copyto.c

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/*-------------------------------------------------------------------------
 *
 * copyto.c
 *      COPY <table> TO file/program/client
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/copyto.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

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

#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/tableam.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "commands/copy.h"
#include "commands/progress.h"
#include "executor/execdesc.h"
#include "executor/executor.h"
#include "executor/tuptable.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "optimizer/optimizer.h"
#include "pgstat.h"
#include "rewrite/rewriteHandler.h"
#include "storage/fd.h"
#include "tcop/tcopprot.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/partcache.h"
#include "utils/rel.h"
#include "utils/snapmgr.h"

/*
 * Represents the different dest cases we need to worry about at
 * the bottom level
 */
typedef enum CopyDest
{
    COPY_FILE,                  /* to file (or a piped program) */
    COPY_FRONTEND,              /* to frontend */
} CopyDest;

/*
 * This struct contains all the state variables used throughout a COPY TO
 * operation.
 *
 * Multi-byte encodings: all supported client-side encodings encode multi-byte
 * characters by having the first byte's high bit set. Subsequent bytes of the
 * character can have the high bit not set. When scanning data in such an
 * encoding to look for a match to a single-byte (ie ASCII) character, we must
 * use the full pg_encoding_mblen() machinery to skip over multibyte
 * characters, else we might find a false match to a trailing byte. In
 * supported server encodings, there is no possibility of a false match, and
 * it's faster to make useless comparisons to trailing bytes than it is to
 * invoke pg_encoding_mblen() to skip over them. encoding_embeds_ascii is true
 * when we have to do it the hard way.
 */
typedef struct CopyToStateData
{
    /* low-level state data */
    CopyDest    copy_dest;      /* type of copy source/destination */
    FILE       *copy_file;      /* used if copy_dest == COPY_FILE */
    StringInfo  fe_msgbuf;      /* used for all dests during COPY TO */

    int         file_encoding;  /* file or remote side's character encoding */
    bool        need_transcoding;   /* file encoding diff from server? */
    bool        encoding_embeds_ascii;  /* ASCII can be non-first byte? */

    /* parameters from the COPY command */
    Relation    rel;            /* relation to copy to */
    QueryDesc  *queryDesc;      /* executable query to copy from */
    List       *attnumlist;     /* integer list of attnums to copy */
    char       *filename;       /* filename, or NULL for STDOUT */
    bool        is_program;     /* is 'filename' a program to popen? */

    CopyFormatOptions opts;
    Node       *whereClause;    /* WHERE condition (or NULL) */

    /*
     * Working state
     */
    MemoryContext copycontext;  /* per-copy execution context */

    FmgrInfo   *out_functions;  /* lookup info for output functions */
    MemoryContext rowcontext;   /* per-row evaluation context */
    uint64      bytes_processed;    /* number of bytes processed so far */

} CopyToStateData;

/* DestReceiver for COPY (query) TO */
typedef struct
{
    DestReceiver pub;           /* publicly-known function pointers */
    CopyToState cstate;         /* CopyToStateData for the command */
    uint64      processed;      /* # of tuples processed */
} DR_copy;

/* NOTE: there's a copy of this in copyfromparse.c */
static const char BinarySignature[11] = "PGCOPY\n\377\r\n\0";


/* non-export function prototypes */
static void EndCopy(CopyToState cstate);
static void ClosePipeToProgram(CopyToState cstate);
static void CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot);
static void CopyAttributeOutText(CopyToState cstate, char *string);
static void CopyAttributeOutCSV(CopyToState cstate, char *string,
                                bool use_quote, bool single_attr);

/* Low-level communications functions */
static void SendCopyBegin(CopyToState cstate);
static void SendCopyEnd(CopyToState cstate);
static void CopySendData(CopyToState cstate, const void *databuf, int datasize);
static void CopySendString(CopyToState cstate, const char *str);
static void CopySendChar(CopyToState cstate, char c);
static void CopySendEndOfRow(CopyToState cstate);
static void CopySendInt32(CopyToState cstate, int32 val);
static void CopySendInt16(CopyToState cstate, int16 val);


/*
 * Send copy start/stop messages for frontend copies.  These have changed
 * in past protocol redesigns.
 */
static void
SendCopyBegin(CopyToState cstate)
{
    StringInfoData buf;
    int         natts = list_length(cstate->attnumlist);
    int16       format = (cstate->opts.binary ? 1 : 0);
    int         i;

    pq_beginmessage(&buf, 'H');
    pq_sendbyte(&buf, format);  /* overall format */
    pq_sendint16(&buf, natts);
    for (i = 0; i < natts; i++)
        pq_sendint16(&buf, format); /* per-column formats */
    pq_endmessage(&buf);
    cstate->copy_dest = COPY_FRONTEND;
}

static void
SendCopyEnd(CopyToState cstate)
{
    /* Shouldn't have any unsent data */
    Assert(cstate->fe_msgbuf->len == 0);
    /* Send Copy Done message */
    pq_putemptymessage('c');
}

