nixos/kubo: make the configuration options idempotent

Without this commit, unsetting any of the `services.kubo.settings` options does not reset the value back to the default. This commit gets rid of this statefulness.
This is achieved by generating the default config, applying the user specified config options to it and then patching the `Identity` and `Pinning` config options from the old config back in. This new config is then applied using `ipfs config replace`.
The only remaining stateful parts of the config are the `Identity` and `Pinning.RemoteServices` settings as those can't be changed with `ipfs config replace`. `Pinning.RemoteServices` also contains secrets that shouldn't be in the Nix store. Setting these options wasn't possible before as it would result in an error when the daemon tried to start. I added some assertions to guard against this case.

nixos/doc/manual/from_md/release-notes/rl-2305.section.xml

@@ -209,6 +209,18 @@
           to upgrade existing repositories.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The <literal>services.kubo.settings</literal> option is now no
+          longer stateful. If you changed any of the options in
+          <literal>services.kubo.settings</literal> in the past and then
+          removed them from your NixOS configuration again, those
+          changes are still in your Kubo configuration file but will now
+          be reset to the default. If you’re unsure, you may want to
+          make a backup of your configuration file (probably
+          /var/lib/ipfs/config) and compare after the update.
+        </para>
+      </listitem>
       <listitem>
         <para>
           The EC2 image module no longer fetches instance metadata in

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -60,6 +60,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - `git-bug` has been updated to at least version 0.8.0, which includes backwards incompatible changes. The `git-bug-migration` package can be used to upgrade existing repositories.
 
+- The `services.kubo.settings` option is now no longer stateful. If you changed any of the options in `services.kubo.settings` in the past and then removed them from your NixOS configuration again, those changes are still in your Kubo configuration file but will now be reset to the default. If you're unsure, you may want to make a backup of your configuration file (probably /var/lib/ipfs/config) and compare after the update.
+
 - The EC2 image module no longer fetches instance metadata in stage-1. This results in a significantly smaller initramfs, since network drivers no longer need to be included, and faster boots, since metadata fetching can happen in parallel with startup of other services.
   This breaks services which rely on metadata being present by the time stage-2 is entered. Anything which reads EC2 metadata from `/etc/ec2-metadata` should now have an `after` dependency on `fetch-ec2-metadata.service`
 

nixos/modules/services/network-filesystems/kubo.nix

@@ -5,6 +5,23 @@ let
 
   settingsFormat = pkgs.formats.json {};
 
+  rawDefaultConfig = lib.importJSON (pkgs.runCommand "kubo-default-config" {
+    nativeBuildInputs = [ cfg.package ];
+  } ''
+    export IPFS_PATH="$TMPDIR"
+    ipfs init --empty-repo --profile=${profile}
+    ipfs --offline config show > "$out"
+  '');
+
+  # Remove the PeerID (an attribute of "Identity") of the temporary Kubo repo.
+  # The "Pinning" section contains the "RemoteServices" section, which would prevent
+  # the daemon from starting as that setting can't be changed via ipfs config replace.
+  defaultConfig = builtins.removeAttrs rawDefaultConfig [ "Identity" "Pinning" ];
+
+  customizedConfig = lib.recursiveUpdate defaultConfig cfg.settings;
+
+  configFile = settingsFormat.generate "kubo-config.json" customizedConfig;
+
   kuboFlags = utils.escapeSystemdExecArgs (
     optional cfg.autoMount "--mount" ++
     optional cfg.enableGC "--enable-gc" ++
@@ -161,9 +178,9 @@ in
           };
         };
         description = lib.mdDoc ''
-          Attrset of daemon configuration to set using {command}`ipfs config`, every time the daemon starts.
+          Attrset of daemon configuration.
           See [https://github.com/ipfs/kubo/blob/master/docs/config.md](https://github.com/ipfs/kubo/blob/master/docs/config.md) for reference.
-          Keep in mind that this configuration is stateful; i.e., unsetting anything in here does not reset the value to the default!
+          You can't set `Identity` or `Pinning`.
         '';
         default = { };
         example = {
@@ -211,6 +228,21 @@ in
   ###### implementation
 
   config = mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = !builtins.hasAttr "Identity" cfg.settings;
+        message = ''
+          You can't set services.kubo.settings.Identity because the ``config replace`` subcommand used at startup does not support modifying any of the Identity settings.
+        '';
+      }
+      {
+        assertion = !((builtins.hasAttr "Pinning" cfg.settings) && (builtins.hasAttr "RemoteServices" cfg.settings.Pinning));
+        message = ''
+          You can't set services.kubo.settings.Pinning.RemoteServices because the ``config replace`` subcommand used at startup does not work with it.
+        '';
+      }
+    ];
+
     environment.systemPackages = [ cfg.package ];
     environment.variables.IPFS_PATH = cfg.dataDir;
 
@@ -262,21 +294,26 @@ in
 
       preStart = ''
         if [[ ! -f "$IPFS_PATH/config" ]]; then
-          ipfs init ${optionalString cfg.emptyRepo "-e"} --profile=${profile}
+          ipfs init ${optionalString cfg.emptyRepo "-e"}
         else
           # After an unclean shutdown this file may exist which will cause the config command to attempt to talk to the daemon. This will hang forever if systemd is holding our sockets open.
           rm -vf "$IPFS_PATH/api"
       '' + optionalString cfg.autoMigrate ''
         ${pkgs.kubo-migrator}/bin/fs-repo-migrations -to '${cfg.package.repoVersion}' -y
       '' + ''
-          ipfs --offline config profile apply ${profile} >/dev/null
         fi
-      '' + ''
-        ipfs --offline config show \
-          | ${pkgs.jq}/bin/jq '. * $settings' --argjson settings ${
-              escapeShellArg (builtins.toJSON cfg.settings)
-            } \
-          | ipfs --offline config replace -
+        ipfs --offline config show |
+          ${pkgs.jq}/bin/jq -s '.[0].Pinning as $Pinning | .[0].Identity as $Identity | .[1] + {$Identity,$Pinning}' - '${configFile}' |
+
+          # This command automatically injects the private key and other secrets from
+          # the old config file back into the new config file.
+          # Unfortunately, it doesn't keep the original `Identity.PeerID`,
+          # so we need `ipfs config show` and jq above.
+          # See https://github.com/ipfs/kubo/issues/8993 for progress on fixing this problem.
+          # Kubo also wants a specific version of the original "Pinning.RemoteServices"
+          # section (redacted by `ipfs config show`), such that that section doesn't
+          # change when the changes are applied. Whyyyyyy.....
+          ipfs --offline config replace -
       '';
       serviceConfig = {
         ExecStart = [ "" "${cfg.package}/bin/ipfs daemon ${kuboFlags}" ];