Use proper path expansion

cmd/backup/config_provider.go

@@ -4,6 +4,7 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -11,6 +12,7 @@ import (
 	"github.com/joho/godotenv"
 	"github.com/offen/docker-volume-backup/internal/errwrap"
 	"github.com/offen/envconfig"
+	shell "mvdan.cc/sh/v3/shell"
 )
 
 type configStrategy string
@@ -99,11 +101,7 @@ func loadConfigsFromEnvFiles(directory string) ([]*Config, error) {
 			continue
 		}
 		p := filepath.Join(directory, item.Name())
-		f, err := os.ReadFile(p)
-		if err != nil {
-			return nil, errwrap.Wrap(err, fmt.Sprintf("error reading %s", item.Name()))
-		}
-		envFile, err := godotenv.Unmarshal(os.ExpandEnv(string(f)))
+		envFile, err := source(p)
 		if err != nil {
 			return nil, errwrap.Wrap(err, fmt.Sprintf("error reading config file %s", p))
 		}
@@ -125,3 +123,39 @@ func loadConfigsFromEnvFiles(directory string) ([]*Config, error) {
 
 	return configs, nil
 }
+
+// source tries to mimic the pre v2.37.0 behavior of calling
+// `set +a; source $path; set -a` and returns the env vars as a map
+func source(path string) (map[string]string, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, errwrap.Wrap(err, fmt.Sprintf("error opening %s", path))
+	}
+
+	result := map[string]string{}
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+		withExpansion, err := shell.Expand(line, nil)
+		if err != nil {
+			return nil, errwrap.Wrap(err, "error expanding env")
+		}
+		m, err := godotenv.Unmarshal(withExpansion)
+		if err != nil {
+			return nil, errwrap.Wrap(err, fmt.Sprintf("error sourcing %s", path))
+		}
+		for key, value := range m {
+			currentValue, currentOk := os.LookupEnv(key)
+			defer func() {
+				if currentOk {
+					os.Setenv(key, currentValue)
+					return
+				}
+				os.Unsetenv(key)
+			}()
+			result[key] = value
+			os.Setenv(key, value)
+		}
+	}
+	return result, nil
+}

cmd/backup/config_provider_test.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"os"
+	"reflect"
+	"testing"
+)
+
+func TestSource(t *testing.T) {
+	tests := []struct {
+		name           string
+		input          string
+		expectError    bool
+		expectedOutput map[string]string
+	}{
+		{
+			"default",
+			"testdata/default.env",
+			false,
+			map[string]string{
+				"FOO": "bar",
+				"BAZ": "qux",
+			},
+		},
+		{
+			"not found",
+			"testdata/nope.env",
+			true,
+			nil,
+		},
+		{
+			"braces",
+			"testdata/braces.env",
+			false,
+			map[string]string{
+				"FOO": "qux",
+				"BAR": "xxx",
+				"BAZ": "",
+			},
+		},
+		{
+			"expansion",
+			"testdata/expansion.env",
+			false,
+			map[string]string{
+				"BAR": "xxx",
+				"FOO": "xxx",
+				"BAZ": "xxx",
+				"QUX": "yyy",
+			},
+		},
+	}
+
+	os.Setenv("QUX", "yyy")
+	defer os.Unsetenv("QUX")
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			result, err := source(test.input)
+			if (err != nil) != test.expectError {
+				t.Errorf("Unexpected error value %v", err)
+			}
+			if !reflect.DeepEqual(test.expectedOutput, result) {
+				t.Errorf("Expected %v, got %v", test.expectedOutput, result)
+			}
+		})
+	}
+}

cmd/backup/testdata/braces.env

@@ -0,0 +1,3 @@
+FOO=${bar:-qux}
+BAR=xxx
+BAZ=$NOPE

cmd/backup/testdata/default.env

@@ -0,0 +1,2 @@
+FOO=bar
+BAZ=qux

cmd/backup/testdata/expansion.env

@@ -0,0 +1,4 @@
+BAR=xxx
+FOO=${BAR}
+BAZ=$BAR
+QUX=${QUX}