[Twisted-Python] Returning a response for an HTTP query that requires upstream IO.
I'd like to develop a server that maintains a TCP connection to an upstream server, and listens for HTTP requests. Upon receiving an HTTP request, the server will send a message upstream, wait for a response, and return an HTTP response to the client which made the request. My background is in writing blocking web services, so my natural instinct is to write a `get_result_for(query)` method that will take a `query` string and return a result from the upstream TCP connection. I'm not sure whether writing such a method is possible in Twisted, since it's basically a blocking method. I suspect I may have to use Continuation-Passing Style instead, that is: provide a callback to `get_result_for(query, callback)`. Even if that's the case, how do I return an HTTP response to the HTTP client once the query result is available?
This section of the documentation might be what you're looking for: https://twistedmatrix.com/documents/current/web/howto/web-in-60/asynchronous... If the tcp request to your upstream server is using some blocking (non-twisted) API, you could look into deferToThread. On Wed, 22 Apr 2020 at 17:17, Go Luhng <goluhng@gmail.com> wrote:
I'd like to develop a server that maintains a TCP connection to an upstream server, and listens for HTTP requests. Upon receiving an HTTP request, the server will send a message upstream, wait for a response, and return an HTTP response to the client which made the request.
My background is in writing blocking web services, so my natural instinct is to write a `get_result_for(query)` method that will take a `query` string and return a result from the upstream TCP connection.
I'm not sure whether writing such a method is possible in Twisted, since it's basically a blocking method. I suspect I may have to use Continuation-Passing Style instead, that is: provide a callback to `get_result_for(query, callback)`.
Even if that's the case, how do I return an HTTP response to the HTTP client once the query result is available?
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Donal McMullan -
Go Luhng