escape json

flake.nix

@@ -1,6 +1,6 @@
 {
   inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
-  outputs = { nixpkgs, ... }@self: let
+  outputs = { nixpkgs, ... }: let
     supportedArchitectures = [
       "aarch64-darwin"
       "aarch64-linux"
@@ -11,12 +11,16 @@
     packages = nixpkgs.lib.genAttrs supportedArchitectures (system: {
       nix_templater = nixpkgs.legacyPackages.${system}.callPackage ./pkgs/nix_templater {};
     });
-    legacyPackages = nixpkgs.lib.genAttrs supportedArchitectures (system: import ./lib.nix {
+    legacyPackages = nixpkgs.lib.genAttrs supportedArchitectures (system: let
       pkgs = nixpkgs.legacyPackages.${system};
+    in import ./lib.nix {
+      inherit pkgs;
+      inherit (pkgs) lib;
       nix_templater = packages.${system}.nix_templater;
     });
     checks = nixpkgs.lib.genAttrs supportedArchitectures (system: {
       template = import ./tests/template.nix { inherit legacyPackages system nixpkgs; };
+      json = import ./tests/json.nix { inherit legacyPackages system nixpkgs; };
     });
   };
 }

lib.nix

@@ -1,5 +1,11 @@
-{ pkgs, nix_templater }:
-{
+{ pkgs, lib, nix_templater }:
+let
+  escapeJson = {
+    "\"" = ''\"'';
+    "\\" = ''\\'';
+  };
+in
+rec {
   # placeholder to be substituted with the content of a secret file
   fileContents = file: {
    outPath = "<${builtins.placeholder "nix_template"}${toString file}${builtins.placeholder "nix_template"}>";
@@ -7,12 +13,12 @@
   };
 
   # make a template with placeholders
-  template_text = { name, text, outPath }:
+  templateText = { name, text, outPath, translations ? {} }:
     pkgs.runCommand name {
       textBeforeTemplate = text;
       script = ''
         #!/bin/sh
-        ${nix_templater}/bin/nix_templater ${builtins.placeholder "out"}/template ${builtins.placeholder "nix_template"} "${outPath}"
+        ${nix_templater}/bin/nix_templater ${builtins.placeholder "out"}/template ${builtins.placeholder "nix_template"} "${outPath}" '${lib.strings.toJSON translations}'
       '';
       passAsFile = [ "script" "textBeforeTemplate" ];
     } ''
@@ -21,4 +27,16 @@
       cp $scriptPath $out/bin/${name}
       chmod +x $out/bin/${name}
     '';
+
+  templateGenerator = translations: generator: { name, value, outPath }: templateText {
+    inherit name outPath translations;
+    text = generator value;
+  };
+
+  templateJsonWith = options: templateGenerator escapeJson (lib.generators.toJSON options);
+  templateYamlWith = options: templateGenerator escapeJson (lib.generators.toYAML options); # just json
+  templateIniWith = options: templateGenerator escapeJson (lib.generators.toINI options);
+  templateJson = templateJsonWith { };
+  templateYaml = templateYamlWith { };
+  templateIni = templateIniWith { };
 }

pkgs/nix_templater/replace.py

@@ -1,10 +1,12 @@
 # replace occurrences of a magic string in a template file
+from json import loads
 import sys
 from pathlib import Path
 
 template_file = sys.argv[1]
 magic_string = sys.argv[2]
 outfile = sys.argv[3]
+translations = loads(sys.argv[4]) if len(sys.argv) >= 4 else {}
 
 if Path(outfile).exists():
     print(f"{outfile} already exists, aborting")
@@ -26,7 +28,7 @@ while True:
     ]
     output += template_bytes[loc : loc + magic_start]
     # TODO handle errors better here
-    output += Path(magic_file.decode()).read_bytes()
+    output += Path(magic_file.decode()).read_bytes().decode().translate(str.maketrans(translations)).encode()
     loc = loc + magic_start + magic_end + len(magic_string) + 1
 
 Path(outfile).write_bytes(output)

tests/json.nix

@@ -0,0 +1,41 @@
+# test injecting a secret into a json template
+{ legacyPackages, system, nixpkgs }:
+let
+  hostPkgs = nixpkgs.legacyPackages.${system};
+  secret_file = hostPkgs.writeText "secret" "secret\\needing\"escaping";
+in (nixpkgs.lib.nixos.runTest {
+    inherit hostPkgs;
+    name = "nix_templates";
+
+    nodes.machine = {pkgs, ...}: {
+      config = {
+        systemd.services.testservice = {
+          wantedBy = [ "multi-user.target" ];
+          serviceConfig = {
+            Type = "oneshot";
+            ExecStartPre = "${legacyPackages.${system}.templateJson {
+              name = "test";
+              value = {
+                foo = "text";
+                bar = legacyPackages.${system}.fileContents secret_file;
+              };
+              outPath = "./test";
+            }}/bin/test";
+            ExecStart = pkgs.writeScript "test_file_got_templates" ''
+              #!/bin/sh
+              cat ./test | grep -q 'secret'
+            '';
+          };
+        };
+      };
+    };
+
+    testScript = ''
+      start_all()
+      print(machine.execute("uname -a"))
+      machine.wait_for_unit("multi-user.target")
+      print(machine.succeed("cat /test"))
+      print(machine.succeed("cat /test | grep -q secret"))
+      print(machine.succeed("cat /test | ${hostPkgs.jq}/bin/jq"))
+    '';
+  })

tests/template.nix

@@ -1,4 +1,4 @@
-# test injecting a secret into a template
+# test injecting a secret into a text template
 { legacyPackages, system, nixpkgs }:
 let
   # this file would usually be outside of the store
@@ -14,7 +14,7 @@ in (nixpkgs.lib.nixos.runTest {
           wantedBy = [ "multi-user.target" ];
           serviceConfig = {
             Type = "oneshot";
-            ExecStartPre = "${legacyPackages.${system}.template_text {
+            ExecStartPre = "${legacyPackages.${system}.templateText {
               name = "test";
               text = ''
               public text