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Exercises/soln8_6.md

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+# Exercise 8.6 - Solution
+
+## (a) Receiving Messages
+
+```python
+# coticker.py
+from structure import Structure
+from validate import String, Integer, Float
+
+class Ticker(Structure):
+    name = String()
+    price = Float()
+    date = String()
+    time = String()
+    change = Float()
+    open = Float()
+    high = Float()
+    low = Float()
+    volume = Integer()
+
+from cofollow import consumer, follow, receive
+from tableformat import create_formatter
+import csv
+
+@consumer
+def to_csv(target):
+    def producer():
+        while True:
+            yield line
+
+    reader = csv.reader(producer())
+    while True:
+        line = yield from receive(str)
+        target.send(next(reader))
+
+@consumer
+def create_ticker(target):
+    while True:
+        row = yield from receive(list)
+        target.send(Ticker.from_row(row))
+
+@consumer
+def negchange(target):
+    while True:
+        record = yield from receive(Ticker)
+        if record.change < 0:
+            target.send(record)
+
+@consumer
+def ticker(fmt, fields):
+    formatter = create_formatter('text')
+    formatter.headings(fields)
+    while True:
+        rec = yield from receive(Ticker)
+        row = [getattr(rec, name) for name in fields]
+        formatter.row(row)
+
+if __name__ == '__main__':
+    follow('Data/stocklog.csv',
+           to_csv(
+           create_ticker(
+           negchange(
+           ticker('text', ['name','price','change'])))))
+```
+
+## (b) Wrapping a Socket
+
+```python
+# server.py
+...
+
+class GenSocket:
+    def __init__(self, sock):
+        self.sock = sock
+
+    def accept(self):
+        yield 'recv', self.sock
+        client, addr = self.sock.accept()
+        return GenSocket(client), addr
+
+    def recv(self, maxsize):
+        yield 'recv', self.sock
+        return self.sock.recv(maxsize)
+
+    def send(self, data):
+        yield 'send', self.sock
+        return self.sock.send(data)
+
+    def __getattr__(self, name):
+        return getattr(self.sock, name)
+
+def tcp_server(address, handler):
+    sock = GenSocket(socket(AF_INET, SOCK_STREAM))
+    sock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
+    sock.bind(address)
+    sock.listen(5)
+    while True:
+        client, addr = yield from sock.accept()
+        tasks.append(handler(client, addr))
+        
+def echo_handler(client, address):
+    print('Connection from', address)
+    while True:
+        data = yield from client.recv(1000)
+        if not data:
+            break
+        yield from client.send(b'GOT:' + data)
+    print('Connection closed')
+
+if __name__ == '__main__':
+    tasks.append(tcp_server(('',25000), echo_handler))
+    run()
+```
+
+## (c) Async/Await
+
+```python
+# server.py
+
+from socket import *
+from select import select
+from collections import deque
+from types import coroutine
+
+tasks = deque()
+recv_wait = {}   #  sock -> task
+send_wait = {}   #  sock -> task
+
+def run():
+    while any([tasks, recv_wait, send_wait]):
+        while not tasks:
+            can_recv, can_send, _ = select(recv_wait, send_wait, [])
+            for s in can_recv:
+                tasks.append(recv_wait.pop(s))
+            for s in can_send:
+                tasks.append(send_wait.pop(s))
+        task = tasks.popleft()
+        try:
+            reason, resource = task.send(None)
+            if reason == 'recv':
+                recv_wait[resource] = task
+            elif reason == 'send':
+                send_wait[resource] = task
+            else:
+                raise RuntimeError('Unknown reason %r' % reason)
+        except StopIteration:
+            print('Task done')
+
+class GenSocket:
+    def __init__(self, sock):
+        self.sock = sock
+
+    @coroutine
+    def accept(self):
+        yield 'recv', self.sock
+        client, addr = self.sock.accept()
+        return GenSocket(client), addr
+
+    @coroutine
+    def recv(self, maxsize):
+        yield 'recv', self.sock
+        return self.sock.recv(maxsize)
+
+    @coroutine
+    def send(self, data):
+        yield 'send', self.sock
+        return self.sock.send(data)
+
+    def __getattr__(self, name):
+        return getattr(self.sock, name)
+
+async def tcp_server(address, handler):
+    sock = GenSocket(socket(AF_INET, SOCK_STREAM))
+    sock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
+    sock.bind(address)
+    sock.listen(5)
+    while True:
+        client, addr = await sock.accept()
+        tasks.append(handler(client, addr))
+        
+async def echo_handler(client, address):
+    print('Connection from', address)
+    while True:
+        data = await client.recv(1000)
+        if not data:
+            break
+        await client.send(b'GOT:' + data)
+    print('Connection closed')
+
+if __name__ == '__main__':
+    tasks.append(tcp_server(('',25000), echo_handler))
+    run()
+```
+
+
+
+[Back](ex8_6.md)