audio: add simple ALSA interface

amodem/__main__.py

@@ -60,8 +60,10 @@ class Decompressor(object):
         self.stream.write(self.obj.flush())
 
 
-def FileType(mode, audio_interface=None):
+def FileType(mode, interface_factory=None):
     def opener(fname):
+        audio_interface = interface_factory() if interface_factory else None
+
         assert 'r' in mode or 'w' in mode
         if audio_interface is None and fname is None:
             fname = '-'
@@ -97,20 +99,11 @@ def get_volume_cmd(args):
                 return c[args.command]
 
 
-class _DummyContextManager(object):
-
-    def __enter__(self):
-        pass
-
-    def __exit__(self, *args):
-        pass
-
-
 def wrap(cls, stream, enable):
     return cls(stream) if enable else stream
 
 
-def create_parser(description, interface):
+def create_parser(description, interface_factory):
     p = argparse.ArgumentParser(description=description)
     subparsers = p.add_subparsers()
 
@@ -135,7 +128,7 @@ def create_parser(description, interface):
             volume_cmd=get_volume_cmd(args)
         ),
         input_type=FileType('rb'),
-        output_type=FileType('wb', interface),
+        output_type=FileType('wb', interface_factory),
         command='send'
     )
 
@@ -162,7 +155,7 @@ def create_parser(description, interface):
             config=config, src=args.src, verbose=args.verbose,
             volume_cmd=get_volume_cmd(args)
         ),
-        input_type=FileType('rb', interface),
+        input_type=FileType('rb', interface_factory),
         output_type=FileType('wb'),
         command='recv'
     )
@@ -194,8 +187,12 @@ def _main():
     description = fmt.format(version.__doc__,
                              config.modem_bps / 1e3, len(config.symbols),
                              config.Nfreq, config.Fs / 1e3)
-    interface = audio.Interface(config=config)
-    p = create_parser(description, interface)
+    interface = None
+
+    def interface_factory():
+        return interface
+
+    p = create_parser(description, interface_factory)
 
     args = p.parse_args()
     if args.verbose == 0:
@@ -218,9 +215,11 @@ def _main():
         import pylab  # pylint: disable=import-error
         args.pylab = pylab
 
-    if args.audio_library == '-':
-        interface = _DummyContextManager()
+    if args.audio_library == 'ALSA':
+        from . import alsa
+        interface = alsa.Interface(config)
     else:
+        interface = audio.Interface(config)
         interface.load(args.audio_library)
 
     with interface:
@@ -232,9 +231,9 @@ def _main():
             else:
                 args.calib(config=config, args=args)
         finally:
-            log.debug('Closing input and output')
             args.src.close()
             args.dst.close()
+            log.debug('Finished I/O')
 
 
 if __name__ == '__main__':

amodem/alsa.py

@@ -0,0 +1,65 @@
+import subprocess
+import logging
+
+log = logging.getLogger(__name__)
+
+
+class Interface(object):
+
+    RECORDER = 'arecord'
+    PLAYER = 'aplay'
+
+    def __init__(self, config):
+        self.config = config
+        rate = int(config.Fs)
+        bits_per_sample = config.bits_per_sample
+        assert bits_per_sample == 16
+
+        args = '-f S{:d}_LE -c 1 -r {:d} -T 100 -q -'
+        args = args.format(bits_per_sample, rate).split()
+
+        self.record_cmd = [self.RECORDER] + args
+        self.play_cmd = [self.PLAYER] + args
+        self.processes = []
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        for p in self.processes:
+            try:
+                p.wait()
+            except OSError:
+                log.warning('%s failed', p)
+
+    def launch(self, **kwargs):
+        log.debug('Launching subprocess: %s', kwargs)
+        p = subprocess.Popen(**kwargs)
+        self.processes.append(p)
+        return p
+
+    def recorder(self):
+        return Recorder(self)
+
+    def player(self):
+        return Player(self)
+
+
+class Recorder(object):
+    def __init__(self, lib):
+        self.p = lib.launch(args=lib.record_cmd, stdout=subprocess.PIPE)
+        self.read = self.p.stdout.read
+        self.bufsize = 4096
+
+    def close(self):
+        self.p.kill()
+
+
+class Player(object):
+    def __init__(self, lib):
+        self.p = lib.launch(args=lib.play_cmd, stdin=subprocess.PIPE)
+        self.write = self.p.stdin.write
+
+    def close(self):
+        self.p.stdin.close()
+        self.p.wait()

tests/test_alsa.py

@@ -0,0 +1,40 @@
+from amodem import alsa, config
+
+import mock
+
+
+def test_alsa():
+    interface = alsa.Interface(config=config.fastest())
+    interface.launch = mock.Mock()
+    with interface:
+        r = interface.recorder()
+        r.read(2)
+        r.close()
+
+    p = mock.call(
+        args='arecord -f S16_LE -c 1 -r 32000 -T 100 -q -'.split(),
+        stdout=-1)
+    assert interface.launch.mock_calls == [p, p.stdout.read(2), p.kill()]
+
+    interface.launch = mock.Mock()
+    with interface:
+        p = interface.player()
+        p.write('\x00\x00')
+        p.close()
+
+    p = mock.call(
+        args='aplay -f S16_LE -c 1 -r 32000 -T 100 -q -'.split(),
+        stdin=-1)
+    assert interface.launch.mock_calls == [
+        p, p.stdin.write('\x00\x00'), p.stdin.close(), p.wait()
+    ]
+
+
+def test_alsa_subprocess():
+    interface = alsa.Interface(config=config.fastest())
+    with mock.patch('subprocess.Popen') as popen:
+        with interface:
+            p = interface.launch(args=['foobar'])
+            p.wait.side_effect = OSError('invalid command')
+            assert interface.processes == [p]
+            assert popen.mock_calls == [mock.call(args=['foobar'])]