vendor/github.com/mattn/go-sqlite3/tracecallback.go - perf - Git at Google

 // Copyright (C) 2016 Yasuhiro Matsumoto <mattn.jp@gmail.com>.
 // TODO: add "Gimpl do foo" team?
 //
 // Use of this source code is governed by an MIT-style
 // license that can be found in the LICENSE file.
 // +build trace

 package sqlite3

 /*
 #ifndef USE_LIBSQLITE3
 #include <sqlite3-binding.h>
 #else
 #include <sqlite3.h>
 #endif
 #include <stdlib.h>

 void stepTrampoline(sqlite3_context*, int, sqlite3_value**);
 void doneTrampoline(sqlite3_context*);
 int traceCallbackTrampoline(unsigned int traceEventCode, void *ctx, void *p, void *x);
 */
 import "C"

 import (
 	"errors"
 	"fmt"
 	"reflect"
 	"strings"
 	"sync"
 	"unsafe"
 )

 // Trace... constants identify the possible events causing callback invocation.
 // Values are same as the corresponding SQLite Trace Event Codes.
 const (
 	TraceStmt    = C.SQLITE_TRACE_STMT
 	TraceProfile = C.SQLITE_TRACE_PROFILE
 	TraceRow     = C.SQLITE_TRACE_ROW
 	TraceClose   = C.SQLITE_TRACE_CLOSE
 )

 type TraceInfo struct {
 	// Pack together the shorter fields, to keep the struct smaller.
 	// On a 64-bit machine there would be padding
 	// between EventCode and ConnHandle; having AutoCommit here is "free":
 	EventCode  uint32
 	AutoCommit bool
 	ConnHandle uintptr

 	// Usually filled, unless EventCode = TraceClose = SQLITE_TRACE_CLOSE:
 	// identifier for a prepared statement:
 	StmtHandle uintptr

 	// Two strings filled when EventCode = TraceStmt = SQLITE_TRACE_STMT:
 	// (1) either the unexpanded SQL text of the prepared statement, or
 	//     an SQL comment that indicates the invocation of a trigger;
 	// (2) expanded SQL, if requested and if (1) is not an SQL comment.
 	StmtOrTrigger string
 	ExpandedSQL   string // only if requested (TraceConfig.WantExpandedSQL = true)

 	// filled when EventCode = TraceProfile = SQLITE_TRACE_PROFILE:
 	// estimated number of nanoseconds that the prepared statement took to run:
 	RunTimeNanosec int64

 	DBError Error
 }

 // TraceUserCallback gives the signature for a trace function
 // provided by the user (Go application programmer).
 // SQLite 3.14 documentation (as of September 2, 2016)
 // for SQL Trace Hook = sqlite3_trace_v2():
 // The integer return value from the callback is currently ignored,
 // though this may change in future releases. Callback implementations
 // should return zero to ensure future compatibility.
 type TraceUserCallback func(TraceInfo) int

 type TraceConfig struct {
 	Callback        TraceUserCallback
 	EventMask       C.uint
 	WantExpandedSQL bool
 }

 func fillDBError(dbErr *Error, db *C.sqlite3) {
 	// See SQLiteConn.lastError(), in file 'sqlite3.go' at the time of writing (Sept 5, 2016)
 	dbErr.Code = ErrNo(C.sqlite3_errcode(db))
 	dbErr.ExtendedCode = ErrNoExtended(C.sqlite3_extended_errcode(db))
 	dbErr.err = C.GoString(C.sqlite3_errmsg(db))
 }

 func fillExpandedSQL(info *TraceInfo, db *C.sqlite3, pStmt unsafe.Pointer) {
 	if pStmt == nil {
 		panic("No SQLite statement pointer in P arg of trace_v2 callback")
 	}

 	expSQLiteCStr := C.sqlite3_expanded_sql((*C.sqlite3_stmt)(pStmt))
 	if expSQLiteCStr == nil {
 		fillDBError(&info.DBError, db)
 		return
 	}
 	info.ExpandedSQL = C.GoString(expSQLiteCStr)
 }

