text: /*-------------------------------------------------------------------------
   *
   * file_fdw.c
   *		  foreign-data wrapper for server-side flat files (or programs).
   *
   * Copyright (c) 2010-2020, PostgreSQL Global Development Group
   *
   * IDENTIFICATION
   *		  contrib/file_fdw/file_fdw.c
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include <sys/stat.h>
  #include <unistd.h>
  
  #include "access/htup_details.h"
  #include "access/reloptions.h"
  #include "access/sysattr.h"
  #include "access/table.h"
  #include "catalog/pg_authid.h"
  #include "catalog/pg_foreign_table.h"
  #include "commands/copy.h"
  #include "commands/defrem.h"
  #include "commands/explain.h"
  #include "commands/vacuum.h"
  #include "foreign/fdwapi.h"
  #include "foreign/foreign.h"
  #include "miscadmin.h"
  #include "nodes/makefuncs.h"
  #include "optimizer/optimizer.h"
  #include "optimizer/pathnode.h"
  #include "optimizer/planmain.h"
  #include "optimizer/restrictinfo.h"
  #include "utils/acl.h"
  #include "utils/memutils.h"
  #include "utils/rel.h"
  #include "utils/sampling.h"
  
  PG_MODULE_MAGIC;
  
  /*
   * Describes the valid options for objects that use this wrapper.
   */
  struct FileFdwOption
  {
  	const char *optname;
  	Oid			optcontext;		/* Oid of catalog in which option may appear */
  };
  
  /*
   * Valid options for file_fdw.
   * These options are based on the options for the COPY FROM command.
   * But note that force_not_null and force_null are handled as boolean options
   * attached to a column, not as table options.
   *
   * Note: If you are adding new option for user mapping, you need to modify
   * fileGetOptions(), which currently doesn't bother to look at user mappings.
   */
  static const struct FileFdwOption valid_options[] = {
  	/* Data source options */
  	{"filename", ForeignTableRelationId},
  	{"program", ForeignTableRelationId},
  
  	/* Format options */
  	/* oids option is not supported */
  	{"format", ForeignTableRelationId},
  	{"header", ForeignTableRelationId},
  	{"delimiter", ForeignTableRelationId},
  	{"quote", ForeignTableRelationId},
  	{"escape", ForeignTableRelationId},
  	{"null", ForeignTableRelationId},
  	{"encoding", ForeignTableRelationId},
  	{"force_not_null", AttributeRelationId},
  	{"force_null", AttributeRelationId},
  
  	/*
  	 * force_quote is not supported by file_fdw because it's for COPY TO.
  	 */
  
  	/* Sentinel */
  	{NULL, InvalidOid}
  };
  
  /*
   * FDW-specific information for RelOptInfo.fdw_private.
   */
  typedef struct FileFdwPlanState
  {
  	char	   *filename;		/* file or program to read from */
  	bool		is_program;		/* true if filename represents an OS command */
  	List	   *options;		/* merged COPY options, excluding filename and
  								 * is_program */
  	BlockNumber pages;			/* estimate of file's physical size */
  	double		ntuples;		/* estimate of number of data rows */
  } FileFdwPlanState;
  
  /*
   * FDW-specific information for ForeignScanState.fdw_state.
   */
  typedef struct FileFdwExecutionState
  {
  	char	   *filename;		/* file or program to read from */
  	bool		is_program;		/* true if filename represents an OS command */
  	List	   *options;		/* merged COPY options, excluding filename and
  								 * is_program */
  	CopyState	cstate;			/* COPY execution state */
  } FileFdwExecutionState;
  
  /*
   * SQL functions
   */
  PG_FUNCTION_INFO_V1(file_fdw_handler);
  PG_FUNCTION_INFO_V1(file_fdw_validator);
  
  /*
   * FDW callback routines
   */
  static void fileGetForeignRelSize(PlannerInfo *root,
  								  RelOptInfo *baserel,
  								  Oid foreigntableid);
  static void fileGetForeignPaths(PlannerInfo *root,
  								RelOptInfo *baserel,
  								Oid foreigntableid);
  static ForeignScan *fileGetForeignPlan(PlannerInfo *root,
  									   RelOptInfo *baserel,
  									   Oid foreigntableid,
  									   ForeignPath *best_path,
  									   List *tlist,
  									   List *scan_clauses,
  									   Plan *outer_plan);
  static void fileExplainForeignScan(ForeignScanState *node, ExplainState *es);
  static void fileBeginForeignScan(ForeignScanState *node, int eflags);
  static TupleTableSlot *fileIterateForeignScan(ForeignScanState *node);
  static void fileReScanForeignScan(ForeignScanState *node);
  static void fileEndForeignScan(ForeignScanState *node);
  static bool fileAnalyzeForeignTable(Relation relation,
  									AcquireSampleRowsFunc *func,
  									BlockNumber *totalpages);
  static bool fileIsForeignScanParallelSafe(PlannerInfo *root, RelOptInfo *rel,
  										  RangeTblEntry *rte);
  
  /*
   * Helper functions
   */
  static bool is_valid_option(const char *option, Oid context);
  static void fileGetOptions(Oid foreigntableid,
  						   char **filename,
  						   bool *is_program,
  						   List **other_options);
  static List *get_file_fdw_attribute_options(Oid relid);
  static bool check_selective_binary_conversion(RelOptInfo *baserel,
  											  Oid foreigntableid,
  											  List **columns);
  static void estimate_size(PlannerInfo *root, RelOptInfo *baserel,
  						  FileFdwPlanState *fdw_private);
  static void estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
  						   FileFdwPlanState *fdw_private,
  						   Cost *startup_cost, Cost *total_cost);
  static int	file_acquire_sample_rows(Relation onerel, int elevel,
  									 HeapTuple *rows, int targrows,
  									 double *totalrows, double *totaldeadrows);
  
  
  /*
   * Foreign-data wrapper handler function: return a struct with pointers
   * to my callback routines.
   */
  Datum
  file_fdw_handler(PG_FUNCTION_ARGS)
  {
  	FdwRoutine *fdwroutine = makeNode(FdwRoutine);
  
  	fdwroutine->GetForeignRelSize = fileGetForeignRelSize;
  	fdwroutine->GetForeignPaths = fileGetForeignPaths;
  	fdwroutine->GetForeignPlan = fileGetForeignPlan;
  	fdwroutine->ExplainForeignScan = fileExplainForeignScan;
  	fdwroutine->BeginForeignScan = fileBeginForeignScan;
  	fdwroutine->IterateForeignScan = fileIterateForeignScan;
  	fdwroutine->ReScanForeignScan = fileReScanForeignScan;
  	fdwroutine->EndForeignScan = fileEndForeignScan;
  	fdwroutine->AnalyzeForeignTable = fileAnalyzeForeignTable;
  	fdwroutine->IsForeignScanParallelSafe = fileIsForeignScanParallelSafe;
  
  	PG_RETURN_POINTER(fdwroutine);
  }
  
  /*
   * Validate the generic options given to a FOREIGN DATA WRAPPER, SERVER,
   * USER MAPPING or FOREIGN TABLE that uses file_fdw.
   *
   * Raise an ERROR if the option or its value is considered invalid.
   */
  Datum
  file_fdw_validator(PG_FUNCTION_ARGS)
  {
  	List	   *options_list = untransformRelOptions(PG_GETARG_DATUM(0));
  	Oid			catalog = PG_GETARG_OID(1);
  	char	   *filename = NULL;
  	DefElem    *force_not_null = NULL;
  	DefElem    *force_null = NULL;
  	List	   *other_options = NIL;
  	ListCell   *cell;
  
  	/*
  	 * Check that only options supported by file_fdw, and allowed for the
  	 * current object type, are given.
  	 */
  	foreach(cell, options_list)
  	{
  		DefElem    *def = (DefElem *) lfirst(cell);
  
  		if (!is_valid_option(def->defname, catalog))
  		{
  			const struct FileFdwOption *opt;
  			StringInfoData buf;
  
  			/*
  			 * Unknown option specified, complain about it. Provide a hint
  			 * with list of valid options for the object.
  			 */
  			initStringInfo(&buf);
  			for (opt = valid_options; opt->optname; opt++)
  			{
  				if (catalog == opt->optcontext)
  					appendStringInfo(&buf, "%s%s", (buf.len > 0) ? ", " : "",
  									 opt->optname);
  			}
  
  			ereport(ERROR,
  					(errcode(ERRCODE_FDW_INVALID_OPTION_NAME),
  					 errmsg("invalid option \"%s\"", def->defname),
  					 buf.len > 0
  					 ? errhint("Valid options in this context are: %s",
  							   buf.data)
  					 : errhint("There are no valid options in this context.")));
  		}
  
  		/*
  		 * Separate out filename, program, and column-specific options, since
  		 * ProcessCopyOptions won't accept them.
  		 */
  		if (strcmp(def->defname, "filename") == 0 ||
  			strcmp(def->defname, "program") == 0)
  		{
  			if (filename)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
  						 errmsg("conflicting or redundant options")));
  
  			/*
  			 * Check permissions for changing which file or program is used by
  			 * the file_fdw.
  			 *
  			 * Only members of the role 'pg_read_server_files' are allowed to
  			 * set the 'filename' option of a file_fdw foreign table, while
  			 * only members of the role 'pg_execute_server_program' are
  			 * allowed to set the 'program' option.  This is because we don't
  			 * want regular users to be able to control which file gets read
  			 * or which program gets executed.
  			 *
  			 * Putting this sort of permissions check in a validator is a bit
  			 * of a crock, but there doesn't seem to be any other place that
  			 * can enforce the check more cleanly.
  			 *
  			 * Note that the valid_options[] array disallows setting filename
  			 * and program at any options level other than foreign table ---
  			 * otherwise there'd still be a security hole.
  			 */
  			if (strcmp(def->defname, "filename") == 0 &&
  				!is_member_of_role(GetUserId(), DEFAULT_ROLE_READ_SERVER_FILES))
  				ereport(ERROR,
  						(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
  						 errmsg("only superuser or a member of the pg_read_server_files role may specify the filename option of a file_fdw foreign table")));
  
