Fix empty strings with default func

CHANGELOG.md

@@ -21,6 +21,7 @@ Unreleased changes are available as `avenga/couper:edge` container.
   * exclude file descriptor limit startup-logs for Windows ([#396](https://github.com/avenga/couper/pull/396), [#383](https://github.com/avenga/couper/pull/383))
   * possible race conditions while updating JWKS for the [JWT access control](./docs/REFERENCE.md#jwt-block) ([#398](https://github.com/avenga/couper/pull/398))
   * panic while accessing primitive variables with a key ([#377](https://github.com/avenga/couper/issues/377))
+  * `default()` function continues to their fallback value if this is a string type and an argument evaluates to an empty string ([#408](https://github.com/avenga/couper/issues/408))
 
 * **Dependencies**
   * Update modules for [OpenAPI](./docs/REFERENCE.md#openapi-block) validation ([#399](https://github.com/avenga/couper/pull/399))

eval/context.go

@@ -497,8 +497,8 @@ func newFunctionsMap() map[string]function.Function {
 	return map[string]function.Function{
 		"base64_decode": lib.Base64DecodeFunc,
 		"base64_encode": lib.Base64EncodeFunc,
-		"coalesce":      lib.CoalesceFunc,
-		"default":       lib.CoalesceFunc,
+		"coalesce":      lib.DefaultFunc,
+		"default":       lib.DefaultFunc,
 		"json_decode":   stdlib.JSONDecodeFunc,
 		"json_encode":   stdlib.JSONEncodeFunc,
 		"merge":         lib.MergeFunc,

eval/lib/coalesce.go → eval/lib/default.go

@@ -8,7 +8,7 @@ import (
 	"github.com/zclconf/go-cty/cty/function"
 )
 
-var CoalesceFunc = function.New(&function.Spec{
+var DefaultFunc = function.New(&function.Spec{
 	VarParam: &function.Parameter{
 		Name:             "vals",
 		Type:             cty.DynamicPseudoType,
@@ -32,6 +32,11 @@ var CoalesceFunc = function.New(&function.Spec{
 				continue
 			}
 
+			// If the fallback type is a string and this argument too but an empty one, consider them as unset.
+			if argVal.Type() == cty.String && argVal.AsString() == "" && retType == cty.String {
+				continue
+			}
+
 			return convert.Convert(argVal, retType)
 		}
 		return cty.NilVal, fmt.Errorf("no non-null or nil-type arguments")

server/http_integration_test.go

@@ -3694,7 +3694,16 @@ func TestFunctions(t *testing.T) {
 	for _, tc := range []testCase{
 		{"merge", "/v1/merge", map[string]string{"X-Merged-1": "{\"foo\":[1,2]}", "X-Merged-2": "{\"bar\":[3,4]}", "X-Merged-3": "[\"a\",\"b\"]"}, http.StatusOK},
 		{"coalesce", "/v1/coalesce?q=a", map[string]string{"X-Coalesce-1": "/v1/coalesce", "X-Coalesce-2": "default", "X-Coalesce-3": "default", "X-Coalesce-4": "default"}, http.StatusOK},
-		{"default", "/v1/default?q=a", map[string]string{"X-Default-1": "/v1/default", "X-Default-2": "default", "X-Default-3": "default", "X-Default-4": "default", "X-Default-5": "prefix-default", "X-Default-6": "default"}, http.StatusOK},
+		{"default", "/v1/default?q=a", map[string]string{
+			"X-Default-1": "/v1/default",
+			"X-Default-2": "default",
+			"X-Default-3": "default",
+			"X-Default-4": "default",
+			"X-Default-5": "prefix-default",
+			"X-Default-6": "default",
+			"X-Default-7": "default",
+			"X-Default-8": "default-8",
+		}, http.StatusOK},
 	} {
 		t.Run(tc.path[1:], func(subT *testing.T) {
 			helper := test.New(subT)
@@ -3711,7 +3720,7 @@ func TestFunctions(t *testing.T) {
 
 			for k, v := range tc.header {
 				if v1 := res.Header.Get(k); v1 != v {
-					subT.Fatalf("%q: unexpected %s response header %#v, got: %#v", tc.name, k, v, v1)
+					subT.Fatalf("%q: unexpected header value for %q: got: %q, want: %q", tc.name, k, v1, v)
 				}
 			}
 		})

server/testdata/integration/functions/01_couper.hcl

@@ -32,6 +32,8 @@ server "api" {
           x-default-4 = default(request.cookies.undef, request.query.q[1], "default", request.path)
           x-default-5 = "prefix-${default(request.cookies.undef, "default")}" # template expr
           x-default-6 = "${default(request.cookies.undef, "default")}" # template wrap expr
+          x-default-7 = default(env.MY_UNSET_ENV, "default")
+          x-default-8 = default(request.query.r, ["default-8"])[0]
         }
       }
     }