/*----------
 * CopySendData sends output data to the destination (file or frontend)
 * CopySendString does the same for null-terminated strings
 * CopySendChar does the same for single characters
 * CopySendEndOfRow does the appropriate thing at end of each data row
 *  (data is not actually flushed except by CopySendEndOfRow)
 *
 * NB: no data conversion is applied by these functions
 *----------
 */
static void
CopySendData(CopyToState cstate, const void *databuf, int datasize)
{
    appendBinaryStringInfo(cstate->fe_msgbuf, databuf, datasize);
}

static void
CopySendString(CopyToState cstate, const char *str)
{
    appendBinaryStringInfo(cstate->fe_msgbuf, str, strlen(str));
}

static void
CopySendChar(CopyToState cstate, char c)
{
    appendStringInfoCharMacro(cstate->fe_msgbuf, c);
}

static void
CopySendEndOfRow(CopyToState cstate)
{
    StringInfo  fe_msgbuf = cstate->fe_msgbuf;

    switch (cstate->copy_dest)
    {
        case COPY_FILE:
            if (!cstate->opts.binary)
            {
                /* Default line termination depends on platform */
#ifndef WIN32
                CopySendChar(cstate, '\n');
#else
                CopySendString(cstate, "\r\n");
#endif
            }

            if (fwrite(fe_msgbuf->data, fe_msgbuf->len, 1,
                       cstate->copy_file) != 1 ||
                ferror(cstate->copy_file))
            {
                if (cstate->is_program)
                {
                    if (errno == EPIPE)
                    {
                        /*
                         * The pipe will be closed automatically on error at
                         * the end of transaction, but we might get a better
                         * error message from the subprocess' exit code than
                         * just "Broken Pipe"
                         */
                        ClosePipeToProgram(cstate);

                        /*
                         * If ClosePipeToProgram() didn't throw an error, the
                         * program terminated normally, but closed the pipe
                         * first. Restore errno, and throw an error.
                         */
                        errno = EPIPE;
                    }
                    ereport(ERROR,
                            (errcode_for_file_access(),
                             errmsg("could not write to COPY program: %m")));
                }
                else
                    ereport(ERROR,
                            (errcode_for_file_access(),
                             errmsg("could not write to COPY file: %m")));
            }
            break;
        case COPY_FRONTEND:
            /* The FE/BE protocol uses \n as newline for all platforms */
            if (!cstate->opts.binary)
                CopySendChar(cstate, '\n');

            /* Dump the accumulated row as one CopyData message */
            (void) pq_putmessage('d', fe_msgbuf->data, fe_msgbuf->len);
            break;
    }

    /* Update the progress */
    cstate->bytes_processed += fe_msgbuf->len;
    pgstat_progress_update_param(PROGRESS_COPY_BYTES_PROCESSED, cstate->bytes_processed);

    resetStringInfo(fe_msgbuf);
}

/*
 * These functions do apply some data conversion
 */

/*
 * CopySendInt32 sends an int32 in network byte order
 */
static inline void
CopySendInt32(CopyToState cstate, int32 val)
{
    uint32      buf;

    buf = pg_hton32((uint32) val);
    CopySendData(cstate, &buf, sizeof(buf));
}

/*
 * CopySendInt16 sends an int16 in network byte order
 */
static inline void
CopySendInt16(CopyToState cstate, int16 val)
{
    uint16      buf;

    buf = pg_hton16((uint16) val);
    CopySendData(cstate, &buf, sizeof(buf));
}

/*
 * Closes the pipe to an external program, checking the pclose() return code.
 */
static void
ClosePipeToProgram(CopyToState cstate)
{
    int         pclose_rc;

    Assert(cstate->is_program);

    pclose_rc = ClosePipeStream(cstate->copy_file);
    if (pclose_rc == -1)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close pipe to external command: %m")));
    else if (pclose_rc != 0)
    {
        ereport(ERROR,
                (errcode(ERRCODE_EXTERNAL_ROUTINE_EXCEPTION),
                 errmsg("program \"%s\" failed",
                        cstate->filename),
                 errdetail_internal("%s", wait_result_to_str(pclose_rc))));
    }
}

/*
 * Release resources allocated in a cstate for COPY TO/FROM.
 */
static void
EndCopy(CopyToState cstate)
{
    if (cstate->is_program)
    {
        ClosePipeToProgram(cstate);
    }
    else
    {
        if (cstate->filename != NULL && FreeFile(cstate->copy_file))
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not close file \"%s\": %m",
                            cstate->filename)));
    }

    pgstat_progress_end_command();

