The RequestPipe uses a socketpair for streaming response body data
from RequestServer to WebContent. On macOS, the default socket buffer
size for AF_LOCAL sockets is only ~8KB, which meant every read/write
syscall could only transfer ~8KB at a time. For large responses, this
resulted in thousands of tiny reads with significant per-read overhead.
Increase the send and receive buffer sizes to 512KB, matching the
approach already used by IPC::TransportSocket. This dramatically
improves throughput for large response bodies -- for example, fetching
a 25MB file from localhost went from ~850ms to ~25ms in testing.
669bc04295