output/jack: enable on Windows

This enables the JACK output plugin on Windows, but doesn't link
against libjack64.dll, instead loads the DLL at runtime with
LoadLibrary().  This kludge avoids the extremely fragile JACK shared
memory protocol by using the system's libjack64.dll, without requiring
the same DLL at build time.

python/build/jack.py

@@ -0,0 +1,47 @@
+import os, shutil
+import re
+
+from .project import Project
+
+# This class installs just the public headers and a fake pkg-config
+# file which defines the macro "DYNAMIC_JACK".  This tells MPD's JACK
+# output plugin to load the libjack64.dll dynamically using
+# LoadLibrary().  This kludge avoids the runtime DLL dependency for
+# users who don't use JACK, but still allows using the system JACK
+# client library.
+#
+# The problem with JACK is that it uses an extremely fragile shared
+# memory protocol to communicate with the daemon.  One needs to use
+# daemon and client library from the same build.  That's why we don't
+# build libjack statically here; it would probably not be compatible
+# with the user's JACK daemon.
+
+class JackProject(Project):
+    def __init__(self, url, md5, installed,
+                 **kwargs):
+        m = re.match(r'.*/v([\d.]+)\.tar\.gz$', url)
+        self.version = m.group(1)
+        Project.__init__(self, url, md5, installed,
+                         name='jack2', version=self.version,
+                         base='jack2-' + self.version,
+                         **kwargs)
+
+    def build(self, toolchain):
+        src = self.unpack(toolchain)
+
+        includes = ['jack.h', 'ringbuffer.h', 'systemdeps.h', 'transport.h', 'types.h', 'weakmacros.h']
+        includedir = os.path.join(toolchain.install_prefix, 'include', 'jack')
+        os.makedirs(includedir, exist_ok=True)
+
+        for i in includes:
+            shutil.copyfile(os.path.join(src, 'common', 'jack', i),
+                            os.path.join(includedir, i))
+
+        with open(os.path.join(toolchain.install_prefix, 'lib', 'pkgconfig', 'jack.pc'), 'w') as f:
+            print("prefix=" + toolchain.install_prefix, file=f)
+            print("", file=f)
+            print("Name: jack", file=f)
+            print("Description: dummy", file=f)
+            print("Version: " + self.version, file=f)
+            print("Libs: ", file=f)
+            print("Cflags: -DDYNAMIC_JACK", file=f)

python/build/libs.py

@@ -9,6 +9,7 @@ from build.autotools import AutotoolsProject
 from build.ffmpeg import FfmpegProject
 from build.openssl import OpenSSLProject
 from build.boost import BoostProject
+from build.jack import JackProject
 
 libmpdclient = MesonProject(
     'https://www.musicpd.org/download/libmpdclient/2/libmpdclient-2.19.tar.xz',
@@ -443,6 +444,12 @@ libnfs = AutotoolsProject(
     autoreconf=True,
 )
 
+jack = JackProject(
+    'https://github.com/jackaudio/jack2/archive/v1.9.17.tar.gz',
+    '38f674bbc57852a8eb3d9faa1f96a0912d26f7d5df14c11005ad499c8ae352f2',
+    'lib/pkgconfig/jack.pc',
+)
+
 boost = BoostProject(
     'https://dl.bintray.com/boostorg/release/1.75.0/source/boost_1_75_0.tar.bz2',
     '953db31e016db7bb207f11432bef7df100516eeb746843fa0486a222e3fd49cb',