interpolate.go

package dbr

import (
	"database/sql/driver"
	"reflect"
	"strconv"
	"strings"
	"time"
)

type interpolator struct {
	Buffer
	Dialect
	IgnoreBinary bool
	N            int
}

// InterpolateForDialect replaces placeholder
// in query with corresponding value in dialect.
//
// It can be also used for debugging custom Builder.
//
// Every time you call database/sql's db.Query("SELECT ...") method,
// under the hood, the mysql driver will create a prepared statement,
// execute it, and then throw it away. This has a big performance cost.
//
// gocraft/dbr doesn't use prepared statements.
// We ported mysql's query escape functionality directly into our package,
// which means we interpolate all of those question marks with
// their arguments before they get to MySQL.
// The result of this is that it's way faster, and just as secure.
//
// Check out these benchmarks from https://github.com/tyler-smith/golang-sql-benchmark.
func InterpolateForDialect(query string, value []interface{}, d Dialect) (string, error) {
	i := interpolator{
		Buffer:  NewBuffer(),
		Dialect: d,
	}
	err := i.interpolate(query, value, true)
	if err != nil {
		return "", err
	}
	return i.String(), nil
}

var escapedPlaceholder = strings.Repeat(placeholder, 2)

func (i *interpolator) interpolate(query string, value []interface{}, topLevel bool) error {
	valueIndex := 0

	for {
		index := strings.Index(query, placeholder)
		if index == -1 {
			break
		}

		// escape placeholder by repeating it twice
		if strings.HasPrefix(query[index:], escapedPlaceholder) {
			i.WriteString(query[:index+1]) // Write placeholder once, not twice
			query = query[index+len(escapedPlaceholder):]
			continue
		}

		if valueIndex >= len(value) {
			return ErrPlaceholderCount
		}

		i.WriteString(query[:index])
		if _, ok := value[valueIndex].([]byte); ok && i.IgnoreBinary {
			i.WriteString(i.Placeholder(i.N))
			i.N++
			i.WriteValue(value[valueIndex])
		} else {
			err := i.encodePlaceholder(value[valueIndex], topLevel)
			if err != nil {
				return err
			}
		}
		query = query[index+len(placeholder):]
		valueIndex++
	}

	if valueIndex != len(value) {
		return ErrPlaceholderCount
	}

	// placeholder not found; write remaining query
	i.WriteString(query)

	return nil
}

var (
	typeTime = reflect.TypeOf(time.Time{})
)

func (i *interpolator) encodePlaceholder(value interface{}, topLevel bool) error {
	if builder, ok := value.(Builder); ok {
		pbuf := NewBuffer()
		err := builder.Build(i.Dialect, pbuf)
		if err != nil {
			return err
		}
		paren := false
		switch value.(type) {
		case *SelectStmt, *union:
			paren = !topLevel
		}
		if paren {
			i.WriteString("(")
		}
		err = i.interpolate(pbuf.String(), pbuf.Value(), false)
		if err != nil {
			return err
		}
		if paren {
			i.WriteString(")")
		}
		return nil
	}

	if valuer, ok := value.(driver.Valuer); ok {
		// get driver.Valuer's data
		var err error
		value, err = valuer.Value()
		if err != nil {
			return err
		}
	}

	if value == nil {
		i.WriteString("NULL")
		return nil
	}
	v := reflect.ValueOf(value)
	switch v.Kind() {
	case reflect.String:
		i.WriteString(i.EncodeString(v.String()))
		return nil
	case reflect.Bool:
		i.WriteString(i.EncodeBool(v.Bool()))
		return nil
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		i.WriteString(strconv.FormatInt(v.Int(), 10))
		return nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		i.WriteString(strconv.FormatUint(v.Uint(), 10))
		return nil
	case reflect.Float32, reflect.Float64:
		i.WriteString(strconv.FormatFloat(v.Float(), 'f', -1, 64))
		return nil
	case reflect.Struct:
		if v.Type() == typeTime {
			i.WriteString(i.EncodeTime(v.Interface().(time.Time)))
			return nil
		}
	case reflect.Slice:
		if v.Type().Elem().Kind() == reflect.Uint8 {
			// []byte
			i.WriteString(i.EncodeBytes(v.Bytes()))
			return nil
		}
		if v.Len() == 0 {
			// FIXME: support zero-length slice
			return ErrInvalidSliceLength
		}
		i.WriteString("(")
		for n := 0; n < v.Len(); n++ {
			if n > 0 {
				i.WriteString(",")
			}
			err := i.encodePlaceholder(v.Index(n).Interface(), topLevel)
			if err != nil {
				return err
			}
		}
		i.WriteString(")")
		return nil
	case reflect.Ptr:
		if v.IsNil() {
			i.WriteString("NULL")
			return nil
		}
		return i.encodePlaceholder(v.Elem().Interface(), topLevel)
	}
	return ErrNotSupported
}