It turns out that eventlet has been injecting a
``Transfer-Encoding`` header as of recent into WSGI application
response headers. The result of this ultimately depends on how
the HTTP client which is passing the request to the server is
written to handle data.
Apache, for example, will return that an invalid response was
received. In part because it sees the request end, with an HTTP
204 response code, but also an encoding indicating there is
a multipart body encoding inbound. Which is confusing.
Other C based HTTP clients can have any number of reactions up to
and including disconnecting sessions. Curl, depending on the
headers present either returns success but notes body weirdness
or actually returns return code 18.
Python-Requests kind of has it a little worse, and we see this
with clients. With it, it tries to prepare a respones content
body based upon the presence of the header indicating there is
a body. But it blows up thinking there is more data to read on
the socket when there is not more data to read.
Regardless, all of this is an RFC7230 violation.
Neither Content-Length nor Transfer-Encoding should be on an HTTP
204 response. However, Content-Length is the lesser evil, and we
have a similar endpoing in Ironic which *does* explicitly get
returned with a zero length content-length, and does not
demonstrate such issues.
As such, in the interest of the lesser evils until Eventlet's evil
ways of header injection are remedied, we're explicitly going to
force a Content-Length header to be sent indicating a zero length
response.
For more information, please see: https://github.com/eventlet/eventlet/issues/746
Change-Id: I014cc65c79222f4d4d7c2b6ff11a76e56659340c
55e47c630b