    MemoryContextDelete(cstate->copycontext);
    pfree(cstate);
}

/*
 * Setup CopyToState to read tuples from a table or a query for COPY TO.
 */
CopyToState
BeginCopyTo(ParseState *pstate,
            Relation rel,
            RawStmt *raw_query,
            Oid queryRelId,
            const char *filename,
            bool is_program,
            List *attnamelist,
            List *options)
{
    CopyToState cstate;
    bool        pipe = (filename == NULL);
    TupleDesc   tupDesc;
    int         num_phys_attrs;
    MemoryContext oldcontext;
    const int   progress_cols[] = {
        PROGRESS_COPY_COMMAND,
        PROGRESS_COPY_TYPE
    };
    int64       progress_vals[] = {
        PROGRESS_COPY_COMMAND_TO,
        0
    };

    if (rel != NULL && rel->rd_rel->relkind != RELKIND_RELATION)
    {
        if (rel->rd_rel->relkind == RELKIND_VIEW)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot copy from view \"%s\"",
                            RelationGetRelationName(rel)),
                     errhint("Try the COPY (SELECT ...) TO variant.")));
        else if (rel->rd_rel->relkind == RELKIND_MATVIEW)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot copy from materialized view \"%s\"",
                            RelationGetRelationName(rel)),
                     errhint("Try the COPY (SELECT ...) TO variant.")));
        else if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot copy from foreign table \"%s\"",
                            RelationGetRelationName(rel)),
                     errhint("Try the COPY (SELECT ...) TO variant.")));
        else if (rel->rd_rel->relkind == RELKIND_SEQUENCE)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot copy from sequence \"%s\"",
                            RelationGetRelationName(rel))));
        else if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot copy from partitioned table \"%s\"",
                            RelationGetRelationName(rel)),
                     errhint("Try the COPY (SELECT ...) TO variant.")));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot copy from non-table relation \"%s\"",
                            RelationGetRelationName(rel))));
    }


    /* Allocate workspace and zero all fields */
    cstate = (CopyToStateData *) palloc0(sizeof(CopyToStateData));

    /*
     * We allocate everything used by a cstate in a new memory context. This
     * avoids memory leaks during repeated use of COPY in a query.
     */
    cstate->copycontext = AllocSetContextCreate(CurrentMemoryContext,
                                                "COPY",
                                                ALLOCSET_DEFAULT_SIZES);

    oldcontext = MemoryContextSwitchTo(cstate->copycontext);

    /* Extract options from the statement node tree */
    ProcessCopyOptions(pstate, &cstate->opts, false /* is_from */ , options);

    /* Process the source/target relation or query */
    if (rel)
    {
        Assert(!raw_query);

        cstate->rel = rel;

        tupDesc = RelationGetDescr(cstate->rel);
    }
    else
    {
        List       *rewritten;
        Query      *query;
        PlannedStmt *plan;
        DestReceiver *dest;

        cstate->rel = NULL;

        /*
         * Run parse analysis and rewrite.  Note this also acquires sufficient
         * locks on the source table(s).
         */
        rewritten = pg_analyze_and_rewrite(raw_query,
                                           pstate->p_sourcetext, NULL, 0,
                                           NULL);

        /* check that we got back something we can work with */
        if (rewritten == NIL)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("DO INSTEAD NOTHING rules are not supported for COPY")));
        }
        else if (list_length(rewritten) > 1)
        {
            ListCell   *lc;

            /* examine queries to determine which error message to issue */
            foreach(lc, rewritten)
            {
                Query      *q = lfirst_node(Query, lc);

                if (q->querySource == QSRC_QUAL_INSTEAD_RULE)
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("conditional DO INSTEAD rules are not supported for COPY")));
                if (q->querySource == QSRC_NON_INSTEAD_RULE)
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("DO ALSO rules are not supported for the COPY")));
            }

            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("multi-statement DO INSTEAD rules are not supported for COPY")));
        }

        query = linitial_node(Query, rewritten);

        /* The grammar allows SELECT INTO, but we don't support that */
        if (query->utilityStmt != NULL &&
            IsA(query->utilityStmt, CreateTableAsStmt))
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("COPY (SELECT INTO) is not supported")));

        Assert(query->utilityStmt == NULL);

        /*
         * Similarly the grammar doesn't enforce the presence of a RETURNING
         * clause, but this is required here.
         */
        if (query->commandType != CMD_SELECT &&
            query->returningList == NIL)
        {
            Assert(query->commandType == CMD_INSERT ||
                   query->commandType == CMD_UPDATE ||
                   query->commandType == CMD_DELETE);

