# Ideas for future development

Patches welcome.

## Properties

- Custom Emacs indentation rules for `DISK:VOLUMES` (and so `DISK:HAS-VOLUMES`), and reindent the examples in docstrings and manual.

## Connections

- Basic infrastructure for connections which work with just input and output streams connected to an interactive POSIX sh somewhere, like TRAMP, and probably using `base64 -d` for WRITE-REMOTE-FILE. Probably the basic connection type will take a command to start up the shell as a keyword argument, and then we can have more specific connection types which take other arguments and construct the full command.

- It might be possible to write an implementation of CONNECTION-UPLOAD for SSH-CONNECTION which can optimise a common case. If it can see that it is the only item in the connection chain, and there is an old version of an item of prerequisite data to upload already on the remote side, it can move that old version to a temporary name, rsync the new version directly to the temporary name so that rsync can do an incremental update, and then rename the file to the new version.

- It would sometimes be useful to have the SSH connection pass `-oHostName=<known IP address>` when `NETWORK:IPV4` and/or `NETWORK:IPV6` have been specified for the host, so that DNS propagation is less likely to get in the way of configuring the host. Some hosts’ SSH daemons might only be accessible over VPNs and the like, however, so it will need to be easy to override this.

- Perhaps `:SSH` ought to enable connection sharing (including `ControlPersist`) on the user’s behalf, rather than relying on users adding this to `~/.ssh/config`.

## Core

- We signal a warning whenever the contents of a property’s function cell is called when that property has a :HOSTATTRS subroutine. Could we figure out catching and muffling the warning when the :HOSTATTRS subroutine did get run?

- A CONCURRENTLY combinator for property application specifications, which means to apply each of the enclosed properties in parallel. Particularly useful surrounding a set of DEPLOYS applications, to concurrently deploy a number of hosts. Now that we don’t call fork(2) while executing deployments, we ought to be able to do this using threads, and so it can work in the root Lisp too. However, we still use `WITH-CURRENT-DIRECTORY` in various places, and temporarily set HOME in `WITH-HOMEDIR`. Perhaps `WITH-CURRENT-DIRECTORY` could be changed to only affect RUN, MRUN etc. for the sake of enabling multithreading.

- It might be useful to have a restart for the case where an attempt is made to apply a list of properties containing some `:LISP` properties with a POSIX-type connection which applies properties up to but not including the first `:LISP` property in the sequence, to get as much work as possible done without violating any dependency relationships (`SEQPROPS` already handles wanting to apply all of the `:POSIX` properties in the sequence). But maybe this is unnecessarily complex – wouldn’t it be better to just fail and fix your deployment definitions?

- Combinator WITH-REQUIREMENTS-FOR-CHANGE to only apply dependencies if the first property’s :CHECK routine indicates that a change it needed. For example, if the chroot already exists, we don’t attempt to install debootstrap. (The `SBCL-AVAILABLE` property in `src/connection/sbcl.lisp` achieves a similar effect in another way.)

- We might want `DEPLOYS`, `DEPLOYS-THESE` to push the host object to the parent host’s hostattrs, under `:CHILD-HOSTS` or something. This means that hosts implicitly defined inline using dotted propapp notation are accessible via their parents, so that a property which gathers up DNS information about all hosts, for example, would be able to find them.

- At debug level 2, when WRITE-REMOTE-FILE makes a change, it could print a diff/patch to show what it did.