fix: prettify error response

pkg/quickwit/quickwit.go

@@ -251,6 +251,7 @@ func (ds *QuickwitDatasource) CallResource(ctx context.Context, req *backend.Cal
 	if err != nil {
 		return err
 	}
+	body = normalizeResourceErrorBody(response.StatusCode, body)
 
 	responseHeaders := map[string][]string{
 		"content-type": {"application/json"},
@@ -266,3 +267,19 @@ func (ds *QuickwitDatasource) CallResource(ctx context.Context, req *backend.Cal
 		Body:    body,
 	})
 }
+
+func normalizeResourceErrorBody(statusCode int, body []byte) []byte {
+	if statusCode >= http.StatusOK && statusCode < http.StatusMultipleChoices || json.Valid(body) {
+		return body
+	}
+
+	payload, err := json.Marshal(QuickwitCreationErrorPayload{
+		Message:    strings.TrimSpace(string(body)),
+		StatusCode: statusCode,
+	})
+	if err != nil {
+		return body
+	}
+
+	return payload
+}

pkg/quickwit/quickwit_test.go

@@ -0,0 +1,42 @@
+package quickwit
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNormalizeResourceErrorBody(t *testing.T) {
+	tests := []struct {
+		name       string
+		statusCode int
+		body       string
+		expected   string
+	}{
+		{
+			name:       "wraps plain text upstream error",
+			statusCode: http.StatusGatewayTimeout,
+			body:       "upstream request timeout\n",
+			expected:   `{"message":"upstream request timeout","status":504}`,
+		},
+		{
+			name:       "preserves JSON error",
+			statusCode: http.StatusBadGateway,
+			body:       `{"message":"upstream unavailable","status":502}`,
+			expected:   `{"message":"upstream unavailable","status":502}`,
+		},
+		{
+			name:       "preserves successful response",
+			statusCode: http.StatusOK,
+			body:       `{"fields":{}}`,
+			expected:   `{"fields":{}}`,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			require.Equal(t, test.expected, string(normalizeResourceErrorBody(test.statusCode, []byte(test.body))))
+		})
+	}
+}