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Use TCP_NOOPT to restrict MSS on BSD-based OSes

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This commit is contained in:
Cameron Gutman 2019-12-01 15:22:18 -08:00
commit e938d84cdb
1 changed files with 11 additions and 2 deletions
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13
src/PlatformSockets.c
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@ -220,7 +220,7 @@ SOCKET connectTcpSocket(struct sockaddr_storage* dstaddr, SOCKADDR_LEN addrlen,
// Note: This only changes the max packet size we can *receive* from the host PC. // Note: This only changes the max packet size we can *receive* from the host PC.
// We still must split our own sends into smaller chunks with TCP_NODELAY enabled to // We still must split our own sends into smaller chunks with TCP_NODELAY enabled to
// avoid MTU issues on the way out to to the target. // avoid MTU issues on the way out to to the target.
#ifdef LC_WINDOWS #if defined(LC_WINDOWS)
// Windows doesn't support setting TCP_MAXSEG but IP_PMTUDISC_DONT forces the MSS to the protocol // Windows doesn't support setting TCP_MAXSEG but IP_PMTUDISC_DONT forces the MSS to the protocol
// minimum which is what we want here. Linux doesn't do this (disabling PMTUD just avoids setting DF). // minimum which is what we want here. Linux doesn't do this (disabling PMTUD just avoids setting DF).
if (dstaddr->ss_family == AF_INET) { if (dstaddr->ss_family == AF_INET) {
@ -235,7 +235,16 @@ SOCKET connectTcpSocket(struct sockaddr_storage* dstaddr, SOCKADDR_LEN addrlen,
Limelog("setsockopt(IPV6_MTU_DISCOVER, IP_PMTUDISC_DONT) failed: %d\n", val, (int)LastSocketError()); Limelog("setsockopt(IPV6_MTU_DISCOVER, IP_PMTUDISC_DONT) failed: %d\n", val, (int)LastSocketError());
} }
} }
#else #elif defined(TCP_NOOPT)
// On BSD-based OSes (including macOS/iOS), TCP_NOOPT seems to be the only way to
// restrict MSS to the minimum. It strips all options out of the SYN packet which
// forces the remote party to fall back to the minimum MSS. TCP_MAXSEG doesn't seem
// to work correctly for outbound connections on macOS/iOS.
val = 1;
if (setsockopt(s, IPPROTO_TCP, TCP_NOOPT, (char*)&val, sizeof(val)) < 0) {
Limelog("setsockopt(TCP_NOOPT, %d) failed: %d\n", val, (int)LastSocketError());
}
#elif defined(TCP_MAXSEG)
val = dstaddr->ss_family == AF_INET ? TCPv4_MSS : TCPv6_MSS; val = dstaddr->ss_family == AF_INET ? TCPv4_MSS : TCPv6_MSS;
if (setsockopt(s, IPPROTO_TCP, TCP_MAXSEG, (char*)&val, sizeof(val)) < 0) { if (setsockopt(s, IPPROTO_TCP, TCP_MAXSEG, (char*)&val, sizeof(val)) < 0) {
Limelog("setsockopt(TCP_MAXSEG, %d) failed: %d\n", val, (int)LastSocketError()); Limelog("setsockopt(TCP_MAXSEG, %d) failed: %d\n", val, (int)LastSocketError());