从REST API返回的图像始终显示为损坏

Question

我正在使用
React 构建一个艺术作品应用程序的内容管理系统。客户端将发布到使用Mongoose插入到
MongoDB中的API 。然后，API向数据库查询新插入的图像，并将其返回
给客户端。

这是我使用Mongoose连接到MongoDB的代码：

mongoose.connect('mongodb://localhost/test').then(() => 
console.log('connected to db')).catch(err => console.log(err))

mongoose.Promise = global.Promise

const db = mongoose.connection

db.on('error', console.error.bind(console, 'MongoDB connection error:'))

const Schema = mongoose.Schema;

const ImgSchema = new Schema({
  img: { data: Buffer, contentType: String }
})

const Img = mongoose.model('Img', ImgSchema)

我正在使用multer和fs处理图像文件。我的POST端点如下
所示：

router.post('/', upload.single('image'), (req, res) => {
  if (!req.file) {
    res.send('no file')
  } else {
    const imgItem = new Img()
    imgItem.img.data = fs.readFileSync(req.file.path)
    imgItem.contentType = 'image/png'
    imgItem
      .save()
      .then(data => 
        Img.findById(data, (err, findImg) => {
          console.log(findImg.img)
          fs.writeFileSync('api/uploads/image.png', findImg.img.data)
          res.sendFile(__dirname + '/uploads/image.png')
        }))
  } 
})

我可以在文件结构中看到writeFileSync正在将映像写入
磁盘。res.sendFile抓取它并将其发送给客户端。

客户端代码如下所示：

handleSubmit = e => {
    e.preventDefault()
    const img = new FormData()
    img.append('image', this.state.file, this.state.file.name)
    axios
      .post('http://localhost:8000/api/gallery', img, {
        onUploadProgress: progressEvent => {
          console.log(progressEvent.loaded / progressEvent.total)
        }
      })
      .then(res => {
        console.log('responsed')
        console.log(res)
        const returnedFile = new File([res.data], 'image.png', { type: 'image/png' })
        const reader = new FileReader()
        reader.onloadend = () => {
          this.setState({ returnedFile, returned: reader.result })
        }
        reader.readAsDataURL(returnedFile)
      })
      .catch(err => console.log(err))
  }

这样确实可以将返回的文件和img数据url都置于状态。但是，在我的应用程序中，图像始终显示为损坏。

Answer 1

避免发送回base64编码的图像（多个图像+大文件+
大编码字符串=非常慢的性能）。我强烈建议创建
一个微服务，该微服务仅处理图像上传和任何其他与图像相关的
获取/发布/放置/删除请求。将其与主应用程序分开。

例如：

• 我使用multer创建图像缓冲区
• 然后使用Sharp或fs保存图像（取决于文件类型）
• 然后，我将文件路径发送到控制器以保存到数据库中
• 然后，前端在尝试访问时发出GET请求: http://localhost:4000/uploads/timestamp-randomstring-originalname.fileext

简单来说，我的微服务就像CDN一样，仅用于图像。

For example, a user sends a post request to
http://localhost:4000/api/avatar/create with some FormData:

It first passes through some Express middlewares:

libs/middlewares.js

...
app.use(cors({credentials: true, origin: "http://localhost:3000" })) // allows receiving of cookies from front-end

app.use(morgan(`tiny`)); // logging framework

app.use(multer({
        limits: {
            fileSize: 10240000,
            files: 1,
            fields: 1
        },
        fileFilter: (req, file, next) => {
            if (!/\.(jpe?g|png|gif|bmp)$/i.test(file.originalname)) {
                req.err = `That file extension is not accepted!`
                next(null, false)
            }
            next(null, true);
        }
    }).single(`file`))

app.use(bodyParser.json()); // parses header requests (req.body)

app.use(bodyParser.urlencoded({ limit: `10mb`, extended: true })); // allows objects and arrays to be URL-encoded

...etc

Then, hits the avatars route:

routes/avatars.js

app.post(`/api/avatar/create`, requireAuth, saveImage, create);

It then passes through some user authentication, then goes through my
saveImage middleware:

services/saveImage.js

const createRandomString = require('../shared/helpers');
const fs = require("fs");
const sharp = require("sharp");
const randomString = createRandomString();

if (req.err || !req.file) {
  return res.status(500).json({ err: req.err || `Unable to locate the requested file to be saved` })
  next();
}

const filename = `${Date.now()}-${randomString}-${req.file.originalname}`;
const filepath = `uploads/${filename}`;

const setFilePath = () => { req.file.path = filepath; return next();}

(/\.(gif|bmp)$/i.test(req.file.originalname))
    ? fs.writeFile(filepath, req.file.buffer, (err) => {
            if (err) { 
              return res.status(500).json({ err: `There was a problem saving the image.`}); 
              next();
            }

            setFilePath();
        })
    : sharp(req.file.buffer).resize(256, 256).max().withoutEnlargement().toFile(filepath).then(() => setFilePath())

If the file is saved, it then sends a req.file.path to my create
controller. This gets saved to my DB as a file path and as an image path (the
avatarFilePath or /uploads/imagefile.ext is saved for removal purposes and
the avatarURL or [http://localhost:4000]/uploads/imagefile.ext is saved
and used for the front-end GET request):

controllers/avatars.js (I’m using Postgres, but you can substitute for
Mongo)

create: async (req, res, done) => {
            try {
                const avatarurl = `${apiURL}/${req.file.path}`;

                await db.result("INSERT INTO avatars(userid, avatarURL, avatarFilePath) VALUES ($1, $2, $3)", [req.session.id, avatarurl, req.file.path]);

                res.status(201).json({ avatarurl });
            } catch (err) { return res.status(500).json({ err: err.toString() }); done(); 
        }

Then when the front-end tries to access the uploads folder via <img src={avatarURL} alt="image" /> or <img src="[http://localhost:4000]/uploads/imagefile.ext" alt="image" />, it gets
served up by the microservice:

libs/server.js

const express = require("express");
const path = app.get("path");
const PORT = 4000;

//============================================================//
// EXPRESS SERVE AVATAR IMAGES
//============================================================//
app.use(`/uploads`, express.static(`uploads`));

//============================================================//
/* CREATE EXPRESS SERVER */
//============================================================//
app.listen(PORT);

What it looks when logging requests:

19:17:54 INSERT INTO avatars(userid, avatarURL, avatarFilePath) VALUES ('08861626-b6d0-11e8-9047-672b670fe126', 'http://localhost:4000/uploads/1536891474536-k9c7OdimjEWYXbjTIs9J4S3lh2ldrzV8-android.png', 'uploads/1536891474536-k9c7OdimjEWYXbjTIs9J4S3lh2ldrzV8-android.png')

POST /api/avatar/create 201 109 - 61.614 ms

GET /uploads/1536891474536-k9c7OdimjEWYXbjTIs9J4S3lh2ldrzV8-android.png 200 3027 - 3.877 ms