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Choose client ports in a well-known range #134

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Choose client ports in a well-known range #134

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24 changes: 11 additions & 13 deletions lib/ZOpenPort.c
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ ZOpenPort(u_short *port)
struct sockaddr_in bindin;
unsigned int len;
int val = 1;
int ret;

(void) ZClosePort();

Expand All @@ -38,17 +39,20 @@ ZOpenPort(u_short *port)
if (setsockopt(__Zephyr_fd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof val) < 0)
return errno;
} else {
bindin.sin_port = 0;
bindin.sin_port = htons(60000);
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Note that Mosh uses almost the same port range, picking the first available port in 60001–60999.

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Mosh's range was prominent in shaping my initial choice here (though I find it amusing that I was off by one for the start port!). Probably I was thinking that a single hole in the firewall would cover both, but some amount of discussion is appropriate before a choice is made.

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I’m a little worried it might break Mosh for users who only open one firewall port for it instead of a range. Only a little, since those users are probably smart enough to figure out what happened. Maybe that risk can be avoided by starting at 60500 or something.

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We had a bit of discussion about this involving Keith from the mosh side and a few other folks. The conclusion (if there could be said to be one) was:

To the extent it matters, though, I guess it's probably better for
every random UDP app that needs a range of port numbers (instead of a
single port that can be multiplexed because each peer will use a
different IP address or port) to 'standardize' on 60000-61000 than for
us all to go separately. So, go for it if you want.

}

bindin.sin_addr.s_addr = INADDR_ANY;

if (bind(__Zephyr_fd, (struct sockaddr *)&bindin, sizeof(bindin)) < 0) {
if (errno == EADDRINUSE && port && *port)
return ZERR_PORTINUSE;
else
return errno;
}
do {
ret = bind(__Zephyr_fd, (struct sockaddr *)&bindin, sizeof(bindin));
if (ret < 0 && !(port && *port))
bindin.sin_port++;
} while (ret < 0 && errno == EADDRINUSE && !(port && *port));
if (ret < 0 && errno == EADDRINUSE)
return ZERR_PORTINUSE;
else if (ret < 0)
return errno;

if (port && *port) {
/* turn SO_REUSEADDR back off so no one else can steal it */
Expand All @@ -57,12 +61,6 @@ ZOpenPort(u_short *port)
return errno;
}

if (!bindin.sin_port) {
len = sizeof(bindin);
if (getsockname(__Zephyr_fd, (struct sockaddr *)&bindin, &len))
return errno;
}

__Zephyr_port = bindin.sin_port;
__Zephyr_open = 1;

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