snapTools.makeSnap: init

doc/functions.xml

@@ -16,6 +16,7 @@
  <xi:include href="functions/fhs-environments.xml" />
  <xi:include href="functions/shell.xml" />
  <xi:include href="functions/dockertools.xml" />
+ <xi:include href="functions/snaptools.xml" />
  <xi:include href="functions/appimagetools.xml" />
  <xi:include href="functions/prefer-remote-fetch.xml" />
  <xi:include href="functions/nix-gitignore.xml" />

doc/functions/snaptools.xml

@@ -0,0 +1,74 @@
+<section xmlns="http://docbook.org/ns/docbook"
+         xmlns:xlink="http://www.w3.org/1999/xlink"
+         xmlns:xi="http://www.w3.org/2001/XInclude"
+         xml:id="sec-pkgs-snapTools">
+ <title>pkgs.snapTools</title>
+
+ <para>
+  <varname>pkgs.snapTools</varname> is a set of functions for creating
+  Snapcraft images. Snap and Snapcraft is not used to perform these operations.
+ </para>
+
+ <section xml:id="ssec-pkgs-snapTools-makeSnap-signature">
+  <title>The makeSnap Function</title>
+
+  <para>
+   <function>makeSnap</function> takes a single named argument,
+   <parameter>meta</parameter>. This argument mirrors
+   <link xlink:href="https://docs.snapcraft.io/snap-format">the upstream
+   <filename>snap.yaml</filename> format</link> exactly.
+  </para>
+
+  <para>
+   The <parameter>base</parameter> should not be be specified, as
+   <function>makeSnap</function> will force set it.
+  </para>
+
+  <para>
+   Currently, <function>makeSnap</function> does not support creating GUI
+   stubs.
+  </para>
+ </section>
+
+ <section xml:id="ssec-pkgs-snapTools-build-a-snap-hello">
+  <title>Build a Hello World Snap</title>
+
+  <example xml:id="ex-snapTools-buildSnap-hello">
+   <title>Making a Hello World Snap</title>
+   <para>
+    The following expression packages GNU Hello as a Snapcraft snap.
+   </para>
+<programlisting><xi:include href="../../pkgs/build-support/snap/example-hello.nix" parse="text" /></programlisting>
+   <para>
+    <command>nix-build</command> this expression and install it with
+    <command>snap install ./result --dangerous</command>.
+    <command>hello</command> will now be the Snapcraft version of the package.
+   </para>
+  </example>
+ </section>
+
+ <section xml:id="ssec-pkgs-snapTools-build-a-snap-firefox">
+  <title>Build a Hello World Snap</title>
+
+  <example xml:id="ex-snapTools-buildSnap-firefox">
+   <title>Making a Graphical Snap</title>
+   <para>
+    Graphical programs require many more integrations with the host. This
+    example uses Firefox as an example, because it is one of the most
+    complicated programs we could package.
+   </para>
+<programlisting><xi:include href="../../pkgs/build-support/snap/example-firefox.nix" parse="text" /></programlisting>
+   <para>
+    <command>nix-build</command> this expression and install it with
+    <command>snap install ./result --dangerous</command>.
+    <command>nix-example-firefox</command> will now be the Snapcraft version of
+    the Firefox package.
+   </para>
+   <para>
+    The specific meaning behind plugs can be looked up in the
+    <link xlink:href="https://docs.snapcraft.io/supported-interfaces">Snapcraft
+    interface documentation</link>.
+   </para>
+  </example>
+ </section>
+</section>

pkgs/build-support/snap/default.nix

@@ -0,0 +1,4 @@
+{ callPackage, hello }:
+{
+  makeSnap = callPackage ./make-snap.nix { };
+}

pkgs/build-support/snap/example-firefox.nix

@@ -0,0 +1,28 @@
+let
+  inherit (import <nixpkgs> { }) snapTools firefox;
+in snapTools.makeSnap {
+  meta = {
+    name = "nix-example-firefox";
+    summary = firefox.meta.description;
+    architectures = [ "amd64" ];
+    apps.nix-example-firefox = {
+      command = "${firefox}/bin/firefox";
+      plugs = [
+        "pulseaudio"
+        "camera"
+        "browser-support"
+        "avahi-observe"
+        "cups-control"
+        "desktop"
+        "desktop-legacy"
+        "gsettings"
+        "home"
+        "network"
+        "mount-observe"
+        "removable-media"
+        "x11"
+      ];
+    };
+    confinement = "strict";
+  };
+}

