cannon: Support gzip compression for JSON files.

cannon/.gitignore

@@ -9,6 +9,7 @@ example/bin
 contracts/out
 state.json
 *.json
+*.json.gz
 *.pprof
 *.out
 bin

cannon/cmd/json.go

 package cmd
 
 import (
+	"compress/gzip"
 	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
 	"os"
+	"strings"
 )
 
 func loadJSON[X any](inputPath string) (*X, error) {
 	if inputPath == "" {
 		return nil, errors.New("no path specified")
 	}
+	var f io.ReadCloser
 	f, err := os.OpenFile(inputPath, os.O_RDONLY, 0)
 	if err != nil {
 		return nil, fmt.Errorf("failed to open file %q: %w", inputPath, err)
 	}
 	defer f.Close()
+	if isGzip(inputPath) {
+		f, err = gzip.NewReader(f)
+		if err != nil {
+			return nil, fmt.Errorf("create gzip reader: %w", err)
+		}
+		defer f.Close()
+	}
 	var state X
 	if err := json.NewDecoder(f).Decode(&state); err != nil {
 		return nil, fmt.Errorf("failed to decode file %q: %w", inputPath, err)
@@ -33,6 +43,11 @@ func writeJSON[X any](outputPath string, value X, outIfEmpty bool) error {
 		}
 		defer f.Close()
 		out = f
+		if isGzip(outputPath) {
+			g := gzip.NewWriter(f)
+			defer g.Close()
+			out = g
+		}
 	} else if outIfEmpty {
 		out = os.Stdout
 	} else {
@@ -48,3 +63,7 @@ func writeJSON[X any](outputPath string, value X, outIfEmpty bool) error {
 	}
 	return nil
 }
+
+func isGzip(path string) bool {
+	return strings.HasSuffix(path, ".gz")
+}

cannon/cmd/json_test.go

+package cmd
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRoundTripJSON(t *testing.T) {
+	dir := t.TempDir()
+	file := filepath.Join(dir, "test.json")
+	data := &jsonTestData{A: "yay", B: 3}
+	err := writeJSON(file, data, false)
+	require.NoError(t, err)
+
+	// Confirm the file is uncompressed
+	fileContent, err := os.ReadFile(file)
+	require.NoError(t, err)
+	err = json.Unmarshal(fileContent, &jsonTestData{})
+	require.NoError(t, err)
+
+	var result *jsonTestData
+	result, err = loadJSON[jsonTestData](file)
+	require.NoError(t, err)
+	require.EqualValues(t, data, result)
+}
+
+func TestRoundTripJSONWithGzip(t *testing.T) {
+	dir := t.TempDir()
+	file := filepath.Join(dir, "test.json.gz")
+	data := &jsonTestData{A: "yay", B: 3}
+	err := writeJSON(file, data, false)
+	require.NoError(t, err)
+
+	// Confirm the file isn't raw JSON
+	fileContent, err := os.ReadFile(file)
+	require.NoError(t, err)
+	err = json.Unmarshal(fileContent, &jsonTestData{})
+	require.Error(t, err, "should not be able to decode without decompressing")
+
+	var result *jsonTestData
+	result, err = loadJSON[jsonTestData](file)
+	require.NoError(t, err)
+	require.EqualValues(t, data, result)
+}
+
+type jsonTestData struct {
+	A string `json:"a"`
+	B int    `json:"b"`
+}