1. The WSGI gateway must send the response headers immediately when the
application yields its first non-empty string.
2. When there is an "100-continue" token in the request "Expect:" header, the
WSGI gateway is allowed to delay sending the "100 Continue" response until the
application reads from environ["wsgi.input"].
Consequently, if there is a 100-continue expectation, then a WSGI application
must not read from wsgi.input after yielding its first non-empty string.
For example, the following application results in undefined (probably
erroneous) behavior:
def application(environ, start_response):
start_response("400 Bad Request", [])
yield "400 Bad Request"
environ["wsgi.input"].read(1)
However, the following application must cause the WSGI gateway to send a
100-continue response:
def application(environ, start_response):
start_response("400 Bad Request", [])
yield ""
environ["wsgi.input"].read(1)
PEP says that "[s]ervers and gateways that implement HTTP 1.1 must provide
transparent support for HTTP 1.1's "expect/continue" mechanism." Should the
application be able to detect whether there is a "100-continue" token in the
Expect header of the request? Or, is the WSGI gateway allowed/required to hide
the token? If the application cannot reliably detect the 100-continue token,
then this implies an ordering constraint between yielding output and reading
input that is not mentioned anywhere in the PEP.
Another consequence is that an application cannot explicitly respond with a
"100 Continue" itself, like this:
def application(environ, start_response):
start_response("100 Continue", [])
yield ""
start_response("200 OK", [])
yield "OK"
The reasons is that start_response cannot be called twice except when an
exception is detected, and also the "100 Continue" would not be sent until
right before the "200 OK" was sent anyway.
Regards,
Brian
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