Send a record in parts cut where a packet is full, not 1000-byte pieces

A record that does not fit what is left of a packet goes in part when at
least 64 bytes fit; its parts keep their cuts, so what a packet carried
is whole parts. The receiver keeps the spans it had of a record, and a
record coming in order from its start fills the line's tail with no
allocation. Packets fall by 8% for 1 KiB records and 10% for 16 KiB;
the CPU a record is the same at 61 B and 1 KiB and 5% less at 16 KiB.

1 files changed, 3 insertions, 2 deletions

diff --git a/link/link-protocol.h b/link/link-protocol.h
index 3f71809..e82e599 100644
--- a/link/link-protocol.h
+++ b/link/link-protocol.h
@@ -32,8 +32,9 @@
  *                shape of the messages (the sender's output and the
  *                receiver's input must have the same): the stream the
  *                records after it are of
- *   0x02 RECORD  u64 number, u32 size, u32 offset, u16 length, bytes: a piece
- *                of a saved send (pieces are 1000 bytes, the last shorter)
+ *   0x02 RECORD  u64 number, u32 size, u32 offset, u16 length, bytes: part
+ *                of a saved send (a send too large for what is left of a
+ *                packet goes in parts, cut where the packet is full)
  *   0x03 ACK     u64 largest number, u32 delay (µs), u8 ranges, each as u64
  *                first and u64 last, newest first
  *   0x04 STORED  source, input (as STREAM), u64 the last number heard