Check out the "Main differences from HTTP" section. It's clearly not the same format as HTTP. Whatever they mean by "GET and POST message formats remain the same" it's not what you're thinking it means.
There's no confusion about the "semantics of OSI" -- you can't take a client that talks only HTTP and get it talk to a server that talks only SPDY (and vice-versa). They are different application level protocols, period.
The "Main differences from HTTP" section says this:
"SPDY is intended to be as compatible as possible with current web-based applications. This means that, from the perspective of the server business logic or application API, nothing has changed. To achieve this, all of the application request and response header semantics are preserved. SPDY introduces a "session" which resides between the HTTP application layer and the TCP transport to regulate the flow of data."
This even explicitly says that SPDY resides underneath the HTTP application layer.
So from the point of view of e.g. GMail, it is making HTTP requests via XmlHttpRequest still is it not? And from the point of view of my Django application sitting behind some future apache/nginx SPDY module I will still be accepting HTTP requests and responding with HTTP responses will I not?
It seems like SPDY sits in the same layer as SSL/TLS in HTTPS. It doesn't replace HTTP, merely changes how the messages are transported over the wire. To use your logic, you can't point an HTTPS-only client at an HTTP server and have it work or vice-versa, and yet I quote from wikipedia:
"HTTP operates at the highest layer of the OSI Model, the Application layer; but the security protocol operates at a lower sublayer, encrypting an HTTP message prior to transmission and decrypting a message upon arrival. Strictly speaking, HTTPS is not a separate protocol, but refers to use of ordinary HTTP over an encrypted SSL/TLS connection."
> So from the point of view of e.g. GMail, it is making HTTP requests via XmlHttpRequest still is it not?
No, it's making SDPY requests. It is, however, making that difference insignificant to the application developer using the xmlHttpRequest API. HTTP is a protocol not an API. This is exactly what the paper says; the protocol is designed to make the API differences very minimal.
> And from the point of view of my Django application sitting behind some future apache/nginx SPDY module I will still be accepting HTTP requests and responding with HTTP responses will I not?
No, Django doesn't talk HTTP -- Django talks WSGI or CGI. That hides many of the details of the protocol in use -- I imagine that you could run Django with a server that sends/receives web requests over FTP. That doesn't make FTP into HTTP.
SPDY does not sit in the same level as SSL. With SSL, HTTP packets are tunneled through it. SDPY replaces HTTP; there is no fully formed HTTP message inside. If SPDY was merely multiplexing and compressing HTTP streams in frames, I would agree that it would be like HTTPS. But SPDY doesn't contain HTTP streams; it's all right there in the document.
> No, Django doesn't talk HTTP -- Django talks WSGI or CGI. That hides many of the details of the protocol in use -- I imagine that you could run Django with a server that sends/receives web requests over FTP.
I don't know how you would make e.g that[1] work on FTP. Basically you would end up encapsulating HTTP inside FTP, not using one in place of the other.
A CGI script takes raw (yet conveniently split by the web server) HTTP data from ENV vars and stdin, and outputs HTTP data directly to stdout. Django HttpRequest and HttpResponse object merely provides a convenient helper for that and does not actually abstract anything. The web server pipes the response as is straight to the client via TCP (unless there is SSL, where it will just obliviously encrypt the stream).
To comply with that, as SPDY is a replacement to HTTP, mod_spdy transcodes stuff live [2].
http://www.chromium.org/spdy/spdy-protocol/spdy-protocol-dra...
Check out the "Main differences from HTTP" section. It's clearly not the same format as HTTP. Whatever they mean by "GET and POST message formats remain the same" it's not what you're thinking it means.
There's no confusion about the "semantics of OSI" -- you can't take a client that talks only HTTP and get it talk to a server that talks only SPDY (and vice-versa). They are different application level protocols, period.