postgres/src/include/funcapi.h

/*-------------------------------------------------------------------------
 *
 * funcapi.h
 *	  Definitions for functions which return composite type and/or sets
 *	  or work on VARIADIC inputs.
 *
 * This file must be included by all Postgres modules that either define
 * or call FUNCAPI-callable functions or macros.
 *
 *
 * Copyright (c) 2002-2022, PostgreSQL Global Development Group
 *
 * src/include/funcapi.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef FUNCAPI_H
#define FUNCAPI_H

#include "access/tupdesc.h"
#include "executor/executor.h"
#include "executor/tuptable.h"
#include "fmgr.h"

/*-------------------------------------------------------------------------
 *	Support to ease writing Functions returning composite types
 *-------------------------------------------------------------------------
 *
 * This struct holds arrays of individual attribute information
 * needed to create a tuple from raw C strings. It also requires
 * a copy of the TupleDesc. The information carried here
 * is derived from the TupleDesc, but it is stored here to
 * avoid redundant cpu cycles on each call to an SRF.
 */
typedef struct AttInMetadata
{
	/* full TupleDesc */
	TupleDesc	tupdesc;

	/* array of attribute type input function finfo */
	FmgrInfo   *attinfuncs;

	/* array of attribute type i/o parameter OIDs */
	Oid		   *attioparams;

	/* array of attribute typmod */
	int32	   *atttypmods;
} AttInMetadata;

/*-------------------------------------------------------------------------
 *		Support struct to ease writing Set Returning Functions (SRFs)
 *-------------------------------------------------------------------------
 *
 * This struct holds function context for Set Returning Functions.
 * Use fn_extra to hold a pointer to it across calls
 */
typedef struct FuncCallContext
{
	/*
	 * Number of times we've been called before
	 *
	 * call_cntr is initialized to 0 for you by SRF_FIRSTCALL_INIT(), and
	 * incremented for you every time SRF_RETURN_NEXT() is called.
	 */
	uint64		call_cntr;

	/*
	 * OPTIONAL maximum number of calls
	 *
	 * max_calls is here for convenience only and setting it is optional. If
	 * not set, you must provide alternative means to know when the function
	 * is done.
	 */
	uint64		max_calls;

	/*
	 * OPTIONAL pointer to miscellaneous user-provided context information
	 *
	 * user_fctx is for use as a pointer to your own struct to retain
	 * arbitrary context information between calls of your function.
	 */
	void	   *user_fctx;

	/*
	 * OPTIONAL pointer to struct containing attribute type input metadata
	 *
	 * attinmeta is for use when returning tuples (i.e. composite data types)
	 * and is not used when returning base data types. It is only needed if
	 * you intend to use BuildTupleFromCStrings() to create the return tuple.
	 */
	AttInMetadata *attinmeta;

	/*
	 * memory context used for structures that must live for multiple calls
	 *
	 * multi_call_memory_ctx is set by SRF_FIRSTCALL_INIT() for you, and used
	 * by SRF_RETURN_DONE() for cleanup. It is the most appropriate memory
	 * context for any memory that is to be reused across multiple calls of
	 * the SRF.
	 */
	MemoryContext multi_call_memory_ctx;

	/*
	 * OPTIONAL pointer to struct containing tuple description
	 *
	 * tuple_desc is for use when returning tuples (i.e. composite data types)
	 * and is only needed if you are going to build the tuples with
	 * heap_form_tuple() rather than with BuildTupleFromCStrings(). Note that
	 * the TupleDesc pointer stored here should usually have been run through
	 * BlessTupleDesc() first.
	 */
	TupleDesc	tuple_desc;

} FuncCallContext;

/*----------
 *	Support to ease writing functions returning composite types
 *
 * External declarations:
 * get_call_result_type:
 *		Given a function's call info record, determine the kind of datatype
 *		it is supposed to return.  If resultTypeId isn't NULL, *resultTypeId
 *		receives the actual datatype OID (this is mainly useful for scalar
 *		result types).  If resultTupleDesc isn't NULL, *resultTupleDesc
 *		receives a pointer to a TupleDesc when the result is of a composite
 *		type, or NULL when it's a scalar result or the rowtype could not be
 *		determined.  NB: the tupledesc should be copied if it is to be
 *		accessed over a long period.
 * get_expr_result_type:
 *		Given an expression node, return the same info as for
 *		get_call_result_type.  Note: the cases in which rowtypes cannot be
 *		determined are different from the cases for get_call_result_type.
 * get_func_result_type:
 *		Given only a function's OID, return the same info as for
 *		get_call_result_type.  Note: the cases in which rowtypes cannot be
 *		determined are different from the cases for get_call_result_type.
 *		Do *not* use this if you can use one of the others.
 *
 * See also get_expr_result_tupdesc(), which is a convenient wrapper around
 * get_expr_result_type() for use when the caller only cares about
 * determinable-rowtype cases.
 *----------
 */