 //export traceCallbackTrampoline
 func traceCallbackTrampoline(
 	traceEventCode C.uint,
 	// Parameter named 'C' in SQLite docs = Context given at registration:
 	ctx unsafe.Pointer,
 	// Parameter named 'P' in SQLite docs (Primary event data?):
 	p unsafe.Pointer,
 	// Parameter named 'X' in SQLite docs (eXtra event data?):
 	xValue unsafe.Pointer) C.int {

 	if ctx == nil {
 		panic(fmt.Sprintf("No context (ev 0x%x)", traceEventCode))
 	}

 	contextDB := (*C.sqlite3)(ctx)
 	connHandle := uintptr(ctx)

 	var traceConf TraceConfig
 	var found bool
 	if traceEventCode == TraceClose {
 		// clean up traceMap: 'pop' means get and delete
 		traceConf, found = popTraceMapping(connHandle)
 	} else {
 		traceConf, found = lookupTraceMapping(connHandle)
 	}

 	if !found {
 		panic(fmt.Sprintf("Mapping not found for handle 0x%x (ev 0x%x)",
 			connHandle, traceEventCode))
 	}

 	var info TraceInfo

 	info.EventCode = uint32(traceEventCode)
 	info.AutoCommit = (int(C.sqlite3_get_autocommit(contextDB)) != 0)
 	info.ConnHandle = connHandle

 	switch traceEventCode {
 	case TraceStmt:
 		info.StmtHandle = uintptr(p)

 		var xStr string
 		if xValue != nil {
 			xStr = C.GoString((*C.char)(xValue))
 		}
 		info.StmtOrTrigger = xStr
 		if !strings.HasPrefix(xStr, "--") {
 			// Not SQL comment, therefore the current event
 			// is not related to a trigger.
 			// The user might want to receive the expanded SQL;
 			// let's check:
 			if traceConf.WantExpandedSQL {
 				fillExpandedSQL(&info, contextDB, p)
 			}
 		}

 	case TraceProfile:
 		info.StmtHandle = uintptr(p)

 		if xValue == nil {
 			panic("NULL pointer in X arg of trace_v2 callback for SQLITE_TRACE_PROFILE event")
 		}

 		info.RunTimeNanosec = *(*int64)(xValue)

 		// sample the error //TODO: is it safe? is it useful?
 		fillDBError(&info.DBError, contextDB)

 	case TraceRow:
 		info.StmtHandle = uintptr(p)

 	case TraceClose:
 		handle := uintptr(p)
 		if handle != info.ConnHandle {
 			panic(fmt.Sprintf("Different conn handle 0x%x (expected 0x%x) in SQLITE_TRACE_CLOSE event.",
 				handle, info.ConnHandle))
 		}

 	default:
 		// Pass unsupported events to the user callback (if configured);
 		// let the user callback decide whether to panic or ignore them.
 	}

 	// Do not execute user callback when the event was not requested by user!
 	// Remember that the Close event is always selected when
 	// registering this callback trampoline with SQLite --- for cleanup.
 	// In the future there may be more events forced to "selected" in SQLite
 	// for the driver's needs.
 	if traceConf.EventMask&traceEventCode == 0 {
 		return 0
 	}

 	r := 0
 	if traceConf.Callback != nil {
 		r = traceConf.Callback(info)
 	}
 	return C.int(r)
 }

 type traceMapEntry struct {
 	config TraceConfig
 }

 var traceMapLock sync.Mutex
 var traceMap = make(map[uintptr]traceMapEntry)

 func addTraceMapping(connHandle uintptr, traceConf TraceConfig) {
 	traceMapLock.Lock()
 	defer traceMapLock.Unlock()

 	oldEntryCopy, found := traceMap[connHandle]
 	if found {
 		panic(fmt.Sprintf("Adding trace config %v: handle 0x%x already registered (%v).",
 			traceConf, connHandle, oldEntryCopy.config))
 	}
 	traceMap[connHandle] = traceMapEntry{config: traceConf}
 	fmt.Printf("Added trace config %v: handle 0x%x.\n", traceConf, connHandle)
 }

 func lookupTraceMapping(connHandle uintptr) (TraceConfig, bool) {
 	traceMapLock.Lock()
 	defer traceMapLock.Unlock()

 	entryCopy, found := traceMap[connHandle]
 	return entryCopy.config, found
 }

 // 'pop' = get and delete from map before returning the value to the caller
 func popTraceMapping(connHandle uintptr) (TraceConfig, bool) {
 	traceMapLock.Lock()
 	defer traceMapLock.Unlock()

 	entryCopy, found := traceMap[connHandle]
 	if found {
 		delete(traceMap, connHandle)
 		fmt.Printf("Pop handle 0x%x: deleted trace config %v.\n", connHandle, entryCopy.config)
 	}
 	return entryCopy.config, found
 }

