Add option to not connect jack ports automatically

NEWS

@@ -12,6 +12,8 @@ ver 0.22 (not yet released)
   - ffmpeg: new plugin based on FFmpeg's libavfilter library
   - hdcd: new plugin based on FFmpeg's "af_hdcd" for HDCD playback
   - volume: convert S16 to S24 to preserve quality and reduce dithering noise
+* output
+  - jack: add option "auto_destination_ports"
 * switch to C++17
   - GCC 7 or clang 4 (or newer) recommended
 

doc/plugins.rst

@@ -864,6 +864,10 @@ The jack plugin connects to a `JACK server <http://jackaudio.org/>`_.
      - The names of the JACK source ports to be created. By default, the ports "left" and "right" are created. To use more ports, you have to tweak this option.
    * - **destination_ports A,B**
      - The names of the JACK destination ports to connect to.
+   * - **auto_destination_ports yes|no**
+     - If set to *yes*, then MPD will automatically create connections between the send ports of
+       MPD and receive ports of the first sound card; if set to *no*, then MPD will only create
+       connections to the contents of *destination_ports* if it is set. Enabled by default.
    * - **ringbuffer_size NBYTES**
      - Sets the size of the ring buffer for each channel. Do not configure this value unless you know what you're doing.
 

src/output/plugins/JackOutputPlugin.cxx

@@ -57,6 +57,8 @@ struct JackOutput final : AudioOutput {
 
 	std::string destination_ports[MAX_PORTS];
 	unsigned num_destination_ports;
+	/* overrides num_destination_ports*/
+	bool auto_destination_ports;
 
 	size_t ringbuffer_size;
 
@@ -201,6 +203,8 @@ JackOutput::JackOutput(const ConfigBlock &block)
 		num_destination_ports = 0;
 	}
 
+	auto_destination_ports = block.GetBlockValue("auto_destination_ports", true);
+
 	if (num_destination_ports > 0 &&
 	    num_destination_ports != num_source_ports)
 		FormatWarning(jack_output_domain,
@@ -498,6 +502,10 @@ JackOutput::Start()
 	const char *dports[MAX_PORTS], **jports;
 	unsigned num_dports;
 	if (num_destination_ports == 0) {
+		/* if user requests no auto connect, we are done */
+		if (!auto_destination_ports) {
+			return;
+		}
 		/* no output ports were configured - ask libjack for
 		   defaults */
 		jports = jack_get_ports(client, nullptr, nullptr,