            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("COPY query must have a RETURNING clause")));
        }

        /* plan the query */
        plan = pg_plan_query(query, pstate->p_sourcetext,
                             CURSOR_OPT_PARALLEL_OK, NULL);

        /*
         * With row-level security and a user using "COPY relation TO", we
         * have to convert the "COPY relation TO" to a query-based COPY (eg:
         * "COPY (SELECT * FROM relation) TO"), to allow the rewriter to add
         * in any RLS clauses.
         *
         * When this happens, we are passed in the relid of the originally
         * found relation (which we have locked).  As the planner will look up
         * the relation again, we double-check here to make sure it found the
         * same one that we have locked.
         */
        if (queryRelId != InvalidOid)
        {
            /*
             * Note that with RLS involved there may be multiple relations,
             * and while the one we need is almost certainly first, we don't
             * make any guarantees of that in the planner, so check the whole
             * list and make sure we find the original relation.
             */
            if (!list_member_oid(plan->relationOids, queryRelId))
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("relation referenced by COPY statement has changed")));
        }

        /*
         * Use a snapshot with an updated command ID to ensure this query sees
         * results of any previously executed queries.
         */
        PushCopiedSnapshot(GetActiveSnapshot());
        UpdateActiveSnapshotCommandId();

        /* Create dest receiver for COPY OUT */
        dest = CreateDestReceiver(DestCopyOut);
        ((DR_copy *) dest)->cstate = cstate;

        /* Create a QueryDesc requesting no output */
        cstate->queryDesc = CreateQueryDesc(plan, pstate->p_sourcetext,
                                            GetActiveSnapshot(),
                                            InvalidSnapshot,
                                            dest, NULL, NULL, 0);

        /*
         * Call ExecutorStart to prepare the plan for execution.
         *
         * ExecutorStart computes a result tupdesc for us
         */
        ExecutorStart(cstate->queryDesc, 0);

        tupDesc = cstate->queryDesc->tupDesc;
    }

    /* Generate or convert list of attributes to process */
    cstate->attnumlist = CopyGetAttnums(tupDesc, cstate->rel, attnamelist);

    num_phys_attrs = tupDesc->natts;

    /* Convert FORCE_QUOTE name list to per-column flags, check validity */
    cstate->opts.force_quote_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
    if (cstate->opts.force_quote_all)
    {
        int         i;

        for (i = 0; i < num_phys_attrs; i++)
            cstate->opts.force_quote_flags[i] = true;
    }
    else if (cstate->opts.force_quote)
    {
        List       *attnums;
        ListCell   *cur;

        attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->opts.force_quote);

        foreach(cur, attnums)
        {
            int         attnum = lfirst_int(cur);
            Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);

            if (!list_member_int(cstate->attnumlist, attnum))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                         errmsg("FORCE_QUOTE column \"%s\" not referenced by COPY",
                                NameStr(attr->attname))));
            cstate->opts.force_quote_flags[attnum - 1] = true;
        }
    }

    /* Convert FORCE_NOT_NULL name list to per-column flags, check validity */
    cstate->opts.force_notnull_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
    if (cstate->opts.force_notnull)
    {
        List       *attnums;
        ListCell   *cur;

        attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->opts.force_notnull);

        foreach(cur, attnums)
        {
            int         attnum = lfirst_int(cur);
            Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);

            if (!list_member_int(cstate->attnumlist, attnum))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                         errmsg("FORCE_NOT_NULL column \"%s\" not referenced by COPY",
                                NameStr(attr->attname))));
            cstate->opts.force_notnull_flags[attnum - 1] = true;
        }
    }

    /* Convert FORCE_NULL name list to per-column flags, check validity */
    cstate->opts.force_null_flags = (bool *) palloc0(num_phys_attrs * sizeof(bool));
    if (cstate->opts.force_null)
    {
        List       *attnums;
        ListCell   *cur;

        attnums = CopyGetAttnums(tupDesc, cstate->rel, cstate->opts.force_null);

        foreach(cur, attnums)
        {
            int         attnum = lfirst_int(cur);
            Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);

            if (!list_member_int(cstate->attnumlist, attnum))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
                         errmsg("FORCE_NULL column \"%s\" not referenced by COPY",
                                NameStr(attr->attname))));
            cstate->opts.force_null_flags[attnum - 1] = true;
        }
    }

    /* Use client encoding when ENCODING option is not specified. */
    if (cstate->opts.file_encoding < 0)
        cstate->file_encoding = pg_get_client_encoding();
    else
        cstate->file_encoding = cstate->opts.file_encoding;