 // RegisterAggregator makes a Go type available as a SQLite aggregation function.
 //
 // Because aggregation is incremental, it's implemented in Go with a
 // type that has 2 methods: func Step(values) accumulates one row of
 // data into the accumulator, and func Done() ret finalizes and
 // returns the aggregate value. "values" and "ret" may be any type
 // supported by RegisterFunc.
 //
 // RegisterAggregator takes as implementation a constructor function
 // that constructs an instance of the aggregator type each time an
 // aggregation begins. The constructor must return a pointer to a
 // type, or an interface that implements Step() and Done().
 //
 // The constructor function and the Step/Done methods may optionally
 // return an error in addition to their other return values.
 //
 // See _example/go_custom_funcs for a detailed example.
 func (c *SQLiteConn) RegisterAggregator(name string, impl interface{}, pure bool) error {
 	var ai aggInfo
 	ai.constructor = reflect.ValueOf(impl)
 	t := ai.constructor.Type()
 	if t.Kind() != reflect.Func {
 		return errors.New("non-function passed to RegisterAggregator")
 	}
 	if t.NumOut() != 1 && t.NumOut() != 2 {
 		return errors.New("SQLite aggregator constructors must return 1 or 2 values")
 	}
 	if t.NumOut() == 2 && !t.Out(1).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
 		return errors.New("Second return value of SQLite function must be error")
 	}
 	if t.NumIn() != 0 {
 		return errors.New("SQLite aggregator constructors must not have arguments")
 	}

 	agg := t.Out(0)
 	switch agg.Kind() {
 	case reflect.Ptr, reflect.Interface:
 	default:
 		return errors.New("SQlite aggregator constructor must return a pointer object")
 	}
 	stepFn, found := agg.MethodByName("Step")
 	if !found {
 		return errors.New("SQlite aggregator doesn't have a Step() function")
 	}
 	step := stepFn.Type
 	if step.NumOut() != 0 && step.NumOut() != 1 {
 		return errors.New("SQlite aggregator Step() function must return 0 or 1 values")
 	}
 	if step.NumOut() == 1 && !step.Out(0).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
 		return errors.New("type of SQlite aggregator Step() return value must be error")
 	}

 	stepNArgs := step.NumIn()
 	start := 0
 	if agg.Kind() == reflect.Ptr {
 		// Skip over the method receiver
 		stepNArgs--
 		start++
 	}
 	if step.IsVariadic() {
 		stepNArgs--
 	}
 	for i := start; i < start+stepNArgs; i++ {
 		conv, err := callbackArg(step.In(i))
 		if err != nil {
 			return err
 		}
 		ai.stepArgConverters = append(ai.stepArgConverters, conv)
 	}
 	if step.IsVariadic() {
 		conv, err := callbackArg(t.In(start + stepNArgs).Elem())
 		if err != nil {
 			return err
 		}
 		ai.stepVariadicConverter = conv
 		// Pass -1 to sqlite so that it allows any number of
 		// arguments. The call helper verifies that the minimum number
 		// of arguments is present for variadic functions.
 		stepNArgs = -1
 	}

 	doneFn, found := agg.MethodByName("Done")
 	if !found {
 		return errors.New("SQlite aggregator doesn't have a Done() function")
 	}
 	done := doneFn.Type
 	doneNArgs := done.NumIn()
 	if agg.Kind() == reflect.Ptr {
 		// Skip over the method receiver
 		doneNArgs--
 	}
 	if doneNArgs != 0 {
 		return errors.New("SQlite aggregator Done() function must have no arguments")
 	}
 	if done.NumOut() != 1 && done.NumOut() != 2 {
 		return errors.New("SQLite aggregator Done() function must return 1 or 2 values")
 	}
 	if done.NumOut() == 2 && !done.Out(1).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
 		return errors.New("second return value of SQLite aggregator Done() function must be error")
 	}

 	conv, err := callbackRet(done.Out(0))
 	if err != nil {
 		return err
 	}
 	ai.doneRetConverter = conv
 	ai.active = make(map[int64]reflect.Value)
 	ai.next = 1

