code: func (w *Whisper) GetEnvelope(hash common.Hash) *Envelope {
  	w.poolMu.RLock()
  	defer w.poolMu.RUnlock()
  	return w.envelopes[hash]
  }
docs: // GetEnvelope retrieves an envelope from the message queue by its hash.
  // It returns nil if the envelope can not be found.