    /*
     * Set up encoding conversion info.  Even if the file and server encodings
     * are the same, we must apply pg_any_to_server() to validate data in
     * multibyte encodings.
     */
    cstate->need_transcoding =
        (cstate->file_encoding != GetDatabaseEncoding() ||
         pg_database_encoding_max_length() > 1);
    /* See Multibyte encoding comment above */
    cstate->encoding_embeds_ascii = PG_ENCODING_IS_CLIENT_ONLY(cstate->file_encoding);

    cstate->copy_dest = COPY_FILE;  /* default */

    MemoryContextSwitchTo(oldcontext);

    if (pipe)
    {
        progress_vals[1] = PROGRESS_COPY_TYPE_PIPE;

        Assert(!is_program);    /* the grammar does not allow this */
        if (whereToSendOutput != DestRemote)
            cstate->copy_file = stdout;
    }
    else
    {
        cstate->filename = pstrdup(filename);
        cstate->is_program = is_program;

        if (is_program)
        {
            progress_vals[1] = PROGRESS_COPY_TYPE_PROGRAM;
            cstate->copy_file = OpenPipeStream(cstate->filename, PG_BINARY_W);
            if (cstate->copy_file == NULL)
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not execute command \"%s\": %m",
                                cstate->filename)));
        }
        else
        {
            mode_t      oumask; /* Pre-existing umask value */
            struct stat st;

            progress_vals[1] = PROGRESS_COPY_TYPE_FILE;

            /*
             * Prevent write to relative path ... too easy to shoot oneself in
             * the foot by overwriting a database file ...
             */
            if (!is_absolute_path(filename))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_NAME),
                         errmsg("relative path not allowed for COPY to file")));

            oumask = umask(S_IWGRP | S_IWOTH);
            PG_TRY();
            {
                cstate->copy_file = AllocateFile(cstate->filename, PG_BINARY_W);
            }
            PG_FINALLY();
            {
                umask(oumask);
            }
            PG_END_TRY();
            if (cstate->copy_file == NULL)
            {
                /* copy errno because ereport subfunctions might change it */
                int         save_errno = errno;

                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not open file \"%s\" for writing: %m",
                                cstate->filename),
                         (save_errno == ENOENT || save_errno == EACCES) ?
                         errhint("COPY TO instructs the PostgreSQL server process to write a file. "
                                 "You may want a client-side facility such as psql's \\copy.") : 0));
            }

            if (fstat(fileno(cstate->copy_file), &st))
                ereport(ERROR,
                        (errcode_for_file_access(),
                         errmsg("could not stat file \"%s\": %m",
                                cstate->filename)));

            if (S_ISDIR(st.st_mode))
                ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("\"%s\" is a directory", cstate->filename)));
        }
    }

    /* initialize progress */
    pgstat_progress_start_command(PROGRESS_COMMAND_COPY,
                                  cstate->rel ? RelationGetRelid(cstate->rel) : InvalidOid);
    pgstat_progress_update_multi_param(2, progress_cols, progress_vals);

    cstate->bytes_processed = 0;

    MemoryContextSwitchTo(oldcontext);

    return cstate;
}

/*
 * Clean up storage and release resources for COPY TO.
 */
void
EndCopyTo(CopyToState cstate)
{
    if (cstate->queryDesc != NULL)
    {
        /* Close down the query and free resources. */
        ExecutorFinish(cstate->queryDesc);
        ExecutorEnd(cstate->queryDesc);
        FreeQueryDesc(cstate->queryDesc);
        PopActiveSnapshot();
    }

    /* Clean up storage */
    EndCopy(cstate);
}

/*
 * Copy from relation or query TO file.
 */
uint64
DoCopyTo(CopyToState cstate)
{
    bool        pipe = (cstate->filename == NULL);
    bool        fe_copy = (pipe && whereToSendOutput == DestRemote);
    TupleDesc   tupDesc;
    int         num_phys_attrs;
    ListCell   *cur;
    uint64      processed;

    if (fe_copy)
        SendCopyBegin(cstate);

    if (cstate->rel)
        tupDesc = RelationGetDescr(cstate->rel);
    else
        tupDesc = cstate->queryDesc->tupDesc;
    num_phys_attrs = tupDesc->natts;
    cstate->opts.null_print_client = cstate->opts.null_print;   /* default */

    /* We use fe_msgbuf as a per-row buffer regardless of copy_dest */
    cstate->fe_msgbuf = makeStringInfo();

