To avoid an xy-problem, could you clarify why you seem to reimplement this functionality? Are you writing a client library?

Interesting... I am writing s client library for something not running ROS.

Could you say something about the platform you're targetting? There are quite a few existing client libraries (even for 'small' systems, or limited ones, like PLCs) which may have already solved this problem. Avoiding duplication of effort is important here.

I am aware of a good portion of the clients available. I don't need one of those I need to understand how to run the checksum in something like I've suggested above. Do you know how to do the most for something like ByteMultiArray. I am just not sure what to do with the square brackets or array part. Any thoughts?

so, the current process for me to recreate what rosmsg md5 does. For example:

$ rosmsg md5 std_msgs/ColorRGBA

Output

$ a29a96539573343b1310c73607334b00

ColorRGBA is made up of 4 float32:

float32 r
float32 g
float32 b
float32 a

The md5 hash for these using a webtool like http://onlinemd5.com/ is exactly the same:

A29A96539573343B1310C73607334B00

When I start to break down something like ByteMultiArray, it contains:

MultiArrayLayout layout
byte[] data

MultiArrayLayout is actually made up of:

MultiArrayDimension[] dim
uint32 data_offset

MultiArrayDimension is made up of:

string label
uint32 size
uint32 stride

So, using rosmsg md5 I can get the has of the actual message type instead of the smaller std_msgs like string, uint32, etc. but my client doesn't have that, so I feel that this should really look like:

string label
uint32 size
uint32 stride
uint32 data_offset
byte[] data

This is the output of the md5 for the breakdown:

9280F1C055E4C32736216B03EC53407A

Not sure what else to do. And what exactly do i do with that byte that has brackets ....

This labview library from Tuftes doesn't seem to work quite right, messages are truncated and cannot add any more messages. Some VI's start up and can't be killed... https://github.com/tuftsBaxter/ROS-for-LabVIEW-Software

@wegunterjr Hope I helped. Could you please update your question to include what you are doing and what results you got (comments #3 and #4 as of now)