在Go中使用元编程来解析网络协议

Question

In JavaScript (Node), I've written a module which accepts a list of fields and their types and returns an object with pack and unpack methods. Below is the code to pack and unpack IPv4:

var ipv4 = proto.add('struct', {
  name: 'IPV4',
  fields: {
    version:       'int:4',
    ihl:           'int:4',
    dscp:          'int:6',
    ecn:           'int:2',
    length:        'int:16',
    id:            'int:16',
    flags:         'int:3',
    offset:        'int:13',
    ttl:           'int:8',
    protocol:      'int:8',
    checksum:      'int:16',
    src:           'IPV4_ADDR',
    dst:           'IPV4_ADDR',
    // TODO: IPv4 OPTIONS
    options:       'raw'
  },
  $length: 'length'
});
//then I can do
ipv4.pack({ version: 4, ... }); //=> buffer
//and
ipv4.unpack(buffer); //=> { ... }

Since JavaScript is dynamic, I can meta-program (reasonably) optimised pack and unpack functions. From what I understand, you cannot dynamically create functions in Go, though it appears this would be possible using the reflect package. Is this worth pursuing? Or would it be too costly to use reflect?

I'm hoping to avoid writing code like this for every network protocol I wish to parse.

Answer 1

If can accept a semi-dynamic solution, you could take inspiration in the numerous JSON alternative packages for Golang that are designed for speed. Their approach is to tag a struct, then run a tool (as part of a make configuration for example) to generate the MarshalJSON and UnmarshalJSON methods for the desired types. Which is clearly faster than using tags.

Some examples to help you :

• https://github.com/pquerna/ffjson
• https://github.com/benbjohnson/megajson