使用BlobstoreUploadHandler处理图像上传并返回JSON消息

Question

我正在尝试将一张图片上传到一个通过create_upload_url()创建的链接上，然后用默认的BlobstoreUploadHandler来处理这个上传，并返回一个JSON消息给客户端，这个消息里包含了通过get_serving_url()获取的图片链接。我的代码如下：

class UploadHandler(blobstore_handlers.BlobstoreUploadHandler):
    def post(self):
        response = {}

        upload_files = self.get_uploads('file')
        blob_info = upload_files[0]

        response['error'] = False
        response['message'] = "Image uploaded."
        response['image_url'] = images.get_serving_url(blob_info.key())

        self.response.headers['Content-Type'] = 'application/json'
        self.response.out.write(json.dumps(response))

app = webapp2.WSGIApplication(
    [('/_ih/upload_handler/', UploadHandler),
    ], debug=True)

问题是客户端没有收到任何响应。AppEngine的日志显示请求的状态是200，这意味着请求成功。当我用flash发起请求时，状态码也是200，但没有响应内容；而使用HTML5时，状态显示为“(已取消)”。我完全不知道发生了什么。从我在网上看到的所有代码片段来看，这个应该是可以工作的。请帮帮我！谢谢。

Answer 1

为了处理文件上传并返回JSON格式的响应，你需要从上传处理程序跳转到一个能够返回JSON响应的处理程序。

下面是一个例子：

class FileUploadHandler(blobstore_handlers.BlobstoreUploadHandler):

    def post(self):
        blob_info = self.get_uploads()[0]       
        self.redirect(self.uri_for("successfulUpload",blob_key = blob_info.key()))


class SuccessfulUpload(BaseHandler):

    def get(self, blob_Key):
        response['error'] = False
        response['message'] = "Image uploaded."
        response['image_url'] = images.get_serving_url(blobstore.BlobKey(blob_Key))
        self.response.headers['Content-Type'] = 'application/json'
        self.response.out.write(json.dumps(response))

Answer 2

原来这是一个HTML5的跨域资源共享问题。你可以通过在响应中添加正确的头信息来解决这个问题：

class UploadHandler(blobstore_handlers.BlobstoreUploadHandler):
    def post(self):
        response = {}

        upload_files = self.get_uploads('file')
        blob_info = upload_files[0]

        response['error'] = False
        response['message'] = "Image uploaded."
        response['image_url'] = images.get_serving_url(blob_info.key())


        self.response.headers.add_header("Access-Control-Allow-Methods", "POST") 
        self.response.headers.add_header("Access-Control-Allow-Origin", "*")

        self.response.headers['Content-Type'] = 'application/json'

        self.response.out.write(json.dumps(response))