convert.go

// This is code from http://golang.org/src/pkg/database/sql/convert.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package freetds

import (
	"database/sql"
	"database/sql/driver"
	"errors"
	"fmt"
	"reflect"
	"strconv"
	"time"
)

var errNilPtr = errors.New("destination pointer is nil") // embedded in descriptive error

// RawBytes is a byte slice that holds a reference to memory owned by
// the database itself. After a Scan into a RawBytes, the slice is only
// valid until the next call to Next, Scan, or Close.
type RawBytes []byte

// convertAssign copies to dest the value in src, converting it if possible.
// An error is returned if the copy would result in loss of information.
// dest should be a pointer type.
func convertAssign(dest, src interface{}) error {
	// Common cases, without reflect.
	switch s := src.(type) {
	case string:
		switch d := dest.(type) {
		case *string:
			if d == nil {
				return errNilPtr
			}
			*d = s
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = []byte(s)
			return nil
		}
	case []byte:
		switch d := dest.(type) {
		case *string:
			if d == nil {
				return errNilPtr
			}
			*d = string(s)
			return nil
		case *interface{}:
			if d == nil {
				return errNilPtr
			}
			*d = cloneBytes(s)
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = cloneBytes(s)
			return nil
		case *RawBytes:
			if d == nil {
				return errNilPtr
			}
			*d = s
			return nil
		}
	case nil:
		switch d := dest.(type) {
		case *interface{}:
			if d == nil {
				return errNilPtr
			}
			*d = nil
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = nil
			return nil
		case *RawBytes:
			if d == nil {
				return errNilPtr
			}
			*d = nil
			return nil
		case *time.Time:
			return nil
		}
	}

	var sv reflect.Value

	switch d := dest.(type) {
	case *string:
		sv = reflect.ValueOf(src)
		switch sv.Kind() {
		case reflect.Bool,
			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
			reflect.Float32, reflect.Float64:
			*d = fmt.Sprintf("%v", src)
			return nil
		}
	case *[]byte:
		sv = reflect.ValueOf(src)
		switch sv.Kind() {
		case reflect.Bool,
			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
			reflect.Float32, reflect.Float64:
			*d = []byte(fmt.Sprintf("%v", src))
			return nil
		}
	case *RawBytes:
		sv = reflect.ValueOf(src)
		switch sv.Kind() {
		case reflect.Bool,
			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
			reflect.Float32, reflect.Float64:
			*d = RawBytes(fmt.Sprintf("%v", src))
			return nil
		}
	case *bool:
		bv, err := driver.Bool.ConvertValue(src)
		if err == nil {
			*d = bv.(bool)
		}
		return err
	case *interface{}:
		*d = src
		return nil
	}

	if scanner, ok := dest.(sql.Scanner); ok {
		return scanner.Scan(src)
	}

	dpv := reflect.ValueOf(dest)
	if dpv.Kind() != reflect.Ptr {
		return errors.New("destination not a pointer")
	}
	if dpv.IsNil() {
		return errNilPtr
	}

	if !sv.IsValid() {
		sv = reflect.ValueOf(src)
	}

	//if types are the same
	dv := reflect.Indirect(dpv)
	if dv.Kind() == sv.Kind() {
		dv.Set(sv)
		return nil
	}

	//My addition.
	//This is added to the original implementation from go source
	//Intention is to skip string conversion for most common cases.
	//Types are almost the same e.g. int -> int32
	switch dv.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		switch sv.Kind() {
		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
			dv.SetInt(sv.Int())
			return nil
		}
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		switch sv.Kind() {
		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
			dv.SetUint(sv.Uint())
			return nil
		}
	case reflect.Float32, reflect.Float64:
		switch sv.Kind() {
		case reflect.Float32, reflect.Float64:
			dv.SetFloat(sv.Float())
			return nil
		}
	}

	//convert to string than back
	switch dv.Kind() {
	case reflect.Ptr:
		if src == nil {
			dv.Set(reflect.Zero(dv.Type()))
			return nil
		} else {
			dv.Set(reflect.New(dv.Type().Elem()))
			return convertAssign(dv.Interface(), src)
		}
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		s := asString(src)
		i64, err := strconv.ParseInt(s, 10, dv.Type().Bits())
		if err != nil {
			return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
		}
		dv.SetInt(i64)
		return nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		s := asString(src)
		u64, err := strconv.ParseUint(s, 10, dv.Type().Bits())
		if err != nil {
			return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
		}
		dv.SetUint(u64)
		return nil
	case reflect.Float32, reflect.Float64:
		s := asString(src)
		f64, err := strconv.ParseFloat(s, dv.Type().Bits())
		if err != nil {
			return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
		}
		dv.SetFloat(f64)
		return nil
	}

	return fmt.Errorf("unsupported driver -> Scan pair: %T -> %T", src, dest)
}

func cloneBytes(b []byte) []byte {
	if b == nil {
		return nil
	} else {
		c := make([]byte, len(b))
		copy(c, b)
		return c
	}
}

func asString(src interface{}) string {
	switch v := src.(type) {
	case string:
		return v
	case []byte:
		return string(v)
	}
	return fmt.Sprintf("%v", src)
}