burgerdev/ocaml-addressmapper-devel repository overview

⁠OCaml-AddressMapper

Implementation of a postfix tcp lookup table⁠ that transforms the requested address according to a configurable set of mapping rules. A common use case is to transform an address to a canonical form.

Built-in mapping rules are accept, reject, match a regular expression and replace a regular expression with a fixed string. Those can be combined with all and first. Additionally, you can use the case transforming rules lower and upper. The mapping rules are specified as S-expressions:

(
 (matches "^.*@example.com$")
 (replace "+[^@]*@" "@")
)

This accepts emails for domain example.com and removes a sub-address (the plus part).

⁠Build

⁠Prerequisites

• Ocaml >= 4.04.2
• Opam

⁠Build on Host

make fetch_deps # installs dependencies using opam
make all

⁠Build in Development Container

There's a special docker image⁠ for building this project. Run the above commands inside the container, or use the docker-build.sh script. The latter builds the development image, compiles the OCaml sources, runs tests (triggered by environment variable CI) and builds the production image.

export CI=true
bash docker-build.sh alpine

⁠Run

./main.native --help

Command line arguments:

• -r <file> path to the rules file on the container (default: /rules/rules.sexp)
• -b <address> IP address to bind to (default: 127.0.0.1)
• -p <port> listening port (default: 30303)
• -u re-read the rules file for each request (default: false)

⁠Docker Image

Run the AddressMapper as a docker container in the background, forward the port to localhost:30303 and use the rules file /tmp/rules.sexp below.

docker run -d -p 30303:30303 -v /tmp/rules.sexp:/rules.sexp:ro burgerdev/ocaml-addressmapper

(
  (lower (replace "+[^@]*@" "@"))

  (not (prefix_matches "sauron"))

  (first
    (
      (
        (matches "^[^@]+@business\.com$")
        (first ((matches "^ceo@.*")
                (matches "^pr@.*"))
        )
      )
      (equals "[email protected]")
    )
  )
)

This file contains the following instructions (see configuration.md⁠ for an explanation of the addressmapper rules):

1. Address sanitizing.
   1. Convert the email address to lower case.
   2. Strip the sub-addresses⁠.
2. Keep Sauron on the far side of the walls.
3. User database. If any of the sub-clauses matches, we got our user.
   1. There are two acceptable users at business.com, the CEO and the Public Relations Department.
   2. The non-profit organization has just one email address, which is reserved for raising funds.

Let's see some examples for how to use the container we spawned:

echo "get [email protected]" | nc localhost 30303
# we convert everything to lower case, so the result should be
# '200 [email protected]'.

echo "get [email protected]" | nc localhost 30303
echo "get [email protected]" | nc localhost 30303
# Both with and without a sub-address, this should result in
# '200 [email protected]'.

echo "get [email protected]" | nc localhost 30303
# Sauron is explicitly excluded, this should be '500 not-found'.

echo "put [email protected]" | nc localhost 30303
# This is not valid postfix mapper syntax, therefore '400 malformed request'.