funcapi.h

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/*-------------------------------------------------------------------------
 *
 * 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) 2002-2021, 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(char prokind,
                                     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, and return that using SFRM_Materialize
 * mode (see fmgr/README).  Alternatively, set up a callback to release
 * resources at query shutdown, using RegisterExprContextCallback().
 *
 *----------
 */

/* from funcapi.c */
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 */