Merge pull request #939 from ibizaman/networking_hosts

Add networking.hosts and .hostFiles from nixos

.github/workflows/test.yml

@@ -47,12 +47,14 @@ jobs:
         sudo cp modules/examples/simple.nix /etc/nix-darwin/configuration.nix
 
         nixConfHash=$(shasum -a 256 /etc/nix/nix.conf | cut -d ' ' -f 1)
+        etcHostsHash=$(shasum -a 256 /etc/hosts | cut -d ' ' -f 1)
         sudo /usr/bin/sed -i.bak \
           "s/# programs.fish.enable = true;/ \
             imports = [ \
               ({ options, ... }: { \
                 nix.settings.access-tokens = [ \"github.com=\${{ secrets.GITHUB_TOKEN }}\" ]; \
                 environment.etc.\"nix\/nix.conf\".knownSha256Hashes = [ \"$nixConfHash\" ]; \
+                environment.etc.hosts.knownSha256Hashes = [ \"$etcHostsHash\" ]; \
                 nix.nixPath = \
                   [ { darwin = \"${PWD////\/}\"; } ] \
                   ++ options.nix.nixPath.default; \
@@ -102,8 +104,9 @@ jobs:
         pushd /etc/nix-darwin
           sudo nix flake init -t $darwin
           nixConfHash=$(shasum -a 256 /etc/nix/nix.conf | cut -d ' ' -f 1)
+          etcHostsHash=$(shasum -a 256 /etc/hosts | cut -d ' ' -f 1)
           sudo /usr/bin/sed -i.bak \
-            "s/# programs.fish.enable = true;/nix.settings.access-tokens = [ \"github.com=\${{ secrets.GITHUB_TOKEN }}\" ]; environment.etc.\"nix\/nix.conf\".knownSha256Hashes = [ \"$nixConfHash\" ];/" \
+            "s/# programs.fish.enable = true;/nix.settings.access-tokens = [ \"github.com=\${{ secrets.GITHUB_TOKEN }}\" ]; environment.etc.\"nix\/nix.conf\".knownSha256Hashes = [ \"$nixConfHash\" ]; environment.etc.hosts.knownSha256Hashes = [ \"$etcHostsHash\" ];/" \
             flake.nix
           sudo /usr/bin/sed -i.bak \
             's/darwinConfigurations."simple"/darwinConfigurations."'$(scutil --get LocalHostName)'"/g' \

doc/known-files/c7dd0e2ed261ce76d76f852596c5b54026b9a894fa481381ffd399b556c0e2da

@@ -0,0 +1,9 @@
+##
+# Host Database
+#
+# localhost is used to configure the loopback interface
+# when the system is booting.  Do not change this entry.
+##
+127.0.0.1	localhost
+255.255.255.255	broadcasthost
+::1             localhost

modules/networking/default.nix

@@ -1,4 +1,4 @@
-{ config, lib, ... }:
+{ config, lib, pkgs, ... }:
 
 with lib;
 
@@ -22,6 +22,8 @@ let
       esac
     '') cfg.knownNetworkServices}
   '';
+
+  localhostMultiple = any (elem "localhost") (attrValues (removeAttrs cfg.hosts [ "127.0.0.1" "::1" ]));
 in
 
 {
@@ -105,9 +107,50 @@ in
         Battery powered devices may require being connected to power.
       '';
     };
+
+    networking.hosts = lib.mkOption {
+      type = types.attrsOf (types.listOf types.str);
+      example = literalExpression ''
+        {
+          "127.0.0.1" = [ "foo.bar.baz" ];
+          "192.168.0.2" = [ "fileserver.local" "nameserver.local" ];
+        };
+      '';
+      description = ''
+        Locally defined maps of hostnames to IP addresses.
+      '';
+      default = {};
+    };
+
+    networking.hostFiles = lib.mkOption {
+      type = types.listOf types.path;
+      defaultText = literalMD "Hosts from {option}`networking.hosts` and {option}`networking.extraHosts`";
+      example = literalExpression ''[ "''${pkgs.my-blocklist-package}/share/my-blocklist/hosts" ]'';
+      description = ''
+        Files that should be concatenated together to form {file}`/etc/hosts`.
+      '';
+    };
+
+    networking.extraHosts = lib.mkOption {
+      type = types.lines;
+      default = "";
+      example = "192.168.0.1 lanlocalhost";
+      description = ''
+        Additional verbatim entries to be appended to {file}`/etc/hosts`.
+        For adding hosts from derivation results, use {option}`networking.hostFiles` instead.
+      '';
+    };
   };
 