  			if (strcmp(def->defname, "program") == 0 &&
  				!is_member_of_role(GetUserId(), DEFAULT_ROLE_EXECUTE_SERVER_PROGRAM))
  				ereport(ERROR,
  						(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
  						 errmsg("only superuser or a member of the pg_execute_server_program role may specify the program option of a file_fdw foreign table")));
  
  			filename = defGetString(def);
  		}
  
  		/*
  		 * force_not_null is a boolean option; after validation we can discard
  		 * it - it will be retrieved later in get_file_fdw_attribute_options()
  		 */
  		else if (strcmp(def->defname, "force_not_null") == 0)
  		{
  			if (force_not_null)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
  						 errmsg("conflicting or redundant options"),
  						 errhint("Option \"force_not_null\" supplied more than once for a column.")));
  			force_not_null = def;
  			/* Don't care what the value is, as long as it's a legal boolean */
  			(void) defGetBoolean(def);
  		}
  		/* See comments for force_not_null above */
  		else if (strcmp(def->defname, "force_null") == 0)
  		{
  			if (force_null)
  				ereport(ERROR,
  						(errcode(ERRCODE_SYNTAX_ERROR),
  						 errmsg("conflicting or redundant options"),
  						 errhint("Option \"force_null\" supplied more than once for a column.")));
  			force_null = def;
  			(void) defGetBoolean(def);
  		}
  		else
  			other_options = lappend(other_options, def);
  	}
  
  	/*
  	 * Now apply the core COPY code's validation logic for more checks.
  	 */
  	ProcessCopyOptions(NULL, NULL, true, other_options);
  
  	/*
  	 * Either filename or program option is required for file_fdw foreign
  	 * tables.
  	 */
  	if (catalog == ForeignTableRelationId && filename == NULL)
  		ereport(ERROR,
  				(errcode(ERRCODE_FDW_DYNAMIC_PARAMETER_VALUE_NEEDED),
  				 errmsg("either filename or program is required for file_fdw foreign tables")));
  
  	PG_RETURN_VOID();
  }
  
  /*
   * Check if the provided option is one of the valid options.
   * context is the Oid of the catalog holding the object the option is for.
   */
  static bool
  is_valid_option(const char *option, Oid context)
  {
  	const struct FileFdwOption *opt;
  
  	for (opt = valid_options; opt->optname; opt++)
  	{
  		if (context == opt->optcontext && strcmp(opt->optname, option) == 0)
  			return true;
  	}
  	return false;
  }
  
  /*
   * Fetch the options for a file_fdw foreign table.
   *
   * We have to separate out filename/program from the other options because
   * those must not appear in the options list passed to the core COPY code.
   */
  static void
  fileGetOptions(Oid foreigntableid,
  			   char **filename, bool *is_program, List **other_options)
  {
  	ForeignTable *table;
  	ForeignServer *server;
  	ForeignDataWrapper *wrapper;
  	List	   *options;
  	ListCell   *lc;
  
  	/*
  	 * Extract options from FDW objects.  We ignore user mappings because
  	 * file_fdw doesn't have any options that can be specified there.
  	 *
  	 * (XXX Actually, given the current contents of valid_options[], there's
  	 * no point in examining anything except the foreign table's own options.
  	 * Simplify?)
  	 */
  	table = GetForeignTable(foreigntableid);
  	server = GetForeignServer(table->serverid);
  	wrapper = GetForeignDataWrapper(server->fdwid);
  
  	options = NIL;
  	options = list_concat(options, wrapper->options);
  	options = list_concat(options, server->options);
  	options = list_concat(options, table->options);
  	options = list_concat(options, get_file_fdw_attribute_options(foreigntableid));
  
  	/*
  	 * Separate out the filename or program option (we assume there is only
  	 * one).
  	 */
  	*filename = NULL;
  	*is_program = false;
  	foreach(lc, options)
  	{
  		DefElem    *def = (DefElem *) lfirst(lc);
  
  		if (strcmp(def->defname, "filename") == 0)
  		{
  			*filename = defGetString(def);
  			options = foreach_delete_current(options, lc);
  			break;
  		}
  		else if (strcmp(def->defname, "program") == 0)
  		{
  			*filename = defGetString(def);
  			*is_program = true;
  			options = foreach_delete_current(options, lc);
  			break;
  		}
  	}
  
  	/*
  	 * The validator should have checked that filename or program was included
  	 * in the options, but check again, just in case.
  	 */
  	if (*filename == NULL)
  		elog(ERROR, "either filename or program is required for file_fdw foreign tables");
  
  	*other_options = options;
  }
  
  /*
   * Retrieve per-column generic options from pg_attribute and construct a list
   * of DefElems representing them.
   *
   * At the moment we only have "force_not_null", and "force_null",
   * which should each be combined into a single DefElem listing all such
   * columns, since that's what COPY expects.
   */
  static List *
  get_file_fdw_attribute_options(Oid relid)
  {
  	Relation	rel;
  	TupleDesc	tupleDesc;
  	AttrNumber	natts;
  	AttrNumber	attnum;
  	List	   *fnncolumns = NIL;
  	List	   *fncolumns = NIL;
  
