funcapi.c

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/*-------------------------------------------------------------------------
 *
 * funcapi.c
 *	  Utility and convenience functions for fmgr functions that return
 *	  sets and/or composite types.
 *
 * Copyright (c) 2002-2008, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/fmgr/funcapi.c,v 1.37.2.1 2008/02/29 02:49:43 neilc Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "catalog/namespace.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
#include "utils/typcache.h"


static void shutdown_MultiFuncCall(Datum arg);
static TypeFuncClass internal_get_result_type(Oid funcid,
						 Node *call_expr,
						 ReturnSetInfo *rsinfo,
						 Oid *resultTypeId,
						 TupleDesc *resultTupleDesc);
static bool resolve_polymorphic_tupdesc(TupleDesc tupdesc,
							oidvector *declared_args,
							Node *call_expr);
static TypeFuncClass get_type_func_class(Oid typid);


/*
 * init_MultiFuncCall
 * Create an empty FuncCallContext data structure
 * and do some other basic Multi-function call setup
 * and error checking
 */
FuncCallContext *
init_MultiFuncCall(PG_FUNCTION_ARGS)
{
	FuncCallContext *retval;

	/*
	 * Bail if we're called in the wrong context
	 */
	if (fcinfo->resultinfo == NULL || !IsA(fcinfo->resultinfo, ReturnSetInfo))
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("set-valued function called in context that cannot accept a set")));

	if (fcinfo->flinfo->fn_extra == NULL)
	{
		/*
		 * First call
		 */
		ReturnSetInfo  *rsi = (ReturnSetInfo *) fcinfo->resultinfo;
		MemoryContext	multi_call_ctx;

		/*
		 * Create a suitably long-lived context to hold cross-call data
		 */
		multi_call_ctx = AllocSetContextCreate(fcinfo->flinfo->fn_mcxt,
											   "SRF multi-call context",
											   ALLOCSET_SMALL_MINSIZE,
											   ALLOCSET_SMALL_INITSIZE,
											   ALLOCSET_SMALL_MAXSIZE);

		/*
		 * Allocate suitably long-lived space and zero it
		 */
		retval = (FuncCallContext *)
			MemoryContextAllocZero(multi_call_ctx,
								   sizeof(FuncCallContext));

		/*
		 * initialize the elements
		 */
		retval->call_cntr = 0;
		retval->max_calls = 0;
		retval->slot = NULL;
		retval->user_fctx = NULL;
		retval->attinmeta = NULL;
		retval->tuple_desc = NULL;
		retval->multi_call_memory_ctx = multi_call_ctx;

		/*
		 * save the pointer for cross-call use
		 */
		fcinfo->flinfo->fn_extra = retval;

		/*
		 * Ensure we will get shut down cleanly if the exprcontext is not run
		 * to completion.
		 */
		RegisterExprContextCallback(rsi->econtext,
									shutdown_MultiFuncCall,
									PointerGetDatum(fcinfo->flinfo));
	}
	else
	{
		/* second and subsequent calls */
		elog(ERROR, "init_MultiFuncCall cannot be called more than once");

		/* never reached, but keep compiler happy */
		retval = NULL;
	}

	return retval;
}

/*
 * per_MultiFuncCall
 *
 * Do Multi-function per-call setup
 */
FuncCallContext *
per_MultiFuncCall(PG_FUNCTION_ARGS)
{
	FuncCallContext *retval = (FuncCallContext *) fcinfo->flinfo->fn_extra;

