for option sanity checking */
    if (opts_out == NULL)
        opts_out = (CopyFormatOptions *) palloc0(sizeof(CopyFormatOptions));

    opts_out->file_encoding = -1;

    /* Extract options from the statement node tree */
    foreach(option, options)
    {
        DefElem    *defel = lfirst_node(DefElem, option);

        if (strcmp(defel->defname, "format") == 0)
        {
            char       *fmt = defGetString(defel);

            if (format_specified)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            format_specified = true;
            if (strcmp(fmt, "text") == 0)
                 /* default format */ ;
            else if (strcmp(fmt, "csv") == 0)
                opts_out->csv_mode = true;
            else if (strcmp(fmt, "binary") == 0)
                opts_out->binary = true;
            else
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("COPY format \"%s\" not recognized", fmt),
                         parser_errposition(pstate, defel->location)));
        }
        else if (strcmp(defel->defname, "freeze") == 0)
        {
            if (freeze_specified)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            freeze_specified = true;
            opts_out->freeze = defGetBoolean(defel);
        }
        else if (strcmp(defel->defname, "delimiter") == 0)
        {
            if (opts_out->delim)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            opts_out->delim = defGetString(defel);
        }
        else if (strcmp(defel->defname, "null") == 0)
        {
            if (opts_out->null_print)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            opts_out->null_print = defGetString(defel);
        }
        else if (strcmp(defel->defname, "header") == 0)
        {
            if (header_specified)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            header_specified = true;
            opts_out->header_line = defGetBoolean(defel);
        }
        else if (strcmp(defel->defname, "quote") == 0)
        {
            if (opts_out->quote)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            opts_out->quote = defGetString(defel);
        }
        else if (strcmp(defel->defname, "escape") == 0)
        {
            if (opts_out->escape)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            opts_out->escape = defGetString(defel);
        }
        else if (strcmp(defel->defname, "force_quote") == 0)
        {
            if (opts_out->force_quote || opts_out->force_quote_all)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            if (defel->arg && IsA(defel->arg, A_Star))
                opts_out->force_quote_all = true;
            else if (defel->arg && IsA(defel->arg, List))
                opts_out->force_quote = castNode(List, defel->arg);
            else
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("argument to option \"%s\" must be a list of column names",
                                defel->defname),
                         parser_errposition(pstate, defel->location)));
        }
        else if (strcmp(defel->defname, "force_not_null") == 0)
        {
            if (opts_out->force_notnull)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            if (defel->arg && IsA(defel->arg, List))
                opts_out->force_notnull = castNode(List, defel->arg);
            else
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("argument to option \"%s\" must be a list of column names",
                                defel->defname),
                         parser_errposition(pstate, defel->location)));
        }
        else if (strcmp(defel->defname, "force_null") == 0)
        {
            if (opts_out->force_null)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options")));
            if (defel->arg && IsA(defel->arg, List))
                opts_out->force_null = castNode(List, defel->arg);
            else
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("argument to option \"%s\" must be a list of column names",
                                defel->defname),
                         parser_errposition(pstate, defel->location)));
        }
        else if (strcmp(defel->defname, "convert_selectively") == 0)
        {
            /*
             * Undocumented, not-accessible-from-SQL option: convert only the
             * named columns to binary form, storing the rest as NULLs. It's
             * allowed for the column list to be NIL.
             */
            if (opts_out->convert_selectively)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            opts_out->convert_selectively = true;
            if (defel->arg == NULL || IsA(defel->arg, List))
                opts_out->convert_select = castNode(List, defel->arg);
            else
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("argument to option \"%s\" must be a list of column names",
                                defel->defname),
                         parser_errposition(pstate, defel->location)));
        }
        else if (strcmp(defel->defname, "encoding") == 0)
        {
            if (opts_out->file_encoding >= 0)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("conflicting or redundant options"),
                         parser_errposition(pstate, defel->location)));
            opts_out->file_encoding = pg_char_to_encoding(defGetString(defel));
            if (opts_out->file_encoding < 0)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                         errmsg("argument to option \"%s\" must be a valid encoding name",
                                defel->defname),
                         parser_errposition(pstate, defel->location)));
        }
        else
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("option \"%s\" not recognized",
                            defel->defname),
                     parser_errposition(pstate, defel->location)));
    }

    /*
     * Check for incompatible options (must do these two before inserting
     * defaults)
     */
    if (opts_out->binary && opts_out->delim)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("cannot specify DELIMITER in BINARY mode")));

    if (opts_out->binary && opts_out->null_print)
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("cannot specify NULL in BINARY mode")));

    /* Set defaults for omitted options */
    if (!opts_out->delim)
        opts_out->delim = opts_out->csv_mode ? "," : "\t";

    if (!opts_out->null_print)
        opts_out->null_print = opts_out->csv_mode ? "" : "\\N";
    opts_out->null_print_len = strlen(opts_out->null_print);

    if (opts_out->csv_mode)
    {
        if (!opts_out->quote)
            opts_out->quote = "\"";
        if (!opts_out->escape)
            opts_out->escape = opts_out->quote;
    }

    /* Only single-byte delimiter strings are supported. */
    if (strlen(opts_out->delim) != 1)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY delimiter must be a single one-byte character")));

    /* Disallow end-of-line characters */
    if (strchr(opts_out->delim, '\r') != NULL ||
        strchr(opts_out->delim, '\n') != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("COPY delimiter cannot be newline or carriage return")));

    if (strchr(opts_out->null_print, '\r') != NULL ||
        strchr(opts_out->null_print, '\n') != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("COPY null representation cannot use newline or carriage return")));