  	List	   *options = NIL;
  
  	rel = table_open(relid, AccessShareLock);
  	tupleDesc = RelationGetDescr(rel);
  	natts = tupleDesc->natts;
  
  	/* Retrieve FDW options for all user-defined attributes. */
  	for (attnum = 1; attnum <= natts; attnum++)
  	{
  		Form_pg_attribute attr = TupleDescAttr(tupleDesc, attnum - 1);
  		List	   *options;
  		ListCell   *lc;
  
  		/* Skip dropped attributes. */
  		if (attr->attisdropped)
  			continue;
  
  		options = GetForeignColumnOptions(relid, attnum);
  		foreach(lc, options)
  		{
  			DefElem    *def = (DefElem *) lfirst(lc);
  
  			if (strcmp(def->defname, "force_not_null") == 0)
  			{
  				if (defGetBoolean(def))
  				{
  					char	   *attname = pstrdup(NameStr(attr->attname));
  
  					fnncolumns = lappend(fnncolumns, makeString(attname));
  				}
  			}
  			else if (strcmp(def->defname, "force_null") == 0)
  			{
  				if (defGetBoolean(def))
  				{
  					char	   *attname = pstrdup(NameStr(attr->attname));
  
  					fncolumns = lappend(fncolumns, makeString(attname));
  				}
  			}
  			/* maybe in future handle other options here */
  		}
  	}
  
  	table_close(rel, AccessShareLock);
  
  	/*
  	 * Return DefElem only when some column(s) have force_not_null /
  	 * force_null options set
  	 */
  	if (fnncolumns != NIL)
  		options = lappend(options, makeDefElem("force_not_null", (Node *) fnncolumns, -1));
  
  	if (fncolumns != NIL)
  		options = lappend(options, makeDefElem("force_null", (Node *) fncolumns, -1));
  
  	return options;
  }
  
  /*
   * fileGetForeignRelSize
   *		Obtain relation size estimates for a foreign table
   */
  static void
  fileGetForeignRelSize(PlannerInfo *root,
  					  RelOptInfo *baserel,
  					  Oid foreigntableid)
  {
  	FileFdwPlanState *fdw_private;
  
  	/*
  	 * Fetch options.  We only need filename (or program) at this point, but
  	 * we might as well get everything and not need to re-fetch it later in
  	 * planning.
  	 */
  	fdw_private = (FileFdwPlanState *) palloc(sizeof(FileFdwPlanState));
  	fileGetOptions(foreigntableid,
  				   &fdw_private->filename,
  				   &fdw_private->is_program,
  				   &fdw_private->options);
  	baserel->fdw_private = (void *) fdw_private;
  
  	/* Estimate relation size */
  	estimate_size(root, baserel, fdw_private);
  }
  
  /*
   * fileGetForeignPaths
   *		Create possible access paths for a scan on the foreign table
   *
   *		Currently we don't support any push-down feature, so there is only one
   *		possible access path, which simply returns all records in the order in
   *		the data file.
   */
  static void
  fileGetForeignPaths(PlannerInfo *root,
  					RelOptInfo *baserel,
  					Oid foreigntableid)
  {
  	FileFdwPlanState *fdw_private = (FileFdwPlanState *) baserel->fdw_private;
  	Cost		startup_cost;
  	Cost		total_cost;
  	List	   *columns;
  	List	   *coptions = NIL;
  
  	/* Decide whether to selectively perform binary conversion */
  	if (check_selective_binary_conversion(baserel,
  										  foreigntableid,
  										  &columns))
  		coptions = list_make1(makeDefElem("convert_selectively",
  										  (Node *) columns, -1));
  
  	/* Estimate costs */
  	estimate_costs(root, baserel, fdw_private,
  				   &startup_cost, &total_cost);
  
  	/*
  	 * Create a ForeignPath node and add it as only possible path.  We use the
  	 * fdw_private list of the path to carry the convert_selectively option;
  	 * it will be propagated into the fdw_private list of the Plan node.
  	 *
  	 * We don't support pushing join clauses into the quals of this path, but
  	 * it could still have required parameterization due to LATERAL refs in
  	 * its tlist.
  	 */
  	add_path(baserel, (Path *)
  			 create_foreignscan_path(root, baserel,
  									 NULL,	/* default pathtarget */
  									 baserel->rows,
  									 startup_cost,
  									 total_cost,
  									 NIL,	/* no pathkeys */
  									 baserel->lateral_relids,
  									 NULL,	/* no extra plan */
  									 coptions));
  
  	/*
  	 * If data file was sorted, and we knew it somehow, we could insert
  	 * appropriate pathkeys into the ForeignPath node to tell the planner
  	 * that.
  	 */
  }
  
  /*
   * fileGetForeignPlan
   *		Create a ForeignScan plan node for scanning the foreign table
   */
  static ForeignScan *
  fileGetForeignPlan(PlannerInfo *root,
  				   RelOptInfo *baserel,
  				   Oid foreigntableid,
  				   ForeignPath *best_path,
  				   List *tlist,
  				   List *scan_clauses,
  				   Plan *outer_plan)
  {
  	Index		scan_relid = baserel->relid;
  
