Try to read more serial bytes in a loop (#248)

rosserial_python/src/rosserial_python/SerialClient.py

@@ -400,12 +400,23 @@ def txStopRequest(self, signal, frame):
 
     def tryRead(self, length):
         try:
-            bytes_read = self.port.read(length)
-            if len(bytes_read) < length:
+            read_start = time.time()
+            read_current = read_start
+            bytes_remaining = length
+            result = bytearray()
+            while bytes_remaining != 0 and read_current - read_start < self.timeout:
+                received = self.port.read(bytes_remaining)
+                if len(received) != 0:
+                    result.extend(received)
+                    bytes_remaining -= len(received)
+                read_current = time.time()
+
+            if bytes_remaining != 0:
                 rospy.logwarn("Serial Port read returned short (expected %d bytes, received %d instead)."
-                              % (length, len(bytes_read)))
+                              % (length, len(length - bytes_remaining)))
                 raise IOError()
-            return bytes_read
+
+            return bytes(result)
         except Exception as e:
             rospy.logwarn("Serial Port read failure: %s", e)
             raise IOError()