initial commit

Signed-off-by: jolheiser <john.olheiser@gmail.com>

.gitignore

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+/nixfig
+/nixfix.exe

LICENSE

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+Copyright (c) 2023 John Olheiser
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# nixfig
+
+Read a nix file as a config.
+
+Essentially just wraps `nix eval (--json) --expr`.
+
+
+Allows parsing the following:
+```nix
+let
+  user = "jolheiser";
+in {
+  log = {
+    level = "warn";
+    # Name the log file after the user....for reasons
+    file = "${user}.log";
+  };
+  http = {
+    host = "0.0.0.0";
+    port = 1234;
+    # Make user an admin, but also make a generic admin user
+    admins = [user "admin"];
+  };
+}
+```
+
+Into a struct like:
+```go
+type Config struct {
+	Log struct {
+		Level string // warn
+		File  string // jolheiser.log
+	}
+	HTTP struct {
+		Host   string   // 0.0.0.0
+		Port   int      // 1234
+		Admins []string // [jolheiser admin]
+	}
+}
+```
+
+It can also marshal a struct into a valid (albeit minified) nix expression.
+
+
+## License
+
+[MIT](LICENSE)

cmd/nixfig/main.go

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+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"go.jolheiser.com/nixfig"
+)
+
+func maine() error {
+	if len(os.Args) != 2 {
+		return errors.New("nixfig requires 1 argument")
+	}
+	fn := os.Args[1]
+
+	data, err := os.ReadFile(fn)
+	if err != nil {
+		return fmt.Errorf("could not read file %q: %w", fn, err)
+	}
+
+	var out []byte
+	var a any
+	switch ext := filepath.Ext(fn); ext {
+	case ".json":
+		if err := json.Unmarshal(data, &a); err != nil {
+			return fmt.Errorf("invalid JSON file: %w", err)
+		}
+		out, err = nixfig.Marshal(a)
+	case ".nix":
+		if err := nixfig.Unmarshal(data, &a); err != nil {
+			return fmt.Errorf("invalid nix file: %w", err)
+		}
+		out, err = json.Marshal(a)
+	default:
+		return fmt.Errorf("unknown extension %q, must be json or nix", ext)
+	}
+	if err != nil {
+		return err
+	}
+
+	fmt.Print(string(out))
+	return nil
+}
+
+func main() {
+	if err := maine(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+}

go.mod

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+module go.jolheiser.com/nixfig
+
+go 1.21.4
+
+require github.com/alecthomas/assert/v2 v2.4.0
+
+require (
+	github.com/alecthomas/repr v0.3.0 // indirect
+	github.com/hexops/gotextdiff v1.0.3 // indirect
+)

go.sum

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+github.com/alecthomas/assert/v2 v2.4.0 h1:/ZiZ0NnriAWPYYO+4eOjgzNELrFQLaHNr92mHSHFj9U=
+github.com/alecthomas/assert/v2 v2.4.0/go.mod h1:fw5suVxB+wfYJ3291t0hRTqtGzFYdSwstnRQdaQx2DM=
+github.com/alecthomas/repr v0.3.0 h1:NeYzUPfjjlqHY4KtzgKJiWd6sVq2eNUPTi34PiFGjY8=
+github.com/alecthomas/repr v0.3.0/go.mod h1:Fr0507jx4eOXV7AlPV6AVZLYrLIuIeSOWtW57eE/O/4=
+github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
+github.com/hexops/gotextdiff v1.0.3/go.mod h1:pSWU5MAI3yDq+fZBTazCSJysOMbxWL1BSow5/V2vxeg=

nixfig.go

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+package nixfig
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+var (
+	// Nix is the command to call for nix
+	Nix            string
+	ErrNixNotFound = errors.New("nix was not found or set. You can set it either with `nixfig.Nix` or the `NIXFIG_NIX` environment variable")
+)
+
+func init() {
+	nixPath, _ := exec.LookPath("nix")
+	Nix = nixPath
+	if envPath, ok := os.LookupEnv("NIXFIG_NIX"); ok {
+		Nix = envPath
+	}
+}
+
+// Unmarshal unmarshals a nix expression as JSON into a struct
+func Unmarshal(data []byte, v any) error {
+	if Nix == "" {
+		return ErrNixNotFound
+	}
+
+	var stdout, stderr bytes.Buffer
+	cmd := exec.Command(Nix, "eval", "--json", "--expr", string(data))
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("could not run %q: %w", Nix, err)
+	}
+	if stderr.Len() > 0 {
+		return errors.New(stderr.String())
+	}
+
+	if err := json.Unmarshal(stdout.Bytes(), v); err != nil {
+		return fmt.Errorf("could not unmarshal nix config as JSON: %w", err)
+	}
+	return nil
+}
+
+// Marshal marshals a struct into a nix expression
+func Marshal(v any) ([]byte, error) {
+	if Nix == "" {
+		return nil, ErrNixNotFound
+	}
+
+	data, err := json.Marshal(v)
+	if err != nil {
+		return nil, fmt.Errorf("could not marshal JSON: %w", err)
+	}
+
+	var stdout, stderr bytes.Buffer
+	cmd := exec.Command(Nix, "eval", "--expr", fmt.Sprintf(`(builtins.fromJSON %q)`, string(data)))
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return nil, fmt.Errorf("could not run %q: %w", Nix, err)
+	}
+	if stderr.Len() > 0 {
+		return nil, errors.New(stderr.String())
+	}
+
+	return stdout.Bytes(), nil
+}

nixfig_test.go

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+package nixfig
+
+import (
+	"os"
+	"testing"
+
+	"github.com/alecthomas/assert/v2"
+)
+
+type Config struct {
+	Log struct {
+		Level string
+		File  string
+	}
+	HTTP struct {
+		Host   string
+		Port   int
+		Admins []string
+	}
+}
+
+var testCfg = Config{
+	Log: struct {
+		Level string
+		File  string
+	}{
+		Level: "warn",
+		File:  "jolheiser.log",
+	},
+	HTTP: struct {
+		Host   string
+		Port   int
+		Admins []string
+	}{
+		Host:   "0.0.0.0",
+		Port:   1234,
+		Admins: []string{"jolheiser", "admin"},
+	},
+}
+
+func TestNixNotFound(t *testing.T) {
+	oldNix := Nix
+	Nix = ""
+
+	_, err := Marshal(nil)
+	assert.IsError(t, err, ErrNixNotFound)
+
+	Nix = oldNix
+}
+
+func TestUnmarshal(t *testing.T) {
+	data, err := os.ReadFile("testdata/config.nix")
+	assert.NoError(t, err)
+
+	var cfg Config
+	err = Unmarshal(data, &cfg)
+	assert.NoError(t, err)
+	assert.Equal(t, testCfg, cfg)
+}
+
+func TestMarshal(t *testing.T) {
+	data, err := Marshal(testCfg)
+	assert.NoError(t, err)
+
+	var cfg Config
+	err = Unmarshal(data, &cfg)
+	assert.NoError(t, err)
+	assert.Equal(t, testCfg, cfg)
+}

testdata/config.nix

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+let
+  user = "jolheiser";
+in {
+  log = {
+    level = "warn";
+    # Name the log file after the user....for reasons
+    file = "${user}.log";
+  };
+  http = {
+    host = "0.0.0.0";
+    port = 1234;
+    # Make user an admin, but also make a generic admin user
+    admins = [user "admin"];
+  };
+}