Twisted Python and Chunked Encoding

When I was first writing a little web service in Twisted Python that would return JSON encoded data, and I was having some issues with loading it up using Javascript, I used Wireshark to trace the whole thing and was surprised at how the response looked.

There were delimiters around the data, and the response headers included a reference to “Chunked Transfer-Encoding”. I had to look it up to find out what it was, and I had no idea how to turn it off so I posted on the Twisted Python mailing list, and got a prompt reply.

Chunked encoding has nothing to do with the content type. It is used if
you do not set a content-length header.

So, figure out your response’s length (in bytes), and set the
content-length header to that.

Aha! So this in my http.Request handler fixed it.


log.info("sending response")
# Set the content length so that we don't respond with chunked
# encoding.
size = len(content)
log.debug("content length is %d bytes" % size)
self.setHeader('Content-Length', size)
self.write(content)
self.finish()
log.info("done")

Well, not a fix really as there was no bug, but I wanted to rule out the chunked encoding as the source of a problem that I was seeing.

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