feat: add passthru client example

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>

examples/jacket_passthru.nim

@@ -0,0 +1,82 @@
+## Simple JACK client, which just passes audio through
+## from its single (mono) input to its single (mono) output.
+
+import std/[logging, os]
+import signal
+import jacket
+
+var
+    jclient: ClientP
+    status: cint
+    exitSignalled: bool = false
+    inpPort, outPort: PortP
+    log = newConsoleLogger(when defined(release): lvlInfo else: lvlDebug)
+
+type JackBufferP = ptr UncheckedArray[DefaultAudioSample]
+
+proc errorCb(msg: cstring) {.cdecl.} =
+    # Suppress verbose JACK error messages when server is not available by 
+    # default. Compile in non-release mode or pass ``lvlDebug`` or lower
+    # when creating the logger above to enable them.
+    debug "JACK error: " & $msg
+
+proc cleanup(sig: cint = 0) =
+    debug "Cleaning up..."
+    if jclient != nil:
+        discard jclient.deactivate()
+        discard jclient.clientClose()
+        jclient = nil
+
+proc signalCb(sig: cint) {.noconv.} =
+    debug "Received signal: " & $sig
+    exitSignalled = true
+
+proc shutdownCb(arg: pointer = nil) {.cdecl.} =
+    warn "JACK server has shut down."
+    exitSignalled = true
+
+proc processCb(nFrames: NFrames, arg: pointer): cint {.cdecl.} =
+    var inpbuf = cast[JackBufferP](portGetBuffer(inpPort, nFrames))
+    var outbuf = cast[JackBufferP](portGetBuffer(outPort, nFrames))
+
+    # copy samples from input to output buffer
+    for i in 0 ..< nFrames:
+        outbuf[i] = inpbuf[i]
+
+addHandler(log)
+
+# Create JACK Client ptr
+setErrorFunction(errorCb)
+jclient = clientOpen("passthru", NullOption, status.addr)
+debug "JACK server status: " & $status
+
+if jclient == nil:
+    error getJackStatusErrorString(status)
+    quit 1
+
+# Register audio input and output ports
+inpPort = jclient.portRegister("in_1", JACK_DEFAULT_AUDIO_TYPE, PortIsInput, 0)
+outPort = jclient.portRegister("out_1", JACK_DEFAULT_AUDIO_TYPE, PortIsOutput, 0)
+
+# Register JACK callbacks
+jclient.onShutdown(shutdownCb)
+
+if jclient.setProcessCallback(processCb, nil) != 0:
+    error "Could not set JACK process callback function."
+    cleanup()
+    quit QuitFailure
+
+# Handle signals
+when defined(windows):
+    setSignalProc(signalCb, SIGABRT, SIGINT, SIGTERM)
+else:
+    setSignalProc(signalCb, SIGABRT, SIGHUP, SIGINT, SIGQUIT, SIGTERM)
+
+# Activate JACK client ...
+if jclient.activate() == 0:
+    # ... and keep running until a signal is received
+    while not exitSignalled:
+        sleep(50)
+
+# Deactivate client and close server connection
+cleanup()