code: func (cli *Client) Ping(ctx context.Context) (types.Ping, error) {
  	var ping types.Ping
  
  	// Using cli.buildRequest() + cli.doRequest() instead of cli.sendRequest()
  	// because ping requests are used during  API version negotiation, so we want
  	// to hit the non-versioned /_ping endpoint, not /v1.xx/_ping
  	req, err := cli.buildRequest("HEAD", path.Join(cli.basePath, "/_ping"), nil, nil)
  	if err != nil {
  		return ping, err
  	}
  	serverResp, err := cli.doRequest(ctx, req)
  	if err == nil {
  		defer ensureReaderClosed(serverResp)
  		switch serverResp.statusCode {
  		case http.StatusOK, http.StatusInternalServerError:
  			// Server handled the request, so parse the response
  			return parsePingResponse(cli, serverResp)
  		}
  	}
  
  	req, err = cli.buildRequest("GET", path.Join(cli.basePath, "/_ping"), nil, nil)
  	if err != nil {
  		return ping, err
  	}
  	serverResp, err = cli.doRequest(ctx, req)
  	defer ensureReaderClosed(serverResp)
  	if err != nil {
  		return ping, err
  	}
  	return parsePingResponse(cli, serverResp)
  }
docs: // Ping pings the server and returns the value of the "Docker-Experimental",
  // "Builder-Version", "OS-Type" & "API-Version" headers. It attempts to use
  // a HEAD request on the endpoint, but falls back to GET if HEAD is not supported
  // by the daemon.