 	// ai must outlast the database connection, or we'll have dangling pointers.
 	c.aggregators = append(c.aggregators, &ai)

 	cname := C.CString(name)
 	defer C.free(unsafe.Pointer(cname))
 	opts := C.SQLITE_UTF8
 	if pure {
 		opts |= C.SQLITE_DETERMINISTIC
 	}
 	rv := sqlite3_create_function(c.db, cname, C.int(stepNArgs), C.int(opts), newHandle(c, &ai), nil, C.stepTrampoline, C.doneTrampoline)
 	if rv != C.SQLITE_OK {
 		return c.lastError()
 	}
 	return nil
 }

 // SetTrace installs or removes the trace callback for the given database connection.
 // It's not named 'RegisterTrace' because only one callback can be kept and called.
 // Calling SetTrace a second time on same database connection
 // overrides (cancels) any prior callback and all its settings:
 // event mask, etc.
 func (c *SQLiteConn) SetTrace(requested *TraceConfig) error {
 	connHandle := uintptr(unsafe.Pointer(c.db))

 	_, _ = popTraceMapping(connHandle)

 	if requested == nil {
 		// The traceMap entry was deleted already by popTraceMapping():
 		// can disable all events now, no need to watch for TraceClose.
 		err := c.setSQLiteTrace(0)
 		return err
 	}

 	reqCopy := *requested

 	// Disable potentially expensive operations
 	// if their result will not be used. We are doing this
 	// just in case the caller provided nonsensical input.
 	if reqCopy.EventMask&TraceStmt == 0 {
 		reqCopy.WantExpandedSQL = false
 	}

 	addTraceMapping(connHandle, reqCopy)

 	// The callback trampoline function does cleanup on Close event,
 	// regardless of the presence or absence of the user callback.
 	// Therefore it needs the Close event to be selected:
 	actualEventMask := uint(reqCopy.EventMask | TraceClose)
 	err := c.setSQLiteTrace(actualEventMask)
 	return err
 }

 func (c *SQLiteConn) setSQLiteTrace(sqliteEventMask uint) error {
 	rv := C.sqlite3_trace_v2(c.db,
 		C.uint(sqliteEventMask),
 		(*[0]byte)(unsafe.Pointer(C.traceCallbackTrampoline)),
 		unsafe.Pointer(c.db)) // Fourth arg is same as first: we are
 	// passing the database connection handle as callback context.

 	if rv != C.SQLITE_OK {
 		return c.lastError()
 	}
 	return nil
 }
	// Copyright (C) 2016 Yasuhiro Matsumoto <mattn.jp@gmail.com>.
	// TODO: add "Gimpl do foo" team?
	//
	// Use of this source code is governed by an MIT-style
	// license that can be found in the LICENSE file.
	// +build trace

	package sqlite3

	/*
	#ifndef USE_LIBSQLITE3
	#include <sqlite3-binding.h>
	#else
	#include <sqlite3.h>
	#endif
	#include <stdlib.h>

	void stepTrampoline(sqlite3_context, int, sqlite3_value*);
	void doneTrampoline(sqlite3_context*);
	int traceCallbackTrampoline(unsigned int traceEventCode, void ctx, void p, void *x);
	*/
	import "C"

	import (
	"errors"
	"fmt"
	"reflect"
	"strings"
	"sync"
	"unsafe"
	)

	// Trace... constants identify the possible events causing callback invocation.
	// Values are same as the corresponding SQLite Trace Event Codes.
	const (
	TraceStmt = C.SQLITE_TRACE_STMT
	TraceProfile = C.SQLITE_TRACE_PROFILE
	TraceRow = C.SQLITE_TRACE_ROW
	TraceClose = C.SQLITE_TRACE_CLOSE
	)

	type TraceInfo struct {
	// Pack together the shorter fields, to keep the struct smaller.
	// On a 64-bit machine there would be padding
	// between EventCode and ConnHandle; having AutoCommit here is "free":
	EventCode uint32
	AutoCommit bool
	ConnHandle uintptr

	// Usually filled, unless EventCode = TraceClose = SQLITE_TRACE_CLOSE:
	// identifier for a prepared statement:
	StmtHandle uintptr

