Use Array to represent the field of array type in a message instead of TypedArray

[minggangw]

By landing f3bcddc, we achieved that enabling TypedArray to improve the performance when the message has a field which has the type of array. e.g. Image.msg, the data field

# This message contains an uncompressed image
# (0, 0) is at top-left corner of image

std_msgs/Header header # Header timestamp should be acquisition time of image
                             # Header frame_id should be optical frame of camera
                             # origin of frame should be optical center of cameara
                             # +x should point to the right in the image
                             # +y should point down in the image
                             # +z should point into to plane of the image
                             # If the frame_id here and the frame_id of the CameraInfo
                             # message associated with the image conflict
                             # the behavior is undefined

uint32 height                # image height, that is, number of rows
uint32 width                 # image width, that is, number of columns

# The legal values for encoding are in file src/image_encodings.cpp
# If you want to standardize a new string format, join
# ros-users@lists.ros.org and send an email proposing a new encoding.

string encoding       # Encoding of pixels -- channel meaning, ordering, size
                      # taken from the list of strings in include/sensor_msgs/image_encodings.h

uint8 is_bigendian    # is this data bigendian?
uint32 step           # Full row length in bytes
uint8[] data          # actual matrix data, size is (step * rows)

We can support the following types of array by leveraging the TypedArray, see here

Here is another story, as the rclnodejs is used as the backend of ros2-web-bridge and the format of the data transferring from the web browser is JSON over websockets. The thing is that the JSON does not have a representation of TypedArray, so you can't get the object back from JSON string. We found this issue when testing the unit test and reported an issue RobotWebTools/ros2-web-bridge#98

In this case, we want to use the normal Array to manipulate the data of array type, also, we have to be aware of the tremendous performance loss.