  	/*
  	 * We have no native ability to evaluate restriction clauses, so we just
  	 * put all the scan_clauses into the plan node's qual list for the
  	 * executor to check.  So all we have to do here is strip RestrictInfo
  	 * nodes from the clauses and ignore pseudoconstants (which will be
  	 * handled elsewhere).
  	 */
  	scan_clauses = extract_actual_clauses(scan_clauses, false);
  
  	/* Create the ForeignScan node */
  	return make_foreignscan(tlist,
  							scan_clauses,
  							scan_relid,
  							NIL,	/* no expressions to evaluate */
  							best_path->fdw_private,
  							NIL,	/* no custom tlist */
  							NIL,	/* no remote quals */
  							outer_plan);
  }
  
  /*
   * fileExplainForeignScan
   *		Produce extra output for EXPLAIN
   */
  static void
  fileExplainForeignScan(ForeignScanState *node, ExplainState *es)
  {
  	char	   *filename;
  	bool		is_program;
  	List	   *options;
  
  	/* Fetch options --- we only need filename and is_program at this point */
  	fileGetOptions(RelationGetRelid(node->ss.ss_currentRelation),
  				   &filename, &is_program, &options);
  
  	if (is_program)
  		ExplainPropertyText("Foreign Program", filename, es);
  	else
  		ExplainPropertyText("Foreign File", filename, es);
  
  	/* Suppress file size if we're not showing cost details */
  	if (es->costs)
  	{
  		struct stat stat_buf;
  
  		if (!is_program &&
  			stat(filename, &stat_buf) == 0)
  			ExplainPropertyInteger("Foreign File Size", "b",
  								   (int64) stat_buf.st_size, es);
  	}
  }
  
  /*
   * fileBeginForeignScan
   *		Initiate access to the file by creating CopyState
   */
  static void
  fileBeginForeignScan(ForeignScanState *node, int eflags)
  {
  	ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
  	char	   *filename;
  	bool		is_program;
  	List	   *options;
  	CopyState	cstate;
  	FileFdwExecutionState *festate;
  
  	/*
  	 * Do nothing in EXPLAIN (no ANALYZE) case.  node->fdw_state stays NULL.
  	 */
  	if (eflags & EXEC_FLAG_EXPLAIN_ONLY)
  		return;
  
  	/* Fetch options of foreign table */
  	fileGetOptions(RelationGetRelid(node->ss.ss_currentRelation),
  				   &filename, &is_program, &options);
  
  	/* Add any options from the plan (currently only convert_selectively) */
  	options = list_concat(options, plan->fdw_private);
  
  	/*
  	 * Create CopyState from FDW options.  We always acquire all columns, so
  	 * as to match the expected ScanTupleSlot signature.
  	 */
  	cstate = BeginCopyFrom(NULL,
  						   node->ss.ss_currentRelation,
  						   filename,
  						   is_program,
  						   NULL,
  						   NIL,
  						   options);
  
  	/*
  	 * Save state in node->fdw_state.  We must save enough information to call
  	 * BeginCopyFrom() again.
  	 */
  	festate = (FileFdwExecutionState *) palloc(sizeof(FileFdwExecutionState));
  	festate->filename = filename;
  	festate->is_program = is_program;
  	festate->options = options;
  	festate->cstate = cstate;
  
  	node->fdw_state = (void *) festate;
  }
  
  /*
   * fileIterateForeignScan
   *		Read next record from the data file and store it into the
   *		ScanTupleSlot as a virtual tuple
   */
  static TupleTableSlot *
  fileIterateForeignScan(ForeignScanState *node)
  {
  	FileFdwExecutionState *festate = (FileFdwExecutionState *) node->fdw_state;
  	TupleTableSlot *slot = node->ss.ss_ScanTupleSlot;
  	bool		found;
  	ErrorContextCallback errcallback;
  
  	/* Set up callback to identify error line number. */
  	errcallback.callback = CopyFromErrorCallback;
  	errcallback.arg = (void *) festate->cstate;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	/*
  	 * The protocol for loading a virtual tuple into a slot is first
  	 * ExecClearTuple, then fill the values/isnull arrays, then
  	 * ExecStoreVirtualTuple.  If we don't find another row in the file, we
  	 * just skip the last step, leaving the slot empty as required.
  	 *
  	 * We can pass ExprContext = NULL because we read all columns from the
  	 * file, so no need to evaluate default expressions.
  	 */
  	ExecClearTuple(slot);
  	found = NextCopyFrom(festate->cstate, NULL,
  						 slot->tts_values, slot->tts_isnull);
  	if (found)
  		ExecStoreVirtualTuple(slot);
  
  	/* Remove error callback. */
  	error_context_stack = errcallback.previous;
  
  	return slot;
  }
  
  /*
   * fileReScanForeignScan
   *		Rescan table, possibly with new parameters
   */
  static void
  fileReScanForeignScan(ForeignScanState *node)
  {
  	FileFdwExecutionState *festate = (FileFdwExecutionState *) node->fdw_state;
  