	// Two strings filled when EventCode = TraceStmt = SQLITE_TRACE_STMT:
	// (1) either the unexpanded SQL text of the prepared statement, or
	// an SQL comment that indicates the invocation of a trigger;
	// (2) expanded SQL, if requested and if (1) is not an SQL comment.
	StmtOrTrigger string
	ExpandedSQL string // only if requested (TraceConfig.WantExpandedSQL = true)

	// filled when EventCode = TraceProfile = SQLITE_TRACE_PROFILE:
	// estimated number of nanoseconds that the prepared statement took to run:
	RunTimeNanosec int64

	DBError Error
	}

	// TraceUserCallback gives the signature for a trace function
	// provided by the user (Go application programmer).
	// SQLite 3.14 documentation (as of September 2, 2016)
	// for SQL Trace Hook = sqlite3_trace_v2():
	// The integer return value from the callback is currently ignored,
	// though this may change in future releases. Callback implementations
	// should return zero to ensure future compatibility.
	type TraceUserCallback func(TraceInfo) int

	type TraceConfig struct {
	Callback TraceUserCallback
	EventMask C.uint
	WantExpandedSQL bool
	}

	func fillDBError(dbErr Error, db C.sqlite3) {
	// See SQLiteConn.lastError(), in file 'sqlite3.go' at the time of writing (Sept 5, 2016)
	dbErr.Code = ErrNo(C.sqlite3_errcode(db))
	dbErr.ExtendedCode = ErrNoExtended(C.sqlite3_extended_errcode(db))
	dbErr.err = C.GoString(C.sqlite3_errmsg(db))
	}

	func fillExpandedSQL(info TraceInfo, db C.sqlite3, pStmt unsafe.Pointer) {
	if pStmt == nil {
	panic("No SQLite statement pointer in P arg of trace_v2 callback")
	}

	expSQLiteCStr := C.sqlite3_expanded_sql((*C.sqlite3_stmt)(pStmt))
	if expSQLiteCStr == nil {
	fillDBError(&info.DBError, db)
	return
	}
	info.ExpandedSQL = C.GoString(expSQLiteCStr)
	}

	//export traceCallbackTrampoline
	func traceCallbackTrampoline(
	traceEventCode C.uint,
	// Parameter named 'C' in SQLite docs = Context given at registration:
	ctx unsafe.Pointer,
	// Parameter named 'P' in SQLite docs (Primary event data?):
	p unsafe.Pointer,
	// Parameter named 'X' in SQLite docs (eXtra event data?):
	xValue unsafe.Pointer) C.int {

	if ctx == nil {
	panic(fmt.Sprintf("No context (ev 0x%x)", traceEventCode))
	}

	contextDB := (*C.sqlite3)(ctx)
	connHandle := uintptr(ctx)

	var traceConf TraceConfig
	var found bool
	if traceEventCode == TraceClose {
	// clean up traceMap: 'pop' means get and delete
	traceConf, found = popTraceMapping(connHandle)
	} else {
	traceConf, found = lookupTraceMapping(connHandle)
	}

	if !found {
	panic(fmt.Sprintf("Mapping not found for handle 0x%x (ev 0x%x)",
	connHandle, traceEventCode))
	}

	var info TraceInfo

	info.EventCode = uint32(traceEventCode)
	info.AutoCommit = (int(C.sqlite3_get_autocommit(contextDB)) != 0)
	info.ConnHandle = connHandle

	switch traceEventCode {
	case TraceStmt:
	info.StmtHandle = uintptr(p)

	var xStr string
	if xValue != nil {
	xStr = C.GoString((*C.char)(xValue))
	}
	info.StmtOrTrigger = xStr
	if !strings.HasPrefix(xStr, "--") {
	// Not SQL comment, therefore the current event
	// is not related to a trigger.
	// The user might want to receive the expanded SQL;
	// let's check:
	if traceConf.WantExpandedSQL {
	fillExpandedSQL(&info, contextDB, p)
	}
	}

	case TraceProfile:
	info.StmtHandle = uintptr(p)

	if xValue == nil {
	panic("NULL pointer in X arg of trace_v2 callback for SQLITE_TRACE_PROFILE event")
	}

	info.RunTimeNanosec = (int64)(xValue)

