Add curio based tcp client example

Author: tiagocoutinho

scripts/examples/simple_curio_tcp_client.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+# scripts/examples/simple_curio_tcp_client.py
+import curio
+
+from umodbus import conf
+from umodbus.client import tcp
+from umodbus.client.tcp.asynch import send_message
+
+
+# Enable values to be signed (default is False).
+conf.SIGNED_VALUES = True
+
+
+class CurioStream:
+    """Adapter from curio socket to StreamReader/Writer"""
+
+    def __init__(self, sock):
+        self.stream = sock.as_stream()
+        self.data = None
+
+    def write(self, data):
+        self._data = data
+
+    async def drain(self):
+        if self._data:
+            await self.stream.write(self._data)
+            self._data = None
+
+    async def readexactly(self, n):
+        return await self.stream.read_exactly(n)
+
+
+async def main():
+    sock = await curio.open_connection('localhost', 502)
+    stream = CurioStream(sock)
+
+    # Returns a message or Application Data Unit (ADU) specific for doing
+    # Modbus TCP/IP.
+    message = tcp.write_multiple_coils(slave_id=1, starting_address=1, values=[1, 0, 1, 1])
+
+    # Response depends on Modbus function code. This particular returns the
+    # amount of coils written, in this case it is.
+    response = await send_message(message, stream, stream)
+
+    await sock.close()
+
+
+curio.run(main)