[mrbadguy]

I’m not sure I understand the packed structs complaint. I have used Go to read binary data and it’s quite easy. You just need to ensure that all of your struct fields have fixed sizes e.g. int32 or [4]int64 or whatever. Unless I’ve misunderstood what you mean?

[guappa]

Yes it works, but you can't state the endianness and you have no control to decide if the compiler will decide to insert padding. It's undefined.

You HOPE it works.

[mrbadguy]

I don’t know about the padding (certainly it never inserted any when I’ve used it) but you can definitely state the byte order upon reading or writing. That would definitely be an oversight. Take a look at the encoding/binary package:

https://pkg.go.dev/encoding/binary

[guappa]

I want a struct, not to having to write the code manually to do a struct every single time.

I know you can do that in go but as I already said: "more error prone than C".

[mrbadguy]

Can you please give me an example of what you don’t like? I’m not sure I understand the “write the code manually to do a struct” bit.

You have to define the struct for sure, but beyond that you just pass it to binary.Read and it comes back with the fields populated. I don’t see how you’d avoid defining the struct.

[dfawcus]

I believe what he wants, is the usual C trick of defining a struct which represents the wire format (with all the usual caveats). Then cast a char pointer to be an instance of a pointer to that struct. Sort of like this:

    https://github.com/danos/vyatta-dataplane/blob/master/src/ecmp.c#L108-L116

It sort of works on x86 chips, but is not so effective on MIPS, PPC, etc where misaligned access are either unavailable, or slow, or even trap and are slower still.

Once one has to handle that sort of situation, and actually copy the data, the lack of language support for such type-punning becomes immaterial.

[mrbadguy]

Oh I see, thanks for the clarification! Personally, I'm fine without that and with something like

  func Foo(r io.Reader) {
      var m MyStruct
      binary.Read(r, binary.LittleEndian, &m)

  }

but we may be operating in different contexts where the underlying copy is or isn't a problem. That said, depending on the implementation of the reader passed in, the bytes might be being streamed from elsewhere, in which case the copying is minimised.

[guappa]

https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.ht...

If the misaligned access is slow… it will be slow whether the compiler reads the variable or if you hand-write even slower and error prone code.

That said, please show me a protocol that generates unaligned accesses on any architecture. People writing protocols aren't noobs :)