ad546ec60
Denys Vlasenko
2013-07-27
Subject
Update docs/tcp.txt
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docs/tcp.txt+18 -1
| @@ -39,11 +39,28 @@ Solution #1: block until sending is done: | |
| close(sock); | |
| Solution #2: tell kernel that you are done sending. | |
| - | This makes kernel send FIN, not RST: |
| + | This makes kernel send FIN after all data is written: |
| shutdown(sock, SHUT_WR); | |
| close(sock); | |
| + | However, experiments on Linux 3.9.4 show that kernel can return from |
| + | shutdown() and from close() before all data is sent, |
| + | and if peer sends any data to us after this, kernel stll responds with |
| + | RST before all our data is sent. |
| + | |
| + | In practice the protocol in use often does not allow peer to send |
| + | such data to us, in which case this solution is acceptable. |
| + | |
| + | If you know that peer is going to close its end after it sees our FIN |
| + | (as EOF), it might be a good idea to perform a read after shutdown(). |
| + | When read finishes with 0-sized result, we conclude that peer received all |
| + | the data, saw EOF, and closed its end. |
| + | |
| + | However, this incurs small performance penalty (we run for a longer time) |
| + | and requires safeguards (nonblocking reads, timeouts etc) against |
| + | malicious peers which don't close the connection. |
| + | |
| Defeating Nagle. | |