pkgs/build-support/snap/example-hello.nix

@@ -0,0 +1,12 @@
+let
+  inherit (import <nixpkgs> { }) snapTools hello;
+in snapTools.makeSnap {
+  meta = {
+    name = "hello";
+    summary = hello.meta.description;
+    description = hello.meta.longDescription;
+    architectures = [ "amd64" ];
+    confinement = "strict";
+    apps.hello.command = "${hello}/bin/hello";
+  };
+}

pkgs/build-support/snap/make-snap.nix

@@ -0,0 +1,84 @@
+{
+  runCommand, squashfsTools, closureInfo, lib, jq, writeText
+}:
+
+{
+  # The meta parameter is the contents of the `snap.yaml`, NOT the
+  # `snapcraft.yaml`.
+  #
+  # - `snap.yaml` is what is inside of the final Snap,
+  # - `snapcraft.yaml` is used by `snapcraft` to build snaps
+  #
+  # Since we skip the `snapcraft` tool, we skip the `snapcraft.yaml`
+  # file. For more information:
+  #
+  #   https://docs.snapcraft.io/snap-format
+  #
+  # Note: unsquashfs'ing an existing snap from the store can be helpful
+  # for determining what you you're missing.
+  #
+  meta
+}: let
+    snap_yaml = let
+      # Validate the snap's meta contains a name.
+      # Also: automatically set the `base` parameter and the layout for
+      # the `/nix` bind.
+      validate = { name, ... } @ args:
+        args // {
+          # Combine the provided arguments with the required options.
+
+          # base: built from https://github.com/NixOS/snapd-nix-base
+          # and published as The NixOS Foundation on the Snapcraft store.
+          base = "nix-base";
+          layout = (args.layout or {}) // {
+            # Bind mount the Snap's root nix directory to `/nix` in the
+            # execution environment's filesystem namespace.
+            "/nix".bind = "$SNAP/nix";
+          };
+        };
+    in writeText "snap.yaml"
+      (builtins.toJSON (validate meta));
+
+  # These are specifically required by snapd, so don't change them
+  # unless you've verified snapcraft / snapd can handle them. Best bet
+  # is to just mirror this list against how snapcraft creates images.
+  # from: https://github.com/snapcore/snapcraft/blob/b88e378148134383ffecf3658e3a940b67c9bcc9/snapcraft/internal/lifecycle/_packer.py#L96-L98
+  mksquashfs_args = [
+    "-noappend" "-comp" "xz" "-no-xattrs" "-no-fragments"
+
+    # Note: We want -all-root every time, since all the files are
+    # owned by root anyway. This is true for Nix, but not true for
+    # other builds.
+    # from: https://github.com/snapcore/snapcraft/blob/b88e378148134383ffecf3658e3a940b67c9bcc9/snapcraft/internal/lifecycle/_packer.py#L100
+    "-all-root"
+  ];
+
+in runCommand "squashfs.img" {
+  nativeBuildInputs = [ squashfsTools jq ];
+
+  closureInfo = closureInfo {
+    rootPaths = [ snap_yaml ];
+  };
+} ''
+  root=$PWD/root
+  mkdir $root
+
+  (
+    # Put the snap.yaml in to `/meta/snap.yaml`, setting the version
+    # to the hash part of the store path
+    mkdir $root/meta
+    version=$(echo $out | cut -d/ -f4 | cut -d- -f1)
+    cat ${snap_yaml} | jq  ". + { version: \"$version\" }" \
+      > $root/meta/snap.yaml
+  )
+
+  (
+    # Copy the store closure in to the root
+    mkdir -p $root/nix/store
+    cat $closureInfo/store-paths | xargs -I{} cp -r {} $root/nix/store/
+  )
+
+  # Generate the squashfs image.
+  mksquashfs $root $out \
+    ${lib.concatStringsSep " " mksquashfs_args}
+''

pkgs/top-level/all-packages.nix

@@ -175,6 +175,8 @@ in
 
   dockerTools = callPackage ../build-support/docker { };
 
+  snapTools = callPackage ../build-support/snap { };
+
   nix-prefetch-docker = callPackage ../build-support/docker/nix-prefetch-docker.nix { };
 
   docker-compose = python3Packages.callPackage ../applications/virtualization/docker-compose {};