server.c kept an array of all of its active clients, calling realloc(3)
everytime its size had to be modified. However, reallocating this array
had the undesired consequence of moving other active clients to other
memory locations.
Potentially, this would result in dangling pointers from other
components that also kept pointers to struct server_client instances
e.g.: handler.c.
For this reason, the array-based approach has been completely dropped,
in favour of a doubly-linked list.
Under some circumstances, clients could cause SIGPIPE to slcl. Since
this signal was not handled by server.c (i.e., via sigaction(3)), slcl
would crash without any error messages printed to stderr.
In such situation, SIGPIPE should not be usually considered a fatal
error, so it is preferrable to close the connection and keep working.
select(2) has a number of well-known issues (e.g.: FD_SETSIZE limiting
the maximum amount of file descriptors to watch) that are mostly solved
by poll(2) and thus can be used as a drop-in replacement.
According to C99 §7.20.3.4:
If memory for the new object cannot be allocated, the old object is not
deallocated and its value is unchanged.
Therefore, a temporary pointer must be used to ensure the original
object can still be deallocated should realloc(3) return a null pointer.
Xavier Del Campo Romero