Output does not work with other existing tools

[computermouth]

I checked out another person's branch, from PR #16 . It solves the nightly compilation issues, and completes without a problem.

However, writing out the payload, and checking it with external tools, I encountered some errors.

    let stdout = io::stdout();
    let mut handle = stdout.lock();

    handle.write_all(&buf).unwrap();
    handle.flush().unwrap();

$ cargo +nightly run > out.mp
serialized 49 bytes

$ mpk msgpacker.mp --to-json
"Kuala Lumpur"

$ ~/go/bin/msgpack-cli decode msgpacker.mp --pp
"Kuala Lumpur"2025/03/13 16:48:48 msgpack decode error [pos 14]: invalid byte descriptor for decoding bytes, got: 0x82

Given that the test clears internally when you parse back in, I have a feeling that the library maybe doesn't implement the spec correctly. This is backed up by rmp and rmp_serde parsing cleanly with the tools.

$ ~/go/bin/msgpack-cli decode rmp-serde.mp --pp
["Kuala Lumpur",{"Street 1":10,"Street 2":20},["Zone 1","Zone 2"]]

$ ~/go/bin/msgpack-cli decode msgpacker.mp --pp
"Kuala Lumpur"2025/03/13 17:06:38 msgpack decode error [pos 14]: invalid byte descriptor for decoding bytes, got: 0x82

$ mpk rmp-serde.mp --to-json
["Kuala Lumpur",{"Street 2":20,"Street 1":10},["Zone 1","Zone 2"]]

$ mpk msgpacker.mp --to-json
"Kuala Lumpur"

Here's the difference in the hex:

$ xxd msgpacker.mp 
00000000: ac4b 7561 6c61 204c 756d 7075 7282 a853  .Kuala Lumpur..S
00000010: 7472 6565 7420 3214 a853 7472 6565 7420  treet 2..Street 
00000020: 310a 92a6 5a6f 6e65 2031 a65a 6f6e 6520  1...Zone 1.Zone 
00000030: 32                                       2

$ xxd rmp-serde.mp 
00000000: 93ac 4b75 616c 6120 4c75 6d70 7572 82a8  ..Kuala Lumpur..
00000010: 5374 7265 6574 2032 14a8 5374 7265 6574  Street 2..Street
00000020: 2031 0a92 a65a 6f6e 6520 31a6 5a6f 6e65   1...Zone 1.Zone
00000030: 2032                                      2

The rmp-serde.mp file starts with a byte 0x93. According to the spec, this is a fixed array delimiter with 3 elements (name, inhabitants_per_street, and zones). It seems these other tools expect the payload to start with either an array, map, or otherwise exclusively contain a single messagepack type -- opposed to this library's list of types with no outer container at the top level

[computermouth]

The following hack fixed the parsing with other tools:

    let field_count = f.named.len();
    let mut field_access_exprs: Vec<syn::Expr> = Vec::new();
    let block_packable: Block = parse_quote! {
        {
            let mut n = 0;
            n += match #field_count {
                0..=15 => {
                    buf.extend(::core::iter::once((#field_count as u8) | 0x90));
                    1
                }
                16..=65535 => {
                    buf.extend(::core::iter::once(0xdc).chain((#field_count as u16).to_be_bytes()));
                    3
                }
                _ => {
                    buf.extend(::core::iter::once(0xdd).chain((#field_count as u32).to_be_bytes()));
                    5
                }
            };
        }
    };

Its turning out to be much more complicated to fix than I originally imagined, and I'm not handy with Rust macros