add black-box debug harness

internal/harness/observe.go

@@ -0,0 +1,92 @@
+package harness
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func timeoutMS(ms int) time.Duration {
+	if ms <= 0 {
+		ms = 5000
+	}
+	return time.Duration(ms) * time.Millisecond
+}
+
+func valueAt(v any, path string) (any, bool) {
+	if path == "" {
+		return v, true
+	}
+	cur := v
+	for _, part := range strings.Split(path, ".") {
+		switch x := cur.(type) {
+		case map[string]any:
+			next, ok := x[part]
+			if !ok {
+				return nil, false
+			}
+			cur = next
+		case []any:
+			i, err := strconv.Atoi(part)
+			if err != nil || i < 0 || i >= len(x) {
+				return nil, false
+			}
+			cur = x[i]
+		default:
+			return nil, false
+		}
+	}
+	return cur, true
+}
+
+func assertJSONValue(raw json.RawMessage, path string, equals any, contains string, allowSubstring bool) error {
+	var v any
+	if err := json.Unmarshal(raw, &v); err != nil {
+		return err
+	}
+	got, ok := valueAt(v, path)
+	if !ok {
+		return fmt.Errorf("path %q not found in %s", path, string(raw))
+	}
+	if equals != nil {
+		if !reflect.DeepEqual(normalizeJSON(equals), normalizeJSON(got)) {
+			return fmt.Errorf("path %q = %#v, want %#v", path, got, equals)
+		}
+	}
+	if contains != "" {
+		switch x := got.(type) {
+		case string:
+			if !strings.Contains(x, contains) {
+				return fmt.Errorf("path %q = %q, does not contain %q", path, x, contains)
+			}
+		default:
+			b, _ := json.Marshal(x)
+			if allowSubstring && strings.Contains(string(b), contains) {
+				return nil
+			}
+			return fmt.Errorf("path %q is not a string: %#v", path, got)
+		}
+	}
+	return nil
+}
+
+func normalizeJSON(v any) any {
+	switch x := v.(type) {
+	case int:
+		return float64(x)
+	case int64:
+		return float64(x)
+	case []any:
+		for i := range x {
+			x[i] = normalizeJSON(x[i])
+		}
+	case map[string]any:
+		for k := range x {
+			x[k] = normalizeJSON(x[k])
+		}
+	}
+	return v
+}