premiere-libtorrent/docs/read_disk_buffers.diagram

                     "copy into peer's"                 "encrypt in place"
+------------------+ "send buffer"    +---------------+ "(no copy)"       +---------------+
| "receive buffer" +----------------->| "send buffer" +------------------>| "encrypted"   |
|                  |                  |               |                   | "send buffer" |
+------------------+                  +---------------+                   +---------------+
        ^                                                                   |
        | "read() from file"                            "write() to socket" | 
        | "(copy)"               "user space"           "(copy)"            | 
- - - - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + - - -
        |                       "kernel space"                              |
        |                                                                   v
+-------+-------------+                                               +-----------------+
| "kernel page cache" |                                               | "socket kernel" |
|                     |                                               | "buffer"        |
+---------------------+                                               +-----------------+