readme: how to update inputs of this flake

README.md

@@ -1,67 +1,70 @@
 # SelfPrivacy NixOS configuration
 
-This is a NixOS config which builds a SelfPrivacy server distribution
+This configuration is not self-contained, as it needs to be plugged as an input of a top-level NixOS configuration flake (i.e. https://git.selfprivacy.org/SelfPrivacy/selfprivacy-nixos-template/). This flake outputs the following function:
-based on data provided in `userdata/userdata.json`.
+```nix
+nixosConfigurations-fun =
+  { hardware-configuration # hardware-configuration.nix file
+  , deployment             # deployment.nix file
+  , userdata               # nix attrset, obtained by fromJSON from userdata.json
+  , top-level-flake        # `self`-reference of the top-level flake
+  , sp-modules             # flake inputs of sp-modules flake
+  }:
+```
+which returns one or more attributes, containing NixOS configurations (created with `nixpkgs.lib.nixosSystem`). (As of 2024-01-10 there is only a single configuration named `default`.)
 
-JSON schema is provided in `userdata/schema.json` for reference.
+## updating flake inputs
 
-**hardware-configuration.nix is not included.**
+We have 2 flake inputs:
+- nixpkgs
+- selfprivacy-api
 
-Example JSON config:
+Both get updated the same ways.
 
-```json
+There are 2 methods:
-{
+1. specify input name only in a command, relying on URL inside `flake.nix`
-    "backblaze": {
+2. specify input name and URL in a command, **overriding** whatever URL is inside `flake.nix` for the input to update (override)
-        "accountId": "BACKBLAZE_KEY_ID",
+
-        "accountKey": "BACKBLAZE_ACCOUNT_KEY",
+In any case a Nix flake input is specified using some special _references_ syntax, including URLs, revisions, etc, described in manual: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#examples. Such reference can be used inside `flake.nix` or as an argument to `nix flake` commands. When a new reference is encountered Nix downloads and extracts it to /nix/store.
-        "bucket": "BACKBLAZE_BUCKET_NAME"
+
-    },
+Before and after running `nix flake lock` (or `nix flake update`) commands you would most likely want to list current inputs using `nix flake metadata`, which are read from `flake.lock` file. Although, Nix should also print a diff between changed referrences once changed.
-    "api": {
+
-        "token": "API_TOKEN",
+`--commit-lock-file` option tells Nix commands to do `git commit flake.lock` automatically, creating a new commit for you.
-        "enableSwagger": false
+
-    },
+### method 1: update specific input
-    "bitwarden": {
+
-        "enable": true
+Example:
-    },
+```console
-    "cloudflare": {
+$ nix flake lock --update-input nixpkgs
-        "apiKey": "CF_TOKEN"
+$ nix flake lock --update-input selfprivacy-api
-    },
+```
-    "databasePassword": "DB_PASSWORD",
+
-    "domain": "DOMAIN",
+Depending on how "precise" the URL was speficied in `flake.nix`, with _unmodified_ `flake.nix` the result might be:
-    "hashedMasterPassword": "HASHED_PASSWORD",
+* URL with `rev` (sha1) parameter => nothing will update (as we're already at exact commit)
-    "hostname": "DOMAIN",
+* URL with `ref` (branch) parameter => input will update to the latest commit of the specified branch
-    "nextcloud": {
+* URL without `rev` nor `ref` => input will update to the latest commit of a default branch!
-        "enable": true,
+
-        "adminPassword": "PASSWORD",
+---
-        "databasePassword": "PASSWORD"
+
-    },
+Once Nix 2.19 stabilizes, a different command _must_ be used for updating a single input, like this:
-    "gitea": {
+```console
-        "enable": true
+$ nix flake update nixpkgs
-    },
+```
-    "jitsi": {
+
-        "enable": true
+
-    },
+### method 2: override specific input
-    "ocserv": {
+
-        "enable": true
+Overriding is more powerful as it allows to change flake input reference to anything just in one command (not only update in the bounds of a branch or a repository).
-    },
+
-    "pleroma": {
+Example:
-        "enable": true
+```console
-    },
+$ nix flake lock --override-input nixpkgs github:nixos/nixpkgs?ref=nixos-23.11
-    "timezone": "Europe/Moscow",
+$ nix flake lock --override-input selfprivacy-api git+https://git.selfprivacy.org/SelfPrivacy/selfprivacy-rest-api.git?ref=flakes
-    "resticPassword": "PASSWORD",
+```
-    "ssh": {
+
-        "enable": true,
+Similarly to update mechanism (described above), depending on the "precision" of an URL, its update scope varies.
-        "rootSshKeys": [
+
-            "ssh-ed25519 KEY user@host"
+Note, that subsequent calls of `nix flake lock --update-input <INPUT>` or `nix flake update` (or `nix flake update INPUT` by Nix 2.19+) will update the input regardless of the prior override. The information about override is stored only in `flake.lock` (`flake.nix` is not altered by Nix).
-        ],
+
-        "passwordAuthentication": true
+---
-    },
+
-    "username": "LUSER",
+Note, that override does not update flake inputs recursively (say, you have a flake inside your flake input). For recursive updates only `nix flake lock --update-input` and `nix flake update` mechanisms are suitable. However, as of 2024-01-10 none of the current inputs contain other flakes, hence override mechanism is fine.
-    "users": [
-        {
-            "hashedPassword": "OTHER_USER_HASHED_PASSWORD",
-            "username": "OTHER_USER"
-        }
-    ]
-}
-```