Pull #54 breaks the Windows version of dump1090 due to a bug in the
inet_aton() windows function.
1) Fix the bug in the windows inet_aton()
2) Modify the command line code to strdup() the command line string.
3) Leave the Modes.net_bind_address pointer NULL if no command line
specified
Pull #54 permits changing the default bind address. The default was
127.0.0.1. This prevents external access unless a command line switch is
used. Since many users of dump1090 are using dump1090 as remote receiver
heads for programs such as plane plotter, this is undesirable. If you
want to lock down your RPi for local use only then use the command line
switch. If not, retain legacy open mode by binding to 0.0.0.0 by
default.
Mostly refactoring the common code that was duplicated
between the different output types so that there aren't
many copies floating around.
This introduces "struct net_writer" to store the state of a
particular type of output service - buffers, time of last write,
connection count etc. prepareWrite() / completeWrite() give access
to the buffer and handle the actual writes and flushing when needed.
Heartbeat and time-based flushing move into a generic periodic-work
function.
Update the SBS output code to use the new infrastructure. This makes
a big different to CPU use when under load.
When we read from some client A, we may end up forwarding a message to other
clients. If we forward to some client B and there is a write error, then
we close B and remove it from the client list. However, if before this happened
A->next == B, then the read loop will still be holding on to a pointer to B,
and we crash.
As it's unpredictable what clients could be closed at what point, the simplest
approach is to retain closed clients in the list until we are at a point where
we know there are no stray pointers on stack, and only then modify the list.
This also simplifies anything that has to loop over clients, as it doesn't need
to worry about the current client being freed under it.
Client disconnection appears as a read of 0 bytes.
Without a test for this, dump1090 continues to poll that client forever.
Also, read() may return EWOULDBLOCK as well as EAGAIN
for "no data right now", so handle that.
I don't know if there is an equivalent Win32 bug here as the Win32
interfaces seem subtly different to vanilla POSIX.
The following test/break can probably be removed if Win32 needs
the same fix.
