Extract parsing logic of "key=val" as `parseKeyValue`

Signed-off-by: Yuichiro Kaneko <spiketeika@gmail.com>

frontend/dockerfile/dockerfile2llb/convert.go

@@ -247,12 +247,8 @@ func Dockerfile2LLB(ctx context.Context, dt []byte, opt ConvertOpt) (*llb.State,
 
 		// initialize base metadata from image conf
 		for _, env := range d.image.Config.Env {
-			parts := strings.SplitN(env, "=", 2)
-			v := ""
-			if len(parts) > 1 {
-				v = parts[1]
-			}
-			d.state = d.state.AddEnv(parts[0], v)
+			k, v := parseKeyValue(env)
+			d.state = d.state.AddEnv(k, v)
 		}
 		if d.image.Config.WorkingDir != "" {
 			if err = dispatchWorkdir(d, &instructions.WorkdirCommand{Path: d.image.Config.WorkingDir}, false); err != nil {
@@ -826,9 +822,8 @@ func splitWildcards(name string) (string, string) {
 func addEnv(env []string, k, v string, override bool) []string {
 	gotOne := false
 	for i, envVar := range env {
-		envParts := strings.SplitN(envVar, "=", 2)
-		compareFrom := envParts[0]
-		if shell.EqualEnvKeys(compareFrom, k) {
+		key, _ := parseKeyValue(envVar)
+		if shell.EqualEnvKeys(key, k) {
 			if override {
 				env[i] = k + "=" + v
 			}
@@ -842,6 +837,16 @@ func addEnv(env []string, k, v string, override bool) []string {
 	return env
 }
 
+func parseKeyValue(env string) (string, string) {
+	parts := strings.SplitN(env, "=", 2)
+	v := ""
+	if len(parts) > 1 {
+		v = parts[1]
+	}
+
+	return parts[0], v
+}
+
 func setKVValue(kvpo instructions.KeyValuePairOptional, values map[string]string) instructions.KeyValuePairOptional {
 	if v, ok := values[kvpo.Key]; ok {
 		kvpo.Value = &v

frontend/dockerfile/dockerfile2llb/convert_test.go

@@ -112,3 +112,17 @@ func TestAddEnv(t *testing.T) {
 	result = addEnv(env, "key3", "val3", true)
 	assert.Equal(t, []string{"key1=val1", "key2=val2", "key3=val3"}, result)
 }
+
+func TestParseKeyValue(t *testing.T) {
+	k, v := parseKeyValue("key=val")
+	assert.Equal(t, "key", k)
+	assert.Equal(t, "val", v)
+
+	k, v = parseKeyValue("key=")
+	assert.Equal(t, "key", k)
+	assert.Equal(t, "", v)
+
+	k, v = parseKeyValue("key")
+	assert.Equal(t, "key", k)
+	assert.Equal(t, "", v)
+}