	/*
	 * Clear the TupleTableSlot, if present.  This is for safety's sake: the
	 * Slot will be in a long-lived context (it better be, if the
	 * FuncCallContext is pointing to it), but in most usage patterns the
	 * tuples stored in it will be in the function's per-tuple context. So at
	 * the beginning of each call, the Slot will hold a dangling pointer to an
	 * already-recycled tuple.	We clear it out here.
	 *
	 * Note: use of retval->slot is obsolete as of 8.0, and we expect that it
	 * will always be NULL.  This is just here for backwards compatibility in
	 * case someone creates a slot anyway.
	 */
	if (retval->slot != NULL)
		ExecClearTuple(retval->slot);

	return retval;
}

/*
 * end_MultiFuncCall
 * Clean up after init_MultiFuncCall
 */
void
end_MultiFuncCall(PG_FUNCTION_ARGS, FuncCallContext *funcctx)
{
	ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;

	/* Deregister the shutdown callback */
	UnregisterExprContextCallback(rsi->econtext,
								  shutdown_MultiFuncCall,
								  PointerGetDatum(fcinfo->flinfo));

	/* But use it to do the real work */
	shutdown_MultiFuncCall(PointerGetDatum(fcinfo->flinfo));
}

/*
 * shutdown_MultiFuncCall
 * Shutdown function to clean up after init_MultiFuncCall
 */
static void
shutdown_MultiFuncCall(Datum arg)
{
	FmgrInfo   *flinfo = (FmgrInfo *) DatumGetPointer(arg);
	FuncCallContext *funcctx = (FuncCallContext *) flinfo->fn_extra;

	/* unbind from flinfo */
	flinfo->fn_extra = NULL;

	/*
	 * Delete context that holds all multi-call data, including the
	 * FuncCallContext itself
	 */
	MemoryContextSwitchTo(flinfo->fn_mcxt);
	MemoryContextDelete(funcctx->multi_call_memory_ctx);
}


/*
 * 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.
 *
 * One hard case that this handles is resolution of actual rowtypes for
 * functions returning RECORD (from either the function's OUT parameter
 * list, or a ReturnSetInfo context node).	TYPEFUNC_RECORD is returned
 * only when we couldn't resolve the actual rowtype for lack of information.
 *
 * The other hard case that this handles is resolution of polymorphism.
 * We will never return polymorphic pseudotypes (ANYELEMENT etc), either
 * as a scalar result type or as a component of a rowtype.
 *
 * This function is relatively expensive --- in a function returning set,
 * try to call it only the first time through.
 */
TypeFuncClass
get_call_result_type(FunctionCallInfo fcinfo,
					 Oid *resultTypeId,
					 TupleDesc *resultTupleDesc)
{
	return internal_get_result_type(fcinfo->flinfo->fn_oid,
									fcinfo->flinfo->fn_expr,
									(ReturnSetInfo *) fcinfo->resultinfo,
									resultTypeId,
									resultTupleDesc);
}

/*
 * get_expr_result_type
 *		As above, but work from a calling expression node tree
 */
TypeFuncClass
get_expr_result_type(Node *expr,
					 Oid *resultTypeId,
					 TupleDesc *resultTupleDesc)
{
	TypeFuncClass result;

	if (expr && IsA(expr, FuncExpr))
		result = internal_get_result_type(((FuncExpr *) expr)->funcid,
										  expr,
										  NULL,
										  resultTypeId,
										  resultTupleDesc);
	else if (expr && IsA(expr, OpExpr))
		result = internal_get_result_type(get_opcode(((OpExpr *) expr)->opno),
										  expr,
										  NULL,
										  resultTypeId,
										  resultTupleDesc);
	else
	{
		/* handle as a generic expression; no chance to resolve RECORD */
		Oid			typid = exprType(expr);

		if (resultTypeId)
			*resultTypeId = typid;
		if (resultTupleDesc)
			*resultTupleDesc = NULL;
		result = get_type_func_class(typid);
		if (result == TYPEFUNC_COMPOSITE && resultTupleDesc)
			*resultTupleDesc = lookup_rowtype_tupdesc_copy(typid, -1);
	}

	return result;
}

/*
 * get_func_result_type
 *		As above, but work from a function's OID only
 *
 * This will not be able to resolve pure-RECORD results nor polymorphism.
 */
TypeFuncClass
get_func_result_type(Oid functionId,
					 Oid *resultTypeId,
					 TupleDesc *resultTupleDesc)
{
	return internal_get_result_type(functionId,
									NULL,
									NULL,
									resultTypeId,
									resultTupleDesc);
}

