File write permission issue

README.md

@@ -19,6 +19,8 @@ This is useful for injecting runtime configuration into static front-end apps wi
 
 If any placeholders have no matching environment variable, the server still writes the file (substituting empty strings for missing values) and logs an error listing the unresolved variables.
 
+**Important:** Since the static-server image runs as `nonroot:nonroot`, the config file must be writable by the `nonroot` user. Use `COPY --chown=nonroot:nonroot` when copying the config file in your Dockerfile (see [example](#1-build-a-docker-image) below).
+
 #### Example
 
 Given a `config.json` template:
@@ -60,7 +62,9 @@ FROM zopdev/static-server:v0.0.8
 COPY /app/out /static
 
 # Set the path to the config file for environment variable hydration at startup
+# The config file must be writable by nonroot for hydration to work
 ENV CONFIG_FILE_PATH=/static/config.json
+COPY --chown=nonroot:nonroot /app/out/config.json $CONFIG_FILE_PATH
 
 # The server listens on port 8000 by default; set HTTP_PORT to change it
 

internal/config/hydrate_test.go

@@ -4,7 +4,6 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"runtime"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -13,30 +12,30 @@ import (
 	"gofr.dev/pkg/gofr/logging"
 )
 
-func writeTempFile(t *testing.T, fs file.FileSystem, content string) string {
+func writeTempFile(t *testing.T, content string, permissions os.FileMode) string {
 	t.Helper()
 
 	dir := t.TempDir()
 	path := filepath.Join(dir, "config.json")
 
-	f, err := fs.Create(path)
+	err := os.WriteFile(path, []byte(content), 0644)
 	require.NoError(t, err)
 
-	_, err = f.Write([]byte(content))
-	require.NoError(t, err)
-
-	require.NoError(t, f.Close())
+	if permissions != 0 {
+		require.NoError(t, os.Chmod(path, permissions))
+	}
 
 	return path
 }
 
 func TestConfig(t *testing.T) {
 	tests := []struct {
-		name     string
-		template string
-		vars     map[string]string
-		expected string
-		wantErr  error
+		name        string
+		template    string
+		vars        map[string]string
+		permissions os.FileMode
+		expected    string
+		wantErr     error
 	}{
 		{
 			name:     "all vars present",
@@ -45,9 +44,9 @@ func TestConfig(t *testing.T) {
 			expected: `{"a":"1","b":"2"}`,
 		},
 		{
-			name:    "no config path is a no-op",
-			vars:    map[string]string{},
-			wantErr: nil,
+			name:     "no config path is a no-op",
+			template: `{"a":"${A}","b":"${B}"}`,
+			vars:     map[string]string{"CONFIG_FILE_PATH": ""},
 		},
 		{
 			name:     "extra vars ignored",
@@ -70,52 +69,42 @@ func TestConfig(t *testing.T) {
 			wantErr:  errMissingVars,
 		},
 		{
-			name:    "invalid config path",
-			vars:    map[string]string{"CONFIG_FILE_PATH": "/no/such/file"},
-			wantErr: errReadConfig,
+			name:     "invalid config path",
+			template: `{"a":"${A}"}`,
+			vars:     map[string]string{"CONFIG_FILE_PATH": "/no/such/file"},
+			wantErr:  errReadConfig,
+		},
+		{
+			name:        "write error on read-only file",
+			template:    `{"a":"${A}"}`,
+			vars:        map[string]string{"A": "1"},
+			permissions: 0444,
+			wantErr:     errWriteConfig,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			fs := file.New(logging.NewMockLogger(logging.ERROR))
 
-			if tt.template != "" {
-				path := writeTempFile(t, fs, tt.template)
-				tt.vars[filePathVar] = path
+			// To not overwrite the file path if already present in the test case
+			if _, ok := tt.vars[filePathVar]; !ok {
+				tt.vars[filePathVar] = writeTempFile(t, tt.template, tt.permissions)
 			}
 
 			err := HydrateFile(fs, config.NewMockConfig(tt.vars))
 
 			require.ErrorIs(t, err, tt.wantErr)
 
-			if tt.expected != "" {
-				rf, readErr := fs.Open(tt.vars[filePathVar])
-				require.NoError(t, readErr)
-				got, readErr := io.ReadAll(rf)
-				require.NoError(t, readErr)
-				require.Equal(t, tt.expected, string(got))
+			if tt.vars[filePathVar] == "" || tt.wantErr != nil {
+				return
 			}
-		})
-	}
-}
-
-func TestHydrateFile_WriteError(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("chmod not effective on Windows")
-	}
-
-	fs := file.New(logging.NewMockLogger(logging.ERROR))
-	path := writeTempFile(t, fs, `{"a":"${A}"}`)
 
-	err := os.Chmod(path, 0444)
-	require.NoError(t, err)
-
-	vars := map[string]string{
-		filePathVar: path,
-		"A":         "1",
+			rf, readErr := os.Open(tt.vars[filePathVar])
+			require.NoError(t, readErr)
+			got, readErr := io.ReadAll(rf)
+			require.NoError(t, readErr)
+			require.Equal(t, tt.expected, string(got))
+		})
 	}
-
-	err = HydrateFile(fs, config.NewMockConfig(vars))
-	require.ErrorIs(t, err, errWriteConfig)
 }

main.go

@@ -22,7 +22,7 @@ func main() {
 
 	app.OnStart(func(ctx *gofr.Context) error {
 		if err := config.HydrateFile(ctx.File, app.Config); err != nil {
-			ctx.Logger.Error(err)
+			ctx.Logger.Error(err.Error())
 		}
 
 		return nil