tornado图片上传与下载，Android客户端

Android客户端，将我们的通用的bitmap转为jpg字节数组：

    static byte[] compress(final Bitmap bitmap) {
        if(bitmap == null){
            return null;
        }
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, QUALILY, out);
        try {
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return out.toByteArray();
    }

然后，我们通过Base64.encodeToString将这个数据加密成一个字符串，就可以当作json的一项作为jsonstring发送给服务端。

Python服务端，解密然后保存到jpg文件即可：
而下载文件更简单，使用PIL.Image，可以读出imagedata，然后写到BytesIO中即可。
服务端的读写代码如下：

from abc import ABC
from tornado.web import RequestHandler
from libs.hooks import check_token
from libs.encode import Encode
import time
import io
from PIL import Image
from settings.config import max_img_size


class ImageHandler(RequestHandler, ABC):
    async def get(self, *args, **kwargs):
        url = self.request.uri
        if url.startswith("/image/") and url.endswith(".jpg"):
            file_name = 'static/upload/{}'.format(url[7:])
            await self.download(file_name)
            pass
        else:
            self.write("Invalid path ")
            self.write_error(404)

    @check_token
    async def post(self):
        url = self.request.uri
        token = self.get_body_argument('token')
        if url.startswith("/image/upload"):
            image = self.get_body_argument('image')
            image_data = Encode.decode(image)
            ut = int(time.time())
            file_name = token + str(ut) + ".jpg"
            save_to = 'static/upload/{}'.format(file_name)
            await self.upload(image_data, save_to)
        self.write_error(404)

    async def download(self, file_name):
        try:
            img = Image.open(file_name)
            height = img.size[1]
            width = img.size[0]
            while (height > max_img_size) or (width > max_img_size):
                height = height//2
                width = width//2
                print(width, height)
            img = img.resize((width, height))
        except FileNotFoundError:
            self.write_error(404)
            return
        bio = io.BytesIO()
        img.save(bio, "PNG")
        self.set_header('Content-Type', 'image/PNG')
        self.write(bio.getvalue())
        pass

    @staticmethod
    async def upload(image_data, save_to):
        with open(save_to, 'wb') as f:
            f.write(image_data)

路由

 (r'/image/(.*)', ImageHandler),

2020年4月9日，补充更简单的图片下载方式：
1）参考StaticFileHandler的get方法：

    async def download(self, file_name):
        try:
            pic = open(file_name, "rb")
        except FileNotFoundError:
            self.write_error(404)
            return
        self.write(pic.read())
        self.set_header('Content-Type', 'image/png')
        pass

注意要以rb方式打开。

2）设置静态文件路径：

(r'/image/(.*)', StaticFileHandler,
     {"path": os.path.join(os.path.dirname(__file__), "../static/upload"), "default_filename": "default.jpg"}),

第二中方法的缺点是谁都可以下载，没法check。