micropython/streampair: Package to create bi-directional linked stream objects.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

micropython/streampair/manifest.py

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+metadata(
+    description="Create a bi-directional linked pair of stream objects", version="0.0.1"
+)
+
+module("streampair.py")

micropython/streampair/streampair.py

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+import io
+
+from collections import deque
+from micropython import ringbuffer, const
+
+try:
+    from typing import Union, Tuple
+except:
+    pass
+
+# From micropython/py/stream.h
+_MP_STREAM_ERROR = const(-1)
+_MP_STREAM_FLUSH = const(1)
+_MP_STREAM_SEEK = const(2)
+_MP_STREAM_POLL = const(3)
+_MP_STREAM_CLOSE = const(4)
+_MP_STREAM_POLL_RD = const(0x0001)
+
+
+def streampair(buffer_size: Union[int, Tuple[int, int]]=256):
+    """
+    Returns two bi-directional linked stream objects where writes to one can be read from the other and vice/versa.
+    This can be used somewhat similarly to a socket.socketpair in python, like a pipe
+    of data that can be used to connect stream consumers (eg. asyncio.StreamWriter, mock Uart)
+    """
+    try:
+        size_a, size_b = buffer_size
+    except TypeError:
+        size_a = size_b = buffer_size
+
+    a = ringbuffer(size_a)
+    b = ringbuffer(size_b)
+    return StreamPair(a, b), StreamPair(b, a)
+
+
+class StreamPair(io.IOBase):
+
+    def __init__(self, own: ringbuffer, other: ringbuffer):
+        self.own = own
+        self.other = other
+        super().__init__()
+
+    def read(self, nbytes=-1):
+        return self.own.read(nbytes)
+
+    def readline(self):
+        return self.own.readline()
+
+    def readinto(self, buf, limit=-1):
+        return self.own.readinto(buf, limit)
+
+    def write(self, data):
+        return self.other.write(data)
+
+    def seek(self, offset, whence):
+        return self.own.seek(offset, whence)
+
+    def flush(self):
+        self.own.flush()
+        self.other.flush()
+
+    def close(self):
+        self.own.close()
+        self.other.close()
+
+    def any(self):
+        return self.own.any()
+
+    def ioctl(self, op, arg):
+        if op == _MP_STREAM_POLL:
+            if self.any():
+                return _MP_STREAM_POLL_RD
+            return 0
+
+        elif op ==_MP_STREAM_FLUSH:
+            return self.flush()
+        elif op ==_MP_STREAM_SEEK:
+            return self.seek(arg[0], arg[1])
+        elif op ==_MP_STREAM_CLOSE:
+            return self.close()
+
+        else:
+            return _MP_STREAM_ERROR

micropython/streampair/test_streampair.py

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+import asyncio
+import unittest
+from streampair import streampair
+
+def async_test(f):
+    """
+    Decorator to run an async test function
+    """
+    def wrapper(*args, **kwargs):
+        loop = asyncio.new_event_loop()
+        # loop.set_exception_handler(_exception_handler)
+        t = loop.create_task(f(*args, **kwargs))
+        loop.run_until_complete(t)
+
+    return wrapper
+
+class StreamPairTestCase(unittest.TestCase):
+
+    def test_streampair(self):
+        a, b = streampair()
+        assert a.write(b"foo") == 3
+        assert b.write(b"bar") == 3
+
+        assert (r := a.read()) == b"bar", r
+        assert (r := b.read()) == b"foo", r
+
+    @async_test
+    async def test_async_streampair(self):
+        a, b = streampair()
+        ar = asyncio.StreamReader(a)
+        bw = asyncio.StreamWriter(b)
+
+        br = asyncio.StreamReader(b)
+        aw = asyncio.StreamWriter(a)
+
+        aw.write(b"foo\n")
+        await aw.drain()
+        assert not a.any()
+        assert b.any()
+        assert (r := await br.readline()) == b"foo\n", r
+        assert not b.any()
+        assert not a.any()
+
+        bw.write(b"bar\n")
+        await bw.drain()
+        assert not b.any()
+        assert a.any()
+        assert (r := await ar.readline()) == b"bar\n", r
+        assert not b.any()
+        assert not a.any()
+
+
+if __name__ == "__main__":
+    unittest.main()