googleapis/mcp-toolbox · warning

empty web_server_url in versions payload

Error message

empty web_server_url in versions payload

What it means

GetHostURL calls sdk.Versions to learn the Looker web_server_url used as the host URL. If the API call errors, or the payload lacks a non-empty WebServerUrl, this synthetic error is recorded as lastFetchErr while the stale cached URL is preserved. It is a transient-fetch failure, not necessarily fatal to the request.

Source

Thrown at internal/sources/looker/looker.go:347

				urlStr = defaultURL
			}
			err := s.lastFetchErr
			s.hostURLMu.RUnlock()
			return urlStr, err
		}
		s.hostURLMu.RUnlock()

		logger, err := util.LoggerFromContext(ctx)
		if err != nil {
			return defaultURL, err
		}

		// Perform network call outside of locks to prevent blocking concurrent readers
		versionInfo, err := sdk.Versions("", s.ApiSettings)
		if err != nil || versionInfo.WebServerUrl == nil || *versionInfo.WebServerUrl == "" {
			fetchErr := err
			if fetchErr == nil {
				fetchErr = fmt.Errorf("empty web_server_url in versions payload")
			}
			s.hostURLMu.Lock()
			s.lastFetchFailed = true
			s.lastFetchTime = time.Now()
			s.lastFetchErr = fetchErr
			// DO NOT overwrite s.cachedHostURL on transient errors; keep the stale valid URL for stale fallbacks
			s.hostURLMu.Unlock()

			if err != nil {
				logger.WarnContext(ctx, fmt.Sprintf("unable to retrieve host_url via versions, using stale/default fallback: %v", err))
			} else {
				logger.DebugContext(ctx, "versions web_server_url is empty, using stale/default fallback")
			}
			return "", fetchErr
		}

		// Validate the retrieved host_url is a valid absolute HTTP/HTTPS URL
		valURL := *versionInfo.WebServerUrl

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Check the Looker instance Admin > General settings and set the correct Web Server URL
2. Retry the operation — the source keeps the last valid host URL and will re-fetch later
3. Verify network/proxy connectivity from the toolbox to the Looker API
4. Pin to a Looker API version that reliably returns web_server_url in the versions payload

if versionInfo.WebServerUrl == nil || *versionInfo.WebServerUrl == "" {
    // rely on stale cached host URL; log warning
}

_, err := src.GetHostURL(ctx, sdk)
if err != nil && strings.Contains(err.Error(), "empty web_server_url") {
    logger.Warn("using stale cached host URL; will retry versions fetch")
}

When it happens

Trigger: sdk.Versions("", s.ApiSettings) returns err == nil but versionInfo.WebServerUrl is nil or an empty string; or the Versions API call itself fails (which then surfaces the original err instead).

Common situations: Looker instance misconfigured (no web_server_url set in the Looker admin settings); API versions endpoint returning a trimmed/unexpected payload; network proxies stripping fields or intermittent API failures.

Related errors

• unable to parse Timeout string as time.Duration: %s
• client_id and client_secret need to be specified
• client id or client secret not valid
• invalid web_server_url format: %q
• description is required for tool %q

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/119ffd2e60387af3. Report an issue: GitHub.