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Re^4: pack and unpack multiple arrays with one common repeat prefix

by hexcoder (Deacon)
on Jun 15, 2017 at 21:56 UTC ( #1192899=note: print w/replies, xml ) Need Help??


in reply to Re^3: pack and unpack multiple arrays with one common repeat prefix
in thread pack and unpack multiple arrays with one common repeat prefix

I wrote a decoder that reads binary telegrams (or messages) with different types (meaning different structures) from a log file. For each telegram type the table has an unpack template that defines the structure of the telegram and a list of names for its fields. The structure is unpacked and the values are formatted with their names to make a readable string representation describing the content of the telegrams.

Currently this works well with simple types and single arrays prefixed with their length. The structure of the telegrams are given and part of an interface. I agree, there could be simpler unified packings, but that is what I have to deal with.

Maybe it is a good idea to allow 'two step unpacking', in order to enable the decoding of more complex structures. Thanks, I have to think about it.
  • Comment on Re^4: pack and unpack multiple arrays with one common repeat prefix

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Re^5: pack and unpack multiple arrays with one common repeat prefix
by kcott (Bishop) on Jun 16, 2017 at 04:52 UTC

    G'day hexcoder,

    Perhaps, instead of a table of just templates, you could use a table of coderefs whose functionality includes preprocessing, unpacking, formatting, and anything else you need.

    Here's a highly contrived and primitive example just to show the technique.

    #!/usr/bin/env perl -l use strict; use warnings; my %decode_type = ( A => sub { "Do TypeA stuff with '$_[0]'" }, B => sub { "Do TypeB stuff with '$_[0]'" }, ); while (<DATA>) { chomp; my ($type, $msg) = split /\s+/, $_, 2; my $decoded = $decode_type{$type}->($msg); print $decoded; } __DATA__ B message B1 A more complex message A1 B message B2

    Output:

    Do TypeB stuff with 'message B1' Do TypeA stuff with 'more complex message A1' Do TypeB stuff with 'message B2'

    I don't know how useful that might be; however, your general description suggested this approach.

    — Ken

      The idea/goal was to seperate the decoding engine (code) from the data structure descriptions (templates) in order to
    • decrease (inter)dependencies
    • reduce code by avoiding (slightly different) duplicates for different structures
    • So, I see your approach as the next best method, when I fail to express the structures with templates in a table. Using a table with handler functions is certainly the most flexible way allowing for very special decoding tasks.

      Thanks, hexcoder

        I'm glad to see that had, at least some, appeal.

        It was, as stated, somewhat "primitive". Expanding upon that a little, the following is more generally what I had in mind, which removes duplicate code and separates the "decoding engine (code)" (putting it into Decoupled.pm).

        The expanded script (note there's no change to the original while loop or input data):

        #!/usr/bin/env perl -l use strict; use warnings; use lib '.'; use Decoupled qw{ preprocess_complex_message handle_generic_message }; my %decode_type = ( A => sub { handle_generic_message( A => preprocess_complex_message($_[0]) ) }, B => sub { handle_generic_message(B => $_[0]) }, ); while (<DATA>) { chomp; my ($type, $msg) = split /\s+/, $_, 2; my $decoded = $decode_type{$type}->($msg); print $decoded; } __DATA__ B message B1 A more complex message A1 B message B2

        The Decoupled module:

        package Decoupled; use strict; use warnings; use Exporter 'import'; our @EXPORT_OK = qw{ preprocess_complex_message handle_generic_message }; sub preprocess_complex_message { $_[0] =~ /more complex (.*)/; $1 } sub handle_generic_message { sprintf "Do Type%s stuff with '%s'", @_ } 1;

        The new output:

        Do TypeB stuff with 'message B1' Do TypeA stuff with 'message A1' Do TypeB stuff with 'message B2'

        — Ken

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