发送不改变用户当前页面的 HTTP 响应

Question

I have a JavaScript bookmarklet that POSTs information to a (Flask powered) server while the user is on some other page (ie not one on my server). I don't want to interrupt the user's browsing by hijacking their session with my server response.

My initial thought was that I could suppress the HTTP response from Flask somehow; prevent it from sending anything to the client so they aren't mysteriously redirected. I was hoping I could do this by perhaps having a null return from a view.

I then thought that might be some HTTP response that lets the client know the information was successfully submitted, but will leave the client on their current page. Suppose a header value like "Here is the result of your request, but you should not alter your current display"?

Answer 1

To answer your amended question, yes there is such a response. From RFC 2616-section 10 (emphasis added):

10.2.5 204 No Content

The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation. The response MAY include new or updated metainformation in the form of entity-headers, which if present SHOULD be associated with the requested variant.

If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent . This response is primarily intended to allow input for actions to take place without causing a change to the user agent's active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent's active view.

The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.

Thus from flask you can do something like this. Remember, the response must not include a message body, so any data you want to send back should be put into a cookie.

@app.route('/')
def index():
    r = flask.Response()
    r.set_cookie("My important cookie", value=some_cool_value)
    return r, 204

Answer 2

No, it is not possible. Flask is built on Werkzeug, which implements the WSGI spec. The WSGI cycle requires sending a response to each request. Droping the response would require control over the TCP/IP connection at a far lower level even that HTTP. This is outside the domain of WSGI, therefore outside the domain of Flask.

You could return an error code, or an empty body, but you have to return something .

return ''  # empty body