/*
 * internal_get_result_type -- workhorse code implementing all the above
 *
 * funcid must always be supplied.	call_expr and rsinfo can be NULL if not
 * available.  We will return TYPEFUNC_RECORD, and store NULL into
 * *resultTupleDesc, if we cannot deduce the complete result rowtype from
 * the available information.
 */
static TypeFuncClass
internal_get_result_type(Oid funcid,
						 Node *call_expr,
						 ReturnSetInfo *rsinfo,
						 Oid *resultTypeId,
						 TupleDesc *resultTupleDesc)
{
	TypeFuncClass result;
	HeapTuple	tp;
	Form_pg_proc procform;
	Oid			rettype;
	TupleDesc	tupdesc;

	/* First fetch the function's pg_proc row to inspect its rettype */
	tp = SearchSysCache(PROCOID,
						ObjectIdGetDatum(funcid),
						0, 0, 0);
	if (!HeapTupleIsValid(tp))
		elog(ERROR, "cache lookup failed for function %u", funcid);
	procform = (Form_pg_proc) GETSTRUCT(tp);

	rettype = procform->prorettype;

	/* Check for OUT parameters defining a RECORD result */
	tupdesc = build_function_result_tupdesc_t(tp);
	if (tupdesc)
	{
		/*
		 * It has OUT parameters, so it's basically like a regular composite
		 * type, except we have to be able to resolve any polymorphic OUT
		 * parameters.
		 */
		if (resultTypeId)
			*resultTypeId = rettype;

		if (resolve_polymorphic_tupdesc(tupdesc,
										&procform->proargtypes,
										call_expr))
		{
			if (tupdesc->tdtypeid == RECORDOID &&
				tupdesc->tdtypmod < 0)
				assign_record_type_typmod(tupdesc);
			if (resultTupleDesc)
				*resultTupleDesc = tupdesc;
			result = TYPEFUNC_COMPOSITE;
		}
		else
		{
			if (resultTupleDesc)
				*resultTupleDesc = NULL;
			result = TYPEFUNC_RECORD;
		}

		ReleaseSysCache(tp);

		return result;
	}

	/*
	 * If scalar polymorphic result, try to resolve it.
	 */
	if (IsPolymorphicType(rettype))
	{
		Oid			newrettype = exprType(call_expr);

		if (newrettype == InvalidOid)	/* this probably should not happen */
			ereport(ERROR,
					(errcode(ERRCODE_DATATYPE_MISMATCH),
					 errmsg("could not determine actual result type for function \"%s\" declared to return type %s",
							NameStr(procform->proname),
							format_type_be(rettype))));
		rettype = newrettype;
	}

	if (resultTypeId)
		*resultTypeId = rettype;
	if (resultTupleDesc)
		*resultTupleDesc = NULL;	/* default result */

	/* Classify the result type */
	result = get_type_func_class(rettype);
	switch (result)
	{
		case TYPEFUNC_COMPOSITE:
			if (resultTupleDesc)
				*resultTupleDesc = lookup_rowtype_tupdesc_copy(rettype, -1);
			/* Named composite types can't have any polymorphic columns */
			break;
		case TYPEFUNC_SCALAR:
			break;
		case TYPEFUNC_RECORD:
			/* We must get the tupledesc from call context */
			if (rsinfo && IsA(rsinfo, ReturnSetInfo) &&
				rsinfo->expectedDesc != NULL)
			{
				result = TYPEFUNC_COMPOSITE;
				if (resultTupleDesc)
					*resultTupleDesc = rsinfo->expectedDesc;
				/* Assume no polymorphic columns here, either */
			}