fix: readable error messages (open-feature#1325)

- Mapped the error codes to easier to read error messages
- Created unit test to check functionality

 open-feature#1100

---------

Signed-off-by: DBlanchard88 <davidblanchard88@gmail.com>
Signed-off-by: Dave <89858058+DBlanchard88@users.noreply.github.com>
Co-authored-by: Todd Baert <todd.baert@dynatrace.com>

core/pkg/model/error.go

@@ -1,5 +1,7 @@
 package model
 
+import "fmt"
+
 const (
 	FlagNotFoundErrorCode = "FLAG_NOT_FOUND"
 	ParseErrorCode        = "PARSE_ERROR"
@@ -8,3 +10,19 @@ const (
 	FlagDisabledErrorCode = "FLAG_DISABLED"
 	InvalidContextCode    = "INVALID_CONTEXT"
 )
+
+var ReadableErrorMessage = map[string]string{
+	FlagNotFoundErrorCode: "Flag not found",
+	ParseErrorCode:        "Error parsing input or configuration",
+	TypeMismatchErrorCode: "Type mismatch error",
+	GeneralErrorCode:      "General error",
+	FlagDisabledErrorCode: "Flag is disabled",
+	InvalidContextCode:    "Invalid context provided",
+}
+
+func GetErrorMessage(code string) string {
+	if msg, exists := ReadableErrorMessage[code]; exists {
+		return msg
+	}
+	return fmt.Sprintf("Unknown error code: %s", code)
+}

flagd/pkg/service/flag-evaluation/flag_evaluator.go

@@ -327,15 +327,16 @@ func formatContextKeys(context *structpb.Struct) []string {
 }
 
 func errFormat(err error) error {
+	ReadableErrorMsg := model.GetErrorMessage(err.Error())
 	switch err.Error() {
 	case model.FlagNotFoundErrorCode, model.FlagDisabledErrorCode:
-		return connect.NewError(connect.CodeNotFound, fmt.Errorf("%s, %s", ErrorPrefix, err.Error()))
+		return connect.NewError(connect.CodeNotFound, fmt.Errorf("%s", ReadableErrorMsg))
 	case model.TypeMismatchErrorCode:
-		return connect.NewError(connect.CodeInvalidArgument, fmt.Errorf("%s, %s", ErrorPrefix, err.Error()))
+		return connect.NewError(connect.CodeInvalidArgument, fmt.Errorf("%s", ReadableErrorMsg))
 	case model.ParseErrorCode:
-		return connect.NewError(connect.CodeDataLoss, fmt.Errorf("%s, %s", ErrorPrefix, err.Error()))
+		return connect.NewError(connect.CodeDataLoss, fmt.Errorf("%s", ReadableErrorMsg))
 	case model.GeneralErrorCode:
-		return connect.NewError(connect.CodeUnknown, fmt.Errorf("%s, %s", ErrorPrefix, err.Error()))
+		return connect.NewError(connect.CodeUnknown, fmt.Errorf("%s", ReadableErrorMsg))
 	}
 
 	return err

flagd/pkg/service/flag-evaluation/flag_evaluator_test.go

@@ -986,3 +986,49 @@ func TestFlag_Evaluation_ErrorCodes(t *testing.T) {
 		}
 	}
 }
+
+func Test_Readable_ErrorMessage(t *testing.T) {
+	tests := []struct {
+		name string
+		code string
+		want string
+	}{
+		{
+			name: "Testing flag not found error",
+			code: model.FlagNotFoundErrorCode,
+			want: model.ReadableErrorMessage[model.FlagNotFoundErrorCode],
+		},
+		{
+			name: "Testing parse error",
+			code: model.ParseErrorCode,
+			want: model.ReadableErrorMessage[model.ParseErrorCode],
+		},
+		{
+			name: "Testing type mismatch error",
+			code: model.TypeMismatchErrorCode,
+			want: model.ReadableErrorMessage[model.TypeMismatchErrorCode],
+		},
+		{
+			name: "Testing general error",
+			code: model.GeneralErrorCode,
+			want: model.ReadableErrorMessage[model.GeneralErrorCode],
+		},
+		{
+			name: "Testing flag disabled error",
+			code: model.FlagDisabledErrorCode,
+			want: model.ReadableErrorMessage[model.FlagDisabledErrorCode],
+		},
+		{
+			name: "Testing invalid context error",
+			code: model.InvalidContextCode,
+			want: model.ReadableErrorMessage[model.InvalidContextCode],
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := model.GetErrorMessage(tt.code); got != tt.want {
+				t.Errorf("GetErrorMessage() Wanted: %v , but got: %v as a ReadableErrorMessage", tt.want, got)
+			}
+		})
+	}
+}