mcproto_codec/
varint.rs

1use std::io::{Read, Write};
2
3use crate::error::{CodecError, CodecKind, InvalidEncodingReason};
4use crate::io::{read_exact_counted, write_all_counted};
5
6pub trait VarIntWrite: Write {
7    #[inline]
8    fn write_varint(&mut self, value: i32) -> Result<(), CodecError> {
9        self.write_varint_with_size(value).map(|_| ())
10    }
11
12    #[inline]
13    fn write_varint_with_size(&mut self, value: i32) -> Result<usize, CodecError> {
14        let mut value = value as u32;
15        let mut bytes_processed = 0;
16
17        loop {
18            let byte = (value & 0x7F) as u8;
19            value >>= 7;
20            let has_next = value != 0;
21            let byte = if has_next { byte | 0x80 } else { byte };
22
23            write_all_counted(self, &[byte], CodecKind::VarInt, bytes_processed)?;
24            bytes_processed += 1;
25
26            if !has_next {
27                return Ok(bytes_processed);
28            }
29        }
30    }
31}
32
33pub trait VarIntRead: Read {
34    #[inline]
35    fn read_varint(&mut self) -> Result<i32, CodecError> {
36        self.read_varint_with_size().map(|(value, _)| value)
37    }
38
39    #[inline]
40    fn read_varint_with_size(&mut self) -> Result<(i32, usize), CodecError> {
41        let mut result = 0u32;
42        let mut shift = 0;
43
44        for i in 0..5 {
45            let mut buf = [0u8; 1];
46            read_exact_counted(self, &mut buf, CodecKind::VarInt, i)?;
47            let byte = buf[0];
48
49            if i == 4 {
50                if (byte & 0x80) != 0 {
51                    return Err(CodecError::invalid_encoding(
52                        CodecKind::VarInt,
53                        i + 1,
54                        InvalidEncodingReason::TooLong { max_bytes: 5 },
55                    ));
56                }
57                if (byte & !0x0F) != 0 {
58                    return Err(CodecError::invalid_encoding(
59                        CodecKind::VarInt,
60                        i + 1,
61                        InvalidEncodingReason::ValueOutOfRange {
62                            terminal_byte: byte,
63                            allowed_mask: 0x0F,
64                        },
65                    ));
66                }
67            }
68
69            let value = (byte & 0x7F) as u32;
70            result |= value << shift;
71
72            if (byte & 0x80) == 0 {
73                return Ok((result as i32, i + 1));
74            }
75
76            shift += 7;
77        }
78
79        unreachable!("the fifth VarInt byte always terminates or returns an error")
80    }
81}
82
83impl<R: Read> VarIntRead for R {}
84impl<W: Write> VarIntWrite for W {}
mcproto_codec/varint.rs

mcproto_codec/
varint.rs
