package httpaf-async

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Published: 13 Jan 2018



http/af is a high-performance, memory-efficient, and scalable web server for OCaml. It implements the HTTP 1.1 specification with respect to parsing, serialization, and connection pipelining as a state machine that is agnostic to the underlying IO mechanism, and is therefore portable across many platform. It uses the Angstrom and Faraday libraries to implement the parsing and serialization layers of the HTTP standard, hence the name.


Install the library and its dependencies via OPAM:

opam install httpaf


The reason for http/af's existence is mirage/ocaml-cohttp#328, which highlights the poor scalability of cohttp. This is due to a number of factors, including poor scheduling, excessive allocation, and starvation of the server's accept loop. Here is a comparison chart of the data from that issue, along with data from an async-based http/af server. This server was run on a VM with 3 virtual cores, the host being circa 2015 MacBook Pro:

The http/af latency histogram, relative to the cohttp histograms, is pretty much flat along the x-axis. Here are some additional statistics from that run (with latencies in milliseconds):

#[Mean    =       27.719, StdDeviation   =       31.570]
#[Max     =      263.424, Total count    =      1312140]
#[Buckets =           27, SubBuckets     =         2048]
  1709909 requests in 1.00m, 3.33GB read




To install development dependencies, pin the package from the root of the repository:

opam pin add -n httpaf .
opam install --deps-only httpaf

After this, you may install a development version of the library using the install command as usual.

Tests can be run via jbuilder:

jbuilder runtest


BSD3, see LICENSE files for its text.

Dependencies (6)

  1. httpaf <= "0.2.0"
  2. async < "v0.13"
  3. faraday-async
  4. angstrom-async < "0.9.0"
  5. jbuilder >= "1.0+beta10"
  6. ocaml >= "4.03.0"

Dev Dependencies


Used by