Go - 将 base64 字符串保存到文件

Question

so.. 我有一个 base64 编码的字符串，我需要对其进行解码，检查它的宽度和高度，然后保存到文件中。但是.. 我一直在保存损坏的图像文件。

package server

import (
    "encoding/base64"
    "errors"
    "io"
    "os"
    "strings"

    "image"
    _ "image/gif"
    _ "image/jpeg"
    _ "image/png"
)

var (
    ErrBucket       = errors.New("Invalid bucket!")
    ErrSize         = errors.New("Invalid size!")
    ErrInvalidImage = errors.New("Invalid image!")
)

func saveImageToDisk(fileNameBase, data, bucket string) (string, error) {
    idx := strings.Index(data, ";base64,")
    if idx < 0 {
        return "", ErrInvalidImage
    }

    reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data[idx+8:]))
    imgCfg, fmt, err := image.DecodeConfig(reader)
    if err != nil {
        return "", err
    }

    if imgCfg.Width != 750 || imgCfg.Height != 685 {
        return "", ErrSize
    }

    fileName := fileNameBase + "." + fmt
    f, err := os.Create(fileName)
    if err != nil {
        return "", err
    }

    _, err = io.Copy(f, reader)
    f.Close()

    return fileName, err
}

它确实保存了一个文件.. 我正在测试的 base64 根据在线 base64 到图像转换器是有效的。有什么帮助吗？

http://pastebin.com/u18eRv7d 这是我正在使用的 base64 字符串（函数中的数据）

Answer 1

另一个答案对我不起作用，我希望能够将图像保存为文件，而不管图像格式如何：

package main

import (
    "bytes"
    "encoding/base64"
    "image/gif"
    "image/jpeg"
    "image/png"
    "log"
    "os"
    "strings"

    _ "github.com/jinzhu/gorm/dialects/postgres"
)

const data = `data:image/gif;base64,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`

func main() {
    idx := strings.Index(data, ";base64,")
    if idx < 0 {
        panic("InvalidImage")
    }
    ImageType := data[11:idx]
    log.Println(ImageType)

    unbased, err := base64.StdEncoding.DecodeString(data[idx+8:])
    if err != nil {
        panic("Cannot decode b64")
    }
    r := bytes.NewReader(unbased)
    switch ImageType {
    case "png":
        im, err := png.Decode(r)
        if err != nil {
            panic("Bad png")
        }

        f, err := os.OpenFile("example.png", os.O_WRONLY|os.O_CREATE, 0777)
        if err != nil {
            panic("Cannot open file")
        }

        png.Encode(f, im)
    case "jpeg":
        im, err := jpeg.Decode(r)
        if err != nil {
            panic("Bad jpeg")
        }

        f, err := os.OpenFile("example.jpeg", os.O_WRONLY|os.O_CREATE, 0777)
        if err != nil {
            panic("Cannot open file")
        }

        jpeg.Encode(f, im, nil)
    case "gif":
        im, err := gif.Decode(r)
        if err != nil {
            panic("Bad gif")
        }

        f, err := os.OpenFile("example.gif", os.O_WRONLY|os.O_CREATE, 0777)
        if err != nil {
            panic("Cannot open file")
        }

        gif.Encode(f, im, nil)
    }
}

这支持 png、gif 和 jpeg。

Answer 2

这些代码的主要问题是，当您阅读 io.Reader 时，光标不会回到第一个。而且您已经阅读了解码图像配置中的 io.Reader。因此，当您将其写入文件时，它将在下一个读取直到 EOF（可能不是您的数据）

我不确切知道如何将 io.Reader 重置回第一个，但我写了一个解决方法来让它工作：

import (
    "encoding/base64"
    "errors"
    "strings"

    "image"
    _ "image/gif"
    _ "image/jpeg"
    _ "image/png"
    "io/ioutil"
    "bytes"
)

var (
    ErrBucket       = errors.New("Invalid bucket!")
    ErrSize         = errors.New("Invalid size!")
    ErrInvalidImage = errors.New("Invalid image!")
)

func saveImageToDisk(fileNameBase, data string) (string, error) {
    idx := strings.Index(data, ";base64,")
    if idx < 0 {
        return "", ErrInvalidImage
    }
    reader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(data[idx+8:]))
    buff := bytes.Buffer{}
    _, err := buff.ReadFrom(reader)
    if err != nil {
        return "", err
    }
    imgCfg, fm, err := image.DecodeConfig(bytes.NewReader(buff.Bytes()))
    if err != nil {
        return "", err
    }

    if imgCfg.Width != 750 || imgCfg.Height != 685 {
        return "", ErrSize
    }

    fileName := fileNameBase + "." + fm
    ioutil.WriteFile(fileName, buff.Bytes(), 0644)

    return fileName, err
}