TCP server example

Author: arnetheduck

docs/examples/tcpserver.nim

@@ -0,0 +1,60 @@
+## Simple TCP/IP server that accepts both IPv4 and IPv6 connections
+import chronos
+
+# Because handleConn runs as an indepented task via `asyncSpawn`, it must
+# handle all errors on its own (or the application will crash)
+proc handleConn(transport: StreamTransport, done: Future[void]) {.
+    async: (raises: []).} =
+  # Handle a single remote connection
+  try:
+    echo "Incoming connection from ", transport.remoteAddress()
+
+    while true:
+      # Read and echo back lines until `q` or `0` is entered
+      let data = await transport.readLine(sep="\n")
+      if data.len > 0:
+        if data[0] == 'q':
+          if not done.finished():
+            # Notify server that it's time to stop - some other client could
+            # have done this already, so we check with `finished` first
+            done.complete()
+            break
+        elif data[0] == '0':
+          break # Stop reading and close the connection
+
+      echo "Echoed ", await transport.write(data & "\n"), " bytes"
+  except CancelledError:
+    raiseAssert "No cancellations in this example"
+  except TransportError as exc:
+    echo "Connection problem! ", exc.msg
+  finally:
+    # Connections must always be closed to avoid resource leaks
+    await transport.closeWait()
+
+proc myApp(server: StreamServer) {.async.} =
+  echo "Accepting connections on ", server.local
+  let done = Future[void].init()
+  try:
+    while true:
+      let
+        accept = server.accept()
+
+      # Wait either for a new connection or that an existing connection signals
+      # that it's time to stop
+      discard await race(accept, done)
+      if done.finished(): break
+
+      # asyncSpawn is used to spawn an independent async task that runs until
+      # it's finished without blocking the current async function - the OS will
+      # clean up these tasks on shutdown but a long-running server will want to
+      # collect them and make sure their associated sockets are closed properly
+      asyncSpawn handleConn(accept.read(), done)
+  finally:
+    await server.closeWait()
+
+let
+  # This server listens on both IPv4 and IPv6 and will pick a port number by
+  # itself
+  server = createStreamServer(AnyAddress6)
+
+waitFor myApp(server)