   config = {
+    assertions = [{
+      assertion = !localhostMultiple;
+      message = ''
+        `networking.hosts` maps "localhost" to something other than "127.0.0.1"
+        or "::1". This will break some applications. Please use
+        `networking.extraHosts` if you really want to add such a mapping.
+      '';
+    }];
 
     warnings = [
       (mkIf (cfg.knownNetworkServices == [] && cfg.dns != []) "networking.knownNetworkServices is empty, dns servers will not be configured.")
@@ -134,5 +177,36 @@ in
       ''}
     '';
 
+    networking.hostFiles = let
+      # Note: localhostHosts has to appear first in /etc/hosts so that 127.0.0.1
+      # resolves back to "localhost" (as some applications assume) instead of
+      # the FQDN!
+      localhostHosts = pkgs.writeText "localhost-hosts" ''
+        ##
+        # Host Database
+        #
+        # localhost is used to configure the loopback interface
+        # when the system is booting.  Do not change this entry.
+        ##
+        127.0.0.1	localhost
+        255.255.255.255	broadcasthost
+        ::1             localhost
+      '';
+      stringHosts =
+        let
+          oneToString = set: ip: ip + " " + concatStringsSep " " set.${ip} + "\n";
+          allToString = set: concatMapStrings (oneToString set) (attrNames set);
+        in pkgs.writeText "string-hosts" (allToString (filterAttrs (_: v: v != []) cfg.hosts));
+      extraHosts = pkgs.writeText "extra-hosts" cfg.extraHosts;
+    in mkBefore [ localhostHosts stringHosts extraHosts ];
+
+    environment.etc.hosts = {
+      knownSha256Hashes = [
+        # Comes from MacOS: Darwin 24.1.0 Darwin Kernel Version 24.1.0.
+        "c7dd0e2ed261ce76d76f852596c5b54026b9a894fa481381ffd399b556c0e2da"
+      ];
+
+      source = pkgs.concatText "hosts" cfg.hostFiles;
+    };
   };
 }

release.nix

@@ -86,6 +86,7 @@ in {
   tests.launchd-daemons = makeTest ./tests/launchd-daemons.nix;
   tests.launchd-setenv = makeTest ./tests/launchd-setenv.nix;
   tests.networking-hostname = makeTest ./tests/networking-hostname.nix;
+  tests.networking-hosts = makeTest ./tests/networking-hosts.nix;
   tests.networking-networkservices = makeTest ./tests/networking-networkservices.nix;
   tests.nix-enable = makeTest ./tests/nix-enable.nix;
   tests.nixpkgs-overlays = makeTest ./tests/nixpkgs-overlays.nix;

tests/networking-hosts.nix

@@ -0,0 +1,20 @@
+{ config, pkgs, ... }:
+
+{
+  networking.hosts = {
+    "127.0.0.1" = [ "my.super.host" ];
+    "10.0.0.1" = [ "my.super.host" "my.other.host" ];
+  };
+
+  test = ''
+    set -v
+    echo checking /etc/hosts file >&2
+
+    file=${config.out}/etc/hosts
+
+    grep '127.0.0.1' $file | head -n1 | grep localhost$
+    grep '127.0.0.1' $file | tail -n1 | grep my.super.host$
+    grep '::1' $file | grep localhost$
+    grep '10.0.0.1' $file | grep my.super.host\ my.other.host$
+  '';
+}