tcp: Weird segmentation

[Dirbaio]

This is a trace of a smoltcp app writing infinite data to a TcpSocket.

First 6 segments are full-sized. Next one is 92 bytes because buffer size is 8192, which is not a multiple of MSS. (1350*6 + 92 = 8192)

After that, segment sizes are completely all over the place. Maybe this is related to Silly Window Syndrome?

18627   246407.367732154   TCP  66     27625 → 8000 [SYN] Seq=0 Win=8192 Len=0 MSS=1350 WS=1 SACK_PERM=1
18628   246407.367759045   TCP  66     8000 → 27625 [SYN, ACK] Seq=0 Ack=1 Win=64240 Len=0 MSS=1460 SACK_PERM=1 WS=128
18629   246407.846954586   TCP  60     27625 → 8000 [ACK] Seq=1 Ack=1 Win=8192 Len=0
18630   246407.881168803   TCP  1404   27625 → 8000 [ACK] Seq=1 Ack=1 Win=8192 Len=1350
18631   246407.881181694   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=1351 Win=63104 Len=0
18632   246407.921754133   TCP  1404   27625 → 8000 [ACK] Seq=1351 Ack=1 Win=8192 Len=1350
18633   246407.921770507   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=2701 Win=63104 Len=0
18634   246408.200335031   TCP  1404   27625 → 8000 [ACK] Seq=2701 Ack=1 Win=8192 Len=1350
18635   246408.200352648   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=4051 Win=63104 Len=0
18636   246408.252340503   TCP  1404   27625 → 8000 [ACK] Seq=4051 Ack=1 Win=8192 Len=1350
18637   246408.252371854   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=5401 Win=63104 Len=0
18638   246408.301253002   TCP  1404   27625 → 8000 [ACK] Seq=5401 Ack=1 Win=8192 Len=1350
18639   246408.301297549   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=6751 Win=63104 Len=0
18640   246408.333256171   TCP  1404   27625 → 8000 [ACK] Seq=6751 Ack=1 Win=8192 Len=1350
18641   246408.333289920   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=8101 Win=63104 Len=0
18642   246408.334007471   TCP  146    27625 → 8000 [PSH, ACK] Seq=8101 Ack=1 Win=8192 Len=92
18643   246408.334022024   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=8193 Win=64128 Len=0
18644   246408.496982823   TCP  455    27625 → 8000 [ACK] Seq=8193 Ack=1 Win=8192 Len=401
18645   246408.497025414   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=8594 Win=63744 Len=0
18646   246408.503911995   TCP  154    27625 → 8000 [ACK] Seq=8594 Ack=1 Win=8192 Len=100
18647   246408.503941886   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=8694 Win=64128 Len=0
18648   246408.657069002   TCP  452    27625 → 8000 [ACK] Seq=8694 Ack=1 Win=8192 Len=398
18649   246408.657094871   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=9092 Win=63744 Len=0
18650   246408.662975286   TCP  157    27625 → 8000 [ACK] Seq=9092 Ack=1 Win=8192 Len=103
18651   246408.662995152   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=9195 Win=64128 Len=0
18652   246408.825227055   TCP  449    27625 → 8000 [ACK] Seq=9195 Ack=1 Win=8192 Len=395
18653   246408.825268865   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=9590 Win=63744 Len=0
18654   246408.832004722   TCP  160    27625 → 8000 [ACK] Seq=9590 Ack=1 Win=8192 Len=106
18655   246408.832034262   TCP  54     8000 → 27625 [ACK] Seq=1 Ack=9696 Win=64128 Len=0

[Dirbaio]

Cause is lack of Nagle's Algorithm.

[Dirbaio]

Turns out that it was caused by #500 too, either way this should be fixed now.