func (a *Agent) BodyString(bodyString string) *Agent
func (a *Agent) Body(body byte) *Agent
// BodyStream sets request body stream and, optionally body size.
// If bodySize is >= 0, then the bodyStream must provide exactly bodySize bytes
// before returning io.EOF.
// If bodySize < 0, then bodyStream is read until io.EOF.
// bodyStream.Close() is called after finishing reading all body data
// if it implements io.Closer.
// Note that GET and HEAD requests cannot have body.
func (a *Agent) BodyStream(bodyStream io.Reader, bodySize int) *Agent