  	EndCopyFrom(festate->cstate);
  
  	festate->cstate = BeginCopyFrom(NULL,
  									node->ss.ss_currentRelation,
  									festate->filename,
  									festate->is_program,
  									NULL,
  									NIL,
  									festate->options);
  }
  
  /*
   * fileEndForeignScan
   *		Finish scanning foreign table and dispose objects used for this scan
   */
  static void
  fileEndForeignScan(ForeignScanState *node)
  {
  	FileFdwExecutionState *festate = (FileFdwExecutionState *) node->fdw_state;
  
  	/* if festate is NULL, we are in EXPLAIN; nothing to do */
  	if (festate)
  		EndCopyFrom(festate->cstate);
  }
  
  /*
   * fileAnalyzeForeignTable
   *		Test whether analyzing this foreign table is supported
   */
  static bool
  fileAnalyzeForeignTable(Relation relation,
  						AcquireSampleRowsFunc *func,
  						BlockNumber *totalpages)
  {
  	char	   *filename;
  	bool		is_program;
  	List	   *options;
  	struct stat stat_buf;
  
  	/* Fetch options of foreign table */
  	fileGetOptions(RelationGetRelid(relation), &filename, &is_program, &options);
  
  	/*
  	 * If this is a program instead of a file, just return false to skip
  	 * analyzing the table.  We could run the program and collect stats on
  	 * whatever it currently returns, but it seems likely that in such cases
  	 * the output would be too volatile for the stats to be useful.  Maybe
  	 * there should be an option to enable doing this?
  	 */
  	if (is_program)
  		return false;
  
  	/*
  	 * Get size of the file.  (XXX if we fail here, would it be better to just
  	 * return false to skip analyzing the table?)
  	 */
  	if (stat(filename, &stat_buf) < 0)
  		ereport(ERROR,
  				(errcode_for_file_access(),
  				 errmsg("could not stat file \"%s\": %m",
  						filename)));
  
  	/*
  	 * Convert size to pages.  Must return at least 1 so that we can tell
  	 * later on that pg_class.relpages is not default.
  	 */
  	*totalpages = (stat_buf.st_size + (BLCKSZ - 1)) / BLCKSZ;
  	if (*totalpages < 1)
  		*totalpages = 1;
  
  	*func = file_acquire_sample_rows;
  
  	return true;
  }
  
  /*
   * fileIsForeignScanParallelSafe
   *		Reading a file, or external program, in a parallel worker should work
   *		just the same as reading it in the leader, so mark scans safe.
   */
  static bool
  fileIsForeignScanParallelSafe(PlannerInfo *root, RelOptInfo *rel,
  							  RangeTblEntry *rte)
  {
  	return true;
  }
  
  /*
   * check_selective_binary_conversion
   *
   * Check to see if it's useful to convert only a subset of the file's columns
   * to binary.  If so, construct a list of the column names to be converted,
   * return that at *columns, and return true.  (Note that it's possible to
   * determine that no columns need be converted, for instance with a COUNT(*)
   * query.  So we can't use returning a NIL list to indicate failure.)
   */
  static bool
  check_selective_binary_conversion(RelOptInfo *baserel,
  								  Oid foreigntableid,
  								  List **columns)
  {
  	ForeignTable *table;
  	ListCell   *lc;
  	Relation	rel;
  	TupleDesc	tupleDesc;
  	AttrNumber	attnum;
  	Bitmapset  *attrs_used = NULL;
  	bool		has_wholerow = false;
  	int			numattrs;
  	int			i;
  
  	*columns = NIL;				/* default result */
  
  	/*
  	 * Check format of the file.  If binary format, this is irrelevant.
  	 */
  	table = GetForeignTable(foreigntableid);
  	foreach(lc, table->options)
  	{
  		DefElem    *def = (DefElem *) lfirst(lc);
  
  		if (strcmp(def->defname, "format") == 0)
  		{
  			char	   *format = defGetString(def);
  
  			if (strcmp(format, "binary") == 0)
  				return false;
  			break;
  		}
  	}
  
  	/* Collect all the attributes needed for joins or final output. */
  	pull_varattnos((Node *) baserel->reltarget->exprs, baserel->relid,
  				   &attrs_used);
  
  	/* Add all the attributes used by restriction clauses. */
  	foreach(lc, baserel->baserestrictinfo)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  		pull_varattnos((Node *) rinfo->clause, baserel->relid,
  					   &attrs_used);
  	}
  
  	/* Convert attribute numbers to column names. */
  	rel = table_open(foreigntableid, AccessShareLock);
  	tupleDesc = RelationGetDescr(rel);
  
  	while ((attnum = bms_first_member(attrs_used)) >= 0)
  	{
  		/* Adjust for system attributes. */
  		attnum += FirstLowInvalidHeapAttributeNumber;
  
  		if (attnum == 0)
  		{
  			has_wholerow = true;
  			break;
  		}
  
  		/* Ignore system attributes. */
  		if (attnum < 0)
  			continue;
  
  		/* Get user attributes. */
  		if (attnum > 0)
  		{
  			Form_pg_attribute attr = TupleDescAttr(tupleDesc, attnum - 1);
  			char	   *attname = NameStr(attr->attname);
  
