[建议]让ctx.getFileStream 支持bytesRead

[ahuigo]

根据 getFileStream 示例
我们在使用egg 上传文件时，使用的是busboy 的FileStream(ReadableStream) 而不是fs 的ReadStream.
所以FileStream 缺少bytesRead.

bytesRead 访问示例：

       // app/controller/test.js
        const rs = await this.ctx.getFileStream()
        const ws = fs.createWriteStream(uploadPath, { flags: 'a' })
        const bytesRead = await new Promise((resolve, reject) => {
          const ps = rs.pipe(ws);
          ps.on('finish', () => {
             resolve(ws.bytesWritten);
             console.log(ws.bytesWritten); //有值
             console.log(rs.bytesRead); //undefined
          })
          ps.on('error', reject)
        })

虽然通过ws/ps 的bytesWritten 可以得到rs.bytesRead,
但是对象属性不完整会给用户带来困惑。（比如我误用FileStream.bytesRead 而调试了很久）

[egg-bot]

Translation of this issue:

---

[Recommended] Let FileStream support bytesRead

According to [getFileStream example] (http://mirror.eggjs.org/zh-cn/basics/controller.html)
When we use egg to upload a file, we use busboy's FileStream(ReadableStream) instead of fs' ReadStream.
So FileStream is missing bytesRead.

Example of bytesRead access:

        Const rs = await this.ctx.getFileStream()
        Const ws = fs.createWriteStream(uploadPath, { flags: 'a' })
        Const bytesRead = await new Promise((resolve, reject) => {
          Const ps = rs.pipe(ws);
          Ps.on('finish', () => {
             Resolve(ws.bytesWritten);
             Console.log(ws.bytesWritten); //valued
             Console.log(rs.bytesRead); //undefined
          })
          Ps.on('error', reject)
        })

Although rs.bytesRead can be obtained through the bytesWritten of ws/ps, ** but the incomplete object properties will be confusing to the user**. (For example, I misused FileStream.bytesRead and debugged it for a long time)

Will you support bytesRead in the future?

[popomore]

这个本来就不是文件 io，为何以 FileStream 为准，可以去 https://github.com/nodejs/node 问是否支持。

[ahuigo]

@popomore 这个不是node 的FileStream, 而是busboy 的FileStream。 我发到busboy 这里了 mscdex/busboy#173

[atian25]

直接给那边提个 PR 吧

[fengmk2]

其实不需要也行的，你可以监听 data 事件，就知道了。

[ahuigo]

其实这个属性可有可无吧。只是有则完备一些吧。

我上面的实例应该是目前最简单的方案了吧。
监听data 也需要要自己count bytesSize 吧