detsys-srv 0.4.0

Rust client for communicating with SRV-located services
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# detsys-srv

[![Test Status](https://github.com/DeterminateSystems/detsys-srv/workflows/Rust/badge.svg?event=push)](https://github.com/DeterminateSystems/detsys-srv/actions)
[![Crate](https://img.shields.io/crates/v/detsys-srv.svg)](https://crates.io/crates/detsys-srv)

Rust client for communicating with services located by DNS SRV records.

## Introduction

SRV Records, as defined in [RFC 2782](https://tools.ietf.org/html/rfc2782),
are DNS records of the form

`_Service._Proto.Name TTL Class SRV Priority Weight Port Target`

For instance, a DNS server might respond with the following SRV records for
`_http._tcp.example.com`:

```
_http._tcp.example.com. 60 IN SRV 1 100 443 test1.example.com.
_http._tcp.example.com. 60 IN SRV 2 50  443 test2.example.com.
_http._tcp.example.com. 60 IN SRV 2 50  443 test3.example.com.
```

A client wanting to communicate with this example service would first try to
communicate with `test1.example.com:443` (the record with the lowest
priority), then with the other two (in a random order, since they are of the
same priority) should the first be unavailable.

`detsys-srv` handles the lookup and caching of SRV records as well as the ordered
selection of targets to use for communication with SRV-located services.

[`SrvClient::new`] creates a client (that should be reused to take advantage of
caching) for communicating with the service located by `_http._tcp.example.com`.
[`SrvClient::execute`] takes in a future-producing closure (emulating async
closures, which are currently unstable) and executes the closure on a series of
targets parsed from the discovered SRV records, stopping and returning the
first `Ok` or last `Err` it obtains.

## Alternative Resolvers and Target Selection Policies

`detsys-srv` provides multiple resolver backends for SRV lookup and by default uses
a target selection policy that maintains affinity for the last target it has
used successfully. Both of these behaviors can be changed by implementing the
[`SrvResolver`] and [`Policy`] traits, respectively.


[`SrvResolver`]: resolver::SrvResolver
[`Policy`]: policy::Policy


## Contributing

1. Clone the repo
2. Make some changes
3. Test: `cargo test`
4. Format: `cargo fmt`
5. Clippy: `cargo clippy --tests -- -Dclippy::all`
6. If modifying crate-level docs (`src/lib.rs`) or `README.tpl`, update `README.md`:
    1. `cargo install cargo-readme`
    2. `cargo readme > README.md`

## History

Forked from https://github.com/deshaw/srv-rs/.