  			/* Skip dropped attributes (probably shouldn't see any here). */
  			if (attr->attisdropped)
  				continue;
  
  			/*
  			 * Skip generated columns (COPY won't accept them in the column
  			 * list)
  			 */
  			if (attr->attgenerated)
  				continue;
  			*columns = lappend(*columns, makeString(pstrdup(attname)));
  		}
  	}
  
  	/* Count non-dropped user attributes while we have the tupdesc. */
  	numattrs = 0;
  	for (i = 0; i < tupleDesc->natts; i++)
  	{
  		Form_pg_attribute attr = TupleDescAttr(tupleDesc, i);
  
  		if (attr->attisdropped)
  			continue;
  		numattrs++;
  	}
  
  	table_close(rel, AccessShareLock);
  
  	/* If there's a whole-row reference, fail: we need all the columns. */
  	if (has_wholerow)
  	{
  		*columns = NIL;
  		return false;
  	}
  
  	/* If all the user attributes are needed, fail. */
  	if (numattrs == list_length(*columns))
  	{
  		*columns = NIL;
  		return false;
  	}
  
  	return true;
  }
  
  /*
   * Estimate size of a foreign table.
   *
   * The main result is returned in baserel->rows.  We also set
   * fdw_private->pages and fdw_private->ntuples for later use in the cost
   * calculation.
   */
  static void
  estimate_size(PlannerInfo *root, RelOptInfo *baserel,
  			  FileFdwPlanState *fdw_private)
  {
  	struct stat stat_buf;
  	BlockNumber pages;
  	double		ntuples;
  	double		nrows;
  
  	/*
  	 * Get size of the file.  It might not be there at plan time, though, in
  	 * which case we have to use a default estimate.  We also have to fall
  	 * back to the default if using a program as the input.
  	 */
  	if (fdw_private->is_program || stat(fdw_private->filename, &stat_buf) < 0)
  		stat_buf.st_size = 10 * BLCKSZ;
  
  	/*
  	 * Convert size to pages for use in I/O cost estimate later.
  	 */
  	pages = (stat_buf.st_size + (BLCKSZ - 1)) / BLCKSZ;
  	if (pages < 1)
  		pages = 1;
  	fdw_private->pages = pages;
  
  	/*
  	 * Estimate the number of tuples in the file.
  	 */
  	if (baserel->pages > 0)
  	{
  		/*
  		 * We have # of pages and # of tuples from pg_class (that is, from a
  		 * previous ANALYZE), so compute a tuples-per-page estimate and scale
  		 * that by the current file size.
  		 */
  		double		density;
  
  		density = baserel->tuples / (double) baserel->pages;
  		ntuples = clamp_row_est(density * (double) pages);
  	}
  	else
  	{
  		/*
  		 * Otherwise we have to fake it.  We back into this estimate using the
  		 * planner's idea of the relation width; which is bogus if not all
  		 * columns are being read, not to mention that the text representation
  		 * of a row probably isn't the same size as its internal
  		 * representation.  Possibly we could do something better, but the
  		 * real answer to anyone who complains is "ANALYZE" ...
  		 */
  		int			tuple_width;
  
  		tuple_width = MAXALIGN(baserel->reltarget->width) +
  			MAXALIGN(SizeofHeapTupleHeader);
  		ntuples = clamp_row_est((double) stat_buf.st_size /
  								(double) tuple_width);
  	}
  	fdw_private->ntuples = ntuples;
  
  	/*
  	 * Now estimate the number of rows returned by the scan after applying the
  	 * baserestrictinfo quals.
  	 */
  	nrows = ntuples *
  		clauselist_selectivity(root,
  							   baserel->baserestrictinfo,
  							   0,
  							   JOIN_INNER,
  							   NULL);
  
  	nrows = clamp_row_est(nrows);
  
  	/* Save the output-rows estimate for the planner */
  	baserel->rows = nrows;
  }
  
  /*
   * Estimate costs of scanning a foreign table.
   *
   * Results are returned in *startup_cost and *total_cost.
   */
  static void
  estimate_costs(PlannerInfo *root, RelOptInfo *baserel,
  			   FileFdwPlanState *fdw_private,
  			   Cost *startup_cost, Cost *total_cost)
  {
  	BlockNumber pages = fdw_private->pages;
  	double		ntuples = fdw_private->ntuples;
  	Cost		run_cost = 0;
  	Cost		cpu_per_tuple;
  
  	/*
  	 * We estimate costs almost the same way as cost_seqscan(), thus assuming
  	 * that I/O costs are equivalent to a regular table file of the same size.
  	 * However, we take per-tuple CPU costs as 10x of a seqscan, to account
  	 * for the cost of parsing records.
  	 *
  	 * In the case of a program source, this calculation is even more divorced
  	 * from reality, but we have no good alternative; and it's not clear that
  	 * the numbers we produce here matter much anyway, since there's only one
  	 * access path for the rel.
  	 */
  	run_cost += seq_page_cost * pages;
  
