Implement DekuRead, DekuWrite for String about deku HOT 5 CLOSED

Some examples in the documentation on how to parse common strings would be really helpful!
For example for fixed size strings with \0 padding, cstrings, etc.

I'm currently stuck at parsing this struct where each field has a fixed size and is filled with \0 until the end of its range:

#[derive(Debug, DekuRead, DekuWrite)]
struct RawRecord {
    #[deku(count = "40")]
    firstname: Vec<u8>,
    #[deku(count = "40")]
    lastname: Vec<u8>,
    #[deku(count = "240")]
    address: Vec<u8>,
    #[deku(endian = "little")]
    age: u32,
}

Help is very much appreciated! :) Thanks in advance!

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I've held off on implementing anything for String in favor of using a custom reader/writer or map, as this is more specific to the implementation of the protocol being serialized/deserialized. I.e. len (u8?, u16?, u64?) + value, null terminated, etc.

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This is a pretty common use of CString and isn't documented in deku, probably should add that.

Anyway, this should work for you:

#[derive(Debug, DekuRead, DekuWrite)]
struct RawRecord {
    #[deku(pad_bytes_after = "4 - firstname.to_bytes_with_nul().len()")]
    firstname: CString,

    #[deku(pad_bytes_after = "5 - lastname.to_bytes_with_nul().len()")]
    lastname: CString,
}

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Thanks a lot! Very much appreciated!

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If I use this solution and Provide a string which is longer than or equal to the given pad bytes an "attempt to subtract with overflow" panikc occurs on trying to convert the Struct with to_bytes.
In Release Mode this doesn't happen, but the bytes are just truncated.
Shouldn't this give a DekuError?
I guess there needs to be a check that pad_bytes_after cannot be zero.

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