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At present, `connlib` only supports DNS over UDP on port 53. Responses
over UDP are size-constrained on the IP MTU and thus, not all DNS
responses fit into a UDP packet. RFC9210 therefore mandates that all DNS
resolvers must also support DNS over TCP to overcome this limitation
[0].
Handling UDP packets is easy, handling TCP streams is more difficult
because we need to effectively implement a valid TCP state machine.
Building on top of a lot of earlier work (linked in issue), this is
relatively easy because we can now simply import
`dns_over_tcp::{Client,Server}` which do the heavy lifting of sending
and receiving the correct packets for us.
The main aspects of the integration that are worth pointing out are:
- We can handle at most 10 concurrent DNS TCP connections _per defined
resolver_. The assumption here is that most applications will first
query for DNS records over UDP and only fall back to TCP if the response
is truncated. Additionally, we assume that clients will close the TCP
connections once they no longer need it.
- Errors on the TCP stream to an upstream resolver result in `SERVFAIL`
responses to the client.
- All TCP connections to upstream resolvers get reset when we roam, all
currently ongoing queries will be answered with `SERVFAIL`.
- Upon network reset (i.e. roaming), we also re-allocate new local ports
for all TCP sockets, similar to our UDP sockets.
Resolves: #6140.
[0]: https://www.ietf.org/rfc/rfc9210.html#section-3-5
Firezone shell scripts
This directory contains various shell scripts used for development, testing, and deployment of the Firezone product.
Developer Setup
We lint shell scripts in CI. To get your PR to pass, you'll want to ensure your local development environment is set up to lint shell scripts:
- Install
shfmt:brew install shfmton macOS- Install shfmt from https://github.com/mvdan/sh/releases for other platforms
- Install
shellcheck:brew install shellcheckon macOSsudo apt-get install shellcheckon Ubuntu
Then just lint and format your shell scripts before you commit:
shfmt -i 4 **/*.sh
shellcheck --severity=warning **/*.sh
You can achieve this more easily by using pre-commit. See
CONTRIBUTING.
Editor setup
- Vim (here's an example using ALE)
- VSCode
Scripting tips
- Use
#!/usr/bin/env bashalong withset -euox pipefailin general for dev and test scripts. - In Docker images and other minimal envs, stick to
#!/bin/shand simplyset -eu.