bacnet_encoding/constructed/
name_value.rs

1//! `BACnetNameValue` framing (Clause 21, corrected by errata 2024-04-29
2//! item 37), the element of a Tags array (#1553).
3//!
4//! A name under primitive context tag 0 is followed by at most one
5//! application-tagged primitive. Date and Time are valid separately; their
6//! pair is not one NameValue. The next array element starts at context tag 0.
7
8use bacnet_types::constructed::BACnetNameValue;
9use bacnet_types::error::Error;
10use bytes::BytesMut;
11
12use super::tagged::decode_ctx_character_string;
13use crate::primitives;
14use crate::tags::{self, TagClass};
15
16const WHAT: &str = "BACnetNameValue";
17
18/// Encode one `BACnetNameValue`, appending to `buf`.
19///
20/// A nonprimitive value (`List` or `ApplicationData`) or a name too long
21/// to encode returns an error before `buf` changes.
22pub fn encode_name_value(buf: &mut BytesMut, value: &BACnetNameValue) -> Result<(), Error> {
23    if value
24        .value
25        .as_ref()
26        .is_some_and(|value| !value.is_primitive())
27    {
28        return Err(Error::Encoding(format!(
29            "{WHAT}: a value must be a primitive datatype"
30        )));
31    }
32    primitives::encode_ctx_character_string(buf, 0, &value.name)?;
33    if let Some(primitive) = &value.value {
34        primitives::encode_property_value(buf, primitive)?;
35    }
36    Ok(())
37}
38
39/// Whether another application-tagged value follows; false at end of input.
40fn next_is_application(data: &[u8], offset: usize) -> Result<bool, Error> {
41    if offset >= data.len() {
42        return Ok(false);
43    }
44    let (tag, _) = tags::decode_tag(data, offset)?;
45    Ok(tag.class == TagClass::Application)
46}
47
48/// Decode one `BACnetNameValue` at `offset`, returning it and the next offset.
49///
50/// The next context-tagged element is left to the caller, which must check
51/// complete consumption when decoding a whole value. Missing or malformed
52/// names, unsupported character sets, unknown application types, truncated
53/// values and a second application value (including Date followed by Time)
54/// are errors.
55pub fn decode_name_value(data: &[u8], offset: usize) -> Result<(BACnetNameValue, usize), Error> {
56    let (name, offset) = decode_ctx_character_string(data, offset, 0, WHAT)?;
57    if !next_is_application(data, offset)? {
58        return Ok((BACnetNameValue { name, value: None }, offset));
59    }
60    let (value, offset) = primitives::decode_application_value(data, offset)?;
61    if next_is_application(data, offset)? {
62        return Err(Error::decoding(
63            offset,
64            format!("{WHAT}: a value must contain only one primitive"),
65        ));
66    }
67    Ok((
68        BACnetNameValue {
69            name,
70            value: Some(value),
71        },
72        offset,
73    ))
74}
bacnet_encoding/constructed/name_value.rs

bacnet_encoding/constructed/
name_value.rs