    /* Get info about the columns we need to process. */
    cstate->out_functions = (FmgrInfo *) palloc(num_phys_attrs * sizeof(FmgrInfo));
    foreach(cur, cstate->attnumlist)
    {
        int         attnum = lfirst_int(cur);
        Oid         out_func_oid;
        bool        isvarlena;
        Form_pg_attribute attr = TupleDescAttr(tupDesc, attnum - 1);

        if (cstate->opts.binary)
            getTypeBinaryOutputInfo(attr->atttypid,
                                    &out_func_oid,
                                    &isvarlena);
        else
            getTypeOutputInfo(attr->atttypid,
                              &out_func_oid,
                              &isvarlena);
        fmgr_info(out_func_oid, &cstate->out_functions[attnum - 1]);
    }

    /*
     * Create a temporary memory context that we can reset once per row to
     * recover palloc'd memory.  This avoids any problems with leaks inside
     * datatype output routines, and should be faster than retail pfree's
     * anyway.  (We don't need a whole econtext as CopyFrom does.)
     */
    cstate->rowcontext = AllocSetContextCreate(CurrentMemoryContext,
                                               "COPY TO",
                                               ALLOCSET_DEFAULT_SIZES);

    if (cstate->opts.binary)
    {
        /* Generate header for a binary copy */
        int32       tmp;

        /* Signature */
        CopySendData(cstate, BinarySignature, 11);
        /* Flags field */
        tmp = 0;
        CopySendInt32(cstate, tmp);
        /* No header extension */
        tmp = 0;
        CopySendInt32(cstate, tmp);
    }
    else
    {
        /*
         * For non-binary copy, we need to convert null_print to file
         * encoding, because it will be sent directly with CopySendString.
         */
        if (cstate->need_transcoding)
            cstate->opts.null_print_client = pg_server_to_any(cstate->opts.null_print,
                                                              cstate->opts.null_print_len,
                                                              cstate->file_encoding);

        /* if a header has been requested send the line */
        if (cstate->opts.header_line)
        {
            bool        hdr_delim = false;

            foreach(cur, cstate->attnumlist)
            {
                int         attnum = lfirst_int(cur);
                char       *colname;

                if (hdr_delim)
                    CopySendChar(cstate, cstate->opts.delim[0]);
                hdr_delim = true;

                colname = NameStr(TupleDescAttr(tupDesc, attnum - 1)->attname);

                CopyAttributeOutCSV(cstate, colname, false,
                                    list_length(cstate->attnumlist) == 1);
            }

            CopySendEndOfRow(cstate);
        }
    }

    if (cstate->rel)
    {
        TupleTableSlot *slot;
        TableScanDesc scandesc;

        scandesc = table_beginscan(cstate->rel, GetActiveSnapshot(), 0, NULL);
        slot = table_slot_create(cstate->rel, NULL);

        processed = 0;
        while (table_scan_getnextslot(scandesc, ForwardScanDirection, slot))
        {
            CHECK_FOR_INTERRUPTS();

            /* Deconstruct the tuple ... */
            slot_getallattrs(slot);

            /* Format and send the data */
            CopyOneRowTo(cstate, slot);

            /*
             * Increment the number of processed tuples, and report the
             * progress.
             */
            pgstat_progress_update_param(PROGRESS_COPY_TUPLES_PROCESSED,
                                         ++processed);
        }

        ExecDropSingleTupleTableSlot(slot);
        table_endscan(scandesc);
    }
    else
    {
        /* run the plan --- the dest receiver will send tuples */
        ExecutorRun(cstate->queryDesc, ForwardScanDirection, 0L, true);
        processed = ((DR_copy *) cstate->queryDesc->dest)->processed;
    }

    if (cstate->opts.binary)
    {
        /* Generate trailer for a binary copy */
        CopySendInt16(cstate, -1);
        /* Need to flush out the trailer */
        CopySendEndOfRow(cstate);
    }

    MemoryContextDelete(cstate->rowcontext);

    if (fe_copy)
        SendCopyEnd(cstate);

    return processed;
}

/*
 * Emit one row during DoCopyTo().
 */
static void
CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot)
{
    bool        need_delim = false;
    FmgrInfo   *out_functions = cstate->out_functions;
    MemoryContext oldcontext;
    ListCell   *cur;
    char       *string;

    MemoryContextReset(cstate->rowcontext);
    oldcontext = MemoryContextSwitchTo(cstate->rowcontext);

    if (cstate->opts.binary)
    {
        /* Binary per-tuple header */
        CopySendInt16(cstate, list_length(cstate->attnumlist));
    }

