CODEWITHSUNDEEP
pythonpython-3.x
shaks
shaks

Reputation: 1

Python 3.1 - Send binary packed message- variable length data

I have a network message of the format msgHdr+payload. The msgHdr has a couple of Longs and a couple of shorts. The Payload is a variable length text. I am not sure how to format the Struct, so that I can send a packed binary stream.

The format for a single message is, 

s = struct.Struct('> L L I I 2110s')
s.pack(*mystruct) # Then I pack it

However, this only works for a fixed size string of 2110. How do I use it for a variable length payload? Should I be using something else?

Upvotes: 0

Views: 853

Answers (2)

Dan Gerhardsson
Dan Gerhardsson

Reputation: 1889

Use struct for the header and just add the payload afterwards.

message = struct.pack('> L L I I', *header) + payload

Upvotes: 1

jkerian
jkerian

Reputation: 17016

It seems like you could create the format string (which is, after all, just a string), and then use it with s.pack as you describe.

If your current syntax is

s = struct.Struct('> L L I I 2110s')
s.pack(*mystruct)

all you would need to do is

s = struct.Struct('> L L I I %ds' % size_of_data)
s.pack(*mystruct)

It might help to create the header first as one struct, then the variable length section, then concatenate them.

Upvotes: 0

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