plctag 0.4.1

a rust wrapper of [libplctag](https://github.com/libplctag/libplctag), with rust style APIs and useful extensions
Documentation 
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// plctag-rs
//
// a rust wrapper of libplctag, with rust style APIs and useful extensions.
// Copyright: 2022, Joylei <leingliu@gmail.com>
// License: MIT

use plctag::{Decode, Encode, RawTag, Result, ValueExt};

// define your UDT
#[derive(Default, Debug, Decode, Encode)]
struct MyUDT {
    #[tag(offset = 0)]
    a: u16,
    #[tag(offset = 2)]
    b: u16,
    #[tag(decode_fn = "my_decode", encode_fn = "my_encode")]
    c: u32,
}

fn my_decode(tag: &RawTag, offset: u32) -> plctag::Result<u32> {
    tag.get_u32(offset + 4).map(|v| v + 1)
}

fn my_encode(v: &u32, tag: &RawTag, offset: u32) -> plctag::Result<()> {
    tag.set_u32(offset + 4, *v - 1)
}

fn main() {
    let timeout = 100; //ms
                       // YOUR TAG DEFINITION
    let path = "protocol=ab-eip&plc=controllogix&path=1,0&gateway=192.168.1.120&name=MyTag2&elem_count=2&elem_size=16";
    let tag = RawTag::new(path, timeout).unwrap();

    //read tag
    let status = tag.read(timeout);
    assert!(status.is_ok());
    let offset = 0;
    let mut value: MyUDT = tag.get_value(offset).unwrap();
    println!("tag value: {:?}", value);

    value.a += 10;
    tag.set_value(offset, value).unwrap();

    //write tag
    let status = tag.write(timeout);
    assert!(status.is_ok());
    println!("write done!");
}