    /* Make sure the tuple is fully deconstructed */
    slot_getallattrs(slot);

    foreach(cur, cstate->attnumlist)
    {
        int         attnum = lfirst_int(cur);
        Datum       value = slot->tts_values[attnum - 1];
        bool        isnull = slot->tts_isnull[attnum - 1];

        if (!cstate->opts.binary)
        {
            if (need_delim)
                CopySendChar(cstate, cstate->opts.delim[0]);
            need_delim = true;
        }

        if (isnull)
        {
            if (!cstate->opts.binary)
                CopySendString(cstate, cstate->opts.null_print_client);
            else
                CopySendInt32(cstate, -1);
        }
        else
        {
            if (!cstate->opts.binary)
            {
                string = OutputFunctionCall(&out_functions[attnum - 1],
                                            value);
                if (cstate->opts.csv_mode)
                    CopyAttributeOutCSV(cstate, string,
                                        cstate->opts.force_quote_flags[attnum - 1],
                                        list_length(cstate->attnumlist) == 1);
                else
                    CopyAttributeOutText(cstate, string);
            }
            else
            {
                bytea      *outputbytes;

                outputbytes = SendFunctionCall(&out_functions[attnum - 1],
                                               value);
                CopySendInt32(cstate, VARSIZE(outputbytes) - VARHDRSZ);
                CopySendData(cstate, VARDATA(outputbytes),
                             VARSIZE(outputbytes) - VARHDRSZ);
            }
        }
    }

    CopySendEndOfRow(cstate);

    MemoryContextSwitchTo(oldcontext);
}

/*
 * Send text representation of one attribute, with conversion and escaping
 */
#define DUMPSOFAR() \
    do { \
        if (ptr > start) \
            CopySendData(cstate, start, ptr - start); \
    } while (0)

static void
CopyAttributeOutText(CopyToState cstate, char *string)
{
    char       *ptr;
    char       *start;
    char        c;
    char        delimc = cstate->opts.delim[0];

    if (cstate->need_transcoding)
        ptr = pg_server_to_any(string, strlen(string), cstate->file_encoding);
    else
        ptr = string;

    /*
     * We have to grovel through the string searching for control characters
     * and instances of the delimiter character.  In most cases, though, these
     * are infrequent.  To avoid overhead from calling CopySendData once per
     * character, we dump out all characters between escaped characters in a
     * single call.  The loop invariant is that the data from "start" to "ptr"
     * can be sent literally, but hasn't yet been.
     *
     * We can skip pg_encoding_mblen() overhead when encoding is safe, because
     * in valid backend encodings, extra bytes of a multibyte character never
     * look like ASCII.  This loop is sufficiently performance-critical that
     * it's worth making two copies of it to get the IS_HIGHBIT_SET() test out
     * of the normal safe-encoding path.
     */
    if (cstate->encoding_embeds_ascii)
    {
        start = ptr;
        while ((c = *ptr) != '\0')
        {
            if ((unsigned char) c < (unsigned char) 0x20)
            {
                /*
                 * \r and \n must be escaped, the others are traditional. We
                 * prefer to dump these using the C-like notation, rather than
                 * a backslash and the literal character, because it makes the
                 * dump file a bit more proof against Microsoftish data
                 * mangling.
                 */
                switch (c)
                {
                    case '\b':
                        c = 'b';
                        break;
                    case '\f':
                        c = 'f';
                        break;
                    case '\n':
                        c = 'n';
                        break;
                    case '\r':
                        c = 'r';
                        break;
                    case '\t':
                        c = 't';
                        break;
                    case '\v':
                        c = 'v';
                        break;
                    default:
                        /* If it's the delimiter, must backslash it */
                        if (c == delimc)
                            break;
                        /* All ASCII control chars are length 1 */
                        ptr++;
                        continue;   /* fall to end of loop */
                }
                /* if we get here, we need to convert the control char */
                DUMPSOFAR();
                CopySendChar(cstate, '\\');
                CopySendChar(cstate, c);
                start = ++ptr;  /* do not include char in next run */
            }
            else if (c == '\\' || c == delimc)
            {
                DUMPSOFAR();
                CopySendChar(cstate, '\\');
                start = ptr++;  /* we include char in next run */
            }
            else if (IS_HIGHBIT_SET(c))
                ptr += pg_encoding_mblen(cstate->file_encoding, ptr);
            else
                ptr++;
        }
    }
    else
    {
        start = ptr;
        while ((c = *ptr) != '\0')
        {
            if ((unsigned char) c < (unsigned char) 0x20)
            {
                /*
                 * \r and \n must be escaped, the others are traditional. We
                 * prefer to dump these using the C-like notation, rather than
                 * a backslash and the literal character, because it makes the
                 * dump file a bit more proof against Microsoftish data
                 * mangling.
                 */
                switch (c)
                {
                    case '\b':
                        c = 'b';
                        break;
                    case '\f':
                        c = 'f';
                        break;
                    case '\n':
                        c = 'n';
                        break;
                    case '\r':
                        c = 'r';
                        break;
                    case '\t':
                        c = 't';
                        break;
                    case '\v':
                        c = 'v';
                        break;
                    default:
                        /* If it's the delimiter, must backslash it */
                        if (c == delimc)
                            break;
                        /* All ASCII control chars are length 1 */
                        ptr++;
                        continue;   /* fall to end of loop */
                }
                /* if we get here, we need to convert the control char */
                DUMPSOFAR();
                CopySendChar(cstate, '\\');
                CopySendChar(cstate, c);
                start = ++ptr;  /* do not include char in next run */
            }
            else if (c == '\\' || c == delimc)
            {
                DUMPSOFAR();
                CopySendChar(cstate, '\\');
                start = ptr++;  /* we include char in next run */
            }
            else
                ptr++;
        }
    }