	// sample the error //TODO: is it safe? is it useful?
	fillDBError(&info.DBError, contextDB)

	case TraceRow:
	info.StmtHandle = uintptr(p)

	case TraceClose:
	handle := uintptr(p)
	if handle != info.ConnHandle {
	panic(fmt.Sprintf("Different conn handle 0x%x (expected 0x%x) in SQLITE_TRACE_CLOSE event.",
	handle, info.ConnHandle))
	}

	default:
	// Pass unsupported events to the user callback (if configured);
	// let the user callback decide whether to panic or ignore them.
	}

	// Do not execute user callback when the event was not requested by user!
	// Remember that the Close event is always selected when
	// registering this callback trampoline with SQLite --- for cleanup.
	// In the future there may be more events forced to "selected" in SQLite
	// for the driver's needs.
	if traceConf.EventMask&traceEventCode == 0 {
	return 0
	}

	r := 0
	if traceConf.Callback != nil {
	r = traceConf.Callback(info)
	}
	return C.int(r)
	}

	type traceMapEntry struct {
	config TraceConfig
	}

	var traceMapLock sync.Mutex
	var traceMap = make(map[uintptr]traceMapEntry)

	func addTraceMapping(connHandle uintptr, traceConf TraceConfig) {
	traceMapLock.Lock()
	defer traceMapLock.Unlock()

	oldEntryCopy, found := traceMap[connHandle]
	if found {
	panic(fmt.Sprintf("Adding trace config %v: handle 0x%x already registered (%v).",
	traceConf, connHandle, oldEntryCopy.config))
	}
	traceMap[connHandle] = traceMapEntry{config: traceConf}
	fmt.Printf("Added trace config %v: handle 0x%x.\n", traceConf, connHandle)
	}

	func lookupTraceMapping(connHandle uintptr) (TraceConfig, bool) {
	traceMapLock.Lock()
	defer traceMapLock.Unlock()

	entryCopy, found := traceMap[connHandle]
	return entryCopy.config, found
	}

	// 'pop' = get and delete from map before returning the value to the caller
	func popTraceMapping(connHandle uintptr) (TraceConfig, bool) {
	traceMapLock.Lock()
	defer traceMapLock.Unlock()

	entryCopy, found := traceMap[connHandle]
	if found {
	delete(traceMap, connHandle)
	fmt.Printf("Pop handle 0x%x: deleted trace config %v.\n", connHandle, entryCopy.config)
	}
	return entryCopy.config, found
	}

	// RegisterAggregator makes a Go type available as a SQLite aggregation function.
	//
	// Because aggregation is incremental, it's implemented in Go with a
	// type that has 2 methods: func Step(values) accumulates one row of
	// data into the accumulator, and func Done() ret finalizes and
	// returns the aggregate value. "values" and "ret" may be any type
	// supported by RegisterFunc.
	//
	// RegisterAggregator takes as implementation a constructor function
	// that constructs an instance of the aggregator type each time an
	// aggregation begins. The constructor must return a pointer to a
	// type, or an interface that implements Step() and Done().
	//
	// The constructor function and the Step/Done methods may optionally
	// return an error in addition to their other return values.
	//
	// See _example/go_custom_funcs for a detailed example.
	func (c *SQLiteConn) RegisterAggregator(name string, impl interface{}, pure bool) error {
	var ai aggInfo
	ai.constructor = reflect.ValueOf(impl)
	t := ai.constructor.Type()
	if t.Kind() != reflect.Func {
	return errors.New("non-function passed to RegisterAggregator")
	}
	if t.NumOut() != 1 && t.NumOut() != 2 {
	return errors.New("SQLite aggregator constructors must return 1 or 2 values")
	}
	if t.NumOut() == 2 && !t.Out(1).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
	return errors.New("Second return value of SQLite function must be error")
	}
	if t.NumIn() != 0 {
	return errors.New("SQLite aggregator constructors must not have arguments")
	}

	agg := t.Out(0)
	switch agg.Kind() {
	case reflect.Ptr, reflect.Interface:
	default:
	return errors.New("SQlite aggregator constructor must return a pointer object")
	}
	stepFn, found := agg.MethodByName("Step")
	if !found {
	return errors.New("SQlite aggregator doesn't have a Step() function")
	}
	step := stepFn.Type
	if step.NumOut() != 0 && step.NumOut() != 1 {
	return errors.New("SQlite aggregator Step() function must return 0 or 1 values")
	}
	if step.NumOut() == 1 && !step.Out(0).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
	return errors.New("type of SQlite aggregator Step() return value must be error")
	}