  	*startup_cost = baserel->baserestrictcost.startup;
  	cpu_per_tuple = cpu_tuple_cost * 10 + baserel->baserestrictcost.per_tuple;
  	run_cost += cpu_per_tuple * ntuples;
  	*total_cost = *startup_cost + run_cost;
  }
  
  /*
   * file_acquire_sample_rows -- acquire a random sample of rows from the table
   *
   * Selected rows are returned in the caller-allocated array rows[],
   * which must have at least targrows entries.
   * The actual number of rows selected is returned as the function result.
   * We also count the total number of rows in the file and return it into
   * *totalrows.  Note that *totaldeadrows is always set to 0.
   *
   * Note that the returned list of rows is not always in order by physical
   * position in the file.  Therefore, correlation estimates derived later
   * may be meaningless, but it's OK because we don't use the estimates
   * currently (the planner only pays attention to correlation for indexscans).
   */
  static int
  file_acquire_sample_rows(Relation onerel, int elevel,
  						 HeapTuple *rows, int targrows,
  						 double *totalrows, double *totaldeadrows)
  {
  	int			numrows = 0;
  	double		rowstoskip = -1;	/* -1 means not set yet */
  	ReservoirStateData rstate;
  	TupleDesc	tupDesc;
  	Datum	   *values;
  	bool	   *nulls;
  	bool		found;
  	char	   *filename;
  	bool		is_program;
  	List	   *options;
  	CopyState	cstate;
  	ErrorContextCallback errcallback;
  	MemoryContext oldcontext = CurrentMemoryContext;
  	MemoryContext tupcontext;
  
  	Assert(onerel);
  	Assert(targrows > 0);
  
  	tupDesc = RelationGetDescr(onerel);
  	values = (Datum *) palloc(tupDesc->natts * sizeof(Datum));
  	nulls = (bool *) palloc(tupDesc->natts * sizeof(bool));
  
  	/* Fetch options of foreign table */
  	fileGetOptions(RelationGetRelid(onerel), &filename, &is_program, &options);
  
  	/*
  	 * Create CopyState from FDW options.
  	 */
  	cstate = BeginCopyFrom(NULL, onerel, filename, is_program, NULL, NIL,
  						   options);
  
  	/*
  	 * Use per-tuple memory context to prevent leak of memory used to read
  	 * rows from the file with Copy routines.
  	 */
  	tupcontext = AllocSetContextCreate(CurrentMemoryContext,
  									   "file_fdw temporary context",
  									   ALLOCSET_DEFAULT_SIZES);
  
  	/* Prepare for sampling rows */
  	reservoir_init_selection_state(&rstate, targrows);
  
  	/* Set up callback to identify error line number. */
  	errcallback.callback = CopyFromErrorCallback;
  	errcallback.arg = (void *) cstate;
  	errcallback.previous = error_context_stack;
  	error_context_stack = &errcallback;
  
  	*totalrows = 0;
  	*totaldeadrows = 0;
  	for (;;)
  	{
  		/* Check for user-requested abort or sleep */
  		vacuum_delay_point();
  
  		/* Fetch next row */
  		MemoryContextReset(tupcontext);
  		MemoryContextSwitchTo(tupcontext);
  
  		found = NextCopyFrom(cstate, NULL, values, nulls);
  
  		MemoryContextSwitchTo(oldcontext);
  
  		if (!found)
  			break;
  
  		/*
  		 * The first targrows sample rows are simply copied into the
  		 * reservoir.  Then we start replacing tuples in the sample until we
  		 * reach the end of the relation. This algorithm is from Jeff Vitter's
  		 * paper (see more info in commands/analyze.c).
  		 */
  		if (numrows < targrows)
  		{
  			rows[numrows++] = heap_form_tuple(tupDesc, values, nulls);
  		}
  		else
  		{
  			/*
  			 * t in Vitter's paper is the number of records already processed.
  			 * If we need to compute a new S value, we must use the
  			 * not-yet-incremented value of totalrows as t.
  			 */
  			if (rowstoskip < 0)
  				rowstoskip = reservoir_get_next_S(&rstate, *totalrows, targrows);
  
  			if (rowstoskip <= 0)
  			{
  				/*
  				 * Found a suitable tuple, so save it, replacing one old tuple
  				 * at random
  				 */
  				int			k = (int) (targrows * sampler_random_fract(rstate.randstate));
  
  				Assert(k >= 0 && k < targrows);
  				heap_freetuple(rows[k]);
  				rows[k] = heap_form_tuple(tupDesc, values, nulls);
  			}
  
  			rowstoskip -= 1;
  		}
  
  		*totalrows += 1;
  	}
  
  	/* Remove error callback. */
  	error_context_stack = errcallback.previous;
  
  	/* Clean up. */
  	MemoryContextDelete(tupcontext);
  
  	EndCopyFrom(cstate);
  
  	pfree(values);
  	pfree(nulls);
  
  	/*
  	 * Emit some interesting relation info
  	 */
  	ereport(elevel,
  			(errmsg("\"%s\": file contains %.0f rows; "
  					"%d rows in sample",
  					RelationGetRelationName(onerel),
  					*totalrows, numrows)));
  
  	return numrows;
  }
  