---
title: client.socket.tcpi_rcv_space
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/client-connection/client-socket-tcpi-rcv-space
---

**Type:** INTEGER  
**Access:** read-only

**Available in:** recv, deliver, log, error

The number of received bytes that were transferred to userspace over 
the previous round trip time (RTT). This supports TCP stack receive 
window (RWIN) auto-tuning and does not have any known VCL use cases.