introduce ability to use custom env_file format

Signed-off-by: Nicolas De Loof <[email protected]>

dotenv/fixtures/custom.format

@@ -0,0 +1,2 @@
+FOO:BAR
+ZOT

dotenv/format.go

@@ -0,0 +1,37 @@
+/*
+   Copyright 2020 The Compose Specification Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package dotenv
+
+import (
+	"fmt"
+)
+
+var formats = map[string]Parser{}
+
+type Parser func(filename string, lookup func(key string) (string, bool)) (map[string]string, error)
+
+func RegisterFormat(format string, p Parser) {
+	formats[format] = p
+}
+
+func ParseWithFormat(filename string, resolve LookupFn, format string) (map[string]string, error) {
+	parser, ok := formats[format]
+	if !ok {
+		return nil, fmt.Errorf("unknown env_file format %q", format)
+	}
+	return parser(filename, resolve)
+}

dotenv/godotenv.go

@@ -86,7 +86,7 @@ func ReadWithLookup(lookupFn LookupFn, filenames ...string) (map[string]string,
 	envMap := make(map[string]string)
 
 	for _, filename := range filenames {
-		individualEnvMap, individualErr := readFile(filename, lookupFn)
+		individualEnvMap, individualErr := ReadFile(filename, lookupFn)
 
 		if individualErr != nil {
 			return envMap, individualErr
@@ -129,7 +129,7 @@ func filenamesOrDefault(filenames []string) []string {
 }
 
 func loadFile(filename string, overload bool) error {
-	envMap, err := readFile(filename, nil)
+	envMap, err := ReadFile(filename, nil)
 	if err != nil {
 		return err
 	}
@@ -150,7 +150,7 @@ func loadFile(filename string, overload bool) error {
 	return nil
 }
 
-func readFile(filename string, lookupFn LookupFn) (map[string]string, error) {
+func ReadFile(filename string, lookupFn LookupFn) (map[string]string, error) {
 	file, err := os.Open(filename)
 	if err != nil {
 		return nil, err

dotenv/godotenv_test.go

@@ -1,6 +1,7 @@
 package dotenv
 
 import (
+	"bufio"
 	"bytes"
 	"errors"
 	"os"
@@ -708,3 +709,44 @@ func TestGetEnvFromFile(t *testing.T) {
 	_, err = GetEnvFromFile(nil, []string{f})
 	assert.Check(t, strings.HasSuffix(err.Error(), ".env is a directory"))
 }
+
+func TestLoadWithFormat(t *testing.T) {
+	envFileName := "fixtures/custom.format"
+	expectedValues := map[string]string{
+		"FOO": "BAR",
+		"ZOT": "QIX",
+	}
+
+	custom := func(f string, lookup func(key string) (string, bool)) (map[string]string, error) {
+		b, err := os.ReadFile(f)
+		if err != nil {
+			return nil, err
+		}
+		r := bytes.NewReader(b)
+		vars := map[string]string{}
+		scanner := bufio.NewScanner(r)
+		for scanner.Scan() {
+			key, value, found := strings.Cut(scanner.Text(), ":")
+			if !found {
+				value, found = lookup(key)
+				if !found {
+					continue
+				}
+			}
+			vars[key] = value
+		}
+		return vars, nil
+	}
+
+	RegisterFormat("custom", custom)
+	env, err := ParseWithFormat(envFileName, func(s string) (string, bool) {
+		switch s {
+		case "ZOT":
+			return "QIX", true
+		default:
+			return "", false
+		}
+	}, "custom")
+	assert.NilError(t, err)
+	assert.DeepEqual(t, expectedValues, env)
+}

schema/compose-spec.json

@@ -828,6 +828,9 @@
                   "path": {
                     "type": "string"
                   },
+                  "format": {
+                    "type": "string"
+                  },
                   "required": {
                     "type": ["boolean", "string"],
                     "default": true