SecondTransfer is a HTTP/1.1 and HTTP/2 server session library, with an emphasis towards experimentation (so far).

This library implements enough of the HTTP/2 to build compliant HTTP/2 servers. It also implements enough of HTTP/1.1 so you can actually use it to build polyglot web-servers.

For HTTP/2, frame encoding and decoding is done with Kazu Yamamoto's http2 package. This library just takes care of making sense of sent and received frames.

The library

• Is concurrent, meaning that you can use amazing Haskell lightweight threads to process the requests.
• Obeys HTTP2 flow control aspects, when talking HTTP2.
• And gives you freedom to (ab)use the HTTP/2 protocol in all the ways envisioned by the standard. In particular you should be able to process streaming requests (long uploads in POST or PUT requests) and to deliver streaming responses. You should even be able to do both simultaneously.

Setting up TLS for HTTP/2 correctly is a shore, so we have bundled here the TLS setup logic. Enable always the threaded ghc runtime in your final programs if you want TLS to work.

Here is how you create a very basic HTTP/2 webserver:

import SecondTransfer(
    AwareWorker
    , Footers
    , DataAndConclusion
    , tlsServeWithALPN
    , http2Attendant
    , http11Attendant
    , coherentToAwareWorker
    )
import SecondTransfer.Sessions(
      makeSessionsContext
    , defaultSessionsConfig
    )

import Data.Conduit


saysHello :: DataAndConclusion
saysHello = do
    -- The data in each yield will be automatically split across multiple
    -- data frames if needed, so you can yield a large block of contents here
    -- if you wish.
    -- If you do multiple yields, no data will be left buffered between them,
    -- so that you can for example implement a chat client in a single HTTP/2 stream.
    -- Not that browsers support that. 
    yield "Hello world!"
    -- The HTTP/2 protocol supports sending headers *after* stream data. So, you usually
    -- return an empty list to signal that you don't want any of those headers. 
    -- In these docs, the post headers are often called "footers".
    return []


helloWorldWorker :: AwareWorker
helloWorldWorker (_request_headers, _maybe_post_data) = coherentToAwareWorker $ do
    dropIncomingData _maybe_post_data
    return (
        [
            (":status", "200")
        ],
        [], -- No pushed streams
        saysHello
        )


-- For this program to work, it should be run from the top of
-- the developement directory.
main = do
    sessions_context <- makeSessionsContext defaultSessionsConfig
    let
        http2_attendant = http2Attendant sessions_context helloWorldWorker
        http11_attendant = http11Attendant sessions_context helloWorldWorker
    tlsServeWithALPN
        "tests/support/servercert.pem"   -- Server certificate
        "tests/support/privkey.pem"      -- Certificate private key
        "127.0.0.1"                      -- On which interface to bind
        [
            ("no-protocol", http11_attendant), -- The first protocol in the list is used when
                                               -- when no ALPN negotiation happens, and the
                                               -- name is really a filler.
            ("h2-14", http2_attendant),    -- Protocols present in the ALPN negotiation
            ("h2",    http2_attendant),    -- they may be slightly different, but for this
                                           -- test it doesn't matter.

            ("http1.1", http11_attendant) -- Let's talk HTTP1.1 if everything else fails.
        ]
        8000

AwareWorker is the type of the basic callback function that you need to implement, but most times you can do with a simplified version called CoherentWorker. The function coherentToAwareWorker does the conversion. The difference between the two callbacks is the level of information that you manage. With AwareWorker, you get a record on the request with all sort of details, things like the session id, the protocol the client is using and in the future things like the remote address.

The callback is used to handle all requests to the server on a given negotiated ALPN protocol. If you need routing functionality (and you most certainly will need it), you need to build that functionality inside the callback.

The above program uses a test certificate by a fake certificate authority. The certificate is valid for the server name ("authority", in HTTP/2 lingo) www.httpdos.com. So, in order for the above program to run, you probably need to add an alias to your /etc/hosts file. You also need very up-to-date versions of OpenSSL (I'm using OpenSSL 1.0.2) to be compliant with the cipher suites demanded by HTTP/2. The easiest way to test the above program is using a fairly recent version of curl. If everything is allright, you should be able to do:

   $ curl -k --http2 https://www.httpdos.com:8000/
   Hello world!

A coherent worker is an abstraction that can dance at the tune of HTTP2 and HTTP1.1. That is, it should be able to take headers from a request first, then a source of data coming in the request (for example, POST data). Even before exhausting the source, the coherent worker can post the response headers and its source for the response data. A coherent worker can also present streams to push to the client.

Use these functions to create your TLS-compliant HTTP/2 server in a snap.