    DUMPSOFAR();
}

/*
 * Send text representation of one attribute, with conversion and
 * CSV-style escaping
 */
static void
CopyAttributeOutCSV(CopyToState cstate, char *string,
                    bool use_quote, bool single_attr)
{
    char       *ptr;
    char       *start;
    char        c;
    char        delimc = cstate->opts.delim[0];
    char        quotec = cstate->opts.quote[0];
    char        escapec = cstate->opts.escape[0];

    /* force quoting if it matches null_print (before conversion!) */
    if (!use_quote && strcmp(string, cstate->opts.null_print) == 0)
        use_quote = true;

    if (cstate->need_transcoding)
        ptr = pg_server_to_any(string, strlen(string), cstate->file_encoding);
    else
        ptr = string;

    /*
     * Make a preliminary pass to discover if it needs quoting
     */
    if (!use_quote)
    {
        /*
         * Because '\.' can be a data value, quote it if it appears alone on a
         * line so it is not interpreted as the end-of-data marker.
         */
        if (single_attr && strcmp(ptr, "\\.") == 0)
            use_quote = true;
        else
        {
            char       *tptr = ptr;

            while ((c = *tptr) != '\0')
            {
                if (c == delimc || c == quotec || c == '\n' || c == '\r')
                {
                    use_quote = true;
                    break;
                }
                if (IS_HIGHBIT_SET(c) && cstate->encoding_embeds_ascii)
                    tptr += pg_encoding_mblen(cstate->file_encoding, tptr);
                else
                    tptr++;
            }
        }
    }

    if (use_quote)
    {
        CopySendChar(cstate, quotec);

        /*
         * We adopt the same optimization strategy as in CopyAttributeOutText
         */
        start = ptr;
        while ((c = *ptr) != '\0')
        {
            if (c == quotec || c == escapec)
            {
                DUMPSOFAR();
                CopySendChar(cstate, escapec);
                start = ptr;    /* we include char in next run */
            }
            if (IS_HIGHBIT_SET(c) && cstate->encoding_embeds_ascii)
                ptr += pg_encoding_mblen(cstate->file_encoding, ptr);
            else
                ptr++;
        }
        DUMPSOFAR();

        CopySendChar(cstate, quotec);
    }
    else
    {
        /* If it doesn't need quoting, we can just dump it as-is */
        CopySendString(cstate, ptr);
    }
}

/*
 * copy_dest_startup --- executor startup
 */
static void
copy_dest_startup(DestReceiver *self, int operation, TupleDesc typeinfo)
{
    /* no-op */
}

/*
 * copy_dest_receive --- receive one tuple
 */
static bool
copy_dest_receive(TupleTableSlot *slot, DestReceiver *self)
{
    DR_copy    *myState = (DR_copy *) self;
    CopyToState cstate = myState->cstate;

    /* Send the data */
    CopyOneRowTo(cstate, slot);

    /* Increment the number of processed tuples, and report the progress */
    pgstat_progress_update_param(PROGRESS_COPY_TUPLES_PROCESSED,
                                 ++myState->processed);

    return true;
}

/*
 * copy_dest_shutdown --- executor end
 */
static void
copy_dest_shutdown(DestReceiver *self)
{
    /* no-op */
}

/*
 * copy_dest_destroy --- release DestReceiver object
 */
static void
copy_dest_destroy(DestReceiver *self)
{
    pfree(self);
}

/*
 * CreateCopyDestReceiver -- create a suitable DestReceiver object
 */
DestReceiver *
CreateCopyDestReceiver(void)
{
    DR_copy    *self = (DR_copy *) palloc(sizeof(DR_copy));

    self->pub.receiveSlot = copy_dest_receive;
    self->pub.rStartup = copy_dest_startup;
    self->pub.rShutdown = copy_dest_shutdown;
    self->pub.rDestroy = copy_dest_destroy;
    self->pub.mydest = DestCopyOut;

    self->cstate = NULL;        /* will be set later */
    self->processed = 0;

    return (DestReceiver *) self;
}