Comments on draft-ietf-httpbis-http2-04

[Michael Sweet <[e-mail]>]

All,

A couple quick comments on draft-ietf-httpbis-http2-04...

In section 8.1.1 Examples I see the following:

   All HTTP Requests that include a body SHOULD include the "content-
   length" header field.  If a server receives a request where the sum
   of the DATA frame payload lengths does not equal the value of the
   "content-length" header field, the server MUST return a 400 (Bad
   Request) error.

I am uncomfortable with this wording primarily because a lot of POST usage consists of streamed content - my particular interest is obviously printing, but any streamed content will necessarily not be able to provide a content-length header field. So instead I would suggest the following two paragraphs instead:

    All HTTP requests that include a body of known length MUST include the "content-length" header field. If a server receives a request where the sum of the DATA frame payload lengths does not equal the value of the "content-length" header field, the server MUST return a 400 (Bad Request) error.

    All HTTP requests that include a body of unknown length MUST NOT include the "content-length" header field. Servers MUST support receiving requests without a "content-length" header field and MUST return a 413 (Request Entity Too Large) error if the body is too large to process.

This clearly defines how clients stream content to servers and defines the error handling required.  And it makes the conformance requirements less squishy...


My other comment is that I don't see any discussion of the Expect header, nor do I see a issue on Github... But this is something that gets used extensively in printing to avoid sending gigabytes of print data to a printer that needs authentication for certain operations...  Perhaps something to add to section 8.1.1, e.g.:


Use of Expect with 100 (Continue) response:

    POST /ipp/print HTTP/1.1            HEADERS
    Host; printer.example.org      ==>    - END_STREAM
    Content-Type: application/ipp         + END_HEADERS
    Transfer-Encoding: chunked              :method = post
    Expect: 100-continue                    :scheme = ipp
                                            :host = printer.example.org
                                            :path = /ipp/print
                                            content-type = application/ipp
                                            expect = 100-continue

    HTTP/1.1 100 Continue          ==>  HEADERS
                                          - END_STREAM
                                          + END_HEADERS
                                            :status = 100

    {binary data from client}      ==>  DATA
                                          + END_STREAM
                                            {binary data}

    HTTP/1.1 200 OK                ==>  HEADERS
    Content-Type: application/ipp         - END_STREAM
    Transfer-Encoding: chunked            + END_HEADERS
                                            :status = 200
    {binary data from server}               content-type = application/ipp

                                        DATA
                                          + END_STREAM
                                            {binary data}

Failed response needing authentication:

    POST /ipp/print HTTP/1.1            HEADERS
    Host; printer.example.org      ==>    - END_STREAM
    Content-Type: application/ipp         + END_HEADERS
    Transfer-Encoding: chunked              :method = post
    Expect: 100-continue                    :scheme = ipp
                                            :host = printer.example.org
                                            :path = /ipp/print
                                            content-type = application/ipp
                                            expect = 100-continue

    HTTP/1.1 401 Unauthorized      ==>  HEADERS
    Content-Type: text/html               - END_STREAM
    Content-Length: 123                   + END_HEADERS
    WWW-Authenticate: Basic ...             :status = 401
                                            www-authenticate = Basic ...
    {HTML error message from server}

Then we'd also need a clarification in section 8.1.3 to allow a single HEADERS response frame with :status = 100.

_________________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair