ReanGD/go-web-search

package database

import (
    "bytes"
    "compress/zlib"
    "database/sql/driver"
    "errors"
    "fmt"
    "io/ioutil"
)

const (
    // ErrScanArgument - Scan argument is not array of bytes
    ErrScanArgument = "Compressed.Scan: argument is not array of bytes"
)

// Compressed - field compressed by zlib
type Compressed struct {
    Data []byte
}

// Compress - compress c.Data value
func (c *Compressed) Compress() []byte {
    if len(c.Data) == 0 {
        return nil
    }

    var zContent bytes.Buffer
    w, _ := zlib.NewWriterLevelDict(&zContent, 6, nil)
    _, _ = w.Write(c.Data)
    _ = w.Close()

    return zContent.Bytes()
}

// Value - prepare value for save to DB
func (c Compressed) Value() (driver.Value, error) {
    return c.Compress(), nil
}

// Scan - load data from DB to value
func (c *Compressed) Scan(value interface{}) error {
    if value == nil {
        var nilResult []byte
        c.Data = nilResult
        return nil
    }

    obj, ok := value.([]byte)
    if !ok {
        return errors.New(ErrScanArgument)
    }

    r, err := zlib.NewReader(bytes.NewReader(obj))
    if err != nil {
        return fmt.Errorf("Compressed.Scan: %s", err)
    }
    result, err := ioutil.ReadAll(r)
    _ = r.Close()
    if err != nil {
        return fmt.Errorf("Compressed.Scan: %s", err)
    }
    c.Data = result

    return nil
}