A Lazy Reverse Proxy

I want vlc to stream video from a webcam onto the internet.

This works, but the problem is that the vlc instance is running all of the time, taking up CPU even when nobody is connected to the stream.

If only vlc would stop processing video where there are no clients.

Here's an idea: shut down vlc when there are no clients, and start it again when somebody connects. Concurrent connections can share the same vlc instance.

$ ./on-demand-server :8000 :8080 -- cvlc -v v4l2:///dev/video2 --sout '#transcode{vcodec=theo,fps=4}:standard{access=http,mux=ogg,dst=:8080}'

./on-demand-server is the server that will act as a reverse proxy to vlc, managing the vlc instance (child process) as needed.
:8000 is the interface on which on-demand-server will listen. That's port 8000, and since the host was omitted it defaults to 0.0.0.0 ("all interfaces").
:8080 is the interface to which on-demand-server will connect to contact the vlc child process. That's port 8080, and since the host was omitted it defaults to 127.0.0.1.
-- separates the on-demand-server options from the child process command invocation.
cvlc -v ... is the command the on-demand-server will run to spawn the vlc server.

Example

dummy.js is an example echo server that you can use to play with on-demand-server. It listens on port 1337.

In one shell,

$ ./on-demand-server localhost:8000 :1337 -- node dummy.js
main listening on localhost:8000

Then, in another shell:

$ telnet localhost 8000
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

After a moment, you'll see this is the first shell:

Received connection.
num_open_connections incremented to 1
backend stdout> dummy listening on 127.0.0.1:1337

and then you can interact with the dummy in the second shell:

Echo server
hello
echo line> hello
it works
echo line> it works
^]
telnet> Connection closed.

The disconnect will decrement the child process's connection count. Now being zero, the child process is terminated after a few seconds.

num_open_connections decremented to 0
backend stdout> dummy received signal SIGTERM.

If you connect again, a new dummy.js child process will be spawned.

dgoffredo/on-demand-server

A Lazy Reverse Proxy

Example