/* Type categories for get_call_result_type and siblings */
typedef enum TypeFuncClass
{
	TYPEFUNC_SCALAR,			/* scalar result type */
	TYPEFUNC_COMPOSITE,			/* determinable rowtype result */
	TYPEFUNC_COMPOSITE_DOMAIN,	/* domain over determinable rowtype result */
	TYPEFUNC_RECORD,			/* indeterminate rowtype result */
	TYPEFUNC_OTHER				/* bogus type, eg pseudotype */
} TypeFuncClass;

extern TypeFuncClass get_call_result_type(FunctionCallInfo fcinfo,
										  Oid *resultTypeId,
										  TupleDesc *resultTupleDesc);
extern TypeFuncClass get_expr_result_type(Node *expr,
										  Oid *resultTypeId,
										  TupleDesc *resultTupleDesc);
extern TypeFuncClass get_func_result_type(Oid functionId,
										  Oid *resultTypeId,
										  TupleDesc *resultTupleDesc);

extern TupleDesc get_expr_result_tupdesc(Node *expr, bool noError);

extern bool resolve_polymorphic_argtypes(int numargs, Oid *argtypes,
										 char *argmodes,
										 Node *call_expr);

extern int	get_func_arg_info(HeapTuple procTup,
							  Oid **p_argtypes, char ***p_argnames,
							  char **p_argmodes);

extern int	get_func_input_arg_names(Datum proargnames, Datum proargmodes,
									 char ***arg_names);

extern int	get_func_trftypes(HeapTuple procTup, Oid **p_trftypes);
extern char *get_func_result_name(Oid functionId);

extern TupleDesc build_function_result_tupdesc_d(char prokind,
												 Datum proallargtypes,
												 Datum proargmodes,
												 Datum proargnames);
extern TupleDesc build_function_result_tupdesc_t(HeapTuple procTuple);


/*----------
 *	Support to ease writing functions returning composite types
 *
 * External declarations:
 * TupleDesc BlessTupleDesc(TupleDesc tupdesc) - "Bless" a completed tuple
 *		descriptor so that it can be used to return properly labeled tuples.
 *		You need to call this if you are going to use heap_form_tuple directly.
 *		TupleDescGetAttInMetadata does it for you, however, so no need to call
 *		it if you call TupleDescGetAttInMetadata.
 * AttInMetadata *TupleDescGetAttInMetadata(TupleDesc tupdesc) - Build an
 *		AttInMetadata struct based on the given TupleDesc. AttInMetadata can
 *		be used in conjunction with C strings to produce a properly formed
 *		tuple.
 * HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values) -
 *		build a HeapTuple given user data in C string form. values is an array
 *		of C strings, one for each attribute of the return tuple.
 * Datum HeapTupleHeaderGetDatum(HeapTupleHeader tuple) - convert a
 *		HeapTupleHeader to a Datum.
 *
 * Macro declarations:
 * HeapTupleGetDatum(HeapTuple tuple) - convert a HeapTuple to a Datum.
 *
 * Obsolete routines and macros:
 * TupleDesc RelationNameGetTupleDesc(const char *relname) - Use to get a
 *		TupleDesc based on a named relation.
 * TupleDesc TypeGetTupleDesc(Oid typeoid, List *colaliases) - Use to get a
 *		TupleDesc based on a type OID.
 * TupleGetDatum(TupleTableSlot *slot, HeapTuple tuple) - get a Datum
 *		given a tuple and a slot.
 *----------
 */

#define HeapTupleGetDatum(tuple)		HeapTupleHeaderGetDatum((tuple)->t_data)
/* obsolete version of above */
#define TupleGetDatum(_slot, _tuple)	HeapTupleGetDatum(_tuple)

extern TupleDesc RelationNameGetTupleDesc(const char *relname);
extern TupleDesc TypeGetTupleDesc(Oid typeoid, List *colaliases);

/* from execTuples.c */
extern TupleDesc BlessTupleDesc(TupleDesc tupdesc);
extern AttInMetadata *TupleDescGetAttInMetadata(TupleDesc tupdesc);
extern HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values);
extern Datum HeapTupleHeaderGetDatum(HeapTupleHeader tuple);