    /*
     * Disallow unsafe delimiter characters in non-CSV mode.  We can't allow
     * backslash because it would be ambiguous.  We can't allow the other
     * cases because data characters matching the delimiter must be
     * backslashed, and certain backslash combinations are interpreted
     * non-literally by COPY IN.  Disallowing all lower case ASCII letters is
     * more than strictly necessary, but seems best for consistency and
     * future-proofing.  Likewise we disallow all digits though only octal
     * digits are actually dangerous.
     */
    if (!opts_out->csv_mode &&
        strchr("\\.abcdefghijklmnopqrstuvwxyz0123456789",
               opts_out->delim[0]) != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("COPY delimiter cannot be \"%s\"", opts_out->delim)));

    /* Check header */
    if (!opts_out->csv_mode && opts_out->header_line)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY HEADER available only in CSV mode")));

    /* Check quote */
    if (!opts_out->csv_mode && opts_out->quote != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY quote available only in CSV mode")));

    if (opts_out->csv_mode && strlen(opts_out->quote) != 1)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY quote must be a single one-byte character")));

    if (opts_out->csv_mode && opts_out->delim[0] == opts_out->quote[0])
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("COPY delimiter and quote must be different")));

    /* Check escape */
    if (!opts_out->csv_mode && opts_out->escape != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY escape available only in CSV mode")));

    if (opts_out->csv_mode && strlen(opts_out->escape) != 1)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY escape must be a single one-byte character")));

    /* Check force_quote */
    if (!opts_out->csv_mode && (opts_out->force_quote || opts_out->force_quote_all))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY force quote available only in CSV mode")));
    if ((opts_out->force_quote || opts_out->force_quote_all) && is_from)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY force quote only available using COPY TO")));

    /* Check force_notnull */
    if (!opts_out->csv_mode && opts_out->force_notnull != NIL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY force not null available only in CSV mode")));
    if (opts_out->force_notnull != NIL && !is_from)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY force not null only available using COPY FROM")));

    /* Check force_null */
    if (!opts_out->csv_mode && opts_out->force_null != NIL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY force null available only in CSV mode")));

    if (opts_out->force_null != NIL && !is_from)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY force null only available using COPY FROM")));

    /* Don't allow the delimiter to appear in the null string. */
    if (strchr(opts_out->null_print, opts_out->delim[0]) != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("COPY delimiter must not appear in the NULL specification")));

    /* Don't allow the CSV quote char to appear in the null string. */
    if (opts_out->csv_mode &&
        strchr(opts_out->null_print, opts_out->quote[0]) != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("CSV quote character must not appear in the NULL specification")));
}

/*
 * CopyGetAttnums - build an integer list of attnums to be copied
 *
 * The input attnamelist is either the user-specified column list,
 * or NIL if there was none (in which case we want all the non-dropped
 * columns).
 *
 * We don't include generated columns in the generated full list and we don't
 * allow them to be specified explicitly.  They don't make sense for COPY
 * FROM, but we could possibly allow them for COPY TO.  But this way it's at
 * least ensured that whatever we copy out can be copied back in.
 *
 * rel can be NULL ... it's only used for error reports.
 */
List *
CopyGetAttnums(TupleDesc tupDesc, Relation rel, List *attnamelist)
{
    List       *attnums = NIL;

    if (attnamelist == NIL)
    {
        /* Generate default column list */
        int         attr_count = tupDesc->natts;
        int         i;

        for (i = 0; i < attr_count; i++)
        {
            if (TupleDescAttr(tupDesc, i)->attisdropped)
                continue;
            if (TupleDescAttr(tupDesc, i)->attgenerated)
                continue;
            attnums = lappend_int(attnums, i + 1);
        }
    }
    else
    {
        /* Validate the user-supplied list and extract attnums */
        ListCell   *l;

        foreach(l, attnamelist)
        {
            char       *name = strVal(lfirst(l));
            int         attnum;
            int         i;

            /* Lookup column name */
            attnum = InvalidAttrNumber;
            for (i = 0; i < tupDesc->natts; i++)
            {
                Form_pg_attribute att = TupleDescAttr(tupDesc, i);

                if (att->attisdropped)
                    continue;
                if (namestrcmp(&(att->attname), name) == 0)
                {
                    if (att->attgenerated)
                        ereport(ERROR,
                                (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                                 errmsg("column \"%s\" is a generated column",
                                        name),
                                 errdetail("Generated columns cannot be used in COPY.")));
                    attnum = att->attnum;
                    break;
                }
            }
            if (attnum == InvalidAttrNumber)
            {
                if (rel != NULL)
                    ereport(ERROR,
                            (errcode(ERRCODE_UNDEFINED_COLUMN),
                             errmsg("column \"%s\" of relation \"%s\" does not exist",
                                    name, RelationGetRelationName(rel))));
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_UNDEFINED_COLUMN),
                             errmsg("column \"%s\" does not exist",
                                    name)));
            }
            /* Check for duplicates */
            if (list_member_int(attnums, attnum))
                ereport(ERROR,
                        (errcode(ERRCODE_DUPLICATE_COLUMN),
                         errmsg("column \"%s\" specified more than once",
                                name)));
            attnums = lappend_int(attnums, attnum);
        }
    }

    return attnums;
}