	stepNArgs := step.NumIn()
	start := 0
	if agg.Kind() == reflect.Ptr {
	// Skip over the method receiver
	stepNArgs--
	start++
	}
	if step.IsVariadic() {
	stepNArgs--
	}
	for i := start; i < start+stepNArgs; i++ {
	conv, err := callbackArg(step.In(i))
	if err != nil {
	return err
	}
	ai.stepArgConverters = append(ai.stepArgConverters, conv)
	}
	if step.IsVariadic() {
	conv, err := callbackArg(t.In(start + stepNArgs).Elem())
	if err != nil {
	return err
	}
	ai.stepVariadicConverter = conv
	// Pass -1 to sqlite so that it allows any number of
	// arguments. The call helper verifies that the minimum number
	// of arguments is present for variadic functions.
	stepNArgs = -1
	}

	doneFn, found := agg.MethodByName("Done")
	if !found {
	return errors.New("SQlite aggregator doesn't have a Done() function")
	}
	done := doneFn.Type
	doneNArgs := done.NumIn()
	if agg.Kind() == reflect.Ptr {
	// Skip over the method receiver
	doneNArgs--
	}
	if doneNArgs != 0 {
	return errors.New("SQlite aggregator Done() function must have no arguments")
	}
	if done.NumOut() != 1 && done.NumOut() != 2 {
	return errors.New("SQLite aggregator Done() function must return 1 or 2 values")
	}
	if done.NumOut() == 2 && !done.Out(1).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
	return errors.New("second return value of SQLite aggregator Done() function must be error")
	}

	conv, err := callbackRet(done.Out(0))
	if err != nil {
	return err
	}
	ai.doneRetConverter = conv
	ai.active = make(map[int64]reflect.Value)
	ai.next = 1

	// ai must outlast the database connection, or we'll have dangling pointers.
	c.aggregators = append(c.aggregators, &ai)

	cname := C.CString(name)
	defer C.free(unsafe.Pointer(cname))
	opts := C.SQLITE_UTF8
	if pure {
	opts \|= C.SQLITE_DETERMINISTIC
	}
	rv := sqlite3_create_function(c.db, cname, C.int(stepNArgs), C.int(opts), newHandle(c, &ai), nil, C.stepTrampoline, C.doneTrampoline)
	if rv != C.SQLITE_OK {
	return c.lastError()
	}
	return nil
	}

	// SetTrace installs or removes the trace callback for the given database connection.
	// It's not named 'RegisterTrace' because only one callback can be kept and called.
	// Calling SetTrace a second time on same database connection
	// overrides (cancels) any prior callback and all its settings:
	// event mask, etc.
	func (c SQLiteConn) SetTrace(requested TraceConfig) error {
	connHandle := uintptr(unsafe.Pointer(c.db))

	_, _ = popTraceMapping(connHandle)

	if requested == nil {
	// The traceMap entry was deleted already by popTraceMapping():
	// can disable all events now, no need to watch for TraceClose.
	err := c.setSQLiteTrace(0)
	return err
	}

	reqCopy := *requested

	// Disable potentially expensive operations
	// if their result will not be used. We are doing this
	// just in case the caller provided nonsensical input.
	if reqCopy.EventMask&TraceStmt == 0 {
	reqCopy.WantExpandedSQL = false
	}

	addTraceMapping(connHandle, reqCopy)

	// The callback trampoline function does cleanup on Close event,
	// regardless of the presence or absence of the user callback.
	// Therefore it needs the Close event to be selected:
	actualEventMask := uint(reqCopy.EventMask \| TraceClose)
	err := c.setSQLiteTrace(actualEventMask)
	return err
	}

	func (c *SQLiteConn) setSQLiteTrace(sqliteEventMask uint) error {
	rv := C.sqlite3_trace_v2(c.db,
	C.uint(sqliteEventMask),
	(*[0]byte)(unsafe.Pointer(C.traceCallbackTrampoline)),
	unsafe.Pointer(c.db)) // Fourth arg is same as first: we are
	// passing the database connection handle as callback context.

	if rv != C.SQLITE_OK {
	return c.lastError()
	}
	return nil
	}