[fictrac] non-blocking receive call in example python script

scripts/socket_client.py

@@ -1,58 +1,75 @@
 #!/usr/bin/env python3
 
 import socket
+import select
 
 HOST = '127.0.0.1'  # The (receiving) host IP address (sock_host)
 PORT = ????         # The (receiving) host port (sock_port)
 
+# TCP
 # Open the connection (ctrl-c / ctrl-break to quit)
-with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:		# UDP
-#with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:	# TCP
-    sock.bind((HOST, PORT))		# UDP
-#    sock.connect((HOST, PORT))	# TCP
-
-    data = ""
+#with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+#    sock.connect((HOST, PORT))
+
+# UDP
+# Open the connection (ctrl-c / ctrl-break to quit)
+with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:
+    sock.bind((HOST, PORT))
+    sock.setblocking(0)
 
     # Keep receiving data until FicTrac closes
+    data = ""
+    timeout_in_seconds = 1
     while True:
-        # Receive one data frame
-        new_data = sock.recv(1024)
-        if not new_data:
-            break
-
-        # Decode received data
-        data += new_data.decode('UTF-8')
-
-        # Find the first frame of data
-        endline = data.find("\n")
-        line = data[:endline]       # copy first frame
-        data = data[endline+1:]     # delete first frame
-
-        # Tokenise
-        toks = line.split(", ")
-
-		# Check that we have sensible tokens
-        if ((len(toks) < 24) | (toks[0] != "FT")):
-            print('Bad read')
-            continue
-
-        # Extract FicTrac variables
-        # (see https://github.com/rjdmoore/fictrac/blob/master/doc/data_header.txt for descriptions)
-        cnt = int(toks[1])
-        dr_cam = [float(toks[2]), float(toks[3]), float(toks[4])]
-        err = float(toks[5])
-        dr_lab = [float(toks[6]), float(toks[7]), float(toks[8])]
-        r_cam = [float(toks[9]), float(toks[10]), float(toks[11])]
-        r_lab = [float(toks[12]), float(toks[13]), float(toks[14])]
-        posx = float(toks[15])
-        posy = float(toks[16])
-        heading = float(toks[17])
-        step_dir = float(toks[18])
-        step_mag = float(toks[19])
-        intx = float(toks[20])
-        inty = float(toks[21])
-        ts = float(toks[22])
-        seq = int(toks[23])
+        # Check to see whether there is data waiting
+        ready = select.select([sock], [], [], timeout_in_seconds)
+
+        # Only try to receive data if there is data waiting
+        if ready[0]:
+            # Receive one data frame
+            new_data = sock.recv(1024)
+
+            # Uh oh?
+            if not new_data:
+                break
+
+            # Decode received data
+            data += new_data.decode('UTF-8')
+
+            # Find the first frame of data
+            endline = data.find("\n")
+            line = data[:endline]       # copy first frame
+            data = data[endline+1:]     # delete first frame
+
+            # Tokenise
+            toks = line.split(", ")
+
+            # Check that we have sensible tokens
+            if ((len(toks) < 24) | (toks[0] != "FT")):
+                print('Bad read')
+                continue
+
+            # Extract FicTrac variables
+            # (see https://github.com/rjdmoore/fictrac/blob/master/doc/data_header.txt for descriptions)
+            cnt = int(toks[1])
+            dr_cam = [float(toks[2]), float(toks[3]), float(toks[4])]
+            err = float(toks[5])
+            dr_lab = [float(toks[6]), float(toks[7]), float(toks[8])]
+            r_cam = [float(toks[9]), float(toks[10]), float(toks[11])]
+            r_lab = [float(toks[12]), float(toks[13]), float(toks[14])]
+            posx = float(toks[15])
+            posy = float(toks[16])
+            heading = float(toks[17])
+            step_dir = float(toks[18])
+            step_mag = float(toks[19])
+            intx = float(toks[20])
+            inty = float(toks[21])
+            ts = float(toks[22])
+            seq = int(toks[23])
+
+            # Do something ...
+            print(cnt)
 
-        # Do something ...
-        print(cnt)
+        else:
+            # Didn't find any data - try again
+            print('retrying...')