servant-http2-client
This package provides a way to generate HTTP2 client code from Servant API descriptions.
Please consider this package somewhat unstable. The author would appreciate feedbacks and benchmarks in real-world deployments.
Usage
The usage is pretty similar to servant-client
but uses an HTTP2Client rather
than a Manager. See also the section below to highlight differences between
servant-client
and servant-http2-client
.
HTTP2 uses a flow-control mechanism, which http2-client
exposes but
servant-http2-client
hides: as a client you have nothing to do and
DATA-credit is immediately sent to the server. This mechanism is easy for the
user but effectively disables flow control at the application level. Further,
this easy-to-use mechanism may have some slight overhead for sending many small
control frames. Future version of the library will expose more control points
(at an increased cost).
You can find a full example at ./test/Spec.hs
.
Differences with servant-client
The client leverages http2-client
and hence behave slightly differently from
servant-client
, which uses http-client
. Most notably, HTTP/2 uses a single
TCP connection for performing concurrent requests, whereas HTTP/1.x at best
pipelines request sequentially over a same connection.
The servant-client
library uses a connection Manager to create new TCP
connections or try re-using existing connections. This servant-http2-client
makes no use of such a Manager. This difference is mostly important for
load-balancing and unstable network environments. When targeting a
load-balanced server, a servant-http2-client
will always hit the same
TCP-endpoint whereas a servant-client
may hit different TCP-endpoint for each
request. Also, after handling a connection error, a servant-client
will open
a new TCP connection without any decision from the programmer. Conversely, a
broken servant-http2-client
will be of no practical use and the programmer
must create a new H2ClientEnv. A Manager abstraction may be added to
http2-client
later.
The servant-client
package offers Cookies handling, whereas
servant-http2-client
has no such feature. Please consider opening a
pull-request for adding the support.
Finally, it's always good to remember that HTTP2 allows concurrent queries, that is, many API calls may fail when a single TCP connection dies out.