/*----------
 *		Support for Set Returning Functions (SRFs)
 *
 * The basic API for SRFs using ValuePerCall mode looks something like this:
 *
 * Datum
 * my_Set_Returning_Function(PG_FUNCTION_ARGS)
 * {
 *	FuncCallContext    *funcctx;
 *	Datum				result;
 *	MemoryContext		oldcontext;
 *	<user defined declarations>
 *
 *	if (SRF_IS_FIRSTCALL())
 *	{
 *		funcctx = SRF_FIRSTCALL_INIT();
 *		// switch context when allocating stuff to be used in later calls
 *		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
 *		<user defined code>
 *		<if returning composite>
 *			<build TupleDesc, and perhaps AttInMetadata>
 *		<endif returning composite>
 *		<user defined code>
 *		// return to original context when allocating transient memory
 *		MemoryContextSwitchTo(oldcontext);
 *	}
 *	<user defined code>
 *	funcctx = SRF_PERCALL_SETUP();
 *	<user defined code>
 *
 *	if (funcctx->call_cntr < funcctx->max_calls)
 *	{
 *		<user defined code>
 *		<obtain result Datum>
 *		SRF_RETURN_NEXT(funcctx, result);
 *	}
 *	else
 *		SRF_RETURN_DONE(funcctx);
 * }
 *
 * NOTE: there is no guarantee that a SRF using ValuePerCall mode will be
 * run to completion; for example, a query with LIMIT might stop short of
 * fetching all the rows.  Therefore, do not expect that you can do resource
 * cleanup just before SRF_RETURN_DONE().  You need not worry about releasing
 * memory allocated in multi_call_memory_ctx, but holding file descriptors or
 * other non-memory resources open across calls is a bug.  SRFs that need
 * such resources should not use these macros, but instead populate a
 * tuplestore during a single call, as set up by SetSingleFuncCall() (see
 * fmgr/README).  Alternatively, set up a callback to release resources
 * at query shutdown, using RegisterExprContextCallback().
 *
 *----------
 */

/* from funcapi.c */

/* flag bits for SetSingleFuncCall() */
#define SRF_SINGLE_USE_EXPECTED	0x01	/* use expectedDesc as tupdesc */
#define SRF_SINGLE_BLESS		0x02	/* validate tuple for SRF */
extern void SetSingleFuncCall(FunctionCallInfo fcinfo, bits32 flags);

extern FuncCallContext *init_MultiFuncCall(PG_FUNCTION_ARGS);
extern FuncCallContext *per_MultiFuncCall(PG_FUNCTION_ARGS);
extern void end_MultiFuncCall(PG_FUNCTION_ARGS, FuncCallContext *funcctx);

#define SRF_IS_FIRSTCALL() (fcinfo->flinfo->fn_extra == NULL)

#define SRF_FIRSTCALL_INIT() init_MultiFuncCall(fcinfo)

#define SRF_PERCALL_SETUP() per_MultiFuncCall(fcinfo)

#define SRF_RETURN_NEXT(_funcctx, _result) \
	do { \
		ReturnSetInfo	   *rsi; \
		(_funcctx)->call_cntr++; \
		rsi = (ReturnSetInfo *) fcinfo->resultinfo; \
		rsi->isDone = ExprMultipleResult; \
		PG_RETURN_DATUM(_result); \
	} while (0)

#define SRF_RETURN_NEXT_NULL(_funcctx) \
	do { \
		ReturnSetInfo	   *rsi; \
		(_funcctx)->call_cntr++; \
		rsi = (ReturnSetInfo *) fcinfo->resultinfo; \
		rsi->isDone = ExprMultipleResult; \
		PG_RETURN_NULL(); \
	} while (0)

#define  SRF_RETURN_DONE(_funcctx) \
	do { \
		ReturnSetInfo	   *rsi; \
		end_MultiFuncCall(fcinfo, _funcctx); \
		rsi = (ReturnSetInfo *) fcinfo->resultinfo; \
		rsi->isDone = ExprEndResult; \
		PG_RETURN_NULL(); \
	} while (0)

/*----------
 *	Support to ease writing of functions dealing with VARIADIC inputs
 *----------
 *
 * This function extracts a set of argument values, types and NULL markers
 * for a given input function. This returns a set of data:
 * - **values includes the set of Datum values extracted.
 * - **types the data type OID for each element.
 * - **nulls tracks if an element is NULL.
 *
 * variadic_start indicates the argument number where the VARIADIC argument
 * starts.
 * convert_unknown set to true will enforce the conversion of arguments
 * with unknown data type to text.
 *
 * The return result is the number of elements stored, or -1 in the case of
 * "VARIADIC NULL".
 */
extern int	extract_variadic_args(FunctionCallInfo fcinfo, int variadic_start,
								  bool convert_unknown, Datum **values,
								  Oid **types, bool **nulls);

#endif							/* FUNCAPI_H */