clientdetails: handle error interfaces in Details somewhat

internal/worker/clienterrors/errors.go

@@ -1,7 +1,9 @@
 package clienterrors
 
 import (
+	"encoding/json"
 	"fmt"
+	"reflect"
 )
 
 const (
@@ -58,6 +60,70 @@ func (e *Error) String() string {
 	return fmt.Sprintf("Code: %d, Reason: %s, Details: %v", e.ID, e.Reason, e.Details)
 }
 
+func ensureNoErrs(v reflect.Value) error {
+	switch v.Kind() {
+	case reflect.Interface:
+		if errIf, ok := v.Interface().(error); ok {
+			if errIf != nil {
+				return fmt.Errorf("%v", errIf.Error())
+			}
+		}
+	case reflect.Ptr:
+		if err := ensureNoErrs(v.Elem()); err != nil {
+			return err
+		}
+	case reflect.Struct:
+		for i := 0; i < v.NumField(); i++ {
+			if err := ensureNoErrs(v.Field(i)); err != nil {
+				return err
+			}
+		}
+	case reflect.Slice, reflect.Array:
+		for i := 0; i < v.Len(); i++ {
+			if err := ensureNoErrs(v.Index(i)); err != nil {
+				return err
+			}
+		}
+	case reflect.Map:
+		for _, key := range v.MapKeys() {
+			if err := ensureNoErrs(v.MapIndex(key)); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (e *Error) MarshalJSON() ([]byte, error) {
+	var details interface{}
+	switch v := e.Details.(type) {
+	case error:
+		details = v.Error()
+	case []error:
+		details = make([]string, 0, len(v))
+		for _, err := range v {
+			if err != nil {
+				details = append(details.([]string), err.Error())
+			}
+		}
+	default:
+		if err := ensureNoErrs(reflect.ValueOf(v)); err != nil {
+			return nil, fmt.Errorf("found nested error in %+v: %v", e.Details, err)
+		}
+		details = e.Details
+	}
+
+	return json.Marshal(&struct {
+		ID      ClientErrorCode `json:"id"`
+		Reason  string          `json:"reason"`
+		Details interface{}     `json:"details,omitempty"`
+	}{
+		ID:      e.ID,
+		Reason:  e.Reason,
+		Details: details,
+	})
+}
+
 const (
 	JobStatusSuccess        = "2xx"
 	JobStatusUserInputError = "4xx"

internal/worker/clienterrors/errors_test.go

@@ -0,0 +1,65 @@
+package clienterrors_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/osbuild/osbuild-composer/internal/worker/clienterrors"
+)
+
+type customErr struct{}
+
+func (ce *customErr) Error() string {
+	return "customErr"
+}
+
+func TestErrorInterface(t *testing.T) {
+	for _, tc := range []struct {
+		err         error
+		expectedStr string
+	}{
+		{fmt.Errorf("some error"), "some error"},
+		{&customErr{}, "customErr"},
+	} {
+		wce := clienterrors.WorkerClientError(2, "reason", tc.err)
+		assert.Equal(t, fmt.Sprintf("Code: 2, Reason: reason, Details: %s", tc.expectedStr), wce.String())
+	}
+}
+
+func TestErrorJSONMarshal(t *testing.T) {
+	for _, tc := range []struct {
+		err         interface{}
+		expectedStr string
+	}{
+		{fmt.Errorf("some-error"), `"some-error"`},
+		{[]error{fmt.Errorf("err1"), fmt.Errorf("err2")}, `["err1","err2"]`},
+		{"random detail", `"random detail"`},
+	} {
+		json, err := json.Marshal(clienterrors.WorkerClientError(2, "reason", tc.err))
+		assert.NoError(t, err)
+		assert.Equal(t, fmt.Sprintf(`{"id":2,"reason":"reason","details":%s}`, tc.expectedStr), string(json))
+	}
+}
+
+func TestErrorJSONMarshalDetectsNestedErrs(t *testing.T) {
+	details := struct {
+		Unrelated string
+		NestedErr error
+		Nested    struct {
+			DeepErr error
+		}
+	}{
+		Unrelated: "unrelated",
+		NestedErr: fmt.Errorf("some-nested-error"),
+		Nested: struct {
+			DeepErr error
+		}{
+			DeepErr: fmt.Errorf("deep-err"),
+		},
+	}
+	_, err := json.Marshal(clienterrors.WorkerClientError(2, "reason", details))
+	assert.Equal(t, `json: error calling MarshalJSON for type *clienterrors.Error: found nested error in {Unrelated:unrelated NestedErr:some-nested-error Nested:{DeepErr:deep-err}}: some-nested-error`, err.Error())
+}