nanondef 0.0.1

A no-std, no-alloc, minimal NDEF encoding and decoding library.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149

use crate::{
    error::Truncated, Error, Error::BlockTruncated, Range,
};
use crate::tag::{message::DecodeMessage, Block, BlockTag};
use core::marker::PhantomData;

#[derive(Debug, Clone)]
pub struct IterBlock<'b, M: DecodeMessage<'b>> {
    bytes: &'b [u8],
    pos: usize,
    _marker: PhantomData<M>,
}

impl<'b, M: DecodeMessage<'b>> IterBlock<'b, M> {
    #[inline]
    pub fn new(bytes: &'b [u8]) -> Self {
        Self { bytes, pos: 0, _marker: PhantomData }
    }

    #[inline(always)]
    fn read_len(&mut self) -> crate::Result<usize> {
        let len = self.bytes.len();
        if self.pos >= len {
            return Err(BlockTruncated(Truncated { got: len, want: self.pos + 1 }));
        }

        let first = self.bytes[self.pos];
        self.pos += 1;

        if first != 0xFF {
            return Ok(first as usize);
        }

        if self.pos + 1 >= len {
            return Err(BlockTruncated(Truncated { got: len, want: self.pos + 2 }));
        }

        let hi = self.bytes[self.pos] as usize;
        let lo = self.bytes[self.pos + 1] as usize;
        self.pos += 2;

        Ok((hi << 8) | lo)
    }
}

impl<'b, M: DecodeMessage<'b>> Iterator for IterBlock<'b, M> {
    type Item = crate::Result<Block<'b, M>>;

    #[cfg_attr(feature = "tracing", tracing::instrument(level = "trace", ret, skip(self),))]
    fn next(&mut self) -> Option<Self::Item> {
        let bytes = self.bytes;
        let len = bytes.len();

        if self.pos >= len {
            #[cfg(feature = "tracing")]
            tracing::debug!("Reached end of TLV at {} bytes", self.pos);

            return None;
        }

        let tag_byte = bytes[self.pos];
        self.pos += 1;

        let tag = BlockTag::from(tag_byte);

        #[cfg(feature = "tracing")]
        tracing::debug!("New TLV tag: {tag:?}");

        match tag {
            BlockTag::Null => {
                // NULL TLV has no length
                #[cfg(feature = "tracing")]
                tracing::trace!("Matched NULL TLV");
                Some(Ok(Block::Null))
            },
            BlockTag::Terminator => {
                #[cfg(feature = "tracing")]
                tracing::trace!("Matched terminator TLV");
                None
            },

            BlockTag::Message => {
                #[cfg(feature = "tracing")]
                tracing::trace!("Matched message TLV");

                let block_len = match self.read_len() {
                    Ok(l) => l,
                    Err(e) => return Some(Err(e)),
                };

                let block_range = Range::new(self.pos, self.pos + block_len);

                #[cfg(feature = "tracing")]
                tracing::debug!(%block_range, "Message TLV range calculated");

                if block_range.end > len {
                    #[cfg(feature = "tracing")]
                    tracing::warn!("Message TLV end exceeds {len} available bytes");

                    return Some(Err(BlockTruncated(Truncated {
                        got: len,
                        want: block_range.end,
                    })));
                }

                match M::decode_message(&bytes[block_range]).map_err(Error::implementation_error) {
                    Ok(message) => Some(Ok(Block::Message(message, block_range))),
                    Err(e) => Some(Err(e)),
                }
            },

            // unknown block
            tag => {
                #[cfg(feature = "tracing")]
                tracing::trace!(?tag, "Matched unknown TLV");

                let block_len = match self.read_len() {
                    Ok(l) => l,
                    Err(e) => return Some(Err(e)),
                };

                let block_range = Range::new(self.pos, self.pos + block_len);

                #[cfg(feature = "tracing")]
                tracing::debug!(%block_range, "Unknown TLV range calculated");

                if block_range.end > len {
                    #[cfg(feature = "tracing")]
                    tracing::warn!("Unknown TLV end exceeds {len} available bytes");

                    return Some(Err(BlockTruncated(Truncated {
                        got: len,
                        want: block_range.end,
                    })));
                }

                Some(Ok(match tag {
                    BlockTag::Proprietary => {
                        Block::Proprietary(&bytes[block_range.as_core()], block_range)
                    },
                    BlockTag::Other(_) => {
                        Block::Other(tag, &bytes[block_range.as_core()], block_range)
                    },
                    _ => unreachable!("shouldn't reach here with unknown tag"),
                }))
            },
        }
    }
}