fix: preserve literal dollar signs in config values

cmd/remco/config.go

@@ -12,6 +12,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 
 	"github.com/BurntSushi/toml"
@@ -23,6 +24,9 @@ import (
 	"github.com/pkg/errors"
 )
 
+// bracedEnvRegex matches the ${VAR} form of environment variable references.
+var bracedEnvRegex = regexp.MustCompile(`\$\{([A-Za-z_][A-Za-z0-9_]*)\}`)
+
 // BackendConfigs holds every individually backend config.
 // The values are filled with data from the configuration file.
 type BackendConfigs struct {
@@ -129,13 +133,24 @@ type Resource struct {
 	Name string
 }
 
+// expandEnvBraced expands only the ${VAR} form of environment variables.
+// Unlike os.ExpandEnv it leaves a bare "$" untouched, so literal dollar signs
+// in configuration values (for example a password like "secret$Q$") are
+// preserved instead of being stripped.
+func expandEnvBraced(s string) string {
+	return bracedEnvRegex.ReplaceAllStringFunc(s, func(match string) string {
+		name := match[2 : len(match)-1]
+		return os.Getenv(name)
+	})
+}
+
 func readFileAndExpandEnv(path string) ([]byte, error) {
 	buf, err := ioutil.ReadFile(path)
 	if err != nil {
 		return buf, errors.Wrap(err, "read file failed")
 	}
-	// expand the environment variables
-	buf = []byte(os.ExpandEnv(string(buf)))
+	// expand only ${VAR} style environment variables
+	buf = []byte(expandEnvBraced(string(buf)))
 	return buf, nil
 }
 

cmd/remco/config_env_test.go

@@ -0,0 +1,71 @@
+/*
+ * This file is part of remco.
+ * © 2016 The Remco Authors
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// TestReadFileAndExpandEnv verifies that configuration values containing a
+// literal "$" (for example a password like "uhQhu4watyTgn$Q$") are not
+// corrupted, while the ${VAR} form is still expanded.
+//
+// It exercises readFileAndExpandEnv, the function that actually parses the
+// on-disk config, so it fails on the previous os.ExpandEnv implementation
+// (which stripped the "$Q$" portion) and passes on the braced-only expander.
+func TestReadFileAndExpandEnv(t *testing.T) {
+	os.Setenv("REMCO_TEST_TOKEN", "s3cr3t")
+	defer os.Unsetenv("REMCO_TEST_TOKEN")
+
+	cases := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{
+			name: "braced var is expanded",
+			in:   "password = \"${REMCO_TEST_TOKEN}\"",
+			want: "password = \"s3cr3t\"",
+		},
+		{
+			name: "literal dollar signs are preserved",
+			in:   "password = \"uhQhu4watyTgn$Q$\"",
+			want: "password = \"uhQhu4watyTgn$Q$\"",
+		},
+		{
+			name: "bare dollar without braces is preserved",
+			in:   "value = \"costs $5 today\"",
+			want: "value = \"costs $5 today\"",
+		},
+		{
+			name: "mixing braced var and literal dollar",
+			in:   "conn = \"${REMCO_TEST_TOKEN}:uhQhu4watyTgn$Q$\"",
+			want: "conn = \"s3cr3t:uhQhu4watyTgn$Q$\"",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+			p := filepath.Join(dir, "config.toml")
+			if err := os.WriteFile(p, []byte(tc.in), 0o644); err != nil {
+				t.Fatal(err)
+			}
+			got, err := readFileAndExpandEnv(p)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(got) != tc.want {
+				t.Errorf("readFileAndExpandEnv(%q) = %q, want %q", tc.in, string(got), tc.want)
+			}
+		})
+	}
+}